Blowing Mufflers

[Dave G]

I wish I could give you exact part numbers but I can't, or at least it
wouldn't be certain. My current TB was updated by using an earlier TB and
increasing the bore to 1.8 or so and using the higher pressure/smaller
injectors. There was some guy somewhere that had been doing it for awhile.
I have had very good performance from it but feel I am wasting a lot of
energy to overheat my fuel. I think a pump that produces 35 - 50 PSI would
be ideal, the lower the better. I may add an accumulator if pressure loss
on acceleration becomes a problem. Looking for best flow but not high
pressure. What did GM use in the 94-95 Chevy trucks, or at least what was
the spec output. I have even considered using a regulator with a pre-TB
return in addition to the return on my TB just so I get pressure under
control. Thanks!

 

[dave stragand1]

Something isn't right with that. I can't imagine any fuel pump being able to actually heat a tank full of fuel to boiling. Even if it were specifically a 12v heater, it would have a heck of a time doing so. Are other heat souces like exhaust located too close to the tank?
-Dave
1978 Transmode near Pittsburgh
________________________________
From: gmcmh-efi on behalf of Dave G
Sent: Monday, July 31, 2023 11:03 PM
To: GMCMH EFI
Subject: Re: [GMCMH-EFI] Blowing Mufflers
I wish I could give you exact part numbers but I can't, or at least it wouldn't be certain. My current TB was updated by using an earlier TB and increasing the bore to 1.8 or so and using the higher pressure/smaller injectors. There was some guy somewhere that had been doing it for awhile. I have had very good performance from it but feel I am wasting a lot of energy to overheat my fuel. I think a pump that produces 35 - 50 PSI would be ideal, the lower the better. I may add an accumulator if pressure loss on acceleration becomes a problem. Looking for best flow but not high pressure. What did GM use in the 94-95 Chevy trucks, or at least what was the spec output. I have even considered using a regulator with a pre-TB return in addition to the return on my TB just so I get pressure under control. Thanks!
Dave G:
" This is a modified TB from a '95. I think a 50 psi output would supply plenty of fuel given these were originally using 9 - 11 psi."
" I am using the 94-95 setup slightly modified by AFI. Its internal regulator is set to 30"
If you can provide the Rochester and injector part numbers, we might be able to research their specs and recommend a pump.
Opps, my bad, its Keith Vasilakes who I believe has a GM based EFI system with the higher pressure Rochester TB.
-------- Forwarded Message --------
Subject: Re: [GMCMH-EFI] Blowing Mufflers
Date: Mon, 31 Jul 2023 16:39:39 -0400
From: Bruce Hislop
To: GMC Motorhome EFI Group
There was a GM throttle body EFI system used in 94 or 95 that used smaller injectors at about 30 psi. I believe that is what Randy Van Winkle is using and also KevinV (or is Kelvin? Sorry on my cellphone)
Check with them to be sure which system you are using before ordering a new pump.
Bruce Hislop
Thanks to everyone who replied with suggestions! I have considered all of them and am very grateful for your thoughts. With some guidance from Dick Patterson I have installed an all-new ignition system. ATM I am addressing the fuel system which I think delivers way to much pressure for my throttle body (rated for 30) psi. I am boiling my gas and processing copious amounts of fuel through my system, most of which is returned to the tank. The current pump easily puts out 100 PSI and I believe it is overpowering the built in regulator. I would like to know what external fuel pump/filter others are running and hoping to drop the pressure significantly. This is a modified TB from a '95. I think a 50 psi output would supply plenty of fuel given these were originally using 9 - 11 psi.
If you are blowing mufflers up, you have unturned fuel in them. That should NEVER happen, no matter if you have a Carburetor, or anyone's fuel injection. That is unburned fuel passing completely through the engine. Because you stated that you have had it more than once, I would look first at your O2 sensor placement. Then, fuel/air ratios. That should give you a place to start.
Jim Hupy
Salem, Oregon
Hello friends, my first time posting here. Some of you may know me on FB as Dave Gee.
I have made every mistake possible in trying to convert to EFI on my GMC coach. I am now on my 3rd TB and am still exploding mufflers. The coach seems to run well enough but I have now destroyed 4 mufflers. I started with the Holley Quadrajet and Hyperspark. After multiple hardware failures I decided to try AFI's GM TBI system for a mid 90's truck. It runs very well but has blown up mufflers. I may have fixed the problem by installing a new retrofitted HEI with computer control. The old distributor was in pretty bad shape despite the engine running well. I also switched from E3 plugs to NGK Iridium. Since I am not sure the problem is solved I want to do further diagnostics and have purchased an AEM wideband sensor/gauge set and also purchased the ALDL to USB cable for use with Tunerpro.
I am trying to find the files to load for a $31 mask as well as a concise tutorial for using Tunerpro. It seems that every site I have looked at was either gone or no longer administrated.
I know I should have started here first. Bill Van Vlack and others were kind enough to reach out to me a long time ago before I went with Holley. What a mistake that was!
Any guidance and links to the resources I need are appreciated! Thank you!
--
gmcmh-efi+...

--
gmcmh-efi+...

--
gmcmh-efi+...

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[Biggamehunter]

So you are using a modified 4.3/305/350 TBI unit. Not a 7.4/454 unit(2”).
Leave the pump alone. If you want the fuel cooler you will need to use a fuel cooler , something like a transmission cooler.
Get Outlook for iOS https://aka.ms/o0ukef
________________________________
From: gmcmh-efi on behalf of Dave G
Sent: Monday, July 31, 2023 8:03:12 PM
To: GMCMH EFI
Subject: Re: [GMCMH-EFI] Blowing Mufflers
I wish I could give you exact part numbers but I can't, or at least it wouldn't be certain. My current TB was updated by using an earlier TB and increasing the bore to 1.8 or so and using the higher pressure/smaller injectors. There was some guy somewhere that had been doing it for awhile. I have had very good performance from it but feel I am wasting a lot of energy to overheat my fuel. I think a pump that produces 35 - 50 PSI would be ideal, the lower the better. I may add an accumulator if pressure loss on acceleration becomes a problem. Looking for best flow but not high pressure. What did GM use in the 94-95 Chevy trucks, or at least what was the spec output. I have even considered using a regulator with a pre-TB return in addition to the return on my TB just so I get pressure under control. Thanks!
Dave G:
" This is a modified TB from a '95. I think a 50 psi output would supply plenty of fuel given these were originally using 9 - 11 psi."
" I am using the 94-95 setup slightly modified by AFI. Its internal regulator is set to 30"
If you can provide the Rochester and injector part numbers, we might be able to research their specs and recommend a pump.
Opps, my bad, its Keith Vasilakes who I believe has a GM based EFI system with the higher pressure Rochester TB.
-------- Forwarded Message --------
Subject: Re: [GMCMH-EFI] Blowing Mufflers
Date: Mon, 31 Jul 2023 16:39:39 -0400
From: Bruce Hislop
To: GMC Motorhome EFI Group
There was a GM throttle body EFI system used in 94 or 95 that used smaller injectors at about 30 psi. I believe that is what Randy Van Winkle is using and also KevinV (or is Kelvin? Sorry on my cellphone)
Check with them to be sure which system you are using before ordering a new pump.
Bruce Hislop
Thanks to everyone who replied with suggestions! I have considered all of them and am very grateful for your thoughts. With some guidance from Dick Patterson I have installed an all-new ignition system. ATM I am addressing the fuel system which I think delivers way to much pressure for my throttle body (rated for 30) psi. I am boiling my gas and processing copious amounts of fuel through my system, most of which is returned to the tank. The current pump easily puts out 100 PSI and I believe it is overpowering the built in regulator. I would like to know what external fuel pump/filter others are running and hoping to drop the pressure significantly. This is a modified TB from a '95. I think a 50 psi output would supply plenty of fuel given these were originally using 9 - 11 psi.
If you are blowing mufflers up, you have unturned fuel in them. That should NEVER happen, no matter if you have a Carburetor, or anyone's fuel injection. That is unburned fuel passing completely through the engine. Because you stated that you have had it more than once, I would look first at your O2 sensor placement. Then, fuel/air ratios. That should give you a place to start.
Jim Hupy
Salem, Oregon
Hello friends, my first time posting here. Some of you may know me on FB as Dave Gee.
I have made every mistake possible in trying to convert to EFI on my GMC coach. I am now on my 3rd TB and am still exploding mufflers. The coach seems to run well enough but I have now destroyed 4 mufflers. I started with the Holley Quadrajet and Hyperspark. After multiple hardware failures I decided to try AFI's GM TBI system for a mid 90's truck. It runs very well but has blown up mufflers. I may have fixed the problem by installing a new retrofitted HEI with computer control. The old distributor was in pretty bad shape despite the engine running well. I also switched from E3 plugs to NGK Iridium. Since I am not sure the problem is solved I want to do further diagnostics and have purchased an AEM wideband sensor/gauge set and also purchased the ALDL to USB cable for use with Tunerpro.
I am trying to find the files to load for a $31 mask as well as a concise tutorial for using Tunerpro. It seems that every site I have looked at was either gone or no longer administrated.
I know I should have started here first. Bill Van Vlack and others were kind enough to reach out to me a long time ago before I went with Holley. What a mistake that was!
Any guidance and links to the resources I need are appreciated! Thank you!
--
gmcmh-efi+...

--
gmcmh-efi+...

--
gmcmh-efi+...

--

 

[MikeB]

Fuel pressure for 94-95 7.4 L was 26-32psi. I checked the fuel pumps for
that year 7.4l TBI offered by RockAuto and they range from 43 to 55 psi.
If you have a set up from AFI you probably have the 4.3L injectors with a
stronger spring to duplicate the 7.4L inj flow or 7.4L injectors if they
had them in stock.
Summit racing offers fuel coolers for $58 +.

 

[Dave G]

Yes, I believe it is a modified 4.3 TB. I installed an AEM AFR gauge and
can see the I am achieving 14.7:1. I am also using ALDLDroid to monitor and
log data. I have had fuel overheating issues since I first installed the
Holley. The fuel pump has a very loud and irritating whine. The large
volume of fuel being returned to the tank from the hot throttle body very
quickly heats the fuel in the tank and from what I have read in other
posts, the new gas formulations have a lower boiling point. I am hoping to
kill two birds at once here, The loud pump and the boiling gas. The only
heat source is the TB pushing a very large volume of hot fuel to the tanks.
I am tired of dealing with this problem. I was going to order from Applied
but when questioned on price (over $3000) JK got mad and hung up on me. I
am not a rich guy and they charge every penny that the market will bear. I
just bought a transmision module gear for $7 that they wanted $44 for. I
believe in supporting our vendors but they need to support us too. Now I am
considering finding one of the larger TB for the 7.4 that runs on lower
fuel pressure 9 - 12 psi and not 100. Right now I am considering replacing
my filters as pushing high volumes of fuel through them would likely clog
them after this much time. Thanks for all the input!

 

[Dave G]

Yes, fuel pressure for 94 - 95 was 26 - 32 (THANK YOU) but is appears that
is an in-tank fuel pump. I need to find an external in the same range and
having difficulty finding one.

 

[MikeB]

Dave Walbro pumps are us made. Here is one you may like. https://www.summitracing.com/parts/vpn-f30000271?seid=srese1&gclid=Cj0KCQjw2qKmBhCfARIsAFy8buLK6z7dYS5lOxtUsalHTLpcePyX1y4CeWhOtS3QesBu1R22b4ck4QEaAtspEALw_wcB"]https://www.summitracing.com/parts/vpn-f30000271?seid=srese1&gclid=Cj0KCQjw2qKmBhCfARIsAFy8buLK6z7dYS5lOxtUsalHTLpcePyX1y4CeWhOtS3QesBu1R22b4ck4QEaAtspEALw_wcB]https://www.summitracing.com/parts/vpn-f30000271?seid=srese1&gclid=Cj0KCQjw2qKmBhCfARIsAFy8buLK6z7dYS5lOxtUsalHTLpcePyX1y4CeWhOtS3QesBu1R22b4ck4QEaAtspEALw_wcB[/url][/url][/url]
Sent from my iPhone
[/QUOTE]

Yes, fuel pressure for 94 - 95 was 26 - 32 (THANK YOU) but is appears that is an in-tank fuel pump. I need to find an external in the same range and having difficulty finding one.

Yes, I believe it is a modified 4.3 TB. I installed an AEM AFR gauge and can see the I am achieving 14.7:1. I am also using ALDLDroid to monitor and log data. I have had fuel overheating issues since I first installed the Holley. The fuel pump has a very loud and irritating whine. The large volume of fuel being returned to the tank from the hot throttle body very quickly heats the fuel in the tank and from what I have read in other posts, the new gas formulations have a lower boiling point. I am hoping to kill two birds at once here, The loud pump and the boiling gas. The only heat source is the TB pushing a very large volume of hot fuel to the tanks. I am tired of dealing with this problem. I was going to order from Applied but when questioned on price (over $3000) JK got mad and hung up on me. I am not a rich guy and they charge every penny that the market will bear. I just bought a transmision module gear for $7 that they wanted $44 for. I believe in supporting our vendors but they need to support us too. Now I am considering finding one of the larger TB for the 7.4 that runs on lower fuel pressure 9 - 12 psi and not 100. Right now I am considering replacing my filters as pushing high volumes of fuel through them would likely clog them after this much time. Thanks for all the input!

So you are using a modified 4.3/305/350 TBI unit. Not a 7.4/454 unit(2”).
Leave the pump alone. If you want the fuel cooler you will need to use a fuel cooler , something like a transmission cooler.
Get Outlook"]https://aka.ms/o0ukef]Outlook for iOS[/url]
From: on behalf of Dave G
Sent: Monday, July 31, 2023 8:03:12 PM
To: GMCMH EFI
Subject: Re: [GMCMH-EFI] Blowing MufflersI wish I could give you exact part numbers but I can't, or at least it wouldn't be certain. My current TB was updated by using an earlier TB and increasing the bore to 1.8 or so and using the higher pressure/smaller injectors. There was some guy somewhere
that had been doing it for awhile. I have had very good performance from it but feel I am wasting a lot of energy to overheat my fuel. I think a pump that produces 35 - 50 PSI would be ideal, the lower the better. I may add an accumulator if pressure loss
on acceleration becomes a problem. Looking for best flow but not high pressure. What did GM use in the 94-95 Chevy trucks, or at least what was the spec output. I have even considered using a regulator with a pre-TB return in addition to the return on my TB
just so I get pressure under control. Thanks!

Dave G:

" This is a modified TB from a '95. I think a 50 psi output would supply plenty of fuel given these were originally using 9 - 11 psi."

" I am using the 94-95 setup slightly modified by AFI. Its internal regulator is set to 30"

If you can provide the Rochester and injector part numbers, we might be able to research their specs and recommend a pump.

Opps, my bad, its Keith Vasilakes who I believe has a GM based EFI system with the higher pressure Rochester TB.
-------- Forwarded Message -----
Subject:
Re: [GMCMH-EFI] Blowing Mufflers
Date:
Mon, 31 Jul 2023 16:39:39 -0400
From:
Bruce Hislop
To:
GMC Motorhome EFI Group
There was a GM throttle body EFI system used in 94 or 95 that used smaller injectors at about 30 psi. I believe that is what Randy Van Winkle is using and also KevinV (or is Kelvin? Sorry on my cellphone)
Check with them to be sure which system you are using before ordering a new pump.
Bruce Hislop

Thanks to everyone who replied with suggestions! I have considered all of them and am very grateful for your thoughts. With some guidance from Dick Patterson I have installed an all-new ignition system. ATM I am addressing the fuel system which I think delivers
way to much pressure for my throttle body (rated for 30) psi. I am boiling my gas and processing copious amounts of fuel through my system, most of which is returned to the tank. The current pump easily puts out 100 PSI and I believe it is overpowering the
built in regulator. I would like to know what external fuel pump/filter others are running and hoping to drop the pressure significantly. This is a modified TB from a '95. I think a 50 psi output would supply plenty of fuel given these were originally using
9 - 11 psi.

If you are blowing mufflers up, you have unturned fuel in them. That should NEVER happen, no matter if you have a Carburetor, or anyone's fuel injection. That is unburned fuel passing completely through the engine. Because you stated that you
have had it more than once, I would look first at your O2 sensor placement. Then, fuel/air ratios. That should give you a place to start.
Jim Hupy
Salem, Oregon

Hello friends, my first time posting here. Some of you may know me on FB as Dave Gee.
I have made every mistake possible in trying to convert to EFI on my GMC coach. I am now on my 3rd TB and am still exploding mufflers. The coach seems to run well enough but I have now destroyed 4 mufflers. I started with the Holley Quadrajet and Hyperspark.
After multiple hardware failures I decided to try AFI's GM TBI system for a mid 90's truck. It runs very well but has blown up mufflers. I may have fixed the problem by installing a new retrofitted HEI with computer control. The old distributor was in pretty
bad shape despite the engine running well. I also switched from E3 plugs to NGK Iridium. Since I am not sure the problem is solved I want to do further diagnostics and have purchased an AEM wideband sensor/gauge set and also purchased the ALDL to USB cable
for use with Tunerpro.
I am trying to find the files to load for a $31 mask as well as a concise tutorial for using Tunerpro. It seems that every site I have looked at was either gone or no longer administrated.
I know I should have started here first. Bill Van Vlack and others were kind enough to reach out to me a long time ago before I went with Holley. What a mistake that was!
Any guidance and links to the resources I need are appreciated! Thank you!
.

.

.

.

 

[Keith V]

About 75% of these answers are so wrong as to be dangerous. Comon people.
I highly doubt you have a 4.3 TB, it uses smaller bores and would never support 455 cubes.
(Unless it was bored out)
I also use the later 30psi TB on my .030 over 455. It does run out of fuel at the big end, but i dont run there. Otherwise its a better TB.
I use a pump.out of a ford. Im not home now, but I can get the pn tonight.
It does sound like the pump is suspect, i can barely hear mine run, but its heavily vibration damped.
Look on the photo site, i have a fuel injection album. Im sure the pn is there
Sent from my T-Mobile 5G Device
Get Outlook for Android https://aka.ms/AAb9ysg
________________________________
From: gmcmh-efi on behalf of Michael Beam
Sent: Tuesday, August 1, 2023 10:02:46 AM
To: gmcmh-efi
Subject: Re: [GMCMH-EFI] Blowing Mufflers
Dave
Walbro pumps are us made. Here is one you may like. [URL]https://www.summitracing.com/parts/vpn-f30000271?seid=srese1&gclid=Cj0KCQjw2qKmBhCfARIsAFy8buLK6z7dYS5lOxtUsalHTLpcePyX1y4CeWhOtS3QesBu1R22b4ck4QEaAtspEALw_wcB[/url][/url]
Sent from my iPhone
Yes, fuel pressure for 94 - 95 was 26 - 32 (THANK YOU) but is appears that is an in-tank fuel pump. I need to find an external in the same range and having difficulty finding one.
Yes, I believe it is a modified 4.3 TB. I installed an AEM AFR gauge and can see the I am achieving 14.7:1. I am also using ALDLDroid to monitor and log data. I have had fuel overheating issues since I first installed the Holley. The fuel pump has a very loud and irritating whine. The large volume of fuel being returned to the tank from the hot throttle body very quickly heats the fuel in the tank and from what I have read in other posts, the new gas formulations have a lower boiling point. I am hoping to kill two birds at once here, The loud pump and the boiling gas. The only heat source is the TB pushing a very large volume of hot fuel to the tanks. I am tired of dealing with this problem. I was going to order from Applied but when questioned on price (over $3000) JK got mad and hung up on me. I am not a rich guy and they charge every penny that the market will bear. I just bought a transmision module gear for $7 that they wanted $44 for. I believe in supporting our vendors but they need to support us too. Now I am considering finding one of the larger TB for the 7.4 that runs on lower fuel pressure 9 - 12 psi and not 100. Right now I am considering replacing my filters as pushing high volumes of fuel through them would likely clog them after this much time. Thanks for all the input!
So you are using a modified 4.3/305/350 TBI unit. Not a 7.4/454 unit(2”).
Leave the pump alone. If you want the fuel cooler you will need to use a fuel cooler , something like a transmission cooler.
Get Outlook for iOS https://aka.ms/o0ukef
________________________________
From: gmcm... on behalf of Dave G
Sent: Monday, July 31, 2023 8:03:12 PM
To: GMCMH EFI
Subject: Re: [GMCMH-EFI] Blowing Mufflers
I wish I could give you exact part numbers but I can't, or at least it wouldn't be certain. My current TB was updated by using an earlier TB and increasing the bore to 1.8 or so and using the higher pressure/smaller injectors. There was some guy somewhere that had been doing it for awhile. I have had very good performance from it but feel I am wasting a lot of energy to overheat my fuel. I think a pump that produces 35 - 50 PSI would be ideal, the lower the better. I may add an accumulator if pressure loss on acceleration becomes a problem. Looking for best flow but not high pressure. What did GM use in the 94-95 Chevy trucks, or at least what was the spec output. I have even considered using a regulator with a pre-TB return in addition to the return on my TB just so I get pressure under control. Thanks!
Dave G:
" This is a modified TB from a '95. I think a 50 psi output would supply plenty of fuel given these were originally using 9 - 11 psi."
" I am using the 94-95 setup slightly modified by AFI. Its internal regulator is set to 30"
If you can provide the Rochester and injector part numbers, we might be able to research their specs and recommend a pump.
Opps, my bad, its Keith Vasilakes who I believe has a GM based EFI system with the higher pressure Rochester TB.
-------- Forwarded Message --------
Subject: Re: [GMCMH-EFI] Blowing Mufflers
Date: Mon, 31 Jul 2023 16:39:39 -0400
From: Bruce Hislop
To: GMC Motorhome EFI Group
There was a GM throttle body EFI system used in 94 or 95 that used smaller injectors at about 30 psi. I believe that is what Randy Van Winkle is using and also KevinV (or is Kelvin? Sorry on my cellphone)
Check with them to be sure which system you are using before ordering a new pump.
Bruce Hislop
Thanks to everyone who replied with suggestions! I have considered all of them and am very grateful for your thoughts. With some guidance from Dick Patterson I have installed an all-new ignition system. ATM I am addressing the fuel system which I think delivers way to much pressure for my throttle body (rated for 30) psi. I am boiling my gas and processing copious amounts of fuel through my system, most of which is returned to the tank. The current pump easily puts out 100 PSI and I believe it is overpowering the built in regulator. I would like to know what external fuel pump/filter others are running and hoping to drop the pressure significantly. This is a modified TB from a '95. I think a 50 psi output would supply plenty of fuel given these were originally using 9 - 11 psi.
If you are blowing mufflers up, you have unturned fuel in them. That should NEVER happen, no matter if you have a Carburetor, or anyone's fuel injection. That is unburned fuel passing completely through the engine. Because you stated that you have had it more than once, I would look first at your O2 sensor placement. Then, fuel/air ratios. That should give you a place to start.
Jim Hupy
Salem, Oregon
Hello friends, my first time posting here. Some of you may know me on FB as Dave Gee.
I have made every mistake possible in trying to convert to EFI on my GMC coach. I am now on my 3rd TB and am still exploding mufflers. The coach seems to run well enough but I have now destroyed 4 mufflers. I started with the Holley Quadrajet and Hyperspark. After multiple hardware failures I decided to try AFI's GM TBI system for a mid 90's truck. It runs very well but has blown up mufflers. I may have fixed the problem by installing a new retrofitted HEI with computer control. The old distributor was in pretty bad shape despite the engine running well. I also switched from E3 plugs to NGK Iridium. Since I am not sure the problem is solved I want to do further diagnostics and have purchased an AEM wideband sensor/gauge set and also purchased the ALDL to USB cable for use with Tunerpro.
I am trying to find the files to load for a $31 mask as well as a concise tutorial for using Tunerpro. It seems that every site I have looked at was either gone or no longer administrated.
I know I should have started here first. Bill Van Vlack and others were kind enough to reach out to me a long time ago before I went with Holley. What a mistake that was!
Any guidance and links to the resources I need are appreciated! Thank you!
--
gmcmh-efi+...

--
gmcmh-efi+...

--
gmcmh-efi+...

--
gmcmh-efi+...

--




--

 

[MikeB]

He said he had an Affordable Fuel Injection TBI. Email response to my inquiry to their set up: “ Michael,
With engines that require 7.4L throttle bodies we either use 4.3L OEM gm injectors with a stronger spring to duplicate 7.4L flow or we use OEM 7.4L injectors if we have them in stock. The larger bore throttle bodies are the 1.68" 2 bbl Rochester throttle body that we then cnc the bore out to 1.89" 2 bbl. These are not the true 2" 2bbl throttle bodies.
A standard 1.68" 2bbl throttle body runs 350.00. A bored out throttle body would run 550.00.”
Sent from my iPhone
[/QUOTE]


About 75% of these answers are so wrong as to be dangerous. Comon people.
I highly doubt you have a 4.3 TB, it uses smaller bores and would never support 455 cubes.
(Unless it was bored out)
I also use the later 30psi TB on my .030 over 455. It does run out of fuel at the big end, but i dont run there. Otherwise its a better TB.
I use a pump.out of a ford. Im not home now, but I can get the pn tonight.
It does sound like the pump is suspect, i can barely hear mine run, but its heavily vibration damped.
Look on the photo site, i have a fuel injection album. Im sure the pn is there
Sent from my T-Mobile 5G Device
Get Outlook"]https://aka.ms/AAb9ysg]Outlook for Android[/url]
From: gmcmh-efi on behalf of Michael Beam
Sent: Tuesday, August 1, 2023 10:02:46 AM
To: gmcmh-efi
Subject: Re: [GMCMH-EFI] Blowing Mufflers
Dave
Walbro pumps are us made. Here is one you may like. https://www.summitracing.com/parts/vpn-f30000271?seid=srese1&gclid=Cj0KCQjw2qKmBhCfARIsAFy8buLK6z7dYS5lOxtUsalHTLpcePyX1y4CeWhOtS3QesBu1R22b4ck4QEaAtspEALw_wcB"]https://www.summitracing.com/parts/vpn-f30000271?seid=srese1&gclid=Cj0KCQjw2qKmBhCfARIsAFy8buLK6z7dYS5lOxtUsalHTLpcePyX1y4CeWhOtS3QesBu1R22b4ck4QEaAtspEALw_wcB]https://www.summitracing.com/parts/vpn-f30000271?seid=srese1&gclid=Cj0KCQjw2qKmBhCfARIsAFy8buLK6z7dYS5lOxtUsalHTLpcePyX1y4CeWhOtS3QesBu1R22b4ck4QEaAtspEALw_wcB[/url][/url][/url]
Sent from my iPhone

Yes, fuel pressure for 94 - 95 was 26 - 32 (THANK YOU) but is appears that is an in-tank fuel pump. I need to find an external in the same range and having difficulty finding one.

Yes, I believe it is a modified 4.3 TB. I installed an AEM AFR gauge and can see the I am achieving 14.7:1. I am also using ALDLDroid to monitor and log data. I have had fuel overheating issues since I first installed the Holley. The fuel pump has a very
loud and irritating whine. The large volume of fuel being returned to the tank from the hot throttle body very quickly heats the fuel in the tank and from what I have read in other posts, the new gas formulations have a lower boiling point. I am hoping to
kill two birds at once here, The loud pump and the boiling gas. The only heat source is the TB pushing a very large volume of hot fuel to the tanks. I am tired of dealing with this problem. I was going to order from Applied but when questioned on price (over
$3000) JK got mad and hung up on me. I am not a rich guy and they charge every penny that the market will bear. I just bought a transmision module gear for $7 that they wanted $44 for. I believe in supporting our vendors but they need to support us too. Now
I am considering finding one of the larger TB for the 7.4 that runs on lower fuel pressure 9 - 12 psi and not 100. Right now I am considering replacing my filters as pushing high volumes of fuel through them would likely clog them after this much time. Thanks
for all the input!

So you are using a modified 4.3/305/350 TBI unit. Not a 7.4/454 unit(2”).
Leave the pump alone. If you want the fuel cooler you will need to use a fuel cooler , something like a transmission cooler.
Get
Outlook for iOS
From:
on behalf of Dave G
Sent: Monday, July 31, 2023 8:03:12 PM
To: GMCMH EFI
Subject: Re: [GMCMH-EFI] Blowing Mufflers
I wish I could give you exact part numbers but I can't, or at least it wouldn't be certain. My current TB was updated by using an earlier TB and increasing the bore to 1.8 or so and using the higher pressure/smaller injectors. There was some guy somewhere
that had been doing it for awhile. I have had very good performance from it but feel I am wasting a lot of energy to overheat my fuel. I think a pump that produces 35 - 50 PSI would be ideal, the lower the better. I may add an accumulator if pressure loss
on acceleration becomes a problem. Looking for best flow but not high pressure. What did GM use in the 94-95 Chevy trucks, or at least what was the spec output. I have even considered using a regulator with a pre-TB return in addition to the return on my TB
just so I get pressure under control. Thanks!

Dave G:

" This is a modified TB from a '95. I think a 50 psi output would supply plenty of fuel given these were originally using 9 - 11 psi."

" I am using the 94-95 setup slightly modified by AFI. Its internal regulator is set to 30"

If you can provide the Rochester and injector part numbers, we might be able to research their specs and recommend a pump.

Opps, my bad, its Keith Vasilakes who I believe has a GM based EFI system with the higher pressure Rochester TB.
-------- Forwarded Message -----
Subject:
Re: [GMCMH-EFI] Blowing Mufflers
Date:
Mon, 31 Jul 2023 16:39:39 -0400
From:
Bruce Hislop
To:
GMC Motorhome EFI Group
There was a GM throttle body EFI system used in 94 or 95 that used smaller injectors at about 30 psi. I believe that is what Randy Van Winkle is using and also KevinV (or is Kelvin? Sorry on my cellphone)
Check with them to be sure which system you are using before ordering a new pump.
Bruce Hislop

Thanks to everyone who replied with suggestions! I have considered all of them and am very grateful for your thoughts. With some guidance from Dick Patterson I have installed an all-new ignition system. ATM I am addressing the fuel system which I think delivers
way to much pressure for my throttle body (rated for 30) psi. I am boiling my gas and processing copious amounts of fuel through my system, most of which is returned to the tank. The current pump easily puts out 100 PSI and I believe it is overpowering the
built in regulator. I would like to know what external fuel pump/filter others are running and hoping to drop the pressure significantly. This is a modified TB from a '95. I think a 50 psi output would supply plenty of fuel given these were originally using
9 - 11 psi.

If you are blowing mufflers up, you have unturned fuel in them. That should NEVER happen, no matter if you have a Carburetor, or anyone's fuel injection. That is unburned fuel passing completely through the engine. Because you stated that you
have had it more than once, I would look first at your O2 sensor placement. Then, fuel/air ratios. That should give you a place to start.
Jim Hupy
Salem, Oregon

Hello friends, my first time posting here. Some of you may know me on FB as Dave Gee.
I have made every mistake possible in trying to convert to EFI on my GMC coach. I am now on my 3rd TB and am still exploding mufflers. The coach seems to run well enough but I have now destroyed 4 mufflers. I started with the Holley Quadrajet and Hyperspark.
After multiple hardware failures I decided to try AFI's GM TBI system for a mid 90's truck. It runs very well but has blown up mufflers. I may have fixed the problem by installing a new retrofitted HEI with computer control. The old distributor was in pretty
bad shape despite the engine running well. I also switched from E3 plugs to NGK Iridium. Since I am not sure the problem is solved I want to do further diagnostics and have purchased an AEM wideband sensor/gauge set and also purchased the ALDL to USB cable
for use with Tunerpro.
I am trying to find the files to load for a $31 mask as well as a concise tutorial for using Tunerpro. It seems that every site I have looked at was either gone or no longer administrated.
I know I should have started here first. Bill Van Vlack and others were kind enough to reach out to me a long time ago before I went with Holley. What a mistake that was!
Any guidance and links to the resources I need are appreciated! Thank you!
.

.

.

.

[/QUOTE]

 

[Dave G]

Yes, bored out throttle body 30 psi to smaller injectors. Was running great
on my 10 days in Ohio until a muffler blew about 40 minutes from home. I
think I am going to build a new fuel sending unit with a 100 micron pre and
a 10 micron post filter using the Walbro pump recommended or similar. I
will likely hard connect the filters and pump using aftermarket and marine
products. Still listening to all suggestions.

 

[billvv]

Some folks have mounted the filters and pump on a plate that hinges or
drops down to allow inspection and maintenance; all inboard of the frame
rail rather than on the more vulnerable outside.

 

[Dave G]

I have a plate (not hinged yet) I installed when I first put the holley
system on. The hinge looks like a good idea but mine is pretty simple and
practical, two bolts and it drops down for service. Right now I am
considering ordering the Welbro pump (44 psi) and two cartridge (cleanable
10 and 100 micron) filters that have hard fittings between them and the
pump. I appreciate all the input, I want to order the parts today.

 

[cbirky]

I will admit to wishing this was posted a week ago! I just installed my
pumps on the frame rail and they are not very serviceable in that location.

 

[george beckman]

Yes. I am not a fan of gas outside of the frame.
Some folks have mounted the filters and pump on a plate that hinges or drops down to allow inspection and maintenance; all inboard of the frame rail rather than on the more vulnerable outside.
---------
Best Wishes,
George
gbeckman

 

[GMC Nick]

I wish I could give you exact part numbers but I can't, or at least it
wouldn't be certain. My current TB was updated by using an earlier TB and
increasing the bore to 1.8 or so and using the higher pressure/smaller
injectors. There was some guy somewhere that had been doing it for awhile.
I have had very good performance from it but feel I am wasting a lot of
energy to overheat my fuel. I think a pump that produces 35 - 50 PSI would
be ideal, the lower the better. I may add an accumulator if pressure loss
on acceleration becomes a problem. Looking for best flow but not high
pressure. What did GM use in the 94-95 Chevy trucks, or at least what was
the spec output. I have even considered using a regulator with a pre-TB
return in addition to the return on my TB just so I get pressure under
control. Thanks!

Hi Dave,
I'm a relative new member but old time (over 30 years) GMC Motorhome guy.

I too installed a AFI EFI system last summer and have a love/hate relationship with the system. Have you been successful in connecting TunerPro to your system? My thoughts are headed in that direction.
Thanks, Nick

 

[RF_Burns]

Hi Dave,
I'm a relative new member but old time (over 30 years) GMC Motorhome guy.

I too installed a AFI EFI system last summer and have a love/hate relationship with the system. Have you been successful in connecting TunerPro to your system? My thoughts are headed in that direction.
Thanks, Nick

AFI appears to use a GM 7747 Engine Control Module (ECM). These ECM's used a PROM memory chip that was programmed for the engine which it was controlling. The only way to change the programming of the ECM is to remove the memory chip and having it reprogrammed. Unless you are an electronics guy, this procedure is not for the faint of heart. There are Tuner guys out there that do this, or AFI can do it for you. Trouble is, you need to be able to tell them what changes to make, which takes skill and equipment.

The programming file (the "Tune") is called a "Bin" file and TunerPro is used to make modifications to the Bin file. This file is then used to program the memory chip, or if you have an EBL upgrade, you just download the Bin file into the ECM.

Dynamic EFI supplied a circuit board (called the EBL) which replaced the logic board in the GM 7747 ECM. The EBL used modern "Flash" re-programmable memory so you could change the programming using a laptop. This was a great improvement over the fixed 7747 setup supplied by Howell or AFI. Unfortunately, Dynamic EFI was a one-man business and he passed away last summer, so there are no more EBLs that I know of. If you see an EBL Flash or Flash II for sale, grab it! The EBL can also self-tune it's fuel tables.

At this point, the alternative to the EBL upgrade is a Mega-Squirt. MS directly replaces the 7747. MS is more expensive than the EBL, but has lots of support and is Open Source. @Wally uses Mega-Squirt.

As far as the fuel pump goes, the fuel pressure regulator sets the fuel pressure no matter the maximum pressure rating of the pump. The regulator bypasses fuel to keep its set pressure. As someone previously mentioned, Howell used a 100PSI rated pump on 13PSI systems. What matters is the pressure allows each of the two injectors to pass approximately 80 pounds of fuel per hour (PPH) at wide open throttle.

So unless Affordable EFI was supplying their ECM's with the EBL upgrade, you can't directly use TunerPro.

When I purchased my Howell EFI system (which used a Holley TB) I had many problems with it including backfires and stumbling. It turned out that Holley had changed the injectors used in their largest TB from 80 PPH to 60 PPH. This caused lean operation whenever Fuel Enrichment was called for, such as when stepping on the gas to accelerate. The fix was to increase to the fuel pressure from 13 PSI to 20 PSI. The Holley TB had a built-in fuel pressure regulator, but it maxed out at about 17 PSI and above 16 PSI it was not a stable pressure. An external regulator was the best fix. I eventually installed a Rochester TB with 80PPH injectors and an EBL.

I now used dual fuel pumps without a fuel tank selector valve. They are AirTex 8094 (I believe) but it seems AirTex North America was purchased by another company (unknown name). The 8094 was rated at 13PSI for GM Throttle Bodies.

I still like a GM based EFI system. Parts are widely available and not proprietary.

 

[GMC Nick]

AFI appears to use a GM 7747 Engine Control Module (ECM). These ECM's used a PROM memory chip that was programmed for the engine which it was controlling. The only way to change the programming of the ECM is to remove the memory chip and having it reprogrammed. Unless you are an electronics guy, this procedure is not for the faint of heart. There are Tuner guys out there that do this, or AFI can do it for you. Trouble is, you need to be able to tell them what changes to make, which takes skill and equipment.

The programming file (the "Tune") is called a "Bin" file and TunerPro is used to make modifications to the Bin file. This file is then used to program the memory chip, or if you have an EBL upgrade, you just download the Bin file into the ECM.

Dynamic EFI supplied a circuit board (called the EBL) which replaced the logic board in the GM 7747 ECM. The EBL used modern "Flash" re-programmable memory so you could change the programming using a laptop. This was a great improvement over the fixed 7747 setup supplied by Howell or AFI. Unfortunately, Dynamic EFI was a one-man business and he passed away last summer, so there are no more EBLs that I know of. If you see an EBL Flash or Flash II for sale, grab it! The EBL can also self-tune it's fuel tables.

At this point, the alternative to the EBL upgrade is a Mega-Squirt. MS directly replaces the 7747. MS is more expensive than the EBL, but has lots of support and is Open Source. @Wally uses Mega-Squirt.

As far as the fuel pump goes, the fuel pressure regulator sets the fuel pressure no matter the maximum pressure rating of the pump. The regulator bypasses fuel to keep its set pressure. As someone previously mentioned, Howell used a 100PSI rated pump on 13PSI systems. What matters is the pressure allows each of the two injectors to pass approximately 80 pounds of fuel per hour (PPH) at wide open throttle.

So unless Affordable EFI was supplying their ECM's with the EBL upgrade, you can't directly use TunerPro.

When I purchased my Howell EFI system (which used a Holley TB) I had many problems with it including backfires and stumbling. It turned out that Holley had changed the injectors used in their largest TB from 80 PPH to 60 PPH. This caused lean operation whenever Fuel Enrichment was called for, such as when stepping on the gas to accelerate. The fix was to increase to the fuel pressure from 13 PSI to 20 PSI. The Holley TB had a built-in fuel pressure regulator, but it maxed out at about 17 PSI and above 16 PSI it was not a stable pressure. An external regulator was the best fix. I eventually installed a Rochester TB with 80PPH injectors and an EBL.

I now used dual fuel pumps without a fuel tank selector valve. They are AirTex 8094 (I believe) but it seems AirTex North America was purchased by another company (unknown name). The 8094 was rated at 13PSI for GM Throttle Bodies.

I still like a GM based EFI system. Parts are widely available and not proprietary.

Great explanation, thank you. I too, like the GM based system for the same reasons. The ECM is service# 16197427, a pretty commonly used unit. I'm very familiar with eprom programming and have the equipment to do it as well. By getting a " turnkey" system I had hoped not to have to get into it but after a lot of going around, I will have no choice if I want this coach running to my expectations.

My curiosity is about folk's experiences with TunerPro in their application with their GMC, mask and .xdf selection etc. The devil is in the detail with this. Getting into fuel and timing tables is easier said than done.

Mega-Squirt is what I likely would have gone with if I decided to build my own system before going with AFI. BTW, moates.net has a great selection of eprom/eeprom adapters, cables etc.. They are wonderful folks.

 

[RF_Burns]

Back 15 years ago when I installed my Howell and had problems right off (no one knew Holley had gone to smaller injectors) I was using a piece of software to log the OBD port info (can't remember what it was called now). I then had to use a Hex editor to change the bin file and re-write it. The only choice in PROMs was UV erasable at the time. I then discovered I could use a Flash memory chip by leaving 4 leads hanging by stacking chip sockets. That sped things up quite a bit.

With TunerPro there is a different XDF file for each ECM model. There is even a XDF file specific to the EBL Bins. The XDF for your ECM looks to be 31.xdf.

I may be wrong in some of my recollections... its been 15 years since I was up to my elbows in this stuff.

 

[GMC Nick]

Back 15 years ago when I installed my Howell and had problems right off (no one knew Holley had gone to smaller injectors) I was using a piece of software to log the OBD port info (can't remember what it was called now). I then had to use a Hex editor to change the bin file and re-write it. The only choice in PROMs was UV erasable at the time. I then discovered I could use a Flash memory chip by leaving 4 leads hanging by stacking chip sockets. That sped things up quite a bit.

With TunerPro there is a different XDF file for each ECM model. There is even a XDF file specific to the EBL Bins. The XDF for your ECM looks to be 31.xdf.

I may be wrong in some of my recollections... its been 15 years since I was up to my elbows in this stuff.

I believe you're absolutely right, the 31.xdf has parsed things correctly. I've read the bin from my memcal as a starting point but can't help but think there's successful tunes (.bins) out there that might be better starting points for coach engines. Right now it's education, education and more education.

 

[RF_Burns]

I believe you're absolutely right, the 31.xdf has parsed things correctly. I've read the bin from my memcal as a starting point but can't help but think there's successful tunes (.bins) out there that might be better starting points for coach engines. Right now it's education, education and more education.

My laptop from that era has long since bit the dust, and any bins I had were for the 7747 ECM anyway.