Blowing Mufflers

J

Jim Hupy

New member
May 28, 2010
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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
 
Nearly all the muffler problems I’ve seen are related to excessive spark plug gaps (greater than .038), coil failure, leading to dumping fuel into the air pump that is the engine, which then pumps it into the muffler. Should the ignition system decide to throw a couple of sparks, it blows out the muffler.
Recommendations -
1. Make certain your charging system is making the right amount of DC, and that it’s not all noisy indicating rectifier failure. I’ve seen many bad alternators cause module problems.
2. Replace the Coil and the Module with new, Delco parts.
3. fresh wires
4. Clean those plugs and gap at .038
HTH
Dolph Santorine
Dolph
Excuse me for not being my usual wordy and sporadically verbose self. This message is sent from my iPhone.
No trees were killed in the sending of this message and few long dead dinosaurs were involved. A large number of electrons were terribly inconvenienced.
[/QUOTE]
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 HupySalem, 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!
Click to expand...
Click to expand...
 
Start off with a set of AC spark plugs for the year and motor in your coach. In the dealerships and aftermarket shops that I have worked in I have fixed numerous misfires and drivability concerns with OEM spark plugs. I have that the aftermarket just doesn’t work correctly. Stick with copper core as anything else is a waist and a potential problem.Do you have a scan tool to read live data with?If so what is the blocklearn and intergrader at? Ideal is 128+-10. What is your fuel pressure? When you turn off is there any fuel in the intake, TBI at full open throttle?
Sent from my iPhone
[/QUOTE]
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 HupySalem, 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!
Click to expand...
Click to expand...
 
Maybe….
My experience was failed cheap mufflers. Local Shop installed them on mine and a friend’s coach…. So 6 failed mufflers between us in just a couple summers. Then another shop swapped out the last blown ones to a good quality one and that has been fine for a long time.
Never really noticed any backfiring. But sure have seen many blown up cheap mufflers.
 
If you are having the same problem with different FI systems installed, my
guess is that it isn't the FI system causing the problem. Ignition
components, intake and / or exhaust leak.
 
We have to remember our long time guru friend Dick Patterson’s wry comment on issues like this. 90% of all carburetor/EFI problems are ignition. I cannot begin to tell the oddities caused by the ignition module, but here is a recent example:
Fitech was running very lean with other problems.(The rear bumper was blued from the exhaust heat.) The handheld showed that upon throttle release, the RPMs went to idle. The analog tach connected to the same tach post showed proper (e.g. 2300 RPMs). Owner changed the module and the handheld and other problems corrected. I still say, that this is impossible—can’t happen. Apparently, the Fitech is analyzing the "tach signal” differently. I always assumed it was a simple pulse signal.
If you are having the same problem with different FI systems installed, my guess is that it isn't the FI system causing the problem. Ignition components, intake and / or exhaust leak.
---------
Best Wishes,
George
gbeckman
 
And the O2 sensor couldn't care less about extra fuel in the exhaust. It only registers the O2 levels. When a cylinder misses, no O2 is used, and the O2 sensor assumes there was not enough fuel to use up the O2—a lean condition. The EFI adds more fuel to the mixture. The firing cylinders run richer, and more fuel is dumped by the missing cylinders until the O2 sensor is satisfied enough O2 is being used in the burn.
Yeah, sounds to me like one or two cylinders arent firing and are dumping fuel into the exhaust
---------
Best Wishes,
George
gbeckman
 
The signal from the O2 sensor is an analog signal. The computer only
recognizes a digital signal. So, some conversion is happening before the
data from the O2 sensor gets to the computer, that equates to time in
milliseconds between when the signal is read and the computer sends signals
to the fuel injectors. No wonder mufflers suffer as a result. Cheap ones
flat out don't.
Jim Hupy
Salem, Oregon
 
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.
 
I used an Airtex 8094 for one of my pumps for my GM TBI. It seems to be out
of stock. I think the pressure rating of the pump needs to be just a little
higher than what the built-in regulator supplies so that the amount of
return fuel is minimized. The 8094 is rated for 17psi. I also bought a
Herko K2000 from a friend. They both work fine.
 
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
 
Any pump that you use is going to be regulated by the throttle body, depending on the spring in the regulator. What is the regulated pressure running at? What is your target PSI?On a jeep I put together I was running a 100 PSI pump but had a had 12psi regulated at the throttle body . The pressure return is not a problem. One problem that you can run in to is lack of volume. What size fuel line are you running?
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 HupySalem, 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+...

--


--

 
I am using the 94-95 setup slightly modified by AFI. Its internal regulator
is set to 30 but I am sending it 100 resulting in a large volume of very
hot fuel being sent back to the tanks and they boil. I did try deadheading
it with a regulator set to 30 (the minimum I could get to with a Holley
regulator) and it ran but I did not drive it having been suggested that I
may end up with vapor lock. I currently run 100 PSI to the throttle body
and I think it's overwhelming the internal regulator so I have been looking
for the specs of a 94 - 95 454 chevy fuel pump but have not found the data
yet. The units suggested so far are for the earlier TB that uses a larger
injector with lower pressure.
 
Look around for as set of injectors from a 88-93 GM truck with a 7.4L 454 motor. Replace the pressure regulator spring with a 0-20 pi’s spring set at 13psi. If you feel that the fuel is boiling in the return then install a fuel cooler like a 1st gen Deramax used.
Sent from my iPhone
[/QUOTE]
I am using the 94-95 setup slightly modified by AFI. Its internal regulator is set to 30 but I am sending it 100 resulting in a large volume of very hot fuel being sent back to the tanks and they boil. I did try deadheading it with a regulator set to 30 (the minimum I could get to with a Holley regulator) and it ran but I did not drive it having been suggested that I may end up with vapor lock. I currently run 100 PSI to the throttle body and I think it's overwhelming the internal regulator so I have been looking for the specs of a 94 - 95 454 chevy fuel pump but have not found the data yet. The units suggested so far are for the earlier TB that uses a larger injector with lower pressure.
Any pump that you use is going to be regulated by the throttle body, depending on the spring in the regulator. What is the regulated pressure running at? What is your target PSI?On a jeep I put together I was running a 100 PSI pump but had a had 12psi regulated at the throttle body . The pressure return is not a problem. One problem that you can run in to is lack of volume. What size fuel line are you running?
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 HupySalem, 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!
.
Click to expand...
Click to expand...
gmcmh-efi+....
Click to expand...
gmcmh-efi+....
Click to expand...
Click to expand...
 
The pump supplied by Howell was rated for 100psi to a 12 psi injection
system.
The 100psi is the max the pump can deliver. The regulator bypasses the
extra fuel fuel back to the tank so the system never sees 100psi.
I have two Airtex pumps, but I can't find the North American website.
Something tells me they were purchased and are now called something else?
Bruce Hislop
On Mon, Jul 31, 2023, 4:52 PM MICHAEL ORLANDI
 
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+...



--
Google
Groups "GMCMH
from it,



 
Several GMC owners here in the Northwest have home brewed efi systems using
the GM throttle bodies and 7747 computers. Various 02 sensors and
ignitions. Most work well with minimal "twiddling" with BIN files. Most are
not very complex.
Jim Hupy
Salem, Oregon
 
If memory serves me I believe that those systems ran at 20 psi. They would have intank pumps.
Get Outlook for iOS https://aka.ms/o0ukef
________________________________
From: gmcmh-efi on behalf of James Hupy
Sent: Monday, July 31, 2023 5:35:31 PM
To: gmcmh-efi
Subject: Re: [GMCMH-EFI] Blowing Mufflers
Several GMC owners here in the Northwest have home brewed efi systems using the GM throttle bodies and 7747 computers. Various 02 sensors and ignitions. Most work well with minimal "twiddling" with BIN files. Most are not very complex.
Jim Hupy
Salem, Oregon
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+...

--


--


--

 
If you can provide the Rochester and injector part numbers, we might be
able to research their specs and recommend a pump.
 
GMCMI Fall 2026 Rally
Applied GMC

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