Issue with rough idle and stalling with electric fuel pump

Tom Lins

Tom Lins

New member
Dec 30, 2005
939
0
1
Elkton, FL
I have what to me is a strange issue that I don't understand.
I am hoping someone has run into this before or has some things I can check.

Just got the coach out of the storage area and brought it to the house for some cleaning in anticipation on takeing some short trips.
It had been sitting for 8 months or so with fuel stabilizer and an almost full tank.
It was running a little rough so I changed the plugs (NGK) and wires.
It ran noticeably better so I called it a day after doing some cleaning.
Next day I went out to drive it back to the storage yard and during warming it up it started to run very rough and stall.

Some background:
I replaced the failed isolater with a yandina combiner last week and during troubleshooting I got a 20v reading on the center post of the isolater.
I do not have a mechanical fuel pump only a Carter electric pump. That was done by one of the PO's
The carb is a rebuilt I got from JimK just before the Pandemic when I had 2 FITech EFI's go belly up in 2019.
So this carb has not been run more than 500 miles.

Right now when I start it and warm it up it runs rough like it is missing unless I turn off the the electric fuel pump (there is a switch on the
dash)
When I turn off the electric pump after 5 to 7 seconds the idle smooths out at about 900 rpm.
When I turn on the fuel pump after 5 t0 10 seconds it starts running rough and will stall if I do not touch the gas pedal.
I have also noticed that when I turn on the pump the volt meter on the dash drops from about 14 to about 13.

--
Tom Lins
St Augustine, FL
77 GM Rear Twin, Dry Bath, 455, Aluminum Radiator Quad-Bag Suspension Solar Panel
Manuals on DVD
YOUTUBE Channel: GMC Dealer Training Tapes
http://www.bdub.net/tomlins/
 
What is your fuel pressure with the pump on?
________________________________
From: Tom Lins
Sent: Wednesday, June 23, 2021 11:23 AM
To: gmclist
Subject: [GMCnet] Issue with rough idle and stalling with electric fuel pump

I have what to me is a strange issue that I don't understand.
I am hoping someone has run into this before or has some things I can check.

Just got the coach out of the storage area and brought it to the house for some cleaning in anticipation on takeing some short trips.
It had been sitting for 8 months or so with fuel stabilizer and an almost full tank.
It was running a little rough so I changed the plugs (NGK) and wires.
It ran noticeably better so I called it a day after doing some cleaning.
Next day I went out to drive it back to the storage yard and during warming it up it started to run very rough and stall.

Some background:
I replaced the failed isolater with a yandina combiner last week and during troubleshooting I got a 20v reading on the center post of the isolater.
I do not have a mechanical fuel pump only a Carter electric pump. That was done by one of the PO's
The carb is a rebuilt I got from JimK just before the Pandemic when I had 2 FITech EFI's go belly up in 2019.
So this carb has not been run more than 500 miles.

Right now when I start it and warm it up it runs rough like it is missing unless I turn off the the electric fuel pump (there is a switch on the
dash)
When I turn off the electric pump after 5 to 7 seconds the idle smooths out at about 900 rpm.
When I turn on the fuel pump after 5 t0 10 seconds it starts running rough and will stall if I do not touch the gas pedal.
I have also noticed that when I turn on the pump the volt meter on the dash drops from about 14 to about 13.

--
Tom Lins
St Augustine, FL
77 GM Rear Twin, Dry Bath, 455, Aluminum Radiator Quad-Bag Suspension Solar Panel
Manuals on DVD
YOUTUBE Channel: GMC Dealer Training Tapes
http://www.bdub.net/tomlins/
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
 
Tom,

If possible, you need to put a fuel pressure gauge at the inlet to the card
to check the output pressure of the electric pump, 'cause it sure sounds
like the carb's float is being "sunk" (overpowered) by that pressure,
causing you to have an over-rich idle mixture.

JMHO,

Ken H.

> I have what to me is a strange issue that I don't understand.
> I am hoping someone has run into this before or has some things I can
> check.
>
> Just got the coach out of the storage area and brought it to the house for
> some cleaning in anticipation on takeing some short trips.
> It had been sitting for 8 months or so with fuel stabilizer and an almost
> full tank.
> It was running a little rough so I changed the plugs (NGK) and wires.
> It ran noticeably better so I called it a day after doing some cleaning.
> Next day I went out to drive it back to the storage yard and during
> warming it up it started to run very rough and stall.
>
> Some background:
> I replaced the failed isolater with a yandina combiner last week and
> during troubleshooting I got a 20v reading on the center post of the
> isolater.
> I do not have a mechanical fuel pump only a Carter electric pump. That was
> done by one of the PO's
> The carb is a rebuilt I got from JimK just before the Pandemic when I had
> 2 FITech EFI's go belly up in 2019.
> So this carb has not been run more than 500 miles.
>
> Right now when I start it and warm it up it runs rough like it is missing
> unless I turn off the the electric fuel pump (there is a switch on the
> dash)
> When I turn off the electric pump after 5 to 7 seconds the idle smooths
> out at about 900 rpm.
> When I turn on the fuel pump after 5 t0 10 seconds it starts running rough
> and will stall if I do not touch the gas pedal.
> I have also noticed that when I turn on the pump the volt meter on the
> dash drops from about 14 to about 13.
>
>
> --
> Tom Lins
> St Augustine, FL
> 77 GM Rear Twin, Dry Bath, 455, Aluminum Radiator Quad-Bag Suspension
> Solar Panel
> Manuals on DVD
> YOUTUBE Channel: GMC Dealer Training Tapes
> http://www.bdub.net/tomlins/
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>
 
Yes your electric pump may be putting out too high a pressure should be less then 7psi also make sure your float level is set correctly.
--
Roy Keen
Minden,NV
76 X Glenbrook
 
> What is your fuel pressure with the pump on?

I had not checked that
I have ordered a new Carter P4070.
It should be here tomorrow so I will check the new one after I install it.
Could an over pressure issue cause the rough idle?
--
Tom Lins
St Augustine, FL
77 GM Rear Twin, Dry Bath, 455, Aluminum Radiator Quad-Bag Suspension Solar Panel
Manuals on DVD
YOUTUBE Channel: GMC Dealer Training Tapes
http://www.bdub.net/tomlins/
 
> Yes your electric pump may be putting out too high a pressure should be less then 7psi also make sure your float level is set correctly.

I ordered a new Carter P4070 I will check the pressure on the new one.
I need to sit down in the shade with a nice cold one at the moment.

--
Tom Lins
St Augustine, FL
77 GM Rear Twin, Dry Bath, 455, Aluminum Radiator Quad-Bag Suspension Solar Panel
Manuals on DVD
YOUTUBE Channel: GMC Dealer Training Tapes
http://www.bdub.net/tomlins/
 
> Tom,
>
> If possible, you need to put a fuel pressure gauge at the inlet to the card
> to check the output pressure of the electric pump, 'cause it sure sounds
> like the carb's float is being "sunk" (overpowered) by that pressure,
> causing you to have an over-rich idle mixture.
>
> JMHO,
>
> Ken H.
>

>
> Well Ken your HO turned out correct as usual.
>
> put my FI pressure meter on the fuel line and measured 25 lbs of pressure.
> I am leaving the meter connected so I can measure the pressure once the new P4070 is installed.
>
> Thank you all.
>
> I will report back after the new pump is in

--
Tom Lins
St Augustine, FL
77 GM Rear Twin, Dry Bath, 455, Aluminum Radiator Quad-Bag Suspension Solar Panel
Manuals on DVD
YOUTUBE Channel: GMC Dealer Training Tapes
http://www.bdub.net/tomlins/
 
It sure sounds like you found your problem. 25 PSI is nowhere near close to the 7 PSI maximum you should have. I believe that is called a 5 PSI
pump with a maximum tolerance of 7 PSI.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
Sounds like the pressure relief valve in the pump is stuck. This could happen while sitting over the winter. I don't have my /Carter pump handy but I
think there is an external screw with a spring under it and the relief shuttle. See if you can find it and if the shuttle is stuck.
--
DAVE KING
lurker, wannabe
Toronto, Ontario, Canada
 
He has a pump that was for Fuel injection. It's a high(er) pressure pump.
It needs a pressure regulator or a lower pressure pump

Keith Vasilakes
Mounds View MN
76 exRoyale
MicroLevelhttp://www.gmcmotorhomemarketplace.com/vasilakes/microlevel_intro.pdf

________________________________
From: Dave King
Sent: Wednesday, June 23, 2021 9:41 PM
To: gmclist
Subject: [GMCnet] Re: Issue with rough idle and stalling with electric fuel pump

Sounds like the pressure relief valve in the pump is stuck. This could happen while sitting over the winter. I don't have my /Carter pump handy but I
think there is an external screw with a spring under it and the relief shuttle. See if you can find it and if the shuttle is stuck.
--
DAVE KING
lurker, wannabe
Toronto, Ontario, Canada
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No it is not a pump for fuel injection, I removed it when I took the FI-Tech fuel injection off.
What was on there was a Carter P4070 which is supposed to put out 4 to 6 psi and it was putting out 25
I installed a new Carter P4070 today and checked the pressure going to the Quadrajet and it is around 5 psi although it is hard
to be precise as the gauge is meant to measure pressure on EFI systems but it is what I have on hand.

After measuring the pressure I warmed up the engine and it settled into a nice smooth idle. Road test has to wait until tomorrow as the afternoon frog
strangler is about to start.

There was a step in the installation instructions that was not on the instructions for the pump that failed.
They want a filter before the pump, I wonder if some crud caused the pressure issue. So now there are filters before and after the pump.

--
Tom Lins
St Augustine, FL
77 GM Rear Twin, Dry Bath, 455, Aluminum Radiator Quad-Bag Suspension Solar Panel
Manuals on DVD
YOUTUBE Channel: GMC Dealer Training Tapes
http://www.bdub.net/tomlins/
 
> Sounds like the pressure relief valve in the pump is stuck. This could happen while sitting over the winter. I don't have my /Carter pump handy
> but I think there is an external screw with a spring under it and the relief shuttle. See if you can find it and if the shuttle is stuck.

This Carter P4070 is a sealed unit.
--
Tom Lins
St Augustine, FL
77 GM Rear Twin, Dry Bath, 455, Aluminum Radiator Quad-Bag Suspension Solar Panel
Manuals on DVD
YOUTUBE Channel: GMC Dealer Training Tapes
http://www.bdub.net/tomlins/
 
> He has a pump that was for Fuel injection. It's a high(er) pressure pump.
> It needs a pressure regulator or a lower pressure pump
>
> Keith Vasilakes
> Mounds View MN
> 76 exRoyale
> MicroLevel

Keith
Sorry I was not more precise in my initial post as the pump was a Carter P4070 and the new one is also a Carter P4070.

--
Tom Lins
St Augustine, FL
77 GM Rear Twin, Dry Bath, 455, Aluminum Radiator Quad-Bag Suspension Solar Panel
Manuals on DVD
YOUTUBE Channel: GMC Dealer Training Tapes
http://www.bdub.net/tomlins/
 
Ah the pump change wasn't clear in the OP.
Glad you got it fixed, I wonder what caused the pressure increase, debris in the relief valve?
________________________________
From: Tom Lins
Sent: Thursday, June 24, 2021 3:48 PM
To: gmclist
Subject: [GMCnet] Re: Issue with rough idle and stalling with electric fuel pump

> Sounds like the pressure relief valve in the pump is stuck. This could happen while sitting over the winter. I don't have my /Carter pump handy
> but I think there is an external screw with a spring under it and the relief shuttle. See if you can find it and if the shuttle is stuck.

This Carter P4070 is a sealed unit.
--
Tom Lins
St Augustine, FL
77 GM Rear Twin, Dry Bath, 455, Aluminum Radiator Quad-Bag Suspension Solar Panel
Manuals on DVD
YOUTUBE Channel: GMC Dealer Training Tapes
http://www.bdub.net/tomlins/
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
 
Frog strangler??

Sully
Bellevue wa

> Ah the pump change wasn't clear in the OP.
> Glad you got it fixed, I wonder what caused the pressure increase, debris
> in the relief valve?
> ________________________________
> From: Tom Lins
> Sent: Thursday, June 24, 2021 3:48 PM
> To: gmclist
> Subject: [GMCnet] Re: Issue with rough idle and stalling with electric
> fuel pump
>

> > Sounds like the pressure relief valve in the pump is stuck. This could
> happen while sitting over the winter. I don't have my /Carter pump handy
> > but I think there is an external screw with a spring under it and the
> relief shuttle. See if you can find it and if the shuttle is stuck.
>
>
> This Carter P4070 is a sealed unit.
> --
> Tom Lins
> St Augustine, FL
> 77 GM Rear Twin, Dry Bath, 455, Aluminum Radiator Quad-Bag Suspension
> Solar Panel
> Manuals on DVD
> YOUTUBE Channel: GMC Dealer Training Tapes
> http://www.bdub.net/tomlins/
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>
 
What is your system voltage? I didn’t see a good resolution to that mentioned 20V issue. Pump output is pretty tied to voltage and tracks pretty
close. I prefer a good 120A isolator, then add the combiner to that using the binding posts on the isolator as a convenient junction block.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
> What is your system voltage? I didn’t see a good resolution to that mentioned 20V issue. Pump output is pretty tied to voltage and tracks pretty
> close. I prefer a good 120A isolator, then add the combiner to that using the binding posts on the isolator as a convenient junction block.

The voltage is normal now and was normal while the pump was producing 25 psi
Don't know what caused the pump to start putting out 25 psi
Possibly crud from the tank? or voltage spike?
--
Tom Lins
St Augustine, FL
77 GM Rear Twin, Dry Bath, 455, Aluminum Radiator Quad-Bag Suspension Solar Panel
Manuals on DVD
YOUTUBE Channel: GMC Dealer Training Tapes
http://www.bdub.net/tomlins/
 
> Frog strangler??
>
> Sully
> Bellevue wa

We get thunder storms that at times seem like they could strangle a frog.
Most afternoons this time of year.
--
Tom Lins
St Augustine, FL
77 GM Rear Twin, Dry Bath, 455, Aluminum Radiator Quad-Bag Suspension Solar Panel
Manuals on DVD
YOUTUBE Channel: GMC Dealer Training Tapes
http://www.bdub.net/tomlins/
 
Aha

Sully

> > Frog strangler??
> >
> > Sully
> > Bellevue wa
>
> We get thunder storms that at times seem like they could strangle a frog.
> Most afternoons this time of year.
> --
> Tom Lins
> St Augustine, FL
> 77 GM Rear Twin, Dry Bath, 455, Aluminum Radiator Quad-Bag Suspension
> Solar Panel
> Manuals on DVD
> YOUTUBE Channel: GMC Dealer Training Tapes
> http://www.bdub.net/tomlins/
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>
 
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