cold star issue revised
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2021 C4 of the Year - Unmodified Finalist
cold star issue revised
You may recall recently I had a post up about cold start valve problems. I got some very good help from very good people.
It turns out it is not the cold start valve or injector at all. It is the residual pressure valve in under the plenum AND (if you can believe this) a faulty valve on the fuel pump pick-up.
So the fuel is bleeding back out of the system overnight. Also apparently the fuel pump was replaced just before we bought the car but it was replaced with a NAPA generic pump and it ain't got the ***** to do the job. The pump has to be replaced with an OEM pump when everthing else is done.
I will keep you posted. PS thanks for all the input from the folks that helped. I will PM diagnostics if anyone is interested.
phat
It turns out it is not the cold start valve or injector at all. It is the residual pressure valve in under the plenum AND (if you can believe this) a faulty valve on the fuel pump pick-up.
So the fuel is bleeding back out of the system overnight. Also apparently the fuel pump was replaced just before we bought the car but it was replaced with a NAPA generic pump and it ain't got the ***** to do the job. The pump has to be replaced with an OEM pump when everthing else is done.
I will keep you posted. PS thanks for all the input from the folks that helped. I will PM diagnostics if anyone is interested.
phat
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Joined: Aug 2004
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Originally Posted by phat87
You may recall recently I had a post up about cold start valve problems. I got some very good help from very good people.
It turns out it is not the cold start valve or injector at all. It is the residual pressure valve in under the plenum AND (if you can believe this) a faulty valve on the fuel pump pick-up.
So the fuel is bleeding back out of the system overnight. Also apparently the fuel pump was replaced just before we bought the car but it was replaced with a NAPA generic pump and it ain't got the ***** to do the job. The pump has to be replaced with an OEM pump when everthing else is done.
I will keep you posted. PS thanks for all the input from the folks that helped. I will PM diagnostics if anyone is interested.
phat
It turns out it is not the cold start valve or injector at all. It is the residual pressure valve in under the plenum AND (if you can believe this) a faulty valve on the fuel pump pick-up.
So the fuel is bleeding back out of the system overnight. Also apparently the fuel pump was replaced just before we bought the car but it was replaced with a NAPA generic pump and it ain't got the ***** to do the job. The pump has to be replaced with an OEM pump when everthing else is done.
I will keep you posted. PS thanks for all the input from the folks that helped. I will PM diagnostics if anyone is interested.
phat
How did you arrive at this conclusion and have you changed the parts?
Last edited by lefoy84; Nov 3, 2006 at 06:21 PM.
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Originally Posted by rick lambert
I've been using a NAPPA fuel pump for the past 4-5 years and its worked just fine.
That's why I asked what parts were changed.
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Fuel pump
I haven't changed out any parts yet. I can hear the fuel pump working when I wsitch on the ignition. I let is cycle through twice and then the pump doesn't engage again, (its primed itself) After that I have to very quickly just tap the ignition a couuple of times to purge the air from the line. (push fuel up) and then it will start.
All the electrical checks were positive according the diagnostic flow chart. It was the flow chart sequence that led to the check valve and fuel pump diagnosis.
NAPA parts may be fine, but I gotta tell ya I'm battin' zero for three on their stuff so far.
All the electrical checks were positive according the diagnostic flow chart. It was the flow chart sequence that led to the check valve and fuel pump diagnosis.
NAPA parts may be fine, but I gotta tell ya I'm battin' zero for three on their stuff so far.
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Have you put a fuel press gauge on the rail? The car is designed to run the fuel pump for 2 secs when the key is turned to on. This is due to the fact that most fuel delivery systems will leak down over time. I don't remember the details of your previous thread. Does it still have the same problem? Even though the system press may have leaked down, there should not be any air in the lines. Just fuel at ambient pressure.
Last edited by lefoy84; Nov 3, 2006 at 06:53 PM.
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From: The Top of Utah
Originally Posted by phat87
So the fuel is bleeding back out of the system overnight. Also apparently the fuel pump was replaced just before we bought the car but it was replaced with a NAPA generic pump and it ain't got the ***** to do the job. The pump has to be replaced with an OEM pump when everthing else is done.
The fuel (pressure) can escape to the tank via either the check valve in the fuel pump (unlikely with a new pump) or through a weak, defective, fuel pressure regulator ("the residual pressure valve in under the plenum"). A little testing and trouble shooting can tell you which save you some time and money.
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CFI-EFI is right. My gut says you have been given some bad advice. The GM service manual has an excellent troubleshooting guide that I used to find what was causing my fuel press to leak down rapidly. Turned out it was the fuel pulsator.
Last edited by lefoy84; Nov 3, 2006 at 06:58 PM.
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From: Summerland B.C. Canada
Originally Posted by phat87
After that I have to very quickly just tap the ignition a couuple of times to purge the air from the line. (push fuel up) and then it will start.
Toss the dampner above fuel pump and you will probably cure your initial low pressure. Mine would drop like a rock before i replaced the dampner with hose and clamps. You can test the pump check valve while you have it out for the dampner removal.
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Originally Posted by AGENT 86
Where is this air comming from ?
Toss the dampner above fuel pump and you will probably cure your initial low pressure. Mine would drop like a rock before i replaced the dampner with hose and clamps. You can test the pump check valve while you have it out for the dampner removal.
Toss the dampner above fuel pump and you will probably cure your initial low pressure. Mine would drop like a rock before i replaced the dampner with hose and clamps. You can test the pump check valve while you have it out for the dampner removal.