99 tahoe with 5.7 won’t stay running!

[ANder]

Hey all. I have a 99 tahoe with the 5.7l motor. Just replaced fuel pump and filter. It will start after cycling the key a few times. It will rev in park and neutral as high as I can get it. If I put it in gear and give it gas it will run, and idle. If I try to just roll in forward or reverse it dies and I need to cycle key a few times to get it running again. The fuel pressure at the rail was about 40 psi before I changed the pump and filter. Have not tested since change. Anyone ever deal with this issue? Any thoughts are much appreciated.

 

[OR VietVet]

Check the pressure, that is basics. If you can, attach with long enough hose to watch what the pressure does when it is running and you go thru the same steps as before. What brand pump? Why was it replaced to begin with? When I look at application in RA I see a 2 door and a 4 door version. Which one?

 

[ANder]

Thanks for reply. It’s a four door. 5.7l with 4l60 trans. The pump is a Delphi. I brought it to a shop to get diagnosed. They told me it was the pump. Changed it myself at home. No go. Thanks.

 

[ANder]

Thanks for reply. It’s a four door. 5.7l with 4l60 trans. The pump is a Delphi. I brought it to a shop to get diagnosed. They told me it was the pump. Changed it myself at home. No go. Thanks.

Also when I cycle the key the pressure gets up in the 50’s and pretty much stays there. First turn of the key it hits 40 and stays there.

 

[Fless]

Is there a fuel filter on it and, if so, has it been changed recently?

 

[ANder]

Is there a fuel filter on it and, if so, has it been changed recently?

Yes. Brand new filter today. Thanks for the reply!

 

[OR VietVet]

Ok, I will ask it again, what is the part # for the pump you go from Delphi? FG0089 is the 4 door version at RA.

Plus, I am assuming you cannot watch the pressure while driving?

Sorry, but if I ask the question, I want to get some type of answer.

You said you had it at a shop and was diagnosed, for what? Is the problem now the same problem you took it to the tech for?

 

[exp500]

Any codes ? Have you swapped fuel pump relay? You can diagnose/fix 95 percent of problems with a bluetooth scanner, Spark tester, fuel pressure guage and multmeter. More than a sentance in your request will usually get a reasonable response.

 

[OR VietVet]

Your problem may be related to this part: https://www.rockauto.com/en/moreinfo.php?pk=88851&cc=1353721&pt=6072&jsn=959, Idle Air Control Valve.

That valve adjusts at the throttle body, for the air/fuel mixture, when it senses a load on the system, such as accel from stop or turn a/c on....etc. The passage where it threads in to tends to build up carbon and crud and does not allow the IAC to do it's job. In that case it would require an attempt to clean it or replace the throttle body.

Not saying this is the problem but am saying it could factor in.

 

[ANder]

FG0089 is the Delphi part number. No codes. Will check fuel pressure while running tomorrow evening. I have not swapped relay. Thanks for giving me a couple things to think about. It won’t stay running in order to check pressure while driving. Brought it to the shop because it would not start and had low fuel pressure. Was sitting in the road where I couldn’t work on it. The tech said it was the fuel pump that needed replacing. Sorry if I’m not being thorough enough. I know my way around a vehicle but not a pro mechanic.

 

[exp500]

If it will not stay running, I can guarantee 95 percent you have a code. May only be a temporary (soft) code, but enough for the computer to notice. See Live data on your scanner.
Next do a spark test at Dist coil terminal, and again at IGN Coil terminal, Report findings.

 

[Donnie Yukonie]

If it will not stay running, I can guarantee 95 percent you have a code. May only be a temporary (soft) code, but enough for the computer to notice. See Live data on your scanner.
Next do a spark test at Dist coil terminal, and again at IGN Coil terminal, Report findings.

Not always. may be unrelated to this problem but the old plastic fuel spiders when they would go bad they would just kill the truck at slow speeds like he's describing. and you wouldn't get a DTC. As for his issue I agree he needs to get a gauge on it while running. last year I had a problem with a 5.7 TBI that would drop fuel pressure just enough to drop the idle and under load would stall the engine.

 

[Eman85]

As it sits now when you turn the key to start it will it start right away or are you still cycling the key to start it? If you turn the key to the on position and the pump turns on and you get fuel pressure without trying to start it does the fuel pressure hold or does it drop? You say you have no codes, what are you reading codes with and did it have any codes previously when it first started giving problems?

 

[east302]

x2 on the above.
Spec is 60-66 psi with key on, engine off. Turn key off and see what the pressure does.

A drop could be a check valve at the pump, leaking injector or leaking regulator/return back to the tank.

There is a way to diagnose it, but I’d wonder if your shop just took the “most likely” and ran with the fuel pump since it was quicker.

 

[ANder]

So here is what the tech said at the second shop I brought it to.


Vehicle initially started very hard, like a lack of fuel pressure, but eventually started and continued running. Scanned codes. Verified EGR operation and the actual position matched the desired. All scan data, including fuel trims, 02 readings, MAF sensor value and MAP reading are all normal. Connected fuel pressure gauge and vehicle starts and runs normally. Fuel pressure is 55 psi cranking and53 psi at idle and holds when engine is shut off. Blocked return line but pressure did not increase. Suspect fuel pump but unable to determine at this time.

Update: let vehicle sit and had an extended crank again. Fuel pressure was only 30 psi and slowly built up until engine started. Recommend replacing the fuel pump.

One code that came up was o2 heater circut bank 1 sensor 2
I don’t know what that means. Tech was not concerned about it

The fuel pump has been replaced and the same issues remain as before the pump was changed. It will drive but when you hit the gas it quietly wants to die. Will get up to speed if you slowly ease into the gas. Fuel pressure holds as it should after shutting off vehicle. The EGR valve has also been replaced. I’m starting to think the problem may be in the ignition system somewhere. Any thoughts? Thanks

 

[ANder]

Ok I see code p0141 o2 sensor had a bad reading. Could that really resolve this issue?

 

[Eman85]

Bank 1 sensor 2 is the O2 sensor behind the cat on the left bank. Not going to effect performance at all. So fuel pressure is good when you turn the key on and it holds good pressure but when you step on the throttle it wants to die, is that correct? Does it do this in park or only under load? Can you read fuel pressure when it does this?

 

[exp500]

See post 14, Fuel pump out of spec.Won't usually start/run below 60. Don't worry about O2 sensors till it runs right.
Does your theft light flash? Have you changed fuel pump relay?
Do you have a spark tester and multimeter?
What fuel pump did you install? FG0089? Did you install new connector harness?

 

[ANder]

See post 14, Fuel pump out of spec.Won't usually start/run below 60. Don't worry about O2 sensors till it runs right.
Does your theft light flash? Have you changed fuel pump relay?
Do you have a spark tester and multimeter?
What fuel pump did you install? FG0089? Did you install new connector harness?

No lights flashing. Have not changed fuel pump relay. Delphi FG0089 is the pump I installed. I wired in the new harness three years ago when the pump failed. Ran like a top after that. So I replaced the pump this time with the same Delphi part. I do not have a spark tester but do have a multimeter. Thanks for the response. Been working 12 hr days so it’s been tough to get to this thing.

 

[ANder]

Bank 1 sensor 2 is the O2 sensor behind the cat on the left bank. Not going to effect performance at all. So fuel pressure is good when you turn the key on and it holds good pressure but when you step on the throttle it wants to die, is that correct? Does it do this in park or only under load? Can you read fuel pressure when it does this?

What you described is correct. Only does it with load in gear when stepping on throttle. Have not read fuel pressure going down road.