99 tahoe with 5.7 won’t stay running!

[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.