Weird Starting Issue After Truck Sits More Than A Few Hours

[TylerHagerdorn]

My 2004 Suburban has an issue with starting if the truck has sat for more than 6 hours or overnight. I'll go to crank it and it acts like it wants to fire but then just cranks. If you crank it long enough it may start. If I put my foot down on the accelerator pedal it'll fire up almost immediately, and then it'll smell like gas. It's throwing a P0443 purge valve circuit code, which I replaced with a standard from O'Reilly as nobody had the Delco one. The harness to it and wires look ok. It also throws a Fuel Composition Sensor code as well. Once the truck has started it'll fire up all day long no issue. I also replaced the fuel cap and the evap large leak code went away. I'm not going to just throw parts at it. If someone knows exactly what the issue is then I will pick that part up.

I just had a major surgery and I need it to be good so my wife can use it if she needs to. I do all my own work and I'm usually really good with diagnosing things and this isn't my first GMT800 but it is my first flexfuel one. Any advice would be super helpful. Thank you all.

 

[Doubeleive]

you will probably want to start with doing a fuel pressure test, after it has sat as noted, key-on only pressure should be 50-65psi
if you do not have that pressure pre-start then it's likely a fuel pump issue, but...it could maybe the fuel pump control module also but it is much more likely to be the pump
another thing you could maybe try is to reach under the truck and smack the gas tank with a hammer a couple times first and see if that makes any difference if it does then you know it's probably the pump.

 

[Fless]

^^^ ditto on the fuel pressure test @Doubeleive suggested. Measure before a cold start, after the truck has been sitting. If it's low, cycle the key off and on a few times to see if the pressure comes up.

KOEO specs for NBS V8 engines:
Non-Flex: 55 to 62 psi
Flex: 48 to 54 psi

Also, if you aren't running E85, but your fuel composition sensor (incorrectly) thinks you are, the ECM is going to add too much fuel. What do your long- and short-term fuel trims look like for both banks?

On a cold start, have you tried clear flood mode by flooring the accelerator?

 

[George B]

Another quick check is the fuel pressure regulator on the drivers side fuel rail. Pull the vacuum connector off and check for fuel in the line.

 

[Bill 1960]

Foot down starting (do you mean WOT or something less?) is the procedure to clear a flooded engine. Putting that together with the purge valve issue it sounds to me like a stuck open purge valve flooding the engine with fuel vapors.

Could be a sticky injector.

I agree with the recommendation to test fuel pressures but your description sounds like flooded, not lack of fuel.

 

[Scottydoggs]

being its a flex fuel truck might need the content sensor for the e85 reset. sometimes they get all whacked out. you can check your own fuel trims to see if they are out of whack theres got to be a reason for it. like in this vid.

 

[Fless]

The 2004 should have the physical fuel composition sensor. Still, if something's wrong with it and you're not running E85, perhaps there's a reset for it in the Tech 2 menus. Don't reset it if you have more than 10 or 15% alcohol in the tank.

 

[TylerHagerdorn]

Foot down starting (do you mean WOT or something less?) is the procedure to clear a flooded engine. Putting that together with the purge valve issue it sounds to me like a stuck open purge valve flooding the engine with fuel vapors.

Could be a sticky injector.

I agree with the recommendation to test fuel pressures but your description sounds like flooded, not lack of fuel.

Yeah if I hold my foot down to the floor and crank it it'll start and it then smells like straight fuel and bunch of exhaust smoke comes pouring out for a few seconds. It does not seem like a lack of fuel as it'll fire up during the day without an issue and I have records of the pump being done twice at the Chevy dealer, one being quite recent. I looked under the truck yesterday as I was checking grounds for another issue and the fuel filter is brand new and the composition sensor doesn't look rusted or corroded. It also appears someone replaced the fuel lines that run into the engine bay as I noticed what looked like the old ones zip tied and laying next to it. The truck was religiously serviced at the dealer the first 16 years of it's 17 year life. I haven't pulled the FPR hose to see if there's fuel there. But I replaced the purge valve under the hood and it seemed fine for a day and then back to square one. So, maybe it's the valve back by the canister? It seems like it's not purging the vapors back like it's supposed to be. The code I was getting was P0178(Fuel Composition Sensor Circuit Low)

 

[TylerHagerdorn]

It doesn't seem like a lack of fuel. The code I'm getting besides the P0443 is a P0178(Fuel Composition Sensor Circuit Low) just like the purge valve code is a circuit code. It's had a recent fuel pump at a Chevy dealer and it's been done twice at the dealer. Once at 143k and once at 220k. Years and years apart though. It seems like it's not purging the vapors back like it should be. It's strange that both codes are for circuit. I don't remember what the fuel trims were but they looked just fine. I checked the wiring to the purge valve under the hood and it looks fine as does the connector. Has a brand new fuel filter as well. I don't run E85 and never will. I don't believe it's ever had E85 in it either, but I'm not sure.

 

[Fless]

This thread might interest you. I think the first video posted gives the most info.

p0178 error code

Good evening everyone, I am sure i am gonna sound like a broken record but I have a 2002 tahoe that is throwing a p0178 error code (fuel consumption sensor low voltage). i have already replaced the sensor itself and the pcm/ecu. i checked the voltage on the three wire connector and am...

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