Fixes and.then maybe not!

[Livebai8]

Ok guys...need some help and knowledge...ive replaced my fuel sending Unit, the fuel pressure regulator, charcoal canister, and pcv valve...but not my fuel filter just yet ( I can't get the effing tool to work)... when cold, the truck idle seems to be fine...when at temp and giving it gas...the idle drops low and struggles to get back to 500 rpm...or dies...itll also die when going into gear. After driving it several miles the idle seems to be ok and the truck runs fine but in park it'll want to die after giving it gas...anyone know what's going on or what i should look into next?


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[Splorg]

Check your battery first. Is the truck charging hard when it's running properly? Does the gauge plummet when the idle is low, or just before the idle drops? Only takes a few minutes to rule it out - a weak battery or improper charging can cause havoc with the sensors the computer depends on to manage idle and air/fuel and can cause problems like you describe.

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[Fless]

What year, model, engine?

 

[Livebai8]

Check your battery first. Is the truck charging hard when it's running properly? Does the gauge plummet when the idle is low, or just before the idle drops? Only takes a few minutes to rule it out - a weak battery or improper charging can cause havoc with the sensors the computer depends on to manage idle and air/fuel and can cause problems like you describe.

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At start up idle...i can give it gas and it will plummet and either devout or creep back up to idle (500_700 when cd)...im not showing any codes either. My battery is from 2017. I'll have it tested.

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[Livebai8]

What year, model, engine?

2002 5.3l flex fuel z motor

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[Livebai8]

At start up idle...i can give it gas and it will plummet and either die out or creep back up to idle (500_700 when cd)...im not showing any codes either. My battery is from 2017. I'll have it tested.

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[swathdiver]

You'll want to know your fuel pressure, key on and while idling and then under load while underway.

 

[Livebai8]

You'll want to know your fuel pressure, key on and while idling and then under load while underway.

For sure . Doing that tomorrow. Thanks.

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[Sam Harris]

MAF...?

 

[Livebai8]

MAF...?

Don't think so. I 've cleaned it and sum not throwing any codes.

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[Sam Harris]

Don't think so. I 've cleaned it and sum not throwing any codes.

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One more thing off the list..

 

[Scottydoggs]

do you use e85? sometimes these flex fuel set ups need the content sensor reset. need a tech two or the likes to do this tho.

 

[Fless]

Cleaned the throttle body?

 

[Livebai8]

do you use e85? sometimes these flex fuel set ups need the content sensor reset. need a tech two or the likes to do this tho.

No...ive never really trusted the e85.

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[Livebai8]

Cleaned the throttle body?

Yes...i have cleaned.

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[Fless]

You'll want to know your fuel pressure, key on and while idling and then under load while underway.

The Flex Fuel KOEO (Key On, Engine Off) pressure spec is 48 to 54 psi. And, as @swathdiver said, monitor and log it under the various good and bad conditions when running.

I'd also be looking at short- and long-term fuel trims as it warms up.

 

[Livebai8]

The Flex Fuel KOEO (Key On, Engine Off) pressure spec is 48 to 54 psi. And, as @swathdiver said, monitor and log it under the various good and bad conditions when running.

I'd also be looking at short- and long-term fuel trims as it warms up.

I haven't checked FP just yet...but I am in Tahoe now...at start it would idle but dies when putting gear...it did this several times up until I was able to travel a mile or so before coming to a stop...it hesitated a bit but didn't die out...got on hwy at 65 for about three miles before coming to a light and truck idled at 500 and at 500 now in parking lot. When dropping into reverse idle fluctuated down to 400 but back up at 500 but not dying out.

I'll check FP later this evening after cool down and dinner.

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[Scottydoggs]

No...ive never really trusted the e85.

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see if this vid has the same issues as yours.

 

[Livebai8]

see if this vid has the same issues as yours.

No...good video but doesn't reflect what my e is doing. I'm not throwing any codes.

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[Fless]

No...good video but doesn't reflect what my e is doing. I'm not throwing any codes.

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Your engine will have an actual fuel composition sensor, and if that's wacky -- one of my oft-used technical terms -- the PCM may have switched to the ethanol tables, codes or not. The sensors are not cheap, and you might look for a way to disable it if the facts point to an issue with it.

Although you'd see this in excessive fuel trim values (as in the video) it wouldn't hurt to check to see if you can view the sensed ethanol % on a scan tool.

The more info you have, the more likely you'll be able to diagnose it. Personally I think you have a vacuum leak that changes with warmup, but that's a WAG on my part, due to the information I have at hand.