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chevrolet silverdo fuel trims

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5 years 4 months ago #39618 by kool
chevrolet silverdo fuel trims was created by kool
hello guys,
many garages failed..

my codes are p0171 p0174

new MAF
new fuelpump module now 55psi.
new catalyst

smoke tested, see nothing.
what could it be im lost
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5 years 4 months ago #39624 by tech25
Replied by tech25 on topic chevrolet silverdo fuel trims
what is the year, make and exact model??

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5 years 4 months ago #39626 by guafa
Replied by guafa on topic chevrolet silverdo fuel trims
Hi Kool,

I would check first if fuel pressureis ok. Not complete sure, but i have the idea is should be 60 psi.

Please confirm guys.

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5 years 4 months ago #39629 by Cheryl
Replied by Cheryl on topic chevrolet silverdo fuel trims
Was this screen shot at idle?? Try pinching off brake booster hose? What does fuel alcohol content read?? Fuel sample?

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5 years 4 months ago #39648 by kool
Replied by kool on topic chevrolet silverdo fuel trims
The fuel pressure with old pump was 42 psi.

fatory spec is 55 to 65 psi

so thats good..

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5 years 4 months ago #39649 by kool
Replied by kool on topic chevrolet silverdo fuel trims
this is at idle..
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5 years 4 months ago #39654 by Cheryl
Replied by Cheryl on topic chevrolet silverdo fuel trims
What do the trims look like at 3000 rpm? Try a fuel trim reset after fuel pump replacement??? The short terms don’t look that bad in the pic

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5 years 4 months ago #39657 by kool
Replied by kool on topic chevrolet silverdo fuel trims
short terms are oke! you always need to reset trims or they wil compensate by them self?

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  • juergen.scholl
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5 years 4 months ago #39670 by juergen.scholl
Replied by juergen.scholl on topic chevrolet silverdo fuel trims

kool wrote: short terms are oke! you always need to reset trims or they wil compensate by them self?


Over time fuel trims will relearn by themselves but, depending on make and model, it can take quite a while.
An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.

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5 years 4 months ago #39675 by guafa
Replied by guafa on topic chevrolet silverdo fuel trims
Hi guys,

I think the problem is still there.

Is worth it (at idle) try to strangle fuel return line to increase a little bit the fuel pressure and see how fuel trims change. (Some time ago, I was figthing with a bad fuel pressure reg. which was giving me 55psi)

About trims, STFT should be about -29% after fuel pump replacement.

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5 years 4 months ago #39677 by Tyler
Replied by Tyler on topic chevrolet silverdo fuel trims

tech25 wrote: what is the year, make and exact model??


Quoting for emphasis.
The following user(s) said Thank You: Noah, juergen.scholl

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5 years 4 months ago #39683 by kool
Replied by kool on topic chevrolet silverdo fuel trims
2008 4.8 v8 4x4 crewcab lt

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5 years 4 months ago #39687 by Tyler
Replied by Tyler on topic chevrolet silverdo fuel trims

kool wrote: 2008 4.8 v8 4x4 crewcab lt


There we go. B) Thanks!

Cheryl is on the right track here. Pinch off the brake booster hose and see if trims improve. Verify if this truck is flex fuel or not. Either way, take a fuel sample to check ethanol content.

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5 years 4 months ago #39691 by kool
Replied by kool on topic chevrolet silverdo fuel trims
no change in trims when pinch of brakebooster...
here in the netherlands i only fill up unleaded 98 octane . its no flexfuel

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5 years 4 months ago #39692 by kool
Replied by kool on topic chevrolet silverdo fuel trims
maybe this wil help: changed the catalytic converter because 1 side broke in pieces.
they put a new y piece plus cats in but didnt change the 02s for new. i think because of driving long lean condition the converter was overheated and broke? got 118 k miles on it.
maybe the 02s are shot to?

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