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P0174/171 Mystery...need help.



Ok, sooo...


I've been battling P0171 and P0174 codes for the last...however many months. I haven't really noticed a change in driveability since I started getting the codes, but they are annoying me and I'd like to fix the problem and possibly gain some benefit to fuel economy or maybe even a little more oomph.


The issue started last year when I had my friend decat the truck at his shop. I had a couple of spacers installed with the rear 02s that keep the sensors from letting the engine know there's no converter. I'm not getting the no cat codes. Got code right after though (174 or 171 possibly). The light would go on and off every 1-5 days or so.


Recently, I took the truck in and had a smoke test done and no vacuum leaks were found. Fuel pressure was ok too. One of the 02 sensors (passenger side rear) was stuck in lean or rich (i don't remember). I replaced that sensor and since then It's been just the 174 code.


I tried cleaning the maf (a number of times). I would clean it, and soon after the light would go off. However, It would come back on the next day...or some days later. Clean it, same thing.


I thought the problem could be oil from the k&n so I replaced that with a high quality dry filter, cleaned the maf...same thing. Goes off, comes back on later.


Got a remanned maf to see if maybe that was the problem. Cleared codes...codes came back (but interestingly my mpg seems to have gone up 1-2 mpg after changing the maf out). When the light does come on, it seems to come on when the truck is idling. There have been a few times (but not very often) that its been a little sticky going from standing to moving (a little engine rev but not much movement).


Here are the freeze data points for the last time it threw a code:



rpm 520

load: 17.6

air flow rate: 5.35 gr/sec

map sensor: 41 kpa

short term fuel trim: 1 0.0

long term fuel trim: 1 7.0

short term fuel trim: 2 5.4

long term fuel trim: 2 25

short term fuel trim: 3 50

long term fuel trim: 3 45.3

short term fuel trim: 4 20.3

long term fuel trim: 4 50.7

fuel system 1: closed

fuel system 2: closed

throttle position: 4.7


Any help? Thanks!

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6 answers to this question

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Don't want to be throwing a lot of "this happened to me" but... my wife's Envoy keep throwing the same code. Finally ended up tightening the intake manifold bolts. They were so loose, one feel off the mainfold into my hand when I touched it. Good luck!

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throwing more parts at it works to or get some brake cleaner and spray along the intake ,if the rpms rise ,then thats it ,,,,IF NOT,,,,,take it in and stop the finacial hemeraging you are experiencing


broken record off







again ..

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