My very own P0171 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 04-22-2008, 04:24 PM   #1
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Default My very own P0171

It throws the code while idling & the fuel trims at idle are:
Short term +20%
Long term +16%
At 2000 rpm the short term drops to 10%
At 2500 rpm the short term is right around 0%
This lead me to believe the problem is vacuum related & not a fuel supply issue.
Here'* a video - I'm going in!

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Old 04-22-2008, 07:42 PM   #2
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Whoop..there it is.
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Old 04-23-2008, 01:21 AM   #3
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I thought it was just the lower intake gaskets that fail.

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Old 04-24-2008, 01:40 AM   #4
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...I hope the rest of it is stuck to the underbelly of the blower.
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Old 04-27-2008, 06:26 PM   #5
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Some of the gasket was stuck to the supercharger but you can see 2 major leaks in the lower picture.

Here'* the fuel trims after the repair. Is the -11.7 within the normal range?

It'* a good thing we got in there and changed the lower intake gasket. Looks to me like it wouldn't have been much longer before coolant flooded the crankcase.

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Old 04-28-2008, 07:48 PM   #6
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nodnod - looks like good timing on your part.
Now, the trim numbers that the 'gauge' software is reflecting is unfamiliar to me. Was this at idle? I'm also not familiar with the normal operating trim specs for the Bonneville. It'* certainly not stoichiometric. How long did it take you from start to finish?
What program is that which you're using?
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Old 04-28-2008, 08:26 PM   #7
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I'm using the AutoTap software. All the readings were at idle. When the gasket was broken it was running lean at idle. The PCM then increases the fuel trimsto richen the mixture. When the trims max out (20% & 16%) then Code P0171 is thrown. I might change the O2 sensor & see what happens.

This was the first time I changed the gaskets on a 3800. I'd guess I spent 5-6 hours a day for three days. Probably as much time spent cleaning parts as actual assembly/disassembly.
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Old 04-28-2008, 09:06 PM   #8
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your SC gasked didnt fail, its just stuck to the other side of the SC. totally normal when removing the charger for it to look like that

Lean bank 1 is not because of the fuel trims. Yes that code can set becaused of wacked trims, but that is not the only thing that causes it. Have you looked at the battery cables....remember another members nightmares....it 0171 was caused soly by the battery cables....

did you reset fuel trims....you Must do this if your going to get an accurate reading...-11.7 is not a good LTFT
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Old 04-28-2008, 09:14 PM   #9
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Did you see the video & look carefully at the second picture. Oh yeah - & what about the results!
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Old 04-28-2008, 09:57 PM   #10
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i've had that issue on my 98..the SC gasket cracked or was re-used..not sure but I had a massive vaccum leak which casued the car dealer to think the engine was on its way out.
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