P0171 code, system too lean fuel bank 1

HOFESTAS

MEMBER
1996 CHEVROLET SUBURBAN
0.5L
V8
4WD
AUTOMATIC
208,000 MILES

Service engine soon light on always! Gave it a tune up and replaced MAS. Found a vacuum leak where the air cleaner mounts on top of engine. Replaced gasket and still have smoke coming from what appears to be the same area. Anything else in that area that would leak on a smoke test? Thank you!

3 Replies

KASEKENNY

MECHANIC
18,907 POSTS

Couple questions, can you get a picture of where you found this leak? Also, did you use a smoke test to find it?

The only issue I have is if the leak was found before the air flow sensor then it would not effect the engine to cause this code. Here is a guide that will help with this:

https://www.2carpros.com/articles/repair-lean-mixture-codes-p0171-or-p0174-on-some-manufacturers

Take a look at this info below on this code and that will help figure this out.

Also, here is a guide that will give a different way to test for a vacuum leak. Using the starter fluid method as shown is a more effective way just because it tells us when there is a leak and it effects the RPM, then that tells us it is changing the air/fuel ratio.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Let me know if you have questions. Thanks

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Tuesday, March 2nd, 2021 AT 4:48 PM

HOFESTAS

MEMBER
7 POSTS

Thank you so much! I bought this used and the leak is where the air intake mounting gasket is. It didn't have one at all! But the whole air box was replaced before I bought it I noticed. The ones on the market look to simple to be right though. I built a temporary one and did a smoke test and it worked. But it's still running rough. Tachometer is going up and down. But it runs and only surges on the highway at cruising speed. I was looking at the fuel pump but when I hit the gas she goes strong? Any suggestions appreciated. Thanks!

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Wednesday, March 3rd, 2021 AT 2:04 PM

KASEKENNY

MECHANIC
18,907 POSTS

Let's run through this guide for surging because depending on what we find here it could take us in different directions. There are a number of things that can cause this so let us know what you find with this and we can go from there.

https://www.2carpros.com/articles/engine-surges

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Wednesday, March 3rd, 2021 AT 6:10 PM