Fuel system

DBIEKS

MEMBER
1999 CHEVROLET TAHOE
5.7L
V8
4WD
AUTOMATIC
180,000 MILES

I have had this problem for almost two years now so any help would be great. I have two service engine codes that I cannot get rid of.
po171 bank 1 to lean
po174 bank 2 to lean

I have had three legit repair shops go through it and could not repair it. Here is what I had done in the last year:
Two fuel pumps, fuel filter, fuel regulator, cleaned fuel injectors, had a smoke test done and they fixed one vacuum leak, replaced several fuel system sensors and had the computer checked and it came out positive. They were stumped and now I am lost for options. Is there anything we may have overlooked?

Again any ideas would be great.
Thank you for your time.
Dan B

1 Reply

JACOBANDNICKOLAS

MECHANIC
108,289 POSTS

Hi and thanks for using 2CarPros. Com.

Based on what you have had done, I have to question the VCM, vehicle control module. Basically, if the O2 sensors are working correctly, they send a signal to the VCM based on readings in the air flow. If the system is lean, the VCM increases the amount of fuel being delivered to the engine. The opposite happens if the fuel trim is rich. A live data scanner can watch how the VCM is controlling the fuel mixture.

What I have done is attach the specific flow charts for the DTC's you listed. See if they are helpful. When you look through them, note that one section indicates possible problems when both codes are present. Focus on that. This could be as simple as a bad PCV valve or exhaust leak which weren't mentioned as being checked. The third picture attached is the specific section which discusses both codes at the same time. Pictures 1, 2 and 3 are for P0171. Pictures 4, 5 and 6 are code P0174 and the last is when both are present.

Let me know if this helps or if you have other questions.

Take care,
Joe

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