P0174 2012 Camaro (occurs when feathering gas to maintain speed)

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1 week 1 day ago #203769 by seang2340
Hello everyone. I am attempting to identify what is causing this lean code on bank 2 of my 2012 Chevy Camaro 6.2 liter SS automatic transmission vehicle. I have chased this thing down many paths and have had it evaluated at two dealerships. So here goes. Initially I had a CAT code on bank two along with the P0174, which I believe was caused by the lean condition and overcompensation of adding fuel that ruined the cat. So I changed the cat and O2 sensors and the CAT code is gone.

That said in attempting to diagnose the lean condition I have changed the following and it hasn't changed: new spark plugs, new wires, exhaust manifold gaskets, intake manifold gaskets, throttle body gaskets, valve cover gaskets and grommets, all the injectors on bank two, intake manifold (new), EVAP purge solenoid canister, all vacuum lines, MAF, MAP. The only gasket I have changed is the oil filler neck gasket, which is on bank 2, and ECM, all to no avail.

All that said in my pursuit to diagnose or have it diagnosed I have monitored the fuel trims and noticed it occurs while at operating temperature, and if you are slightly pressing the gas and maintaining cruising speed. If I drive the vehicle in a fashion where I accelerate fast and let off the pedal and coast and don't maintain speed by feathering the gas it won't go lean. You can see the lean condition occur at the first portion of pressing the accelerator and drop off as it passes the approximately 20% throttle position.

The strange thing is it only occurs on bank 2, I have had smoke tests done and no leaks were found. I did a compression test and they are all good. I was hopeful in reading a post on this site about a secondary air injection system that was found to be faulty due to a stuck solenoid on a Blazer, however, I cannot find that this vehicle (Camaro) has that on the car. Any suggestions? Oh, and you cannot notice any issues while driving the vehicle, it drives fine and the lean condition isn't noticeable other than with a scan tool.

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6 days 2 hours ago #203776 by college man
What are the fuel trims reading when this happens? have you checked the actual fuel pressure?

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6 days 25 minutes ago #203777 by seang2340
I have checked the fuel pressure at the rail. It was around 60 psi. And when monitoring it while driving with the scan to it is around 57 to 58 psi. The long term fuel trim will shoot up to 18 on the initial throttle response, if you keep it lightly feathered it gradually increases up to 24.2 and will store a code. If you quickly throttle it and let go in that fashion or if you accelerate faster it won't go high. On bank 1 it stays below 10 no matter the driving style. I will monitor the pressure at the initial throttle and see if it drops but I haven't seen it do that before.

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5 days 5 hours ago #203778 by college man
You may want to use an actual fuel pressure gauge when driving. you could have pressure but not volume.
With fuel trims going that positive, the computer is trying to add fuel. Either the fuel delivery is not there or
a vacuum leak is suspect. Have you tried searching for vacuum leaks? Try using water.

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5 days 5 hours ago #203779 by seang2340
I have done several vacuum leak searches. I have replaced the PCV hose and the purge solenoid hoses. The injectors are new on that side and I even swapped the ignition rail to see if something was causing it on that side. I have change the gaskets on the exhaust manifold, I have changed the gaskets on the intake manifold, I have changed the gaskets on the valve cover to include the grommets. I have had the dealership check it and they did a smoke test and I have had another shop look at it and they did a smoke test. So far I am the only one that has dialed it down to the specific action that it occurs which is when you are barely touching the gas pedal. Anything outside of that the trims are good. It is just strange that it is on one side, which would make you think it was a vacuum leak. My last step is maybe the oil filler neck and gaskets. I haven't changed that. It is on bank 2, that is the only thing I can think of. If it was the fuel pump or regulator etc. I would it expect the lean condition on both sides. I have tested the PSI on the fuel rail with a manual gauge and the psi was at 60. I monitored it yesterday and the fuel pressure stayed around 57 psi to 58 psi. It is just odd that it only occurs when the pedal is barely depressed and held in that position, basically the lightest you can touch it that opens the throttle position. Let's say it is a vacuum leak I haven't found it is odd that it would go lean only at that point.

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4 days 5 hours ago #203789 by college man
Lets test the o2 sensor. With the car running and the scan tool monitoring the o2 sensor live data. Soot some
carb spray down the intake to see if the o2 sensor goes rich right away. This will tell you if the 02 is responding or not.

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