Hello all...any help is much appreciated. (2002 Tahoe, 4WD, 5.3FlexFuel)

OBD P0174 showed up and I've replaced both upstream O2 sensors. The check engine light went off and the code disappeared.

Now the code is reappearing, as luck would have it when I was getting an inspection...

Any thoughts on what else would make the system run lean? It has brand new fuel filter, the plugs / wires are less than 2 years old. I'm going to clean the MAF sensor next....

thanks

 

Maf sensor is where I would look next, then fuel pressure.

 

O2 sensors will not cause a lean code they are what sees the lean condition. Plugs and wires have zero effect on fuel problem. If it where a bad or dirty MAF sensor you would also have a PO171 Lean bank 1. I would highly suspect a bad intake gasket. The gasket has been updated for this problem.

 

If it's only lean running on one bank, and not the other...you need to look at what would affect ONLY that bank. The MAF would affect both banks if it were malfunctioning.

Look for anyplace that you can get additional air introduced into the intake between the MAF and the block. Any air intrusion beyond the MAF would be not measured by the computer to calculate the air fuel mixture, leading to a lean running and possibly driveability problem. Particularly like MDTAHOE said, the intake manifold. It is where the air is separated and diverted into each bank.

My money is on a bad intake gasket

 

Thanks all for the help. It now does show both banks lean so I'm going MAF first....God help me if I have to replace the intake manifold! Got quoted $1400 labor from Pep Boys today on it..

 

Quote seems very high only calls for 2.6 hours. Even at $100.00 per hour that's $260 for labor and gasket set from dealer is around $100.00. No coolant or oil needed. You should call someone else. Even the dealer would be way less money.

 

If they quoted you that much labor, I would never take your car there ever again. A skilled mechanic should be able to remove and re-install both cylinder heads with less labor than that. Even if that number includes the part price, they are screwing you.

It took me 2 hours to remove and re-install my intake manifold, and it was my first time. It has to be removed to replace the knock sensors. A good bit of that 2 hours was figuring out how to remove the fuel rails without damaging them, then looking for the o-rings from the injectors. Like I said, a skilled mechanic could do it in 1.5 hours in my estimation.

Just curious why you suspect your MAF? In my experience if it was going bad it would also be tossing an error code. Not always, but normally.

 

Thanks all for the help. I decided to start from the air filter in...thinking I'd try the cheap fixes first.

Turns out replacing the MAF sensor did the trick. At least the codes cleared and I got my inspection sticker!

I'm sure the intake manifold gaskets will go soon...but at 250K miles she's still running strong!

 

Glad you got it fixed, thanks for reporting the solution.