Burn lean codes on both banks.

[tandkelectric1]

I have a chevy 2004 express 1500 3.8 liter. I have p0174 and p0171 burn lean codes on both banks. I replaced fuel filter air filter mas air flow sensor. When I go from 30 mph and up I have no fault codes, When I slow down In town driving the C.I.L. comes on and there are the same codes. Please help.

[justen]

What is happening in this case, is the air/fuel mixture is incorrect, which is causing a lean burn code on both banks. I see you replaced the mass airflow sensor, thats usually the problem 99% of the time, Now you'll have to look at fuel injectors and fuel regulator. Also sometimes a MAP sensor can cause trouble like this. Isn't this vehicle still under warranty?

[dougbfresh]

Look for vacuum leaks first, this will make both banks run lean.

[tandkelectric1]

The warranty ran out at 36000 Its at 40000 now. Whats the best way to look for a vacume leak besides air noise? Thanks for the reply.

[dougbfresh]

Vacuum gauge-normal manifold vacuum should be 15-20" of STEADY vacuum. Another technique is to spray carb cleaner around till the rpm's drop (that's where the cleaner is gettin pulled in). Another (more questionable) technique is to use a propane touch-just open the valve (DO NOT LIGHT) and poke around the intake till the RPM's go UP, the propane getting pulled in will raise the RPM's.

[carsandcycles]

The easiest, first way to look, is to listen. If it's big enough you'll hear a hissing sound. And for sure, what Dough said, is the next thing to do.

[FieroSpeeder]

Originally Posted by dougbfresh

Vacuum gauge-normal manifold vacuum should be 15-20" of STEADY vacuum. Another technique is to spray carb cleaner around till the rpm's drop (that's where the cleaner is gettin pulled in). Another (more questionable) technique is to use a propane touch-just open the valve (DO NOT LIGHT) and poke around the intake till the RPM's go UP, the propane getting pulled in will raise the RPM's.

Normal vacuum is 18-22. Your number is unrealistic


And why would carb cleaner cause the rpms to drop while propane cause it to go up?

[Racerock]

Originally Posted by tandkelectric1

The warranty ran out at 36000 Its at 40000 now. Whats the best way to look for a vacume leak besides air noise? Thanks for the reply.

Question, when did the emissions warranty expire. The emissions is typically different and often way longer than the vehicle warranty.

For example, on my Acura, I have a 14 year, 150,000 emissions warranty (and that is not a typo!) Try to get GM to agree to do that!

[Racerock]

Originally Posted by tandkelectric1

The warranty ran out at 36000 Its at 40000 now. Whats the best way to look for a vacume leak besides air noise? Thanks for the reply.

Not sure about yours, but the 2004 Avalanch is 5 yr, 50,000 miles:

2004 Chubby Avalanch Emissions

Check your warranty book and make an appointment.

[tandkelectric1]

Would the pvc valve going into the valve cover cause a problem if it was leakink? I did find a leak there and so far no codes. Also the plastic valve cover on the driver side might be leaking. When I push down on it on the corner I see oil squezing out almost like a sponge.

[tandkelectric1]

I caled the dealer and told them and they said I was out of luck! The waranty they said was up at 36000.

[thecarguy]

Yes. ANY unmeetered air in the system will cause a lean condition. A leak to atmosphere in a valve cover or PCV will cause an introduction of unmeetered air. I personally use a nitrogen/smoke machine to find vac leaks. You hook up to the air box and pressurize the intake system with smoke...where theres smoke coming out, there is air going in when the engine is running.

[Racerock]

Originally Posted by tandkelectric1

I caled the dealer and told them and they said I was out of luck! The waranty they said was up at 36000.

Pull out your warranty book, and tell us what the Federal Emissions Warranty says.

If it is as stated above (5 yr, 50K miles), call another dealer.

Personally, I'd be raising hell if they did not cover this one.

The Federal Emissions Warranty is totally different than the Vehicle Warranty. It also applies to specific situations, and equipment. But, from what you state above, it seems to me that it would apply. Do you have a state emissions test? If so, the Federal Emissions Warranty applies if your vehicle fails the test. In our state, if the light is on, it fails. OBDII does not need the treadmill, they just plug the cable in, check out he system.

PS - if there is a cover on the connector on the dash, or it is hidden, they only check to make sure:

-it is working (comes on when key is put in and put in start)
-turns off when the car is running

[tandkelectric1]

Thank every one for there answers. I found this problem myself thanks to this forum. It was the pvc valve leaking that caused all this!!!!! Thanks.

[justen]

good news, and a cheap fix, If your valve cover(s) are still loose it wouldn't hurt to snug them up as well. Do not go over the recommended torque specs on them bolts.