So I'm having a problem with trouble code P0171. It says it could be a vacuum leak, O2 sensor or mass air flow sensor net bank one is lean. My 08 base model Manuel ls3 is stock except for a BBK intake and axle back exhaust. I have removed the mass airflow sensor and cleaned it. I have also replaced the bank 1 driver side front O2 sensor. I am able to clear the code and drive for 40 or so miles until it throws the check engine light again. I'm able to clear it again and drive another 40 miles or so. The cars drive ability has decreased. At idle the RPM's will drop and then come back up almost to where the car cuts off. It doesn't do it all the time but stopped at a light it made do it 3 or 4 times. There doesn't seem to be any rhythm or pattern idle drop. Under acceleration you can feel hesitation as well. The fact that I can clear out the cide and it'll take some driving before the check engine light comes on makes me think that it's probably not a vacuum leak or it would start immediately?. It seems to be greatly affected the heart of the car gets. Any suggestions? I have heard everything from it being the BBK intake that is cast aluminum that is causing so much heat to be thrown into the motor. To that the car needs a tune. I had been driving the car fine with the BBK intake for several thousand miles and never had a problem. Anyone have any ideas?

 

Are you confident the MAF is good?

 

Not 100%. I was thinking of replacing it. Just don't want to to get into a huge hole where I start replacing everything just to find out that it didn't help like I did already with the 02.

 

Probably not a intake leak as you would have P0174 also which is a lean error with the other bank as well.
Here's two links to read about. This one is a TSB for the condition and the possible problems.
http://www.autocodes.com/uploads/gmc/03-06-04-030F.pdf

The other link is a broader review of other causes.

http://www.autocodes.com/p0171_chevrolet.html

Since you replaced the O2 sensor, I'm more incline to say a dirty/clogged injector if your car has some mileage on it.
Fuel pressure is another likely cause. See this problem with our test engines in a engine lab environment.
Take a reading of the pressure, should be ~ 55lbs. min all the time.

GL

 

Also. Been through the gas leak problem. Both pumps were replaced. But now that the car is having this driveability problem I am getting a strong smell of gas once again. It's very hard to tell if it's coming from the exhaust because of it running lean. But the gas smell only increases once the check engine light comes on or has recently been cleared. Because the car is running lean is there anywhere that there should be a vapor release because of the excess gas being thrown into the motor?

 

Cool, thanks for the links. I'll read over them..the car has about 75k on it.

 

Yeah, I understand. I'm not one for just replacing things until something works.

Extrapilot has some good info here to look into. I agree with him too about the possibility of an injector problem on the leftside bank. Do you have any datalogging capability? Something that will record LT and ST fuel trims?

 

OK... It's possible to smell raw gas at the exhaust and have a lean condition also if the engine is misfiring. Does the engine seem to shake when throttling it up under a load?
Could you be having issues with the tank system again not supplying enough fuel pressure because of a leak?

 

The engine doesn't seem to shake. it seems like a jerky hesitation. I would think that it wasn't the tank problem again only because I did take it to one shop and they saw the fuel output on the high end when they hooked it up to the computer and increased the RPMs which explains the lean reading. Their thought was that it needs to be tuned.

 

I don't agree with the tune. If you're completely stock, you want to correct a P code, not try to tune it out of the car. You want to tune a healthy engine. Otherwise, these engine management systems are self-tuning if you're looking to maintain factory performance.

 

I agree. I didn't think it was a good idea to tune it while it was sick. I might just try to backpedal step. Put the factory intake back on and see if by any chance it went back to not having problems. At least that is free. If it works and the aftermarket intake is the problem then the tune might be worth it.

 

Absolutely...

 

Got nothing to loss, but your description of the rough idle and hesitation leads me thinking injectors clogging.
May get lucky and throw some injector cleaner in the tank.

 

Some shop manual info:

TSB #08-06-04-040
Condition
Some customers may comment that the check engine light is on.

A scan tool may reveal DTCs P0171 and/or P0174 set in history or current. If the air flow to the air intake/air cleaner assembly is disturbed, the DTCs may be induced.

Cause
This condition may be caused by a gap between the upper radiator air baffle and the bumper beam combined with some beam holes. The gap and holes may cause an air flow disturbance to the air intake/air cleaner assembly. Refer to the pictures below for further clarification.

TSB #03-06-04-030F: Various Driveability Symptoms Due to Clogged Fuel Injectors, MIL/SES DTCs P0171, P0172, P0174, P0300, P1174, P1175
Condition
Some customers may comment on any of the following various driveability symptoms:

• Extended Crank Time

• Hard to Start

• MIL/SES Illuminated with DTCs

• Hesitation

• Lack of Power

• Surge or Chuggle

• Rough Idle

• Light or Intermittent Misfire

Cause
Due to various factors, the fuel injectors may become restricted. Extensive testing has demonstrated that fuel related issues are the cause of clogged injectors. At this point, no specific fuel, fuel constituent, or engine condition has been identified as causing the restriction. The restriction causes the engine to operate at a lean air fuel ratio. This may either trigger the MIL to illuminate or the engine to develop various driveability symptoms.

Circuit/System Testing
P0171 or P0174
Allow the engine to reach operating temperature. With the engine running, observe the affected Long Term FT parameter with a scan tool. The reading should be between 0-19 percent.

⇒ If not within the specified range, inspect for the following:

• With the ignition ON and the engine OFF, observe the manifold absolute pressure (MAP) sensor parameter. The MAP sensor pressure should be within the range specified for your altitude. Refer to Altitude Versus Barometric Pressure.

⇒ Refer to DTC P0106 if the MAP sensor does not indicate the correct barometric pressure.

• With the engine idling, observe the mass air flow (MAF) sensor parameter. The MAF sensor parameter should be within 2-6 g/s at idle.

⇒ Refer to DTC P0101 or P1101 or DTC P0102 or P0103 if the MAF sensor parameter is not within 2-6 g/s at idle.

• Vacuum hoses for splits, kinks, and improper connections--Refer to Evaporative Emissions Hose Routing Diagram.

• Insufficient fuel in the tank

• Low fuel pressure--Refer to Fuel System Diagnosis.

• Fuel contamination--Refer to Alcohol/Contaminants-in-Fuel Diagnosis.

• Malfunctioning fuel injectors--Refer to Fuel Injector Diagnosis.

• Missing, loose, or leaking exhaust components from the HO2S forward--Refer to Symptoms - Engine Exhaust.

• Vacuum leaks at the intake manifold, the throttle body, and the injector O-rings

• The air induction system and the air intake ducts for leaks or for a missing air filter element

• A cracked EVAP canister

• Evaporative pipes obstructed or leaking

• The crankcase ventilation system for leaks--Refer to Crankcase Ventilation System Inspection/Diagnosis.

• The HO2S for improper installation and for electrical wires or connectors that may have contacted the exhaust system

• The HO2S signal circuit open, shorted to ground, or shorted to the low reference circuit

• Malfunctioning engine components--Refer to Symptoms - Engine Mechanical.

 

Lean condition indication and stalling issue both point to an intake leak. Not familiar with GM MAFs, but others have a bypass for idle and the internal butterfly closes completely. A dirty MAF would probably not be evident except at idle. You have an aftermarket intake that has a bad/leaky gasket or crack would be wher I'd look.

 

Funny, how you can read something and completely miss it. I didn't "connect" with the BBK intake unitl just now. That would now make the top of the list or right next to dirty FIs. A leaking intake gasket will do it.

 

Already tried the injector cleaner in the tank with no luck. Going to try a smoke test on vacuum lines. Also recheck the gas leak problem. I'm thinking a loss in pressure could cause the problem too. I know that you could get raw gas smell out the tail pipes but enough fumes to completely fill my garage and 1st and 2nd floors of my house? That really made me think today that the pump leaking could be part of the problem.

 

Definitely going to check this because of the extreme gas smell once the car gets hot on a hot day.

 

I checked the connections on the intake and everyhting seems to be snug. Still may try putting the stock one back on and see if it changes anything.

 

Could be but usually a vapor leak will throw a code for either a large leak or small leak once the OBD does its' routine of self checks of the emissions systems.
Could also be that you do have a injector that is poorly atomizing which could lead to gaseous fumes from the exhaust.