Lean Air bank 1 and 2 codes (P0171, P0151)

**MeanGreen98** · 05-24-2010, 02:46 PM

About 4 weeks ago my A4 98 'maro took 2 good cranks to start and once it did it was in limp mode with a MIL. I blamed it on the girlfriend after hearing that she put 87 in the tank (it normally gets 93). After two tanks of 93 failed to fix the problem, I took it to Advanced to get the MIL checked out, The codes were: P0131, P0137, P0151, and P0157. Low volts on all oxygen sensors. I assumed it needed new sensors bc the car was at 55,000 and had never had new ones. So I bought 4 boschs and swapped them in on Saturday. After getting the MIL cleared the car started well and ran well until i took it on the highway and romped on it. It throws the MIL as soon as I go WOT and returns to limp mode. I checked the codes again and they read P0131 and P0151. After researching the codes I found that they correspond to a lean air problem. I then checked the MAF and TB for anything and they were clean. Also a visual inspection for vacuum leaks didn't show any bad/cracked hoses. Any opinions would be greatly appreciated.

For reference: GM replaced my fuel pump and filter @ 52,300 last Oct. That's the last service beside the new sensors and regular oil changes. I also have a K&N ram air kit.

**35th-ANV-SS** · 05-24-2010, 02:51 PM

You mentioned you checked the MAF and it looked clean. Did you physically clean it? Running lean on both banks is either a) vacuum leak or b) dirty/faulty MAF sensor I would think.

A MAF can "look" clean and actually be dirty. I would spend the $6 and buy a can of CRC MAF cleaner found at any autoparts store and start with that to at least eliminate the possibility of it being the MAF.

**MeanGreen98** · 05-24-2010, 03:07 PM

I visually inspected the MAF i.e. I didn't spray it. A friend mentioned the cleaner, I will get some tomorrow.

**Cutlass** · 05-24-2010, 05:55 PM

Low fuel pressure can also cause a lean condition. Shouldn't be a problem for you considering your recent fuel pump and filter change, but you should check the pressure anyways.
Is this a stock, unmodified GM MAF sensor?
I think cleaning it with CRC MAF cleaner is a good idea especially with a K&N filter. Sometimes the oil on those filters comes off and coats the sensor and skews its readings

**MeanGreen98** · 05-24-2010, 07:16 PM

This is a stock MAF, I'm worried that there is an underlying problem that ruined my stock fuel pump and is now causing more problems.

**MeanGreen98** · 05-24-2010, 07:20 PM

I should pull out the MAF and spray it down right? Not just undo one side and spray the s#!% out of it?

**35th-ANV-SS** · 05-24-2010, 07:24 PM

Originally Posted by MeanGreen98

I should pull out the MAF and spray it down right? Not just undo one side and spray the s#!% out of it?

I completely removed mine when i cleaned it. I believe it states this in the directions on the can also. Unplug it and take it out and spray the &^%$ out of it. be sure to fully let it dry before hooking it back up.

**MeanGreen98** · 05-24-2010, 07:33 PM

10-4. What about the pcv? I've had people at work mention that as well. Can the ball inside that just be stuck too? If it is, brake cleaner would loosen that up?

**35th-ANV-SS** · 05-24-2010, 07:46 PM

Originally Posted by MeanGreen98

10-4. What about the pcv? I've had people at work mention that as well. Can the ball inside that just be stuck too? If it is, brake cleaner would loosen that up?

If you take it off and can hear the ball moving freely I would say you are fine. If not, you can try cleaning it, but depending on price I would replace it.

Your symptoms really do sound like a MAF problem to me though. lean on both banks is usually an air leak or MAF faulty reading, causing the computer to either retard fuel or dump more fuel into the mix than is needed...causing a lean or rich condition.

In your case, which is lean, this is the worse of the two. You do not want to be running your car lean. It can lead to major problems if not fixed properly.

**MeanGreen98** · 05-24-2010, 09:17 PM

Major problems? I.e. detonation or other things? Doesn't limp mode keep me from exploding it?

**35th-ANV-SS** · 05-24-2010, 09:19 PM

Originally Posted by MeanGreen98

Major problems? I.e....

Running lean makes the engine run hot. This tends to lead to pinging/knocking, or pre-ignition. This causes greatly increased cylinder pressures and heat, and can damage internal engine components like bearings, piston rings/ring lands, burn pistons and valves, bend/break rods, etc...

**383ls6** · 05-25-2010, 05:03 AM

do you have access to a scanner that will allow you to read live data(fuel trims,MAF gps)?

**rkvette** · 05-25-2010, 05:47 AM

i had somthing like that happen to me on my 2002 covette conv... i bought a hand held tuner, try to get a couple more horses... i thought i did a good job ,but did not !! vette stared to miss at low speeds and turned a light on.?. went to my friendly gm dealer and they found couple bad spark plugs, car had only 1,200 miles.. i put in tune,, too lean !! melted couple plugs they replaced all n/c., no problem- never try that again, vette went down strip 7 tens quicker with right drag tires,mid to low 13 seconds when i got out of the hole,right and good shifts on the 6 speed, got into 4 th just before finish..rkvette

**MeanGreen98** · 05-25-2010, 03:34 PM

Much to my delight, when I purchased a can of MAF cleaner from Advance I got a can of TB cleaner free. After spraying them both down, I took the car out and did notice a slight SOP difference but the car is still in nanny mode. I'm gonna go back out in a few minutes and see if the car starts on one crank.

*It didn't.

**MeanGreen98** · 05-25-2010, 07:48 PM

Originally Posted by 383ls6

do you have access to a scanner that will allow you to read live data(fuel trims,MAF gps)?

I do not. A friend may be passing by me on his way to Parkersburg this weekend, hopefully he'll bring his scanner and stop by.

**0rion** · 05-25-2010, 08:00 PM

check your fuel pressure....also, check the back of the pcv hose where it bends to go into the intake. Those like to crack there. Replacing the fuel pump with a stock pump was a bad idea...probably pretty expensive too. How many miles are on that pump? It could also be a cracked hose in the tank that goes to the pump.....that's not unheard of either. First step is to check your fuel pressure. The not cranking on the first crank makes me believe it's pump/pressure related.

**MeanGreen98** · 05-25-2010, 08:05 PM

Originally Posted by 0rion

how many miles are on that pump?

~1500

**MeanGreen98** · 05-27-2010, 04:30 PM

Since my friend canceled his trip I was forced to go out and buy a fuel pressure tester. I found out that at idle the car hovers at ~33 psi. When I move the throttle the pressure drops slightly and never makes it to 50. So I'm quite confident it's a fuel problem. I'm ruling out the pump and filter for now b/c they are pretty freakin new, (less than 2,000 mi), and they are bonafide parts from the general. What about the fuel damper?

**Cutlass** · 05-27-2010, 06:27 PM

No I don't think the damper would do that. Its gotta be the pump or the filter. Unless you got a bad fuel pressure gauge...unlikely.

**0rion** · 05-27-2010, 08:16 PM

Originally Posted by MeanGreen98

Since my friend canceled his trip I was forced to go out and buy a fuel pressure tester. I found out that at idle the car hovers at ~33 psi. When I move the throttle the pressure drops slightly and never makes it to 50. So I'm quite confident it's a fuel problem. I'm ruling out the pump and filter for now b/c they are pretty freakin new, (less than 2,000 mi), and they are bonafide parts from the general. What about the fuel damper?

other than the fuel pump/filter about the only other option you have is a split hose in the tank. Definitely pump related IMO.