Post #22294 of this thread:
I pulled a code today - P0171 - System Too Lean - Bank 1
The printout reads:
Definition
Lean Air/Fuel Ratio bank 1
(Cylinder number 1 denotes bank 1)
Probable cause
#1 - low fuel pressure
#2 - Large vacuum leak
#3 - Dirty/defective MAF sensor
#4 - Engine mechanical condition
The symptoms are that the car stumbles badly when in WOT and boosting, especially in fourth gear. The code goes away after a while if I drive like a granny. If I go WOT again, the CEL come back.
I think I must be the fifth member on these boards to throw this code this week alone.
Boost gauge reads -21 at idle, and boost is steady at 8.5psi until the stumbling begins. I replaced my MAF yesterday, so I doubt that's it.
The common suggestion seems to be a leak in the intake piping, but I don't think that's it. My MAF is relocated, so I think that it would run lean from such a leak. I've also replaced my MAF and that didn't fix the issue. I'll be replacing all the couplings anyway. I have some worm clamps and some T-clamps. I'll replace all the worm clamps with T-clamps along with the couplings.
I don't think it would be an exhaust leak, because I think that would just make the ECU adjust to run even richer, wouldn't it? I'll be getting the exhaust checked for leaks anyway.
I'm thinking it's a bad fuel pump or injector. In the meantime, any suggestions would be appreciated.
Is there any way to test/check the fuel pump to see if it has gone bad?
Thanks.
Okay, many of you read this and replied with suggestions and stuff, so I thought I'd update. Wrap your noggins around this:
I ordered new couplings and t-bolt clamps to replace all the old ones on the intake hardpipes I have. They haven't gotten here yet, though.
I have always been a diehard Shell gas station user. I always insisted on Shell gasoline, and never had any reason not to. I had a bad experience with Sunoco gas, so I never used them again.
A few weeks ago, I started using Exxon, because the station near my office had a sale. They'd knock 6 cents per gallon off for supreme (93 octane) gas every Thursday. So I started timing my gas fill-ups to coincide with Thursdays. If I ever found myself short on a different day, I'd just put in $5 or something at some station to get me through to Thursday, when I'd fill up.
I never put two and two together to think my "system too lean" CEL code had anything to do with the timing of my switch to the Exxon station near my office.
So last night I was on my way home from the gym and my low gas warning light went on. I stopped in the Shell station by my house and filled it up. I kid you not, within 2 minutes of driving away from the station, the CEL light went away on its own and the car ran like new. No more stumbling under boost like a donkey having spasms, no more delayed throttle response...nothing but smooth running.
So that leads me to the conclusion that either the Exxon station I was using was mislabeling their 93 octane when they were really selling a lower grade, or they were mixing water (or some other filler) into their gas. (gah)
Now I'm not saying that the Exxon company does this across the board. But I do think that this particular station may have been up to some funny business.
So now I've got a new set of couplings and t-bolt clamps coming my way. I'm not upset about that, since I should have replaced the old ones a while ago. I do get a little razzed when I think about what could have happened. I could have potentially damaged my engine internals, in which case I'd be out a truckload more money.
Before anybody thinks that I just got a bad tankful of gas just once, I made the switch to the Exxon station about 4-5 weeks ago, and the CEL light came on about a day or two later. The CEL stayed on up until last night. It would turned off twice over those the course of those 4-5 weeks, but only because I made some other changes or when I reset my ECU by disconnecting my battery. The CEL would be back in a matter of hours.
So I guess my advice you guys is to pay attention to where & when you fill up and figure out if that may have anything to do with any codes your MSP throws in the future.
