Update on the suspected bad MAF

Well, the new MAF arrived today (gotta hand it to Pacific BMW...). I also finally got around to buying an OBDII code reader at lunch today, thanks to the prodding of Mr.Paddle.Shift, and read out the codes that were lighting my Service Engine Soon indicator.

(Those of you who are familiar with my modification exploits might wonder how I went this long without a scan tool, and you'd be on solid ground with your incredulity; I can't explain myself, so I won't try

)

Here's what's going on:

P0171, 174: Running lean, banks 1 and 2

P0313: Misfire (I know what caused this, so it can be ignored)

P0369: Camshaft position sensor "B" circuit intermittent (this one has me a little concerned, and it showed up again right after I cleared the diag codes out, so needs more investigation; hope it doesn't have anything to do with the engine cleaning I did before the 'fest

)

P1191, 1193: Pre and post cat fuel trim problem

So, the codes that are really meaningful here, 171,174,1191, and 1193, are all consistent with a contaminated MAF. If some oil has gotten on the thin-film/wire in the MAF, it would cause the sensor to indicate less airflow than is actually occurring, resulting in a lean mixture.

I cleared the codes (and the MIL/SES light), and plan to run with my existing MAF until I get an MIL again, then check the codes. If the same, I'll clear it again and go one more round to see what turns up. If I get the same basic faults, I'll swap the MAF, clear the codes, and then see what happens.

I'm betting the MAF's the problem, but I can't know for sure until I disassemble it, which from what I can tell will be a destructive project.

If not, my next step is to invest $122 in some OBDII scanning software for my laptop so I can monitor and record engine operating parameters in real time while driving, and catch the failure. Then I can get a better idea of what's going on. I plan to purchase a copy of Vehicle Explorer, which looks like a pretty decent tool. For the technically minded, you should click the embedded link and check it out.

Reply » Update on the suspected bad MAF

Buy a GT One!

Yeah right.... I wish I could afford one of those...

Reply » Update on the suspected bad MAF

Quote:

Buy a GT One!

Yeah right.... I wish I could afford one of those...

Sorry, buddy... that was the only response that seemed appropriate

As you're probably aware, I was itching to get an Actia PassthruXS+, and was soliciting a joint buy of some sort, but have abandoned that project since apparently BMW is determined to preserve the cash cow of car/key memory setting theft revenue for their "independent" dealers.

Man, that one pissed me off bigtime.

Reply » Update on the suspected bad MAF

Hmm, I think 0369 is what I had when my exhaust camshaft sensor went out (not an uncommon problem). The car will occasionally idle funny (too high in my case, IIRC) and the MIL will go on and off.

Reply » Update on the suspected bad MAF

Dave,

Maybe changing the MAF might work better. Question I have is did the lean code come on during light throttle or heavy throttle, highway or street driving?

As for 0369, it sounds like the sensor is faulty. "Intermittent" is definitely not good.

And what's the reason for 0313?

EDIT: Actually, I was hoping at least a 0100, 0101 or 0102. None of these appeared?

Reply » Update on the suspected bad MAF

First of all, thanks to Mr.Paddle.Shift -- he's a candidate for bonafide savior at this point. 24 hours with a scan tool and the picture is very different.

I've had the chance now to reset and relight the MIL twice since yesterday. The results are very interesting, and completely different than the path I was going down.

So here it is. The problem seems to be the cam sensor. After resetting yesterday, I had another P0369 immediately after starting the motor, without an MIL (must be one of those conditions that has to show twice before it lights the MIL). Cleared that (remember, no MIL), and then started up and went on with my day normally.

After two starts and a drive home, the MIL lit again. Pulled the code: P0369, and no others. Reset yesterday evening, and went on with my life.

This morning, again over the course of two separate starts (leave for work, get gas) and 30 miles of driving, MIL lights again. Pulled the codes. Again, P0369 and nothing else.

A pattern is emerging here, don't ya think? Cleared it again after I got to work, and will run this pattern/cycle again a few more times just to build up a set of data to take to BMW.

Kaz, sounds like I have a bad camshaft sensor. I do notice some performance issues: Idles fast now and then, but I can't discern a particular pattern. My normal idle is around 650, and totally smooth. When it is idling fast, it's around 800, more or less. This is when the engine has been running and warmed up, and I can't make it happen, or go away. Just happens seemingly without cause.

Also, I've noticed a very real power loss at times when the MIL is lit. Not as soon as it lights, but seemingly randomly -- seems to be correlated with start cycles. I.e., get in the car, start it, runs like a rocket. Come back later, get in the car, start it, runs like a slug, even though the motor is very smooth.

When I clear the DTC codes, the car is always peppy afterward.

I can theorize all sorts of scenarios that a bad cam sensor could cause the ECU to be hunting fuel trim and adaptation values to get the O2 readings to come in line, and be doing all the wrong things because of bad data coming in from the cam sensor. Then, when the algorithms fail to find a good fuel trim value/pattern, the ECU falls back on the default "limp home" values, hence the crappy performance.

Through all this I can see how those other DTC codes could result from out-of-spec operation of the motor. Finally, I suspect that what the BMW tech pulled from the ECU was the generally the same set of codes I pulled -- lean mixture, fuel trim problems, etc. This would lead to a possible MAF problem, assuming the other sensors are working right.

The scan tool has been worth its price in just a single 24-hour period, as it has allowed me to do some diagnosis that just wouldn't be possible otherwise... I'll bet if I let things go with the MIL lit long enough, those other errors and codes will eventually show up.

Thoughts?

Page 1 of 3