Update on Fuel Trim DTC (P1193) and some parts prices

[RKT BMR]

In the on-going project to resolve my P1193 "Post-cat fuel trim, bank 2" DTC problem, I did some pre-emptive pricing through Pacific BMW (and elsewhere) to get an idea at what I might be looking at should the absolute worst case turn out to be my problem. Once again, Pacific comes through with the absolutely baddest-ass rock bottom prices:

Cats: 18 40 7 514 502/503: $618.42 ea
gasket: $10.31
O2 sensors (pre and post cat): $97.60 ea

If I have to replace any and/or all of this, it is work I can do myself over a weekend. Not too difficult.

I don't think my cats are bad, judging by the O2 sensor data I've collected on several weeks of driving. However, the bank 2 post-cat sensor looks a tad suspicious.

Note that the motor is performing fabulously at the moment. This fuel trim issue doesn't seem to be impacting operation (although may be impacting emissions).

Now, here's the kicker, especially for Vince :) : I had a contaminated MAF. The pictures tell the story without needing to describe it. After carefully capturing/observing gobs of data under a variety of driving/load conditions -- airflow, short and long term fuel trim values, etc. -- I finally swapped in my new MAF two days ago. Well, KABLAM! The operating data changed enormously, as did the DTCs I've been getting. LTFM values were moving up and down between 6-10% with the old MAF; with the new one, they've settled down at -2%-0%. I was also occasionally getting a P0171 and P0174 (lean running, both banks) with the old MAF, as well as the P1193. Now, just the P1193... no sign of the lean condition.

First, I'm just going to drive for 500 miles or so and let the ECU settle the adaptation values with the new MAF, and see if the P1193 goes away. If not, I'm going to swap the two post-cat sensors and see if the problem moves to the other bank (bank 1, DTC would be P1191). If it does, I'll replace that one O2 sensor and see if the problem clears up.

Here's the old MAF:

http://bimmerfest.com/forums/attachment.php?attachmentid=32187&stc=1

http://bimmerfest.com/forums/attachment.php?attachmentid=32188&stc=1

Now, here's a close-up shot of the metal thin-film sensor that does the actual work in measuring airflow... Yes, boys and girls, that's OIL on the sensor!! Has quite a coating of the stuff. Explains the lean DTCs... MAF was under-reporting airflow due to the contamination.

http://bimmerfest.com/forums/attachment.php?attachmentid=32186&stc=1

I'm going to try and clean this up with some solvent, then put it back in the car and see how it performs. If I can completely fix it with a clean-up, I'll have a spare MAF. It is also something I will need to add to my maintenence routine, probably every six months or so. The contamination is due to what I believe to be a design flaw in the ESS blower kit -- something I will be taking up with ESS.

[neile]

If you do decide to replace your O2 sensors check pricing at http://www.oxygensensors.com/ as well. The Bosch Universals are $89.99 each, and the OEMs are $91.99. It ain't a whole lot, but when you have to replace four ( :yikes: ) it adds up.

Neil

[Kaz]

I've read about the universal Bosches often recently. I know they work great for 80s and 90s German cars, but now I'm starting to hear about people recommending (without knowing if they work or not) in newer cars as well as Japanese and domestics. Are they THAT universal? Somehow I have my doubts.

[RKT BMR]

If you do decide to replace your O2 sensors check pricing at http://www.oxygensensors.com/ as well. The Bosch Universals are $89.99 each, and the OEMs are $91.99. It ain't a whole lot, but when you have to replace four ( :yikes: ) it adds up.Every little bit counts :) Nice to see that Pacific is still a good source for low prices...

Just to be clear, if I determine that I have an O2 sensor problem, it's probably only one, not all four. The bank 2 post-cat sensor was reading in an erratic way compared to the other three, which is what makes me suspicious of it. And the data was not consistent with a bad cat -- rather the behavior was more consistent with an O2 sensor on its way out.

Both cats pass the OBDII cat readiness test, which suggests they are probably okay. Watching the data stream, they both respond as expected to the lambda cycle, and seem to be storing O2 with the capacity they should be and catalyzing during the rich portion of the lambda cycle.

This problem is turning out to have several sources: A disconnected crankcase breather (fixed), a contaminated MAF (replaced), and something else. Each time I've fixed part of the problem, the symptoms have gotten noticably and significantly better. Now I'm just down to the recurring P1193 DTC, which points to either the post-cat O2 sensor -- which is coincidentally suspicious for other reasons -- or the cat. My swap of the two post-cat sensors will be a significant diagnostic step in evaluating that sensor.

Amazing what one can do with a simple OBDII scan tool (not a code reader, a scan tool -- different animal, and a tad more expensive), documentation, and the internet. I've spent way less $$ solving this problem than BMW would have charged me, am learning and having alot of fun in the process, and heck... Me and the RKT BMR are having yet another incredible bonding experience :D

[neile]

Are they THAT universal?

Not a clue :) Just pointing out that they, and OEM ones, are available at somewhat less cost than Pacific BMW.

Neil

[Raffi]

Dave, what type of solvent can you use on the MAF elements to clean them? I may clean mine out next time I recharge my K&N filter, just for the heck of it, if there's no side-effect.

[RKT BMR]

Dave, what type of solvent can you use on the MAF elements to clean them? I may clean mine out next time I recharge my K&N filter, just for the heck of it, if there's no side-effect.I'm not sure, but I'll report back after I do it (next week sometime -- I'm off for some completely unstructured R&R next week!!!!!!!!!!!!)

I thought I'd first just blast the thing out real good with some Gunk Engine Cleaner (safe on the plastic), and then blow it good and dry with compressed air. Then, with Q-tips, do a very thorough cleaning of the metal film sensor with alcohol, acetone, or lacquer thinner, whichever one seems to be the best solvent in a dissolve test in a small cup with a few drops of oil. Blast dry again with compressed air.

I'll post pics after I clean it up, a long with the results of putting it back in the car. As I mentioned in the previous posting, the ESS blower kit has a design flaw in how the crankcase breather is rerouted and handled that resulted in this, but to be realistic, it's really not that big a deal to pull the MAF twice a year or so and clean that sensor with a few Q-tips and solvent, now that I know to do it. What you see in the pictures above is 2 years of contamination.

[Raffi]

Thanks, looking forward to your update. :thumbup:

[neile]

Cleaning the MAF was a pretty common thing to do on my old Jetta. Over at vwvortex.com the preferred way to do it is to put it in a baggie or a container with 99% isopropyl alcohol, shake it around, and then let it dry thoroughly before re-installing. I wouldn't use any compressed air on it since the MAF is a pretty precision instrument and I'd be nervous about the cold/pressure doing something bad. Air dry will work just as well, and all it requires is a bit of patience :)

Note that I've never personally done this, but it's the method that came up over and over again on the Jetta forums.

Neil