# FINAL UPDATE: Fuel trim problem (P1193 DTC)



## RKT BMR (Sep 7, 2002)

Well, it's been long enough now that I feel comfortable declaring the problem I had causing a Service Engine Soon light, and several fuel mixture related DTCs, as discussed here and here is *fixed*.

The final nail in the coffin was the new MAF. I haven't cleaned up the oil contamination in the old one yet, and try putting it back in to see if the problem remains fixed, and don't plan to. Don't fix it if it ain't broke, they say.

I will still clean the thing up and then put it on the shelf, for the future. I won't even know if it still works after dousing it with alcohol to clean it until I have reason to put it back in.

So, here's how the saga finally worked out: After re-attaching the disconnected crankcase breather, and then replacing the MAF with a new one, the lean running codes (P0171, 174) went away. But that dang Post-cat Short-term Fuel Trim Bank 2 DTC, P1193, just wouldn't quit. I cleared the MIL (SES) and codes from the ECU, and within a trip or two, it would come right back. Damn!

I knew, however, that the repair manuals state that the ECUs adaptation values should be cleared any time the MAF is replaced, and of course, lacking a GT1, I'm not able to do this. I also knew that, over time, they these parameters would work their way around to where they needed to be, it just would take longer, and as the repair manual states, failing to clear them might result in further MIL events until adaptation settles.

So, I figured I'd just let the car go for awhile, live with the light, leave it all alone, and see what happened.

The right thing happened! After about a week, the light went off on its own one day. Then came back on later that day. Then, two days later, went off on its own again. It hasn't come back on since, and it's been nearly two weeks.

What's more, I checked in on things with the Autoxray 4000, and found that there are no pending DTCs -- so the 1193 condition has not reared it's ugly head again. The last instance of 1193 is still there as a primary code, but the light is off, which means that the condition hasn't occurred again. I could clear this last instance myself with the tool, but it will clear out on it's own after 43 complete trip cycles from the time it appeared, and I don't want to clear out my now restored OBDII readiness status.

Here's the really interesting part: When the problem first showed up months ago, my Long Term Fuel Trim values had settled up around 7-10% -- pretty high numbers. Indicates the ECU was trying hard to compensate for an overly lean running condition. Immediately after the repairs, the LTFT dropped down to around 2.4% (both banks), and continued heading south more and more slowly. I stopped monitoring it weeks ago, and then took a look yesterday after I declared it fixed...

Adaptation had settle the LTFT values at -7%!!! A huge swing from where they were when I was having problems, and the MAF was contaminated. Seems on the low side to me after the problems when they were +7-10%, but he ECU seems happy, so I am.

If you've read this far (and I know Vince has







), hope it has been interesting. Next tinkering project will be relocating my Intake Air Temperature sensor, but I'll ponitificate on that in a separate thread. Steve Dinan's paper on dyno testing inspired me to take a look at this sensor and what it's doing, and I have been able to effect noticable power increases by messing with it a bit. I'll post that new thread tonight for the interested.


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## Mr Paddle.Shift (Dec 19, 2001)

Man...you're so darn right. As the geek I am, I read through the entire thing. :tsk: But a good read nonetheless! 

You really need to GT1-CLEAR the codes ECU has registered. If you know someone at the dealership, that will be very helpful. Reason I say "GT1-CLEAR" is because no OBDII reader can clear what the ECU has stamped on. Only GT1. 

Also, an often mistaken thing about IAT. It's not, well, the temperature taken at the MAF. The IAT is located on the intake manifold. Or are you already referring to that sensor?


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## Raffi (May 18, 2002)

Dave, check this out: http://www.bimmerfest.com/forums/showthread.php?t=66245


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## RKT BMR (Sep 7, 2002)

Mr Paddle.Shift said:


> Man...you're so darn right. As the geek I am, I read through the entire thing.
> 
> 
> 
> ...


Got it... I'm inclined to hold off unless I start getting DTCs again, though. Steven's Creek BMW will charge me to do it, the bastages, and the ECU seems quite happy at the moment, and the motor is running really nice. So, as I said above, if it ain't broke, don't fix it









Mr Paddle.Shift said:


> Also, an often mistaken thing about IAT. It's not, well, the temperature taken at the MAF. The IAT is located on the intake manifold. Or are you already referring to that sensor?


That's the one. I had the same thoughts you did -- the temp in the intake manifold isn't the same as other locations upstream. Should be warmer. BMW would have tuned for this, right? so putting the IAT sensor upstream in colder air might mess things up, put the engine at risk.

However, the sensors not in the manifold anymore anyway. The ESS kit includes a new sensor, and part of the install involves mounting it in the cabin airfilter housing and hooking it up, abandoning the one in the intake manifold (it stays to plug up the hole). The reason for this is heating of the air by the vortec compressor, which will really throw off the ECU. Don't know if part of the reprogramming that ESS does takes account of this, but the changes with the IAT is part of their design.

So, this, combined with reading Steve Dinan's paper on dyno testing (where he moves the IAT upstream to a place where it's essentially reading outside air temps on a Dinan SC'd car) gives me some confidence that it's relatively safe to play around with this input. Using my scanner and my Humanomics™ brand Buttdyno®, I can clearly see the effects of IAT that he talks about in his paper with some simple experimentation I did a few days ago... cabin fan off, IAT reads about +20°F or more above outside indicated; cabin fan full on and reading drops to +2-5°F fairly quickly. Motor feels noticably torquier, can see the difference in timing advance too on same conditions (level, 60mph, cruise).

With a cab, I've got that fan off (the whole IHKA as a matter of fact) much of the time, 'cause I've got the top down. So, I thought I'd experiment and try what Dinan did in his paper, and move the thing into the intake path, upstream of the MAF.

Since I mix some of Emission's TRICK booster in every fill (max recommended on the can -- 3.2 oz per gallon), I'm getting good know protection, and it also helps the combustion run cooler.

It would be interesting to slap the Autoxray on someone's stock 330 motor when we all get together at the next B&M TS and see what the temp/timing readings look like for some similar driving conditions. Could be a hoot to look at it on your car too, with the AA blower. You never know -- a reasonably safe mod for people to squeeze a little more performance out of a stock engine, especially one that's had just a CAI or something, might be to relocate the IAT.


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## Mr Paddle.Shift (Dec 19, 2001)

Btw, just a minor correction, mine is an ASA SK1 kit not a AA kit. Don't want anything to do with AA really.  

I didn't know the ESS kit actually relocates the IAT sensor. Interesting. Take some pics if you can.

You know there are two other ways to lower the IAT: intercooler and water injection. Incidentally, I have both. With 6.5psi, I can have IAT match the ambient temperature. That is of course given a certain airflow through the intercooler as well. But dealing with WI can be very tricky. Engine has to be heat soaked to be efficient. You know the basic physics, heat transfer stuff. 

In any case, if you really want a significant power increase, think about setting up a intercooler for your system.

Again, c'mon down to the next TS and we will talk.


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