CEL: Lean bank 1 & 2, plus DME says exceeded trim

[Bdc101]

I went on a 600-mile road trip this week, and oddly I got these codes twice during my trip. Fortunately I carry my Foxwell with me so I was able to pull and reset them immediately.



First, about 2 hours in, I got a lean code in Bank 2 (check engine light on dash).



I reset that and then about an hour later I got lean codes in both banks 1 and 2. This time I checked the DME codes as well, and it had codes E3 and E4:

E4 Fuel Trim Bank 2, Permissible Range Exceeded
E3 Fuel Trim Bank 1, Permissible Range Exceeded


I reset these a second time... and then I drove 300 more miles and they never came back. The car did not have any running issues of any kind, even though I drove over 600 miles through temps ranging from 27 to 115 degrees on the same day.



I did a little searching and only found a couple of good threads, most of which were solved by replacing the DISA valve. I replaced my DISA valve and gasket with a GAS unit almost a year ago.


I think the fact that the car ran fine the whole day also precludes any fuel pump problem. The intake elbow is about 3 years old. My best guess is either the MAF is going bad, or there is a small vacuum leak somewhere. I will try to spend a little time looking for a vacuum leak tomorrow.



Any other things I should be looking at, from the more experienced crowd? TIA!

[workingonit]

Originally Posted by Bdc101

I went on a 600-mile road trip this week, and oddly I got these codes twice during my trip. Fortunately I carry my Foxwell with me so I was able to pull and reset them immediately.



First, about 2 hours in, I got a lean code in Bank 2 (check engine light on dash).



I reset that and then about an hour later I got lean codes in both banks 1 and 2. This time I checked the DME codes as well, and it had codes E3 and E4:

E4 Fuel Trim Bank 2, Permissible Range Exceeded
E3 Fuel Trim Bank 1, Permissible Range Exceeded


I reset these a second time... and then I drove 300 more miles and they never came back. The car did not have any running issues of any kind, even though I drove over 600 miles through temps ranging from 27 to 115 degrees on the same day.



I did a little searching and only found a couple of good threads, most of which were solved by replacing the DISA valve. I replaced my DISA valve and gasket with a GAS unit almost a year ago.


I think the fact that the car ran fine the whole day also precludes any fuel pump problem. The intake elbow is about 3 years old. My best guess is either the MAF is going bad, or there is a small vacuum leak somewhere. I will try to spend a little time looking for a vacuum leak tomorrow.



Any other things I should be looking at, from the more experienced crowd? TIA!

Not that experienced, yet, but I battled lean codes for many months, until I resorted to using a cheap MAF sensor, for testing. It cost me $23 at Amazon https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1, was recommended to me by X5chemist, and immediately solved my lean code problems.

I had already smoke-tested several times for a vacuum leak, replaced a possible leaking oil cap/seal, rebuilt my DISA with the GAS kit, cleaned the T-valve, sprayed every hose and fitting with carb cleaner, and tested my fuel pressure...without success. The cheap MAF instantly yielded results.

I'll eventually buy/get a better MAF to replace the cheap one (my original was a Siemens MAF, that I had cleaned twice), but I'll run this cheap one until it quits working...might even get a second one, for my testing equipment stash.

[Bdc101]

Did you have actual check engine lights or just internal DME codes?



Also, what is the T-valve?


I remember reading about this but did you document it in the daily thread, or did you make your own?

[workingonit]

Originally Posted by Bdc101

Did you have actual check engine lights or just internal DME codes?



Also, what is the T-valve?


I remember reading about this but did you document it in the daily thread, or did you make your own?

I mentioned my codes (both P codes and DME codes) on many threads and individual posts over several months, including the longest https://xoutpost.com/bmw-sav-forums/...bout-hour.html. The Service Engine Soon light would come on every time the fuel trims became too high, and the codes were seen on my Foxwell.

The T-valve was the idle control, which I couldn't quite remember the actual name for...here's a drawing from Realoem (see #8):

[Effduration]

There are several places you could have a vac leak… a proper smoke test - not one with a cigar and a fluid pump - is the answer. If you don’t have a good smoke machine.. it’s well worth paying do one to do a smoke test for you..

[workingonit]

Originally Posted by Effduration

There are several places you could have a vac leak… a proper smoke test - not one with a cigar and a fluid pump - is the answer. If you don’t have a good smoke machine.. it’s well worth paying do one to do a smoke test for you..

Though my home-made smoke tester was low-volume, I did use it three times (before the heating element burnt out) for probably 45 minutes runtime; never saw a wisp of smoke, so I switched to spraying carb cleaner anywhere a gasket, seal, or line might leak...I used 3 cans the first time, and two the second time, with zero leaks detected. I'm still wanting to get a legit tester, if not just for now on the X5, but also for my aging fleet of vehicles. And I'm sure that my X5 probably has a small leak I haven't found, but it's not triggering any codes, currently.

I'm almost to the State inspection window, and since the "test" MAF is working OK (I'm not wanting to touch anything that might make a small leak worse), I don't need to put it in a shop, yet, but if I do, then the smoke test will be in order.

Sorta strange, but in all my years working on carbureted drag cars (and some modern, fuel-injected ones), we (my engine builder, tuning expert friends, and I) never used smoke tests to find leaks, just a propane detector or carb spray always did the trick.

[Bdc101]

So if it's a MAF problem, workingonit, did you ever have a breakdown? Just curious because I am 600 miles from home and need to get back.



A vacuum leak shouldn't strand me unless it becomes a much bigger vacuum leak either. (Hopefully.) I will go poke around on the intake in a few minutes.



Would resetting the fuel trims with my Foxwell be a good idea or should I just leave it for now? I have never done this before -- it should just cause the DME to have to figure out the proper trims again on the next trip, right?

[workingonit]

Nope, never had a breakdown, though I was hesitant to drive much, with high fuel trim numbers (fearing the cats would be harmed).

I reset fuel trims three ways:

• 1) by using the Foxwell to reset all adaptations (didn't do much),
• 2) unplugging the MAF while running (reset longterm trims to zero), and
• 3) finally by using the cheap MAF replacement.

I'd certainly not move any vacuum lines around...might make the situation worse...and then at home, try looking for a leak again; resetting thru the Foxwell won't hurt anything, some of my DME codes never reappeared, but a faulty (under-reporting...lean codes) MAF will just keep setting codes, until it doesn't anymore (cleaned or replaced?). It shouldn't disable your car, my codes never did, so it should be OK to try, then drive.

For $23, get that cheap MAF shipped to you before your long drive; it worked for X5chemist (still working after a year) and for me, too, so far.

[Bdc101]

I have been watching the graph of my MAF airflow rate on the foxwell while I am driving, and the flow rate looks like valid data. It keeps tripping the CEL frequently, but it still is not running rough at all. Does an airflow rate of 3.3 g/s or 12 kg/h seem right at idle?

[workingonit]

Originally Posted by Bdc101

I have been watching the graph of my MAF airflow rate on the foxwell while I am driving, and the flow rate looks like valid data. It keeps tripping the CEL frequently, but it still is not running rough at all. Does an airflow rate of 3.3 g/s or 12 kg/h seem right at idle?

You need to be checking the fuel trim numbers; mine were so high they triggered the CEL. Once I installed the new (cheapo) MAF, they started to balance out each other, showing single digit readings, keeping the total fuel trims near zero (instead of plus 25+++ % added).

I think your MAF readings are low, similar to what mine were before the new MAF, indicative of an under-reporting MAF sensor.

Get a second sensor, just to test with, so you can move on to the next test (if needed afterwards). I tried everything prior to the MAF, which took me six months until I figured it had to be worth $23 just to compare with the Siemens unit. Wish I had tried one earlier.