experimental MAF reset switch: which circuit to interrupt? more complications
 

After years of having problems with fuel trim readings being higher than normal, which resulted in setting codes for lean conditions on both banks, and eventually setting a CEL on the dash, I have searched, tested, prodded, and done work-arounds for keeping the abnormal readings at bay. Also, I've checked the tailpipe for bad smells (indicating a real problem), haven't had but one misfire in 3+ years (the engine starts and runs great, always), and monitored the O2 sensors as well (AOK). I've used three different MAF sensors (to see if there was any mis-reporting...the OEM unit was reporting lower than the two, cheap, replacements I now use...one at at time, of course), and done several sight inspections, and more smoke testing (and never found anything amiss), I finally gave up looking, and have resorted to just resetting the fuel trim reporting system by unplugging the MAF, temporarily, and have done so for almost three years.

Since I very seldom drive the X5 (2600 miles over 3 years and 3 months), and 99% done in stop and go, low speed, short hops (maybe 10 miles max, 5 miles or less, usually), I just reset the fuel trims whenever the eventually climb near "10", before any codes might possible get set, and forget about actually fixing the phantom, unfound, underlying problem causing the fuel trims to rise. However, on the very few longer, higher-speed trips I've driven, the fuel trims actually go lower, my overall fuel economy rises, and all is well...until the short-trip cycle starts afresh.

So, just yeasterday, going to the Dr. during a rainstorm, my LTFT's were rising again, and I wondered if I could find a way to do the MAF reset, if I nneded to, during a pouring rain, without going underhood. I thought that I could use an on-off switch to interrupt the circuit (for 10 seconds or so, only), after I pulled oot of traffic, of course, to reset the fuel trims, without getting soaked. My M54 has a 3-wire MAF (ground, signal, and positive), so my first thought would be to interrupt the ground or positive feed (any signal wire going to the DME seems to present the chance of shorting out the DME, in my mind). But, maybe I'm looking at it wrong. Any ideas?

You can reset fuel trims with your scan tool but you should really try to fix the problem too. Having tried 2 cheap mafs doesn't do much to rule out the maf as the problem btw.

diagnose, find nothing, repeat
 

I was talking about a quick reset while running; I can't reset it while using the Torque Pro app I use on my dash-mounted tablet, that I use to monitor many parameters. If I'm not running the engine, I've tried using my Foxwell NT510 Elite, but never found a way to reset the MAF/fuel trims, even after trying "reset adaptaions" several times, as recommended by Andrewwynne.

As I stated above, and in hundreds? of previous posts on the subject, I've tried everything short of replacing the drivetrain, to fix the problem. Eventually, if there is an actual part failure somewhere down the line, then I might actually find the cause. Until then, work-arounds.

Pretty out there workaround for what is clearly some sort of other problem going on. I would start with getting it smoke tested. May also want to check the condition of catalytic converters if it's only the LTFT that is changing.

I suspect I'll find the problem, eventually, but it's not catastophic, yet
 

I have smoke tested it many times, including six times (but only the last three using their "bladder adapter" to perfectly seal the intake) with heavy smoke from my AutoLine Pro Smoke Machine Leak Tester – Shop Series - Automotive Smoke Tester for Vacuum Leak Detection - Car Smoke Machine with Ceramic Smoke Coil,..., and still didn't find leaks. And, I'll not spend $200 an hour for my local shop (not even a EURO shop), to smoke test for me...their prices are going thru the roof.

I have silicone vacuum lines and caps standing-by, to seal leaks, but none were found, also. I'm going to run a couple of bottles of Cataclean through the system, but haven't yet (I don't hear, smell, or feel signs of clogged cats...been there, done that on other cars), and I'll wait until I can drive a long distance at highway speeds before I use it (been busy at home, a lot).

I might just put the X5 on jackstands, and replace all the hoses , caps, and plugs, just because. Espcially those going under the truck, since I couldn't really see under there very well, when smoke-testing, and I previously had a question about fuel pressure regulation (if the vacuum line to the FPR is getting porous, then that MIGHT be the ONE).

In the meantime, anyone want to venture a guess on which wire to get the "switch", if I go ahead with my workaround plan?

Unplugging it is the same as cutting power. Pin 3.

Have you tried a hard solvent fuel injection cleaner? Let me look up a solvent cleaner I'm planning to use on mine. At 168k, the injectors need a good cleaning. You can also ohm each one to check tolerance.

I think you're right about the pin 3. I'll try that.

I put in a bottle of Liquid Moly Jectron 2007 fuel injection cleaner every time I fill the tank, and double up when I let it sit for up to a month. I also occasionally use Stabil 360 if I fill up at Sam's Club (my normal go-to is Quik Trip, with top tier premium, and Shell once). I'd rather have too much additives than not enough...fuel injection requires more care than the carburetion that I grew up and trained for, then used for 45 years!

Also, I checked the operation of my injectors using the BimmerTool android app, which checks for "smooth running" and misfire counts. I did that last year (about 1200 miles ago), and all 6 cylinders were running quite balanced, with no misfires, at that time.

I haven't removed the injectors to physically test them, but the previous owner ( who had purchased the X5 specifically at my request, to swap for my Chevelle in trade) bought and installed new Bremi injectors only about 6 months before we swapped cars (he had renewed & restored most systems that needed work, as per our agreement). So, those injectors probably have only about 4k miles on them, but who knows how many hours, due to my constant testing and trying to find the phantom vacuum leak (and my fan projects, too). But, I plan to get an injector tester when any signs of a misfire occur.



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Injector cleaners have oxygenates. Too many will change O2 readings. Start lowering them with premium fuel. Give it time to adjust to normal fuel. Keep it half tank at least unless you plan to drive it a lot more.

Connector X6965 is a soldering point where all those voltage supply lines are bundled together. It's located in E-box where DME also lives. That would be a good place to cut and make the wiring for the switch. The wiring can be routed thru E-box vent route thru firewall. Perhaps it would be wise to put a separate smaller like 5A fuse near the switch so if the line happens to ground on the chassis that fuse would be easier to replace than the one on E-box fuse pack.

https://bmwteka.com/wds/en/e53/493a47c7#

anything to avoid damaging the DME
 

Whoa, there, since I'm not an electrician, yada yada (I've shown that in detail, in various posts and threads), I surely don't want to cut/splice/solder any wires in the DME, or even close to it.

So, that's why I want to make a removable wiring harness/MAF plug/switch system, where the only wire I'll have to cut/splice (no solder, just connectors), will be on the extra wiring plug/pigtail I'll buy for the EXPERIMENT.

I only need the pigtail and switch, and I could wire it up in 1/2 hour...and remove it in 2 minutes. Remember, this is my final project car (as stated in my signature).

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