more prep work
 

I received the pigtail a couple of days ago, and decided to add small spade connectors to the bare ends, so I could test the amperage of the MAF power wire (input), in order to see what the amperage of the step-down "Buck Converter" should be able to handle, before I order one.

I had to use small spade connectors to be able to just insert them into the existing sensor plug, without cutting any wires (the pigtail will be used for the experiment, and removed afterwards if there are no favorable results... but will be retained, if there are). My only concern is that I might touch them together when inserting them, as there's not much space between them; I've covered them with Liquid Electrical Tape, to prevent them from touching.
Attachment 84462 note that the pigtail shown (top left photo) has the wires arranged differently than on the pigtail I received (bottom photo)

Since the input voltage to the MAF sensor should be no greater than 14.8 volts (the most I've seen on my instruments when the X5 is running), I'll get a step-down Buck converter for that input (I don't need a step-up converter, since my experiment's goal is to be able to reduce the voltage to the hot-film sensor, to trick it into reporting a higher airflow than actual). I could probably use a simple DC motor speed controller (like the one I used to control my electric cooling fan), or a DC dimmer switch (mainly used for LED lighting on RV's), but I haven't quite decided, yet.

Still, knowing the amperage going into the MAF is critical, to find the best device to reduce the temperature of the hot-film's heating element, without exceeding the device's rated capacity. So, I'll install the pigtail, and use my DC amp clamp to measure the amperage going into the MAF sensor, thru the orange wire, before I buy any controlling device. It couldn't be above 20 amps, because the MAF gets its' power from Fuse F3, in the DME fuse carrier, rated at 20 amps, and it supplies power to other circuits, along the way.
Attachment 84463

A voltage step-down, "Buck", converter has a few added features that the motor speed controller or RV light dimmer wouldn't have: circuit protections (settable to limit max/min voltage and amperage, some have short circuit protection too, and even anti-feedback protection), a detailed display (voltage in/out, amperage in/out, wattage, etc.), and a setting to have the device always on, w/o turning off-resetting the MAF system entirely (i.e., setting the fuel trims back to zero, and starting over with the emissions monitors).
Attachment 84464 this one is $20, and has a 5A output rating; others have up to a 20A output rating (for $35-50)

I'll have to postpone my amperage test for a couple of days, while waiting for my wife to get back home (always helping her coterie of friends and family, when they're sick, or dog-sitting for them when they travel...I hope she'll attend to my needs when I get infirm, as I'm 14 years her senior...right now, I'm tending to our menagerie of house & semi-feral , free-ranging, outdoor critters, while she's gone). When she returns, I'll attach the amp clamp, have her sit behind the wheel of the X, and observe the amperage on the orange wire as she revs the truck to 3k rpms. That should give me the info I need, to proceed to the next step of the experiment.

drawing up my nefarious Problemumgehungen (workarounds)
 

While waiting for the wife to help me test the voltage and current going into the MAF sensor (using the jumper pigtail, a DC amp clamp, and a multimeter), I drew up a "revised" wiring plan.

Attachment 84465

I'm still undecided about whether to just get a step-down (Buck) converter, or for about the same price, or opt for a step-up, step-down (Buck-Boost) converter. The wiring I'd need to add would be the same, for either. Might as well get the more versatile unit.

If my experiment to reset and/or tune the MAF's output signal ends up as ineffective, then I can use the Buck-Boost Converter inside the house, as a cheap low-power DC power supply (I've got several old AC-DC power bricks leftover), to test DC devices and perhaps charge them. That is, if my experiment doesn't burn up the converter (and/or my test MAF), first.

My wife is back in town, but the outside temperature will be about 99-100F today, so my test must wait for cooler weather. She doesn't handle temps over 80F very well (she's had 2 trips to the emergency room, due to heat...though I've had many heat-strokes myself, I'm like the Energizer Bunny and I keep on going, though my DR. has warned me against it).

more delays, more problems, wiring revision (as usual)
 

It's been 3+ weeks since my last post here concerning the MAF reset switch project (which mutated into a possible way to tune the airflow reported back to the DME...maybe it'll help with fuel trims? or not). But, there have been delays getting the project started.

I did decide to get the Buck-Boost Converter, so I can use it in the house if the MAF tuning doesn't work out. I also bought the project box, an on/off reset switch (since used on our riding mower), a 12v 80mm fan (to further cool the converter...the fan it came with is TINY), and I need 2 more switches and 2 insulated binding posts (if it does come inside, to serve as a cheap power supply).

I'm waiting on ordering those cheap parts, because of all the car inspections this fall (2 down, 3 to go, and we just had a 3 y.o. high $$$ LG french-door refrigerator fail perhaps a week ago, I think, and we didn't notice it for maybe six days (I was using a second fridge, and the wife was AGAIN out of town). Repairman coming tomorrow, but from what I've read online, the repair bill might be $1200 (I'd rather get another, smaller fridge, than pay that sort of bill). And, of course, everything inside was thrown out, including $$$ of frozen meat.

Meanwhile, I've gathered odds & ends of 14 ga wire, an inline fuse block, and some Wago-type connectors from my parts stash, and actually got the project box started, but since my wife is now semi-permanently always out-of-pocket, she's never here to aid in my testing.

She's been all over, taking care of her sick mother. her sick aunt (both twins, and 82 y.o.; the aunt in Arlington, 25 miles away, and her mother in Tolar, 45 miles away, in the opposite direction, of course, so she stays overnight a lot, at each location). So, I'm left all on my lonesome, caring for our menagerie, and still waiting to have her simply push the accelerator on the X5, while I look at at the amp clamp. I can't do both at the same time, and I can't train our pets to help, at all.

WIRING REVISION, as usual. Maybe it was a good thing the project got delayed, or I might've fried something. P.S. this is only my second homemade automotive wiring "project box"; my previous one was twenty years ago, for my drag-race Chevelle, and nope, my electrical skills have not gotten any better with time.
Attachment 84509

slowly getting there
 

Got the last parts in today, so I decided to plan the wiring in a drawing. Looks very messy,; I wish I had learned CAD in school (it wasn't a thing in '69-'73, at least at my college), or if I still had my K & E drawing board (with swing-arm). But, I'm forced to make-do using Microsoft Paint.

Update 10-21-2024:

Attachment 84520

It will only throw barometric sensor codes if the sensor fails. Often times they don't fail, they just report the wrong data.


I really think this whole thing is pretty crazy. The system is designed to report a problem when something is out of tolerance. Fooling the sensor into thinking it is within tolerance is completely missing the point of why these sensors exist in the first place. It's not hard to imagine causing other problems as a result of this tinkering - the least of which may be other engine codes; and could quite easily also cause engine damage.

it's a project car, afterall
 

I agree with you, it is crazy, but when you've gone over and over and over the engine for three years now, looking for "vacuum leaks" and "fuel pressure problems" etc., and never finding anything wrong, it's time for a "hail Mary" workaround.

I'd rather not experiment with an otherwise healthy engine (only the fuel trims are a problem), due to having little money to repair/replace parts that may be adversely affected, but I've read of many instances where high-performance tuners & racers have modified the MAF and/or MAP signals (either with specific value resistors...which is beyond my current electronic knowledge), or with an aftermarket tuning device, as I displayed in post #24 of this thread https://xoutpost.com/1240938-post24.html.

I decided to try making my own version, using a Buck-Boost converter, because if the experiment to adjust the MAF output signal fails, then I can use the "project box" in my house or garage, to power and/or test other DC items (phones, tablets, case fans, switches, etc.), and not waste my (limited) money on a single-use project.

When tuners modify MAF signals it is to account for a limitation of the MAF signal. This is almost always done with forced induction builds. The MAF sensor itself is not the limitation but rather the DME's interpretation of that data is the limitation. So what they do is put in a specific resistor to alter the signal, let's say by half, and then alter the DME tables to read that halved signal where it would have normally read the unmodified signal. This way they can get 2x the effective range of the MAF, allowing them to read the extra air from the forced induction system properly on the stock MAF. This is a completely different usage case than what you are doing here.

Their goal is to provide the correct reading when they have more airflow. Your goal is to trick the DME into reading an incorrect MAF signal

I appreciate your concern, and I understand why those others were modifying their MAF signals, but still, if by tricking the DME into reading an incorrect, but not TOO far from correct, MAF signal, then perhaps I can make up for the assumed (cheap $20) MAF sensor's built-in inaccuracy. I had no hope for the original Siemens MAF after that last trip, so it was sacrificed for science.

I might not use my device, at all, if my preliminary tests are unsatisfactory. I still have the emissions and safety inspection to pass, later this month, so it'll most likely be November before I'm ready to try.

big delay for this project, maybe for a long time
 

https://xoutpost.com/bmw-sav-forums/...-no-start.html

And, before anyone says that I screwed up my X with this project, I never touched the MAF, DME, or anything. No tests were ever done.

here we go again; more observed MAF weirdness may make me resume my plans
 

It's been two months since I literally shelved my plan to use the "MAF tuner" project box, made to trick my MAF into adjusting the lean fuel trims to lower single digits. I've tried everything else, in 3 years to find the base problem, and have had little-or-no success doing so. By shelving the plan, I mean that I installed the box on a shelf in my home office/"lab", after I decided to not try it yet, and to use it as a variable power supply, instead.

And it's been one month since the new battery was installed, but the X hassn't been driven since then, until today, when we drove to the ranch, retracing the journey last taken in the X, 3.5 months ago, when I gave up on my old Siemens-VDO MAF https://xoutpost.com/1240914-post21.html, which brings me to today's latest MAF weirdness.

Before the drive, I did a once-over underhood, and found the MAF plug loose (unchecked since testing the removable pigtail/jumper, no doubt), so I reset it, and all seemed OK, except that the engine didn't care whether it was plugged-in or not. By the time I got to the gas station a few miles away, the zeroed LTFT's had already climbed to 6.25, each, and varied from there to 9.0 and back, the rest of the trip down. Another thing, the fuel tank cap doesn't seem to be sealing well, probably original, and I'm replacing it this week...could that be a partial vacuum leak/or what keeps my fuel rail pressure just under 50psi? possibly why I get lean codes?


Ok, resuming the story, coming home, my aftermarket fan speed control wasn't working, so when we stopped at a CVS on the way, I opened the hood again, to check the thermostatic switch wiring (wiggled it, and the fan came on...need to re-tighten), and while there, I reset the MAF again (hoping for better numbers). But, instead, while the LTFT's initially stayed at zero for 15 miles, the STFT's were bouncing up to 12-14!, which I hadn't seen before, ever. Eventually, the LTFT's chimed in, and settled going from 6.25-9.0, again, with much better STFT's.

So, now, I'm looking at buying a mid-range compromise MAF, priced between a $$$ Siemens-VDO and the $ ($20 USD) MostPlus cheapo MAF(s) I've been relying on for a couple of years. I might get a BREMI (made in Germany, always a good thing, and I have BREMI injectors already working fine) from FCP, because if it doesn't fix the fuel trims, then I won't feel the same buyer's remorse that I might feel, if I were to spend the extra bucks on a Siemens MAF.

Or, I might have to try my project box, after all.

One more item: monitoring O2 sensors, the downstream ones are getting lazy, slow to respond, though after awhile function as expected. I'll be using my Foxwell to see if they're working ok ( Torque Pro via Bluetooth is sometimes laggy).

I forgot to mention that my M54 still starts on first crank (thanks to the new battery), never misfires, idles smoothly, accelerates like a scalded dog (if I want to ...and who comes up with such analogies?), and the exhaust is smoke and smell-free.