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

[BimmerBreaker]

It's also possible you may just have a weird DME fault causing this - the MS43 has a barometric sensor on the DME board and I've seen similar issues with an MS45 with a barometric sensor problem. The sensor didn't fail - so no code, but it was faulty - the result of this was the erroneous data fed to the DME messed up the fuel trims. The car I was working on would throw consistent O2 sensor codes after enough driving.



There's nothing wrong with creative solutions, but this isn't a solution - it's a bandaid

My advice...

Originally Posted by workingonit

I just reset the fuel trims whenever the eventually climb near "10", before any codes might possible get set

First and foremost, stop doing this. Let it set a code and go from there.

[Happy]

Originally Posted by BimmerBreaker

It's also possible you may just have a weird DME fault causing this - the result of this was the erroneous data fed to the DME messed up the fuel trims.

This is true. I had a bad wire-harness! One of my sensors was leaking oil pressure into the loom, feeding oil all the way to my custom DME!

Readings were all over the place!


E53 RiPPeR
XOuTPoST jUNkiE
ReVELaTiON 22:21

[workingonit]

Originally Posted by BimmerBreaker

It's also possible you may just have a weird DME fault causing this - the MS43 has a barometric sensor on the DME board and I've seen similar issues with an MS45 with a barometric sensor problem. The sensor didn't fail - so no code, but it was faulty - the result of this was the erroneous data fed to the DME messed up the fuel trims. The car I was working on would throw consistent O2 sensor codes after enough driving....

I read about problems with the barometric sensor in the DME causing problems (on E46, E90, E92s), but no solutions or fixes other than a repaired DME.

And Happy, I've looked carefully at the wiring all the way back to the DME, and nothing looks worn or torn. The DME still looks untouched.

So, I don't want to be the guy who opens up a perfectly sealed and working DME, if nothing is amiss inside, so I'll try my Android app "BimmerTool" to see if it will give me data on the baro pressure ( it has a PID on the live data list for it). My other Android apps, Torque Pro and OBDLink, have a similar PID, but don't show data.

I haven't seen anything on my Foxwell about baro pressure, and I'm so far out of practice using Inpa, that I will have to learn all over how to use it, that I might not be able to verify if there's a baro pressure problem causing the MAF to read incorrectly. Also, the O2 readings look good, no matter what MAF sensor I'm using (wouldn't they show a baro problem as well?).



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[workingonit]

I already bought the parts I needed for the on/off MAF reset switch, and was about to assemble them for installation, then reconsidered.

I will wait until after the state inspection (safety & emissions...my '01 is two years away from not having to get the sniffer test, anymore) before I do any experimental work on the MAF system. I'll use Liqui Moly Catalytic System Clean 7110 and Premium gas to prep the fuel system (not the Jectron 2007 that I usually use), drive about 100 highway miles to make sure that all the emission monitors get set, and drive directly to my usual inspection station (before the fuel trims go wacky again). Then, I can experiment.

Researching and reading. I read a lot this past week, seeing how people custom-tune their MAFs, MAPs, and even the old mechanical Air-Flow monitors, from the 80's 'til now, Chevys-Toyotas-Ferraris, all of them. There's actually less info concerning BMWs than most other makes, of course, since BMW wants it that way.

I wish I had been trained in electronics, as most of what I read was basically Greek to me (I might've understood Greek better!). But, I did find a possible way to make minor tweaks to the MAF signal that tells the DME what the airflow is, by tricking the system, using a device to adjust the heated element component in my MAF sensor, without adding resistors or using a custom air intake tube.

If I was to lower the temperature of the hot-film (similar to the old type hot-wire) heating element, it would make the MAF act like there was more airflow than there actually was, then the resulting signal generated and sent to the DME would naturally enrichen the mixture without having a false lean fuel trim reading do the same.

I originally thought my lean fuel trims (triggerring P0171, P0174, and eventually a CEL) were caused by my Siemens-VDO MAF under-reporting airflow. I still think it does. The cheap $20-23 Amazon MAFs I've been using for two years, give better airflow readings, but not perfect. So, my idea here is to further trick the system, by using another cheap device (a "Buck-Boost" converter), to fool the DME into thinking that airflow is greater than in actuality. And maybe quit trying to set lean codes in the process.

I previously used a diagram (in post #1) that was wrong, but found the correct diagram for my '01. It shows that if I would insert a step-up/step-down voltage control ("Buck-Boost" converter) in the 12v wire just before it enters the MAF, then I could use it to either raise the temperature of the hot-film heating element (which would cause a lean signal to be sent), or preferably, in my case, lower the temperature (which would cause a rich signal to be sent).


I see that there are all sorts of circuit protection in the units I've investigated, so no damage to the circuits upstream nor downstream of the device should occur. Of course, I'd also use a fuse ahead of the device, anyway. If, perchance, one of my three MAFs were to fail, then I'd have the excuse to try a mid-grade MAF (from Hella, Bremi, Pierburg, or even Delphi...I'm not ready to buy a Siemens VDO, until I fix the phantom problem first).

I am currently looking at three converters, from $25-34, that I might try. I have no idea what actual amperage/wattage rating is needed, but I've wasted money before...trial and error is often expensive. Of course, I'm watching many videos on how to set them up, but it'll take me awhile to get the gist, if ever.

[workingonit]

Originally Posted by workingonit

... I did find a possible way to make minor tweaks to the MAF signal that tells the DME what the airflow is, by tricking the system, using a device to adjust the heated element component in my MAF sensor, without adding resistors or using a custom air intake tube.

If I was to lower the temperature of the hot-film (similar to the old type hot-wire) heating element, it would make the MAF act like there was more airflow than there actually was, then the resulting signal generated and sent to the DME would naturally enrichen the mixture without having a false lean fuel trim reading do the same.

I originally thought my lean fuel trims (triggering P0171, P0174, and eventually a CEL) were caused by my Siemens-VDO MAF under-reporting airflow. I still think it does. The cheap $20-23 Amazon MAFs I've been using for two years, give better airflow readings, but not perfect. So, my idea here is to further trick the system, by using another cheap device (a "Buck-Boost" converter), to fool the DME into thinking that airflow is greater than in actuality. And maybe quit trying to set lean codes in the process.


...I am currently looking at three converters, from $25-34, that I might try. I have no idea what actual amperage/wattage rating is needed, but I've wasted money before...trial and error is often expensive. Of course, I'm watching many videos on how to set them up, but it'll take me awhile to get the gist, if ever.

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.
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.


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).
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.

[workingonit]

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.



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).

[workingonit]

Originally Posted by workingonit

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 ....

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.

[workingonit]

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:

[BimmerBreaker]

Originally Posted by workingonit

I read about problems with the barometric sensor in the DME causing problems (on E46, E90, E92s), but no solutions or fixes other than a repaired DME.

And Happy, I've looked carefully at the wiring all the way back to the DME, and nothing looks worn or torn. The DME still looks untouched.

So, I don't want to be the guy who opens up a perfectly sealed and working DME, if nothing is amiss inside, so I'll try my Android app "BimmerTool" to see if it will give me data on the baro pressure ( it has a PID on the live data list for it). My other Android apps, Torque Pro and OBDLink, have a similar PID, but don't show data.

I haven't seen anything on my Foxwell about baro pressure, and I'm so far out of practice using Inpa, that I will have to learn all over how to use it, that I might not be able to verify if there's a baro pressure problem causing the MAF to read incorrectly. Also, the O2 readings look good, no matter what MAF sensor I'm using (wouldn't they show a baro problem as well?).



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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.

[workingonit]

Originally Posted by BimmerBreaker

...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.

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.