experimental MAF reset switch: which circuit to interrupt? PLAN REVISED

[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).