S38/M88 Air Flow Meter Refurbish

[BonitaBeast]

Hi all. It's been a while since I've posted.

Just wanted to check if anyone on here has ever refurbished or repaired or cleaned the Potentiometer board in their Bosch Air Flow Meters. If so, what did you do? Has anyone ever replaced the actual board from another AFM? I know a brand new AFMs for S38/M88s cost a pretty penny so I'm hoping not to purchase a new one. I also know some people have gone the route of replacing the AFM with a MAF. Some were successful but many were not.

In my case, about a year ago, I was lucky enough to be able to come back into possession of the M5 I sold about 3 years ago. Unfortunately it is not in the same running condition it was in when I sold it. The person to whom I sold the car had converted the AFM to a MAF using Miller Performance G3. It ran but not smoothly at all. It idled way too high and the motor would hesitate on or around 4,000 rpm under acceleration. So it wasn't really driveable. I removed the MAF and returned the AFM and returned ECU wiring. The car starts but is showing signs of a faulty AFM; which brings me to the reason I am posting this.

If anyone has any input regarding refurbished or repairing AFMs do let me know, please.

Thanks in advance.

[MannyE]

Have you checked these guys?
https://www.programainc.com/categories. ... =8610&cl=1

[demetk]

Not sure if the M5 afm is a 12 volt or 5 volt input, but you can check voltage on the reference pin, see below on checking the afm. Also take a pic of the board and post it.

Here's are my writeup on checking the afm.





And calibrating the afm with the help of an o2 sensor.

[Preyupy]

If you are converting back from a Miller MAF there is a wiring change they make in the harness ( usually right at the connector at the ECU) that you will need to put back to stock before the Stock sensor will work. Go to their site and download the instructions for installing the Hot Wire Sensor and restore the wiring BEFORE you tear into your stock sensor ( it’s probably ok once you fix the wiring)

[BonitaBeast]

If you are converting back from a Miller MAF there is a wiring change they make in the harness ( usually right at the connector at the ECU) that you will need to put back to stock before the Stock sensor will work. Go to their site and download the instructions for installing the Hot Wire Sensor and restore the wiring BEFORE you tear into your stock sensor ( it’s probably ok once you fix the wiring)

Thank you yes I did exactly that. I've returned the wiring back to stock as well. The Miller install involved taking a 12v lead and T'ing it into the socket that goes into the MAF. I reconnected back into the wire going into the ECU.

From what it looks, the mechanic also may have fiddled around with the AFM settings. The circuit board is also damaged. One of the circuits was broken/open/burned.

[BonitaBeast]

Thank you!! I will post my findings. I measured voltage across all parts of the board and found some puzzling numbers. Instead of going in ascending order, mine go in descending order(??)

I also measured the resistance across all the circuits. I will post this as well.

Not sure if the M5 afm is a 12 volt or 5 volt input, but you can check voltage on the reference pin, see below on checking the afm. Also take a pic of the board and post it.

Here's are my writeup on checking the afm.





And calibrating the afm with the help of an o2 sensor.

[BonitaBeast]

Here's where I found the problem with my board


Here's another shot with it back together. I soldered a piece of wire on to complete the circuit


Here are the resistance measurements I took. I realized I did not write down the corresponding voltage outputs though using a reference voltage of 7.2V from an RC battery

[LeiseyJr]

Love threads like these! Thank You Demetk for the 745i info, interesting they used 12V. Maybe it was because it was turbocharged, so they could get greater resolution.

Thank You Bonita Beast for posting an update!

[demetk]

Anyone know whether replacement boards are available for these AFMs?

I did find this. https://www.ebay.com/itm/402642009620

[BonitaBeast]

Anyone know whether replacement boards are available for these AFMs?

I did find this. https://www.ebay.com/itm/402642009620

I am in touch with this gentleman from Ukraine from this ebay post. This is the reason I took resistance measurements from my board. He says he can do it so I will be trying it out. I will send him the measurements shortly. He has some he has already made but none of them match the circuit board from our S38/M88 AFM so I need to send him the specs of my board.

Keeping my fingers crossed.