Looks like my AFM is giving erratic readings. I just ohm'd it and the readings aren't consistent during its sweep. I thought I saw a rebuild write up but I can't find it. Has anyone rebuilt one of these? Also does anyone have a tested and working one for my 81 for sale?

 

You can buy rebuilts online at the 928 Intl, 928 SP and Roger @ 928s'r'us.

Compared to the MAF used on later cars, they should be relatively inexpensive. Good luck!

 

There are currently two for sale on Ebay.

 

Thanks fabio I'll take a look.

 

ok did the ohm checks per the manual. The readings are within range(The ranges are huge). Does anyone know what pins to use for checking the sweep reading? I can't find this info anywhere.

 

Hi Jason,
Drop me a mail on herman.andersson@irf.se and I will return a simple description. Without having disassembled a Bosch L-Jetronic air volume meter, I am quite confident about that erratic function is caused by the air flap measurement potentiometer. It's a mechanical device and either the race, the wiper or both wear over time. This wear will likely give inconsistent R as a function of flap angle.

 

Email sent

 

I'm surprised no one knows the answer to this question. Alan must know he knows everything electrical.

 

While that is true, i dont know that Alan has ever worked with one of the older cars

 

I took mine apart and sprayed it with contact cleaner/lubricant. I should have taken pictures, but it wasn't a planned event.

 

Mines apart I wanna test the sweep readings but can't figure out the correct pins to do it.

 

A picture or a drawing of the allocation of terminals in the AF connector seems not to be documented in the WSM and very hard to find on the web, despite there are many old European cars that have flap AF sensors installed. Some have 5 terminals (928) and some have 7 (912). The allocation of terminals can by using the WSM/Schematics, very esily be deduced by verifying low ohmic connection between the 5 terminals in the disconnected ECU harness connector and the terminals in the disconnected air sensor connector. One long cable is however needed.

The placenent of the AF sensor terminals is not needed in order to measure on the potentiometer. By using the document which I've sent and by moving the flap, it should be obvious which terminals that are connected to the potentiometer.