Article by: Johan
Article applies to: all e31, e32, and e38 models with the M7x engine.
Problem: The EML bulb should show up for a couple of seconds when the ignition is turned on.
On my 750i it didn’t do that anymore. And as a result the acceleration time from 0-100km/h needed to be marked on a calendar.
Somehow the whole shabang was running in some sort of emergency program. The engine did run on 12 cylinders but it took forever to accelerate.
My gearbox was also stuck in 3rd gear without any warning whatsoever.
Solution: I have collected a good number of e32 spares in the past. That included the speedo from a 92 735i which has the same back plate as my 91 750i.
Of course I could just swap code plugs and back plates. But as I remember the cluster did have some problems.
That’s why it never got installed into my 86 735i to resume the count from 299 960km.
I started by measuring the resistance of the EML bulbs that are soldered into the cluster. They are soldered in parallel.
So I guess if one works it’s fine.
These where fine so I had to look elsewhere. As I did once see the EML light flicker on and off I thought there might be an bad track in the PCB.
Of course it’s multi-layered so it’s hard to follow the track.
So I measured the contacts between the white connector’s Pin 16/Pin 17 (they are connected on the PCB) to the contacts above the EML bulbs.
To do this you have to scratch some of the coating from the pins at the white connector.
The measurement of the 750 cluster showed an open:
And the result of the 735 cluster showed a closed circuit:
Ah-HA! So it’s an open connection. The easiest way to fix that is to run a wire parallel to the original track.
And that did the job:
You might want to glue the wire in place with some hot glue to stop it from vibrating against the other contacts and slowly break the insulation.
All there is left to do is replace some of the bulbs, top off the coolant reservoir and bring it to the dealer for an inspection 🙂