No power to CIS? 1991 560SEL
 

It seems my 560 is running fully mechanical as my multimeter shows no power at any of the electronic inputs... the flapper potentiometer, cold start injector, EHA, etc and idling high. I can only change idle via CO screw.

These CIS ECUs seem to be pretty durable, has anyone experienced a dead one before? Any definitive test I can run to see?

Thanks

You have power from the over-voltage relay to the CIS control unit & a good ground?

Battery ground or CIS system ground?

Use battery as ground point. Disconnect ECU and probe (peep FSM for pin) and see if you've got power there. If not, trace it backwards, I believe OVP or MAS might be a provider or at least wired in parallel.

I know Mike had a problem with that big ass connector behind the fuse box. One of the pins would lose contact and drop out all the electronics.

Do you have 12V power to the CIS control unit? Pin # 1
And a good ground at that unit as well? Pin # 20

Does anyone know which way the pins start? i.e. which corner is Pin 1?

Okay found the pin out, will scan later. I have 12V @ Pin 1 and a good ground to Pin 20. :confused:

I think I know where this is headed.

More hair pulling and another CIS unit?

Would be nice to have a sub to try to be sure, but in a case like this I can't imagine it's not. You can try giving the ecu a whack with a rubber mallet, if that helps.

I think my buddy Mike might have a spare 560 ecu out of his MY90 parts car. Not sure on part number.

Something like that would be nice, at least if he would let him borrow it. Of course these aren't vin specific like they are now with all the coding and locking and "marrying", so he could possibly find a used one, but nice to confirm before ordering one up.

Quick ebay search found one for $145, generally they seem to be on there for $200ish
Mercedes 126 107 560SL 560SEL 560SEC Engine Control Unit ECU ECM Module Computer | eBay