My mechanic is geting frustrated with my '88 W250 4X4. Originally it wouldn't start after being parked for a couple of days. I troubleshot as far as not getting any voltage to the primary side of the Ign coil. I took it to my Mechanic (30+ years exp) and he diagnosed a bad ECM. Replaced ECM with a refurb and truck ran fine for a couple days then died while I was driving. He seems to think the problem is in the wiring harnes somewhere...
The truck has been at his garage now for over four months.
Any thoughts? Anyone have similar issues?

 

Find a real mechanic. If he can't find the problem in 4 months get it out of there.

Has the Hall Effect pick-up been checked?

 

He has been working on it in his spare time, It is my spare vehicle and I have known him a long time...He has been in business 30 years. The crankshaft sensor has been checked.

When the key is switched on there is voltage at the coil momentarily, then goes away.

 

In 88 they didn't use a crankshaft sensor. Has the Hall Effect pick-up in the distributor been checked? Has the ASD relay been checked?

 

If it is also known as the pick up coil, yes it has been checked.

 

The pic-up coil was used from 74-87, the Hall Effect was from 88-91, and the camshaft position sensor was from 92-93.

 

Thanks for the info...any ideas on what would cause the voltage at the coil to dissapear? He says it is there when the key is switched on but goes away after a second.

 

Has he checked for voltage at the computer terminal that feeds the coil? In 89 it was pin 2-12 and I think the 88 was the same but not positive. Has the ASD and its associated wiring been checked?

 

I know he said he checked the ASD relay...not sure about pins 2 & 12, I will ask him. If there is voltage present at pins 2&12 what then?

BTW, Thanks for all the help so far.

 

The voltage from pin 2-12 ( pin 12 in connector 2) provides power to the coil in the 1989 model. If there is voltage the problem is in the wire connecting the coil and the computer. If there is no voltage you must check for supply voltage to the computer next.