Can anyone explain this.....

[chinist]

90 m20, 215k.....out of the clear blue wouldn't start. Turns over like but no fire. The only problems leading up to this were some intermittent stumbling at idle after engine warmed up, and an on and off low oil warning. The oil level is fine and I've seen this warning come and go for years. This time I'll admit it's pretty persistent though.
First thing I did was put in a CPS......figured with the mileage I had nothin to lose, but no help. Then spent half a day checking relays, dme output, etc.. Testing pulled plug showed no spark but couldn't come up with a reason why and was ready to condemn motronic unit. Confused as to why I wasn't getting a check engine light with key on, I decided to clear everything and grounded cables together.....Presto, she runs.
So what the hell kinda gremlins am I dealing with here. Do you think the old girl is road worthy or is this going to happen again somewhere other than my driveway ?

[Blitzkrieg Bob]

I'd start shopping ebay for a good DME

[Tiger]

Do diagnostic first... mechanical and electric before you shop for anything.

My first hint is it turns over fast.. sounds like broken timing belt. If so, it would explains no spark as DME does not get any signal from camshaft position sensor.

[chinist]

Maybe was a little strong. I meant to say nothing wrong with battery, starter, etc.. Timing belt must be good as car is running perfect now, and I had replaced belt not too long ago. As for diagnostics, I pretty much did all the usual stuff and concluded the dme wasn't working correctly. What I don't know is if clearing it out is a common fix, and a known indication of it on it's way out. The ebay route seems a little risky unless it's real unusual for them to go bad.....I see some rebuilt one's online for around 300.
Anyway, thought I'd check to see if any of you have had any similar experience's .

[Tiger]

Best bet is to see if you got a friend with same engine and see if you can swap it out to see if that is the problem... otherwise go used... someone should have one you can buy for cheap here...

[tim eh?]

I think it is pretty rare for DMEs to conk out unless they get wet but that said I'll sell you a good one for cheap if you want.

[Tiger]

I agree about the reliability of DME.

[chinist]

I think it is pretty rare for DMEs to conk out unless they get wet but that said I'll sell you a good one for cheap if you want.

PM sent........

[Blitzkrieg Bob]

Do diagnostic first... mechanical and electric before you shop for anything.

My first hint is it turns over fast.. sounds like broken timing belt. If so, it would explains no spark as DME does not get any signal from camshaft position sensor.

is no camshaft sensor on an M20..is all crankshaft position sensor baby!

[Blitzkrieg Bob]

I think it is pretty rare for DMEs to conk out unless they get wet but that said I'll sell you a good one for cheap if you want.

True, but when they due it's usally just the EPROM, diode, or a cap that craps out and makes it unenconomical to repair at a $100 an hour.