Can anyone explain this.....

[chinist]

90 m20, 215k.....out of the clear blue wouldn't start. Turns over like crazy 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 crazy 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 crazy 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 crazy 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.

[Paul in NZ]

check dizzy and rotor.That was my intermitent no staart problem,inside the dizzy was wet and the rotor was 18 years old

[genphreak]

I have this on the M50 atm. It's been dead for 3 weeks, I'm way too busy to fix it(!) Each time I take a few hours to look at it, I get nowhere. But it is a different animal to yours- not just the M50 engine and all the electronics but late models have the DWA IV and the EWS II (it's a 12/95 525it) Drive Away Protection system.

Like you I get cranking and no spark. AFAIC see cranking means the EWS is good. I have fuel and can also hear the pump running in the tank when I jumper the relay. This means your CPS is provding signal, as the ECU won't activatye the Fuel Pump relay otherwise. If your DME is bad, you shouldn't get fuel or spark, though it is possible that an internal fault is limited to just the ignition control circuit. If your fuel is intermittent or dead, it is usually the CPS or Fuel Pump Relay. Can also be the Fuel Pressure Regulator.

The left of field one is the Inclination sensor (NAG), which I think only DWA cars employ. There are some service bulletins that talk about replacing this as a recall, but maybe one should just bypass the thing on an od car like this- at least to see if it is the cause.

I can't find my NAG, so feel my problem might be the aftermarket alarm/immobiliser. It is actaully a dealer fitted BMW branded alarm (Repeller RP2), but no remote key or DWA IV module (they have been removed) by a Previous Owner :p. Non standard wiring... ugh! Looks well done though, if only I could find the people that did it :)

Best of luck, be sure to try a replacement fuel pump relay and check the ECU output that fires the coil. The dealer changed a coil on my first M30 (e28), maybe it could be that... ?

[chinist]

All good advice and I have done most all of it including dist cap...rotor looked and checked good, along with the coil resistance checks and main relay check. But I had no spark . Fuel was much the same, relay good and pumping to the fuel rail sounded strong. I have replaced the pressure regulator not so long ago as preventive maintenance. I guess I can't say for sure that I had fuel as I didn't actually pull an injector to watch it spray. So to me everything go's back to what was the dme doing ? And as I was pondering this, I realized the check engine light wasn't coming on when the key was on. Wasn't sure what to make of that so I did what I always do first with any computer....reboot. And as I said before, she starts like it had never had a problem and has been ok ever since. Except for the stumbling at lower and idle speeds....intermittent and only when it's been running awhile. So, sounds like component heat breakdown or circuit board expansion maybe ? And why come back up after grounding the computer out ?
So you're all saying at this point, enough already, buy Tims dme and be done with it......and I most likely will, but being curious to a fault, I'm going to open up the box sometime this week and see if I can spot an obvious wound. I have an e39 also, so I can play around here until it takes a .........

[Ross]

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

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

Agreed.
Put a timing belt on and check compression with the cam in proper time. Since this happened on start up you may have escaped bad damage.
Good luck