Tremelune

I'm driving along some country roads, enjoying my newly functioning blinkers, good engine temps, and dialed-in suspension, when I start to smell something slight...Smells like maybe something electrical releasing smoke or a hint of plastic burning...Maybe it's just another car with its handbrake on. I check around the cabin and in the rearview for any signs of smoke (none), and then the motor dies rather suddenly, without fanfare, in motion.

I pull off to the side of the road and start looking around, smelling electrical components like a crazy person. Nothing seems particularly fried. The car turns over with gusto, so I don't think it's alternator/battery. No fuel smell; tank half full. I got the car towed home so I can start poking around. Motronic did not feel particularly warm.

The motor is a '95 3.6 installed in an '84. This is what I think I know:

- The DME relay is good.
- There is 12v to the ignition coils with the ignition on Run.
- Test light (barely) flashes on the ignition coil inputs while cranking.
- The fuel pump kicks on while cranking.
- No visible indication that the Motronic DME is fried, front or back of the board.

but no spark.

Current theories:

- DME is toasted somewhere invisibly.
- Both ignition coils are toast.
- Some combination of problems (one dead coil, broken distributor belt).

I wish my test light flashed more prominently during cranking on those ignition coils...I'm not certain it's not just power fluctuations due to load. It sure seems like the DME is toast, but it's friggin' immaculate inside. I'm gonna find a way to test the ignition coils and put an eyeball on that distributor belt...

Anyone have any other ideas for isolating the issue?

Damn thing was driving so well. At least it chose a nice spot by a lake to break down.

OverBoosted28

Crank position sensor? If ya verify coils are functioning properly, then this MAY be an area to look into. GL

Tlaloc75

Beautiful car!

I had a DME go suddenly bad, opened it up and there was no visible sign (that I could find). Cheapest, easiest thing to do first would be to replace the DME and see what happens. Worst case you'll have positively eliminated that as the cause.

In my case it went bad just after fueling up. I was positive I'd gotten bad fuel. Turned out the be the DME ...

Lorenfb

Have you overlooked that the 993 uses an external ignition module to drive the coils?
If not mounted properly, it can easily be damaged.

Tremelune

Is the crank position sensor one of the "speed" or "reference" sensors? I read somewhere that if they are bad, the DME won't bother to get the fuel pump spinning. I dunno. I can't actually find any technical documentation on how the ignition system works on these cars...

A quick check on eBay has these Motronic DMEs going for over a grand...I'd like to be sure before I jump in on that. If the computer is fried, I'm also wondering how it got fried...It would be a real bummer to fry the next one due to bad wiring, but it's tricky to troubleshoot a 55-wire system...

I'll take a look at the ignition module. If it were bad, would the coils get 12v? That would be a convenient culprit, I'm thinking.

IainM

Simple tests first
hook up a spark plug to chassis and confirm spark
check fuel pressure on the rail
go from there

Tremelune

Well. If the ignition module wasn't bad before, it is now. I found this under my seat, resting on metal after some interior work. I guess it got detached, and since it was under the seat, I didn't notice. Current (hopeful) hypothesis is that it was bouncing around, metal moved inside, and it shorted itself out.

One edge of the metal plate was detached, so I gave it a bit of a tug and it came apart. What a weird piece of electronics. It smells a bit burnt, but it also might just be the peanut butter smell of all the gunk this thing is coated in.

Looks like I can pick one up for $50 or so, so...fingers crossed? I would think that the ignition coils wouldn't flicker my test light if this thing was the real problem, right?

Lorenfb

Only one sensor is used on the 964/993.

The 12V power is not supplied by the ignition module. It comes from the ignition switch.

JM993

Thanks Loren. You taught me something new today.

OverBoosted28

If that carmelized ABS plastic isn't your issue, then I'm not sure. Obviously, that's your "burning smell". :-)

Tlaloc75

You'd can get a DME relay for less then $30: http://www.pelicanparts.com/More_Inf...615-227-01-M76

Railmaster.

Just to be sure! When You say DME, do You mean the DME-relay?

Tlaloc75

Yes the relay.

IainM

That's one mashed transistor pack!
bond wires on the black plastic part indicate a clean break ( or did you straighten them for the pic)
i would say plug a new one in then verify spark on both disties
hopefully the ECU drive to transistors is Ok
coils are pretty robust and can be ohmed out with a meter

CalvinC4S

Sorry no help, but damn that car is beautiful!