The last time I drove the car the tach needle was bouncing around a lot, and I sent off for new speed and reference sensors. The car no longer starts and the tach is still, even with the new sensors. I'm getting voltage at the DME between pins 25 and 26 but don't have an oscilliscope to see how much. The bracket the sensors mount to was never moved. Is this looking like a DME issue? With the new sensors I'm pretty much lost here.

 

Your sure you got the sensors connected correctly to the right connectors at the back of the intake manifold? If you got them backwards, it won't start.

Was the car a no start before the sensor replacement also?

I'm sure there are a lot of others with better ideas, coming up soon. Good luck!

 

The original labels are on the harnesses the sensors plug into and I've also tried swapping the connectors just in case they labels are wrong, but they're plugged in the right way. The car wouldn't start before putting in the second new sensor either. Here's the longer version of what's been going on:

The tach needle started bouncing around some, and then the car wouldn't start anymore. Both sensors were 18 years old and I went to a junkyard to get a new sensor. I replaced the front sensor and it ran but still a little rough so I order a new one and install. Car runs much better, but the tach would still would stumble every now and then. Last weekend it got much worse, really fast and on Sunday the car would no longer start. I order a second new sensor to replace the rear one, it came in, and the car still doesn't work (no matter which sensor is in the front). I never could get a tool into the allen head bolts for the bracket they mount in so I'm assuming it didn't move. But it did take a lot of turning and pulling to get the rear sensor out. The last few times I started the car it took a lot more cranking than normal for the engine and tach to catch on. The tach will not budge. Well, pounding on the side of the steering wheel made it jump a little but that might've just shook the needle around.

Right now I have the DME out and can see the top PCB. Nothing obvious jumping out at me right now.

 

Have you opened up the DME? Can you manually fire the coil?

 

The DME cover is off, but the two screws that attach the bottom plate to the connector will only spin. How do you manually fire the coil?

 

Disconnect the ignition coil output wire at the distributor cap.
Connect a spark plug to the end of the ignition coil output wire which you just disconnected.
Connect a ground wire to the threaded portion of the spark plug.
Disconnect the ignition coil ground wire from the negative terminal on the coil (Green Wire).
Connect one end of a ground wire to the ignition coil negative terminal.
Turn the ignition switch to the ON position.
Tap the other end of the ignition coil ground wire jumper on an good grounding point (for example the battery negative terminal) and look for sparks at the spark plug that correspond to the frequency of your tapping of the ground wire.
If you have a good spark at the spark plug, the ignition coil is good.
If you don't get a good spark, check for approximately 12 VDC from the coil positive terminal (black wire) to ground with the ignition switch in the ON position. You should also get approximately 12 VDC from the coil negative terminal (Green wire) to ground


thats a copy and paste from http://www.clarks-garage.com/. I've been following your no start issue because mine happened at the same time..waiting for a new ref sensor bracket to arrive here. Hopefully you'll get your issue wired out too.

When you opened the DME was ther any smell (like something acrid..or burnt)

 

I put the DME back in and got no sparks except for when I put that wire from the coil ground to the negative terminal. Also have just under 12V from either terminal on the coil to ground.

No bad smell or discoloration on the plastic sheeting when I cracked open the DME. I didn't see any signs of... well, anything on the side I can see.

 

I get no connection between the sheeting (pin 78) and pin 23 at the DME. Would this keep the car from running?

 

Here's a bump for the night crowd. I was hoping to have the car up and running by thursday or friday because I wanted to drive it over to my parent's place for Christmas. They don't know about it and it'd make a nice surprise.

 

Sorry..still searching here...I'm an idiot looking everywhere for a 924S schematic when I have the service manuals disk literally 15" from my face!



78 and 23 should ohm out together. Whether that would keep the car from running...I'm not sure. Does the DME to ref sensor plug ohm out ok (pins 25 + 26).

 

Resistance between 26 and 26 are ok. I'm having a hard time seeing it; pin 78 doesn't wind up at some other pin (looks like an 8 or a 3)?

I'm thinking about getting an oscilliscope - would Radio Shack have one for a reasonable price (edit: maybe my multimeter can do it, assuming the disk that came with it is still good)? This is the only time I've ever needed one, but it'd be nice to know if a good signal was getting to the DME or not since that'd rule out a lot of things here.

 

Not to steal pictures or anything...

Are loose solder points a problem with later DMEs? Are they usually something that jumps out at you, or do you have to just go along and resolder all spots? It wouldn't be that bad to redo all of them, just time consuming.

Anything else that it could possibly be other than the sensor, wiring between there and the DME, or DME itself?