ignition problem - no spark
 

I have an 87 944 and am having the same issues as vdkace. It occured twice but fixed itself but now I get no spark at all. I thought of the DME relay first and replaced that. Have also replaced plugs, rotor, dist cap & coil. I have 12V both at the coil and the injectors with the key turned on. Timing belt is good. Did the spark plug check, no spark. Coil wire checks out (0.4 ohms) I measured the resistance for both the reference & speed sensors and they both measure in range. I'm befuddled and would love any advice as to what to check next. Have not done the 12v light test for the sensors. I'll try that next.

12 volt light test is at the coil to see if the DME is firing it. Not at the sensors. You need an oscilliscope to properly test the sensors. Besides checking their resistance with an ohm meter. The sensors generate a 2 volt pulse. You might be able to see the 2 volts with an analog (needle) ohm meter. If the needle isn't dampened.

Hugh, thanks for the advice. I did the 12V light from the positive side of the coil to ground and got no blinking while turning over the motor. So does this definitely indicate a bad reference sensor or do I need to do the LED test? How do you adjust the gap? I pulled both sensors out and don't see any evidence of damage. Which one is the reference sensor...the forward or back one? Do you recommend replacing both as a set? Given everything else I've tried this seems to be the last reasonable thing without getting into into broken wires elsewhere in the system.

0.8mm on the back sensor. The front should follow. Make sure you plug them into their respective terminals.

If you have a timing light you can cross check the coil by placing the timing lights pickup on the coil to dist wire, pulling that wire from the dist. and grounding it.

Did you check the ohms accross the coil? Seldom does a coil go bad but it's possible. Also check from the center contact to one of the outer contacts on the sensors.

Brand new coil. Neither sensor had been touched since having a new clutch put in last summer and has run great ever since. I've replaced nearly everything except the sensors. I have 12V at the coil & injectors, but no blinking on the 12V light test. Is that a pretty positive indicator of a bad reference sensor? I'll do the LED test if you think I need to. Which sensor is the reference sensor? When I turn over the motor, the tach does jump, so I think the speed sensor is likely okay. Your thoughts?

I would do the noid light (diode-resistor) test if you can get it. This goes on the injectors.

The reference is the front sensor. The speed the rear sensor. Yours should also have a third sensor that is unplugged. This is supposed to be used by the dealers. However both (all) sensors follow the bracket adjustment so adjusting the speed clearence to the starter teeth sets the front (reference) sensor.

If you have access to a scope you should see a 2 volt pulse off of the front (reference) sensor and a mostly constant 2 volts off of the rear speed sensor.

All of this may be moot if the coil to dist wire is bad. Sometimes the headlight arm pulls it loose if it catches it after an oil filter change.

I've replaced the DME Relay, plugs, rotor, cap, coil, reference & speed sensors and still get no spark. I have 12V at the coil & injectors with the key in the start and on positions, but no spark. I am going to purchase Porsche WKD 821 troubleshooting supplement, but would sure appreciate any other advice.

......... intermittent no-start issues can sometimes be traced to Porsches phenomenal wiring.........

- I would check the ohm's for the reference and speed sensor at the harness (where the DME plugs in). You can easily have a bad connector or sensor.

Right about that. If you can't find the problem in the engine compartment you have to search back up the harnes.