Another DME/no spark thread

[sad sailor]

Hello everyone. I was hesitant to ask for help because I was rather confident I could solve this problem with enough work and research, but it's not turning out that way. This is my situation:

The engine will not start up. I've tested for a spark (disconnected a spark plug and attempted to ground it out) and it would appear that there is none. I've used what is probably a less-than professional quality multimeter and it measures 1.4 volts at the coil wires, (not the output to the distributor, the coil leads themselves) which, if accurate, is a problem because it should measure 12 volts.

Secondarily, there is an issue with the fuel pump. It doesn't seem to be active when I'm cranking the engine over. I replaced the DME relay (with a Kaehler brand relay) and nothing changed. I used some wire to jump a few of the connections on the old DME, and the result is a fuel pump that stays on whether the key is turned or not, but still no spark as far as I can tell.

My deductions point to a shorted out wire leading to the coil, or possibly that I purchased a defective DME relay? You guys are the professionals, so I want your opinions. I'm going to purchase a better multimeter tonight so I can have a better idea of what these wires are actually trying to tell me.

Thanks in advance, everyone. I hope I can solve this problem before too long.

[szyzygy]

How's the battery? Does it deliver 12V?

[sad sailor]

I've tried at least two 12v batteries. They're definitely not the culprit.

[Oh Haha]

What type/year of car are we talking about?

[sad sailor]

1987 924s

[TibetanT]

Does the tachometer bounce when you are trying to start the car?
If the tachometer does NOT bounce when you're attempting to start the car, then>>>check both reference sensors.
See Clarks Garage website for information on testing the reference sensors.

It could be your DME relay is not working properly.

It is always something fundamental, is what I always say.
1) Is the battery fully charged?
2) Is fuel getting to the cylinders?
3) Is there spark coming to the plugs from the distributor and the coil?

Also worth checking, the connectors for the reference sensors at the rear of the engine near the firewall. Sometimes, the connections come loose and cause this no start issue you are experiencing.

HOPE this helps, and Good luck.

[kfray]

The ignition switch out put #15 supplies 12VDC to terminal 15 the coil primary connection.

[putput6]

If all else checks out good, this is something to consider: I have had more than one DME fail and not supply a pulsed signal to the coil. Each time I disassembled the DME and found the solder points for the Ignition driver transistor had failed. I resoldered them and voila! the car started right up.

This DME came out of an '87 Carrera, I can't remember if yours is the same but it gives you an idea of what you're looking for. If this is the culprit, you will see the cracks in the solder around the pins, just like on a bad DME relay solder joint.

[sad sailor]

I tried something new today. I jumped the coil with a positive lead from the battery just to see if I could get the damn thing to start. I would have only checked for a spark at one of the plugs, but I would have needed a helper to crank the engine for me while I checked, but I didn't have anyone at my disposal today. The fuel pump was active the whole time so I know fuel was getting to the rail, but when I cranked the engine did not start. I can't know for certain if there is a spark at the plug because I cannot check, but if I am, then I know that the next logical step is to check for injector pulsation. Is there anything I'm overlooking here? Should I purchase a third DME relay since it's uncertain if the replacement that I bought is even functioning? This is maddening!

[TibetanT]

Certainly it would help to have the correct DME relay for your car!

However, before you spend more money on parts ensure that you have a tach bounce, because if you don't then you must resolve that in order to have a signal being sent to the ECU and then on to the fuel injectors.

[marbleusmike]

I wouldn't buy another dme relay as long as its the right one for your car... brand shouldn't matter... Have you tried tapping on your DME unit with the handle of a screwdriver? Sometimes there are solder joints in there that give way over time... very common problem. I'm no expert but I'm working on the same fkn problem for some time now... very frustrating.. Google Clarks Garage... He has a lot of information and different tests that can be done to isolate the problem... look into Fuel-16 Troubleshooting Fuel Supply Problems.. even though you think it doesn't have anything to do with your fuel supply... it's all related through the signals ... Also take a look at IGN-04 Ignition System Troubleshooting

[hedward]

Originally Posted by sad sailor

I tried something new today. I jumped the coil with a positive lead from the battery just to see if I could get the damn thing to start. I would have only checked for a spark at one of the plugs, but I would have needed a helper to crank the engine for me while I checked, but I didn't have anyone at my disposal today. The fuel pump was active the whole time so I know fuel was getting to the rail, but when I cranked the engine did not start. I can't know for certain if there is a spark at the plug because I cannot check, but if I am, then I know that the next logical step is to check for injector pulsation. Is there anything I'm overlooking here? Should I purchase a third DME relay since it's uncertain if the replacement that I bought is even functioning? This is maddening!

Hi do you can resolve the problem?

[DannoXYZ]

Originally Posted by hedward

Hi do you can resolve the problem?

Back to basics, most important components are speed/ref sensors. Without proper & clear signal to DME, it will not:

- turn on fuel-pump
- not pulse injectors
- not fire spark plugs.

Everything else can be perfectly fine: fuel-pump, injectors, FPR, fuel-filter, ignition-coil, distributor, rotor, spark-plugs, etc. If DME does not see correct signals from speed/ref sensors, car will not start, much less run. Any time you have no-start condition, very first test should be inspecting their waveforms with oscilloscope. I've fixed close to 100 no-start conditions in less than 5-minutes by looking waveforms. This goes for pretty much any 1980+ car, Toyota, Mazda, Nissan, Volvo, Saab, VW, etc. Most of time, solution is to adjust sensor-spacing to give correct signal voltage peaks.