Carrera 3.2 with no spark
 

Hi, I have started to renovate my 84 3.2 and stripped out all the interior and door glass, unfortunately the cover blew off in a thunderstorm and flooded the ECU. I have had it repaired and it would not start. I then checked the DME relay by jumping it (30-87-87b) and got the fuel pump to work . I am still waiting for a new relay but I'm getting no spark. Any ideas?

Who repaired it? Did it come with a guarantee? If your engine was working prior to this I suspect the only two causes are either a bad DME relay or your DME is still defective.

Did you disconnect your alarm wires by chance?

OK, This is the story so far. I have checked all the fuses . The interior if the Distributor cap has been cleaned and the rotor has been wire wooled I have checked the coil:
There is power between the - terminal and ground. - The is continuity between the + and - teminals(no resistance). - There is 9 Ohms resistance between the center teminal and the - terminal and 9 ohms between the center and the + terminal. There is no resistance between the 2 terminals on the lead between the coil and the distributor. On cranking the engine with the lead to the distributor disconnected I am getting no spark at all when grounding it. I am hoping it is not still the ECU after having spend $500 on the repair. I had it repaired nearly 2 years ago and have only just found the time to get on with the project. Unfortunately I live in France and had to ship it back to the UK for repair. I am assuming that I have not disconnected any alarm wires. The system deactivates and the fuel pump starts. I am assuming if the alarm was still activated then this would not be the case. I have by-passed the DME relay by jumping it (30-87-87b) and got the fuel pump to work.

I thought the '84 doesn't have a factory alarm at least in the U.S. - maybe the Euro models are different. Here are some tests you might want to go through:

Once you switch the ignition to ON you should be able to hear a faint click from the DME relays (1st stage of DME relays is switching on) and the coil + terminal should be energized. You can use a Digital Voltmeter to measure +12 Volts against a grounded metal part of the engine block.

There is an easy way to check whether the digital part of the DME is working: Switch the ignition to ON (don't crank) and touch the idle control valve sitting on top of the engine. It should hum with about 80Hz. It is audible and once you touch it you can feel it. If it is not doing that chances are the CPU in the DME is not working, or the idle control circuit is damaged or you don’t get power to the DME (alarm). Maybe a fuse is blown if you are lucky.

If the ICV is humming you have confirmed that the alarm (if present) is not the culprit and the DME’s CPU is running properly. The next step is to verify whether the second stage of the DME relays is working properly: Once you crank you should hear the second stage switching on and the fuel pump starting. This click is a little more difficult to confirm but you can still hear it or feel it when you put your hand on the relays. Maybe an assistant needs to verify that the fuel pump starts by measuring fuse 3. You should see +12 Volts there once you crank.

Next you need to find out whether you are just missing spark or both fuel and spark. You might want to pick up a cheap injector test light. If you see a fuel injector pulse it tells you the DME is processing the flywheel signals properly. Another easy test is to smell the exhaust. It should start to smell like fuel after several cranking attempts. If that is not the case you can start to suspect you are not getting fuel and not getting spark.

Chances are that the DME is not seeing one of the sensors (reference, speed) from the flywheel. Testing here becomes a little bit more involved: First you can check the signals of both sensors with an oscilloscope. Based on your finding you can decide with some certainty whether you have most likely a bad DME (no spark signal but fuel signal) or maybe bad sensors (no signals at all). Of course all this assumes that the coil is working properly. Search the archives for what the proper DC resistance of the coil is supposed to be.

Good luck and keep us posted on findings,
Ingo

Hi, At the moment I know the DME relay is shot. That is why I have jumped the terminals. I have ordered a new one and I am awaiting delivery. I was under the impression that by jumping the terminal (30/87/87b) that the enginge would start? ....Ok, here is what is happening...the fuel pump is working, I have fuel to the injector bar...I have not checked the actual injectors themselves yet...The idle control valve is working...unfortunately I do not have access to an oscicilloscope...I will wait for the arrival of the new DME relay and let you know the results... The engine was running fine before the flooding....I will update you when I fit the new DME relay....Is there anyway that I can check the ECU itself?

Hi, when you try cranking it, and it does not start, can you smell raw gas fumes at the exhaust? The reason I ask, that would at least let you know that your engine is getting fuel, but just not getting combustion due to the lack of spark. I know first hand that the DME Motronic Systems of our cars can be quite problematic. Good luck!! Tony.

To be honest with you I cannot say that I can smell gas fumes in the exhaust.

And you wouldn't necessarily in a DME car. The car is smart enough to not flood like a carb'd car.

I once had a 944 that would intermittantly not start or flood out while driving. Lots of gas but no spark. It turned out to be a bad DME. (The main unit, not the relay.)

If you do not smell any fuel during all your cranking either the DME is not producing a fuel injection signal or your injectors are stuck shut (quite comon if the car sat for extended periods of time). A friend of mine had that happen. We coud crank forever and the car wouldn't start. No fuel smell. After gently knocking on an injector while cranking it finally started to sputter. Some more convincing and it came back to life.

BTW, how did you determine that you have no spark. Did you use a spare spark plug or did you simply touch the wire to GND?

I think at this point your best shot is to get the new DME relays and do some diagnostics.

To check the spark I removed th plug and held it against the engine casing...Then I replaced the plug and after checking the coil (see previous explanation) I removed the lead to the distributor inserted a bolt into the lead and held that near the engine casing....nothing... Are there any diagnostics I can do on the DME itself as it means shipping it back to the UK from France otherwise.

IIRC, the DME relay is a double relay, so just jumpering the fuel pump is not enough. The relay also provides power to the DME itself.

I left my top off once, went to lunch and the florida rains came out of nowhere... flooded my 911 with 3 inches of water. I removed the DME, drained it and dryed it overnite... next day it fired right up. will it last? too early to tell, it's only been 200k miles since that happened.

HTH,
Chuck.H
'89 TurboLookTarga, 290k miles

Have you messed with the connections at the TDC and crank position sensors?

Car will not start if they are disconnected or reversed.

Picture of correct connection?

Hi, No nothing has been touched. The car was running - then the ECU got flooded and that is when the problem started.

I am waiting for the arrival of a new DME relay. Then I will keep my fingers crossed.

chateau, hopefully that will cure the problem. If it does, order another and keep it in the glove box, "just in case" Good luck!! Tony.

Milt,
Unfortunatley, it is not so smart. If the DME is working, it will fire the injectors during cranking. You could have an electrical problem downstream relative to spark and still not run. For example, bad coil, or bad driver circuitry in the DME, bad rotor, etc.

Try grounding your coil lead to the distributor and see if you smell gas after 10 seconds of cranking. You'll get a contact high.
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Chateau
Did you try cleaning your grounds too, to make sure the DME is getting a good ground?

I'm guessing your DME is still broken, but it pays to check all the connections and grounds first.

Doug

OK - here is the story so far - I have received the new relay, fitted it and held my breath....turned the key.... nothing!! Not even the fuel pump running.

When I jump the teminal in the relay plug the fuel pump runs fine...I am guessing that the DME is shot.

Does anyone know any diagnostics I can try on the DME before I send it off for a second time.