QuestionEvan,
Thanks for the info. I had a guy come to the house with a "Snap-On" "Solus" scanner and the DME/ECM would only intermittantly communicate with the scanner via the engine compartment data connection.... we were able to turn on the fuel pump relay once and then the scanner lost communication with the DME again. While we were trying to figure out why the ECM/DME wouldnt talk, smoke started to pour out of the coil pack along with the black potting material. I don't know if this short was causing the DME not to communicate, but its possible and the coil pack needs to be replaced before I can go any further. It seems to make sense if the coil pack was shorted that it could/would cause any number of other troubles by robbing the other components of voltage.
Again, Thanks for your quick and informative reply,
Sean.
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The text above is a follow-up to ...
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Evan,
We resently spent over $2500 to replace Cat. conv, secondary air pump, and a few other items on my wifes '98 318ti. That was the 3rd cat in 18 months and now it wont start. Turns but no boom-boom I have replaced the fuel pump ($300) as i did not here it run when key was in "run" and the fuse was good. Chiltons manual for this car SUCKS, the relays are mis-identified, but after much searching, I found a wiring diagram from AHDOL.com and have been able to identify the relays by matching the wire color combinations and pin-outs which leads me to the question.... with the car off and the key out the engine control module relay will intermittantly start to chatter on and off. My take on the schematic is that when this relay energizes its out put is 12vdc on the red/white wire that is spliced to provide 12vdc to the fuel injectors, o2 sensors, fuel pump relay, and on and on and on...
do you have any suggestions, tips for isolating the chattering relay??? dont have a clue how to start t-shooting the ECM.... please help.
thanks,
Sean.
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Sean, The engine turns but doesn't start. Lets get back to the basics. You have good compression? You have fuel? Fuel pressure? Fuel injection pulse and delivery? Ignition spark at the coils? Good Plugs? Are the plugs dry or wet with fuel after cranking? My question is what is the engine missing to start (fuel, ignition, compression, valve timing,) Your understanding of the DME main relay is correct for the most part. On the relay terminal 86 on the control/coil side is 4mm Red wire, terminal 85 is a 0.5mm brown with white tracer wire (that seems small but that's what the factory diagram shows). On the work/switching side of the relay terminal 30 is 4mm red wire spliced from the same source as terminal 86 wire. Terminal 87 is your 4mm red with white tracer wire. You can try swapping a similar color relay with same number of pins and same location or you could jump terminal 30 to 87 manually and see what you get. You could also replace the relay if it is questionable, But I think you need to figure out what component of combustion your engine is missing. Start at the Engine and work backwards.
-Evan
AnswerSean, coils are powered constantly by the unloader relay and grounded by the DME. I have seen a faulty DME transistor blow up an ignition coil (exploded). It was pretty cool only because I wasn't working on it though.
Sounds like you found some clues, keep on the chase.
-Evan
