I am trying to help my firend Steve figure out a problem. For some reason his MS setup is not working right. The car will start w/ the 4 pin dist connector unplugged. WHen the 4 pin connector is in place, it will not start unless I cut the white wire (timing control). This is while having the 5v bypass wire disconnected. With the 5v wire, the IM gets fried. Steven and I have checked everything we can. I feel like it's something wrong inside the ECM. Can anyone point me towards the correct way to diagnose the ecm? Steve built it and knows the circuts, we just don't know what to check.

If you can't help with that maybe you know what kind of voltage comes from the (purp/wht reference) wire from the module AND the white wire from the ecm(timing control).

 

I think the ignition advance signal is a 5 volt square wave.

He should double check all the components in the ignition out circuit.

 

The 5v wire should have NO voltage untill the ECM sees that the engine has started...above 300-400rpm! Turn the key on and check for 0volts on that wire! The ECM applies 5v to turn on the module after the engine is running, and allows the ECM to take control of the timing. Toehead is right...the AC wave coming off the the reluctor and pickup magnet is converted to a Square Wave after the 5v is applied, and that square wave's Duty Cycle is varied inside the ECM to advance and retard the timing, based on other engine sensors!
I'm not sure, but...if the module is on before the engine.... I don't think the engine can start with that much timing!!

 

Make sure he has the 5 volt bypass wire wired as per instruction

relay so that the 5 volt is supplied in run but not crank. I used a relay and the power supply for the cd player, which is shut off in crank. I then used a relay to send the 5 v whenever the stereo was on.


You should get an oscilloscope and take a look at the advance signal. It should be a 5 volt square wave. If it is not, then post at MSEFI.com and we'll be able to zone in on the board problem that could cause the symptoms.

 

Thanks for the replies. I'll see if I can get an oscilloscope.

I thought 5v needed to go to the module after the initial startup (rpm) has been reached? That is the tan or brown and white wire...

 

Yes. You are correct, I mis-spoke. I'll edit that now so as not to confuse anybody else!