7MGE Spark Issues

[Nghty89]

I have been working on this issue for several weeks now and have exhausted all resources.

1988 N/A Chassis, 7MGE, R154, Yellow Plug 7MG (M/T) ECU - the ECU has a large sticker that says AU if that matters.

-3 different coils (from working cars)
-2 different ICM's (one grey plug, one green. I couldn't find anything on whether the year mattered or not. Green one is from a known working vehicle)
-Fresh spark wires
-Fresh plugs
-Checked all ECU and harness connections/wiring
-New Cap/Rotor
-Distro tested fine with multimeter
-ECU is from a working car, although it has been sitting for some time in someone else's garage
-All fuses and relays in the car are fine and have been checked
-All grounds are good/correct/connected

The car would not spark at first when I was trying the grey plug ICM, which was the only one I had. Once I was able to try a green plug ICM and coil, I get spark only on the first turn of the key to crank. It sparks once and stops. I can turn the key over and over and get spark, but not while it's cranking. The car crank's beautifully and the harness is a good working pre-89 harness. The ECU is a 7mg (m/t) yellow plug ECU.

I'm stumped and the only thing I can conclude is that it is either the harness in some way, or the ECU itself. Could it be the ICM and do they go bad? I have used the TSRM to multimeter check everything, but the only thing pertaining to the control module is checking the power wire which tested fine. It says if everything else tests fine, then replace the ICM or ECU, but no way to really test the ICM. Any input?

 

[Master_Spazez]

Similar thing happened to me turns out the pins were backwards (order) in the plug. But if it's getting fuel that's not the problem.

 

[3p141592654]

Any codes, especially code 12?

 

[AJ'S 88NA]

ECU grounds connected under the intake manifold?

 

[Nghty89]

All pins are correct, no codes beyond 51 (throttle), and the ECU grounds are hooked to the head just above the injectors where I have always had them in previous 7m builds. Cleaned and shiny lol

 

[bioskyline]

no burnt wires near the dist?

 

[aloshan]

did you find a fix for this?

 

[CRE]

ECU grounds are hooked to the head just above the injectors where I have always had them in previous 7m builds.

There's a dedicated stud for them UNDER the intake plenum.

 

[Nghty89]

Ok, so no burnt wires, and tried the different stud (but that has never caused trouble before). I even tried a new ECU. Time to trace wires, again. Any particular fuses or little boxes I could replace? I checked them all and used a known working main relay - no change. Im going to go with a fuse box issue, but I wont know until I get a chance to test.

Question - what should show on the multimeter if a wire is bad? I may be doing it slightly wrong. I've never had such a difficult electrical issue. Im going through the wiring schematics again today. And im searching other threads too.


*EDIT* I don't know if I mentioned this, but I cut the yellow plugs off of a nasty NA harness and soldered (nicely and professionally, I love clean wiring) them to a clean and working NA yellow plug harness. Wire for wire it was dead on, but this could be a problem IF something got crossed. I think im going to make my own damn harness. I've got enough wire. Lol

Sent from my engine bay.

 

[Nghty89]

Could this be cause by the distributor? Single spark when first turning the key, then nothing. I've checked timing several times, but I admit this is my first distro engine. I followed the tsrm, so no idea....

Sent from my engine bay.

 

[DEFIANT 7M]

Do you have another distributor, pick up could be bad.

 

[Nghty89]

I don't, but if it was bad wouldn't it not spark or weakly spark? It gets one strong spark per key turn. And the distro tested good according to the manual.

 

[87GWSupra]

Its possible the pickup in the dizzy can be bad even with volt meter testing. I personally don't trust testing ignition problems with them just because theirs so many factors they cant test. After the first fire its enough to heat up the circuits and make them stop working. The best way to test them is with an oscilloscope but who wants to spend 10k on a Vantage pro.

 

[Nghty89]

Even if im testing spark on the spark wire from the coil? Or do you mean the dizzy isn't providing the right signal to the ECU for tach? I noticed it doesn't jump during cranking

Sent from my engine bay.

 

[Nghty89]

Turns out it was my wiring all along. Nothing was getting signal including the tachometer (was not jumping on cranking, I was mistaken previously). In the process of repair/replacement. I'll give you guys the outcome soon.

 

[Nghty89]

Bought a new harness. FIXED and running strong! : )

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