15 amp MPEM/Harness #4 fuse problem

[Old but not tired]

Pardon me for "bumping" this two year old problem to the top. I did not fix it last year and would like to try one more time.

2000 GTX DI with relatively few hours, original owner.

The 15 amp fuse on the rightmost station on the mpem keeps blowing, even with the key off. The local shop cannot diagnose the problem and says I need a new MPEM. I sent the MPEM to one of the suppliers on this thread (in Minn?) and it came back as passed.

Narrowed the "problem" down to Harness #4, the leftmost one on the MPEM. No problem when the other 3 harnesses are attached but just attaching the #4 Harness blows the rightmost 15 amp fuse. No key attached. I tried with the two leads to the injectors disconected and same result.

I have read the stator posts but it does not blow when those harnesses are attached.

With Harness #4 disconnected, the engine will crank but not fire.

If the MPEM bench tested fine, can I assume that it is a short in one or more of the wires in the #4 harness? Any likely culprits?

 

[Triorieel]

Same symptoms of mine, but mine was a piece of metal shorting the stator. (My stator was fine, but at times grounded to the engine...until I removed the debris)

Your position crank sensor is part of the same connection. No position crank sensor, no spark plug will be ignited.

In my case, parts of the bendix fell out and was shorting the stator to the magneto. This could change as the engine rotates.

But, there could be other reasons...this was the reason for me.

 

[Mickirig1]

I would do check out procedure on stator. And or wiring to it. I don't know if the rectifier can pop a fuse. Unplug the stator, put a new 15 amp fuse in. Plug in the stator and see if it pops fuse. I chased the same thing. found out stator was shorted to ground. If you change it, make sure you know the procedure. Label and mark how it goes back in. Make sure wires are pull taught, anchored to the same points as before and can't be caught by fly wheel. I would doubt a harness would have a problem, unless it is damaged or frayed. Look inside plug and make sure no metal pieces. Put a light coat of Dielectric grease on male parts of plugs to protect and seal connections.

 

[Old but not tired]

The mystery deepens. I unplugged the stator connector and the fuse would still blow when connecting harness #4. Then I unplugged all the connectors I could find on that harness, except one on the fore end of the engine under the air scoop that I could not unplug. Plugging each one in and checking the fuse after each plug resulted in no failed fuses. So I put in the key, got a beep and it started up.

I cannot say what was the cause or the solution, only the proceedure I used. And if it is any help to others, I found it was easier to reach the stator plug by removing the "glovebox" and reaching through the hole and under the pipe.

If I had to name one suspect it would be one of the two air injector connections on the outside under the fuel injectors. I had previously tested the fuel injector connections and they were not the cause.

Also a shout out to [MENTION=41828]Minnetonka4me[/MENTION] who is the one who tested my MPEM and correctly said it was not the cause.

 

[Mickirig1]

Check the outside insulation of the wires where they touch metal. Vibration of the engine may have rubbed the insulation off. Or cracked it. Figure the machine is 17 years old.