Mystery...No-Spark on 3 and 4 - Second time !

[subaruVWnut]

A few months ago I had a problem with a 98 OBW I bought.....no spark on the 3 and 4 cyls.

 

Swapped ignitor, coil, checked wiring continuity between them...and to the ECU...all good.

 

Finally swapped in a another ECU (used)....Voila! ...Problem solved.. (for a while at least).

 

Two months later....same problem.

 

Check engine light on...but generic FLAPS OBD-II reader doesn't tell me anything but "Misfire on cyl 3" and "Misfire on cyl 4"

 

Now what! Need some tips to diagnose this persistant problem.

 

Fun stick shift car....especially when all 4 cyls are firing.

 

Warren C.

[NoahDL88]

Because the two cylinders are tied together, (wasted spark) a loose wire or bad plug would effect both, can't rule out the basics, and their cheaper anyway.

[subaruVWnut]

Because the two cylinders are tied together, (wasted spark) a loose wire or bad plug would effect both, can't rule out the basics, and their cheaper anyway.

 

Tx....good point....I'll check

 

WC.

[ferret]

Just had something similar on a 96 Caravan. After trying many parts, the PCM (Mopars ECU) was the fix. 2 weeks later problem reoccurred. A mopar mechanic I see in my son's scout troop told me the COIL was blowing the PCM. It's resistance was lowered (possibly a few wires internally shorted making the resistance lower and drawing more current from the PCM and eventually overheating and blowing the driver transistor in the PCM). He said it was a common problem and when they replace the PCM, they also do the coil at the same time.

 

I did put the original coil back in. SOO it was off for another PCM and this time a coil......$$$$ later, Caravan still running.

 

Point of story, did you put the original coil back in as I did on that Caravan? Maybe you have a similar problem.

 

End of my experiences and $.02

[mikkl]

Just wondering, could it be a ground problem? You mentioned that you replaced all the wires--I am wondering if perhaps somewhere in the system the ground wires are losing good contact with the chassis and engine.

 

mikkl

[subaruVWnut]

Just wondering, could it be a ground problem? You mentioned that you replaced all the wires--I am wondering if perhaps somewhere in the system the ground wires are losing good contact with the chassis and engine.

 

mikkl

 

 

But would a bad ground specifically..knock out cyls 3 and 4??

 

Warren

[subaruVWnut]

Just had something similar on a 96 Caravan. After trying many parts, the PCM (Mopars ECU) was the fix. 2 weeks later problem reoccurred. A mopar mechanic I see in my son's scout troop told me the COIL was blowing the PCM. It's resistance was lowered (possibly a few wires internally shorted making the resistance lower and drawing more current from the PCM and eventually overheating and blowing the driver transistor in the PCM). He said it was a common problem and when they replace the PCM, they also do the coil at the same time.

 

I did put the original coil back in. SOO it was off for another PCM and this time a coil......$$$$ later, Caravan still running.

 

Point of story, did you put the original coil back in as I did on that Caravan? Maybe you have a similar problem.

 

End of my experiences and $.02

 

We swapped in another used coil....so it's a different unit.

 

Warren C