2000 Montero sport was running great then one day started to get sluggish and idle bad. then throughout the day just got worse to where it'll barely run and no power at all. Checked plugs and they were full of oil. I replaced plugs, wires, and valve cover gaskets. Zero change. Tested continuity on power transistor 2 prongs did not have continuity. replaced with one from salvage yard that has continuity. Zero change. Pulled the covers off and timing is on the nose. Replaced cam position sensor with zero change. When I pull plug wires off of coil packs there is no change until I get to the first coil 3/5 the vehicle dies. There is spark coming out of the other 2 coils but it is weak. Tested all coils with multi meter the resistance tests fine. Went thru diagnostics tree lead me to believe it's a bad ecm so I replaced that with zero change. I really am lost at this point. I'm suspecting the power transistor unit but don't want to replace any more parts just to be left with zero change. If anyone could point me in the right direction of what I may be overlooking I would really appreciate any and all input.
Forgot to mention I also replaced the fuel pump and fuel filter
Thanks in advance for your time
Chris Wheeler

 

As per your description 3/5 coil is not putting out good spark. Try switchibg that coil with any of the neighboring ones. If weak spark stays on 3/5, you likely have bad ignition modulr. If bad spark moves to another set of cylinders (and 3/5 is OK), then you have bad coil.

 

No 3/5 is the only one that fires good. I've swapped coil 3/5 with coil 1/4 and the problem remains the same. Coils 1/4 and 3/6 put out weak spark and I can unplug those 2 coils completely and it doesn't change how it idles or runs but if I plug those 2 back in and unplug 3/5 the truck stalls instantly

 

Have you tried replacing the ignition control module or checking it's connections? If you're not sure where it's located I've circled it in red below. Good luck!


Ignition Control Module location. 6G72 Montero Sport.

 

Yes I've swapped it with a used one that has continuity where as the old one didn't have continuity on pins 1 and 3. Is it possible for the ptu to cause these conditions and still have continuity?
I tested per the Mitsubishi service manual using 1.5 v to the required pins.

 

That's a real head scratcher... What happens if you put 3/5 coil elsewhere? Does good spark stay on 3/5 or move? I don't know what kind of chances you have of having a faulty new ignition module. I think very small. So, to me that means the problem is elsewhere - PCM or wiring.

 

Yeah unfortunately moving coils doesn't change anything. The icm is off a junkyard vehicle so I'm still slightly expecting that. Pcm has been changed with no luck. Guess I'll dig into the wiring

 

If you figure this out, you'll be doing a few people a favor, I've seen this exact issue posted several times on different forums. Everything you have done is pretty much what everyone else has done. I'm doing my best to think outside the box here so if I suggest something odd just bear with me. Get your alternator tested (take it off the vehicle and get it tested). My thinking on the alternator is perhaps the frequency is not in spec. The hertz range of the alternator must have some sort of +/- range, and if it's out of spec the coils may not operate correctly. Mentally tracing the wiring back from the coils, it appears that the 3/6 coil all the way on the right is the furthest out of the bunch which may have something to do with it functioning correctly if the alternator is out of spec in some way. (Maybe a crapshoot but I have to try )

 

I made a mistake. It's the 5/2 coil that's getting good spark. The first on the left. I have the alternator off and will take it to get tested. I appreciate you giving me ideas. At this point I'm willing to try anything 😅

 

In that case you can 100% eliminate coils as being the culprit. The issue is somewhere upstream with ether the signal to ignition module, or from ignition module to coils. You may need to find a wiring diagram and see which pins on the PCM control signal to igmition module. Then check if there is actually clean signal there.
Nuevos - alternator is an interesting idea, but I'm not sold on that one. To cause so much interference that alternator must act like EMP (electelectro-magnetic pulse) bomb. I know a bad alternator can cause some static or noise on the radio, but to overpower 10k volt spark waveform? I don't see it...
One simple thing is worth checking - all grounds on the engine and ground from battery to body.