No one has any idea at the local dealership, they don't even know if I have the motor rebuilt if it would fix it or not there allot of help. No one here knows either I guess. I have been doing some measuring I think a 4.3 chevy motor, tranny, transfer case will fit will be a fun project I hope. I'm waiting on a few more friends to weigh in on this and will pass it on maybe they can figure it out they have allot of years of experience.

 

I have a similar problem, however mine will stall instead of just mis firing. I am going to try the idle air control valve. This will cause your funky idle. I changed the coil and the ignition control module on advice of a mechanic who charged me 117.00 just for the diagnostic test and he was wrong!!! these parts are too expensive for that kinda nonsense.

 

Elkhutr 1995 Montero 3.5L V6
Mitlaser 1996 Montero LS 3.0L V6

These service bureau recall/updates for your vehicles may give you a direction to search for the causes of your problems:

10-13-007 JUL 10 • Engine Controls - Revised Misfire DTC Information
TT-124-13-001 MAR 06 • Engine - Fouled Spark Plugs causing misfire
TT111-11-001 NOV 04 • Engine - Spark Knock/Ping Diagnostics

An intermittent miss can also be caused by a floating valve caused by a weak valve spring. Don't know of a good way to test it without getting in there and measuring each one.

Since there are multiple "me too's" in this thread I can't recall who's done which test or what so I'll just say in general to everyone check your coils and wires and your Ignition Control Module. Don't forget the Throttle Position Sensor right there on the Throttle Housing. There is also the Crank Angle Sensor. Those without codes check these areas first. If this doesn't apply to you, please ignore!

I'm curious about the problem jumping from #6 to #4 cylinder. The first thing I thought of is that both of these cylinders have the longest wire runs to their cylinders, thereby being more prone to heat and increased resistance. New wires should cure this, but you never know. Also, for those checking out their coils, someone said a coil is either good or bad — not true! A coil can be good at "room temperature" but short out under load when heated up. Try using a hair dryer to heat up a suspected coil that tested normally to see if it then misbehaves.

Previous stated advice to check for grounding is sound. Shorts often show up as intermittent problems since heat increases resistance, but intermittent problems are by nature brain-frackers. It's like, "Just please go ahead and die on me, then I can fix it!"

This thread opened with elkhutr seeking advice on swapping a GM (gasp!) engine with his misbehaving one. All the advice he received was good advice, in my opinion, since it seemed to be a case of spending a million in order to save $10, but I'd also like to suggest that car ownership by nature is not a strictly rational endeavour and what might seem whacked to us might be someone else's dream project. I've seen perfectly beautiful vintage motorcycles chopped and turned into rat bikes. While personally I felt like they should have done this on something already half-trashed to begin with, at the end of the day, I realized that it was what they wanted to do and that everyone has their own idea of what rocks their world.

Anyway, I hope that these intermittent problems sort themselves out and please remember folks to let everyone know what your problem turned out to be. Your solution is gold to someone else reading these posts who may not be posting themselves but reading along hoping to find a solution to their problem.

My 2¢