I have a 1991 3.0 V6 Mitsubishi Montero... The vehicle has been running fine for the past years. Resently it will start and run fine for a while then suddenly it will hesitate and stall... It will start up fine but if u try to rev it past 1200 rpms it will hesitate and if u continue to try to acelerate it will stall... Sometimes it will start and run normaly but resently that hasent been happening. I just changes fuel pump and one of the fuel filters and plan on replacing the second fuel filter to see if that helps. If anyone knows what it could be please post. Thanks Logan

 

Spark plugs and wires.

 

probably failed capacitors on the ECM.

 

i have this same problem on my 90 montero sport with the same motor... i havent fixed it yet due to money issues but i went through the fuel and ignition check and it was getting fuel and was intermittently not getting spark... i started checking the ignition coil and it was showing open circuit on a resistance test. i pulled a plug and hooked it up to the wire and held it against the head and i got no spark while cranking, until all at once i miraculously had a spark again. then i put the plug back in and the thing fired ran for a few minutes then died. checked the coil again and i had open circuit again. put it back together with the spark plug against the head again no spark, then i had spark again checked the coil and it had "in spec" resistance readings. so i am gonna put a new coil in this week and hopefully that will fix it. im hoping its not failed capacitors in the ecm like manybrews said. this would be unfortunate.

 

its most surely the ECM.
remove it and open it up. You'll see damage from leaking electrolyte if the caps are failing.

 

to update this... i got a coil that tested good from a wrecking yard and that did not fix the problem. so i pulled the ecm out and opened it up and low and behold a capacitor exploded and has corroded a good portion of the circuit board. luckily there appeared to be no catastrophic damage. i sent it to my uncle who repairs stuff... all kinds of stuff. and he put a new cap and a ic in it and said it should be good as new. he said that he used a cleaning solution to clean up some of the corrosion and i have to wait a few days for the "lacker to dry" whatever the heck that means. but according to him i am good to go.