Own a 1993 Montero SR 3.0, has a slight misfire at idle,middle driving range ok but misfires at highway speeds when you try to press gas pedal to the floor. No check engine light and no codes stored in ECM. Checked ECM with voltmeter and it sweeped left to right as to check out fine. Replaced spark plugs,dist cap,rotor button and plug wires. None of this has helped. Problem did not begin until I had to spray off motor to remove oil from where oil cooler hose busrt. Had a repair shop check fuel pressure,compression and coil and they say all ok.They could not figure out the problem and I am wondering if it could be the ignition control module or the optic sensor in the distributor. I don't know of any test to perform to check these items.I can't help but think water played an issue in this since it started as soon as I pulled away from spraying it off. Does anyone have any ideas or ever heard of the optic sensor going bad in the distributor? The vehicle runs fine other than this it just lacks power at the higher speeds.

 

It alsmost sounds to me like there is a bad ground

 

Maybe on a corroded connector or loose connection or do you think when it got wet it grounded out?

 

Its almost impossible to tell without a check engine light.

 

I went back behind the mechanic and checked the coil. According to Haynes manual the primary coil ohms reading is much lower than it should be but the secondary resistance is within range. Could this result in a weak spark which would make it misfire under load?

 

Yes : )

More than likely