03 Mitsubishi Montero Limited misfires above 75mph, and knocks when cold on start-up

ekyoteekyote Member Posts: 2
edited September 2014 in Mitsubishi
I have a 2003 Montero Limited, 3.8L V-6, Automatic transmission. 155,000 miles.

Have had these 2 problems for a while, not sure if the symptoms are related. I bought it with these problems.

On cooler mornings (about below 50 deg F) I have a knocking or clicking that happens for a few minutes until the engine warms up. Not sure if fatiqued metal or related to the next problem...

Also, at highway speeds above about 75 MPH I get a sudden vibration that feels like a missing cylinder. It happens as long as I have the accelerator on past about 75 MPH. As soon as as let off the gas pedal it stops. As long as I'm under about 75 MPH it doesn't happen. Sometimes over 75 MPH it's not there either...so it it doesn't always do it, but usually it does.

I have an Check Engine lite on that says "bank 1 burning lean". Also, my skid-traction control does not work (I bought it this way too). Sometimes the dash light comes on saying it's not on, and also that I've lost traction, and sometimes it isn't on.

Today I changed all the spark plugs and wires...the old ones looked fine. It ran the same for a while but then after 2 hours of highway use it began acting like it could hardly stay running and was missing very badly, like never before. I started this behavior after I had the car off for about 30 minutes while I ate lunch. It hardly wanted to start...I had to pump the gas pedal some. Almost like it was out of gas. I checked all the wires and connections and all was good. I drove it less than 60 MPH to get home for about 2 hours, then it stopped missfiring and began running normal again. I've driven it three times since in the same day and it hasn't done it again.

It still does the hi-speed stumble or missfiring, however.

I have not done anything else to the Montero than this: motor oil and filter change, PVC valve, spark plugs and wires.

What are any and all of the issues the highway speed missfiring (or something that feels like it) could be? Could a a knock-sensor or speed sensor have anything to do with the rough running? Fuel feed or filter issue (only does on acceleration, not coasting)? Timing? Timing belt may not have been replaced yet.

What are the possibilities of the cold-morning start noises? Rod knock? Bad sensor? Pully knock? The sound is almost like if I stuck a playing card in the spokes of a bike wheel...steady and about that loud. Not really loud, but noticeable for sure before it goes away (2 to 3 minutes after cold start).


  • anatomyjoeanatomyjoe Member Posts: 1

    Did you ever find out what was causing your knocking sound?

    I have an '03 Montero XLS 4wd w/ 101,000 mi. and have had a 3+yr. slow progressive valve clacking/knocking sound when I first begin driving it in the mornings (i.e. driven cold), ONLY when I am accelerating, and that the knocking goes away when coasting or I let off the gas pedal.
    The knocking sound usually lasts for about 1 to 2 minutes of driving, and then the knocking is no longer an audible sound.

    Please let me know if you were able to solve your issue, as it may be the same issue that I'm having.

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