califnick

Hello All,

I have a 2001 Jeep Cherokee Sport. I have been having an issue for the past year or so where my check engine light comes on and throws a misfire code. There is never any discernable difference in the power level or drivability. It typically occurs when I am at a high elevation. I often drive from San Jose to Reno and the engine light sometimes comes on when I get to the highest elevations--usually before I hit Truckee--and often when I am coasting at a high speed. It doesn't happen every time. After driving a certain distance, or a few times where I have parked and restarted the engine just going about my business, the light goes off and stays off until the next time I drive over the mountain.

When the problem first occurred, the shop diagnosed as a bad ignition coil pack. I changed that and the spark plugs. After a while, it happened again and a different mechanic diagnosed the new coil pack as faulty. They found no other problems. I replaced the coil pack again and had no issues until I took another trip where I had to cross over mountains. The light came on and turned off the next day. This last trip, I was in the eastern Sierras on highway 108. There is a very steep downhill section where the elevation drops rather quickly. I dropped it into 1/2 for better braking and I got a flashing check engine light that went away quickly. It stayed off the rest of the trip and I haven't had an problems for the past three weeks driving around the SF Bay Area.

Any idea what might be causing this to happen? Could it be related to the high elevation? Is it something to be concerned about?

Thanks for your help!

awg

I have read on this forum of others with that issue, and as I recall, the issue is the MAP sensor signal is affected by altitude, which makes sense (measures air pressure)

If it never comes on any other time, I would not worry about it

Ralph77

Took me a bit to remember who brought this up and find it but......

https://www.cherokeeforum.com/f67/br...de-cps-257126/

tjwalker

Post the exact OBD code or codes please. With OBD, the devil is definitely in the details....

4.3L XJ

Your fuel air mixture is too lean, causing a little bit if a misfire going over Donor Pass. Change your O2 sensor and it will probably go away

califnick

Thanks!

califnick

This last time, the Code was P0300 and P0305.

Some other posters have suggested the MAP or and O2 sensor, which a mechanic friend also suggested could be the culprit.

4.3L XJ

Used to live up there. Cars don't run all that well at that altitude