Miss firing issue

[ptac4x4]

We have a 2003 Jeep Liberty limited (with only 18,700 miles). We were driving up a grade on a state highway, when the engine began to run very rough. It continued to run rough off and on for the next 30 to 40 miles. The engine check light kicked on, all other gauges remained within normal range. We took it to a jeep dealer. The code showed multiple mis fires on 5 of the 6 cylinders. They cleared the code and tested the fuel pump. The pump was within specs. They test drove the vehicle and could not get it to misfire or produce the error code again. We drove back to where we live (90 miles) and the engine ran fine. We did fill up with gas before the first trip from the same station I filled my truck up at. (the truck has not had a problem so I don't think it was the gas>

The dealer does not have a clue why it happend. Any ideas what the cause may have been or what we should look for in the future?

 

[2003KJ]

We have a 2003 Jeep Liberty limited (with only 18,700 miles). We were driving up a grade on a state highway, when the engine began to run very rough. It continued to run rough off and on for the next 30 to 40 miles. The engine check light kicked on, all other gauges remained within normal range. We took it to a jeep dealer. The code showed multiple mis fires on 5 of the 6 cylinders. They cleared the code and tested the fuel pump. The pump was within specs. They test drove the vehicle and could not get it to misfire or produce the error code again. We drove back to where we live (90 miles) and the engine ran fine. We did fill up with gas before the first trip from the same station I filled my truck up at. (the truck has not had a problem so I don't think it was the gas>

The dealer does not have a clue why it happend. Any ideas what the cause may have been or what we should look for in the future?

Missfires can come from a variety of things. They can be from dirt in the gas, to plugs that are dirty/worn out, to a connector having popped off somewhere....and i've even heard of extreme climate changes causing missfires (such as 80 one day, and 30 something the next).

What I would do, is to keep driving it. Might have just been a fluke. Maybe some dirt got into the gas, and even though you said you filled up your truck and had no problems, maybe you were just the lucky one and got some dirt in the KJ (it does happen). You say only almost 19,000 miles.....do you do a lot of short distance driving, or just don't drive much? The OEM plugs aren't really known for going the distance (mine and many others were shot around the 25K range). Might not hurt to do a tune up, especially if it comes back again.

 

[ptac4x4]

Thanks for the reply 2003KJ. We just don't drive a lot. I would say that we use the jeep for running around town. At least twice a month we get out for a longer drive to make sure it gets some highway miles. I like the idea of the tune up, even though we have miles to go before its required. I am thinking the fuel pump may be starting to go bad.

 

[2003KJ]

I would start with a tune up, and go from there. The cost of 6 plugs is cheap insurance