1994 Jeep Grand Cherokee,170000 miles 4.0 liter. The Jeep suddenly ran terrible all the time, would barely run. I replaced the crankshaft position sensor, and it ran fine...except for about a 1 minute period during warm up.
The jeep starts and runs great until about 20 minutes passes (in warm weather, 45 minutes in cold weather). At that point the jeep bucks and misses, runs really rough, but never stalls. The onset is gradual (15 seconds). If you're on the interstate, you basically involuntarily slow down to about 40 mph, bucking and missing.
Then, after about a minute of this bucking and missing, the Jeep starts to gradually (in 15 seconds) run better until everything returns to normal. You can drive for hours and hours and it won't happen again. This happens every morning and evening.
Once after this happened, I drove a good distance into a mass of cold air. The engine cooled down to the point of problem occurrence, and it happened again. It is definately temperature related.
It seems like it is the coolant temperature sensor. I took it out (as well as the air temp sensor) and tested them. They seemed to work fine. I replaced the coil, MAP sensor, fuel filter, checked the fuel pressure, spark plugs/wires/rotor. The problem occurs at idle and in Park.
I only get 1 minute at a time to try to monitor things. There are no codes or check engine light.
The jeep starts and runs great until about 20 minutes passes (in warm weather, 45 minutes in cold weather). At that point the jeep bucks and misses, runs really rough, but never stalls. The onset is gradual (15 seconds). If you're on the interstate, you basically involuntarily slow down to about 40 mph, bucking and missing.
Then, after about a minute of this bucking and missing, the Jeep starts to gradually (in 15 seconds) run better until everything returns to normal. You can drive for hours and hours and it won't happen again. This happens every morning and evening.
Once after this happened, I drove a good distance into a mass of cold air. The engine cooled down to the point of problem occurrence, and it happened again. It is definately temperature related.
It seems like it is the coolant temperature sensor. I took it out (as well as the air temp sensor) and tested them. They seemed to work fine. I replaced the coil, MAP sensor, fuel filter, checked the fuel pressure, spark plugs/wires/rotor. The problem occurs at idle and in Park.
I only get 1 minute at a time to try to monitor things. There are no codes or check engine light.
Apr 10, 2007 at 11:59 PM