Let me start by stating that I know nothing about cars. I posted this issue about 6 months ago but miserably procrastinated.
The issue issue: My car has about 120,000 miles, its a '97 V8 Grand Cherokee Laredo. The Check Engine light has been on for about a year - eek. This would be fine if the car was feeling fine but I can tell that something is wrong.
The symptom: When driving at low mph the car feels like it is either going to die or quickly accelerate. When I drive on the highway the Check Engine light stays on but the car feels fine.
1st shop visit: I took the car in a few times last fall and at first I rcvd a $300 tune-up gaining new spark plugs, air filter, rotor and wires, and dist cap. (I shamefully admit I don't know what any of that is/does.)
2nd shop visit: The Check Engine light was off for about 1 day. I returned the car to the shop and the computer analysis said that something was wrong with the #8 cylinder. They checked and replaced the #8 cylinder for $380.
Today: The shop tells me that the light is on b/c there is an internal engine problem. They believe something is possibly collapsing inside the #8 cylinder. They mentioned that something is wrong with the campshaft and its interaction with the #8 cylinder.
I need to get my car fixed but I really don't want to pay tons of cash. If anyone has any advice on what the problem & fix is I would be very appreciative. I will not be performing the work, but I would be able to verify that the mechanics I work with don't waste time/money like my past experiences. I am in the south loop of Chicago - if anyone knows of a good Jeep mechanic nearby, I am all ears. Thanks a bunch. -K

They checked and replaced the #8 cylinder for $380.

That's interesting...How the hell did they do that? lol

OK first of all what DTC (Diagnostic Trouble Code) was set when the check engine light came on? Was it a P0308? This would indicate a #8 cylinder misfire was detected. Basically the crankshaft position sensor monitors the engine speed and identifies #1 cylinder through it's identifier pulse. It knows the firing order through programmed logic and if a difference in speed of the crankshaft occurs during #8's power stroke three consecutive times the computer sees this as a #8 misfire. This will turn on the check engine light (MIL - Malfunction indicator lamp). Several things can cause this to happen. you said you had a tune up done so assuming everything they did correctly, then I would verify injector pulse. That means you are checking to verify that the computer is commanding that fuel injector on. If it is ok then I would check that fuel injector. Also a compression test on #8 cylinder will help verify if it is a mechanical problem. If it is a mechanical problem you would then need to do a cylinder leakage test. This will help you determine if there is a sealability problem in that cylinder ie, worn, broken, stuck rings, bent valve etc. I would go to another garage. That whole replaced a cylinder thing for $380 bucks cracks me up...I wonder what they really did...

Hi, thanks for your response. I have taken my jeep to a different shop and they will be sending out the cylinder parts for a leakage and compression test. The cylinders will be tested and corrected. I was told if the cylinder head is cracked it might cost an extra $400, if not then I am probably looking at $1800. Sound right? Its a tough call b/c the car is a '97 with about 130k miles. Hopefully after this repair I can drive it for 5 more years. Thanks.

Hi, thanks for your response. I have taken my jeep to a different shop and they will be sending out the cylinder parts for a leakage and compression test. The cylinders will be tested and corrected. I was told if the cylinder head is cracked it might cost an extra $400, if not then I am probably looking at $1800. Sound right? Its a tough call b/c the car is a '97 with about 130k miles. Hopefully after this repair I can drive it for 5 more years. Thanks.

Well I'm with YtseJam454 you don't take cylinders out of the motor and send them out to be checked. :grinno:

But you've said you don't know much about cars so perhaps what you are telling us has been jumbled up a bit?

In order for people here on the board to help try to get us the diagnostic code. If we know it's something like a P0308 that will start us out toward whats going on. But not knowing for sure people here can only guess. I turned 190K last week on my 93. A 97 with 120K has plenty of life left in it.