97 GC Laredo Check Engine light

[KerryEva]

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

[YtseJam454]

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...

[KerryEva]

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.

[bringselpup]

Originally Posted by KerryEva

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.

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.