Hi- New to this forum. 99 Cherokee Sport, all stock, mostly street use, 140,000 miles. It's never given me much trouble- all of a sudden, it started running rough last night- very rough at idle, and I just experienced a burning smell on my commute home. Could it be the cat? (it's the original) Any advice on what to look for? Anyone else experience this? Thanks!

 

It sounds like it's skipping.

Check the ignition system, check for fuel pump and injector operation, and check for a vacuum leak.

Do you have a Check Engine Light on? If so, scan the system for codes and data. Use that information to diagnose problem.

Don't just haphazardly replace parts.

 

1st clean the throttle body and all the sensor ports very well with some TB cleaner.

 

Correct me if I'm wrong, but the '99s still used a distributor. If so, run the engine so that it's idling rough - at night. Open the hood and listen for electrical snapping and look for sparks emitted from the plug wire boots to ground. If the wires, cap, and rotor haven't been changed, they're past due for maintenance.

 

Thanks- it's been a while between tuneups, so I went ahead and changed the rotor and cap, and also the plugs (I was really hoping to see something fouled up, but no such luck) I ran it for a few minutes- still very rough with a faint burning smell. After shutdown, I could hear liquid draining somewhere, and a LOT of water came out the tailpipe and the muffler weep hole. I'm really fearing a headgasket. I'm about to go and check my fluids for any visible contamination. Oh- and the check engine light is on.

 

Did 99's have a map sensor? If so I would check that, and the vac line running to it.

Edit yes they did check that.

 

Latest check- sweet smelling steam coming from under the intake manifold. Head gasket. WHEEEE!

 

You have steam comming from under the intake manifold?

 

Coolant in a cylinder will make your engine skip, but usually only at start up since after evaporating what leak in during shut down combustion pressures won't allow coolant to enter while running.

Perform the appropriate tests before concluding that it's a head gasket or cracked cylinder head. Test cooling system pressure, cylinder leakage, and/or for exhaust gases in the coolant.

Water naturally appears with the combustion of a hydrocarbon, but sweet-smelling steam is a definite concern.

 

The most likely cause for the sound of "liquid draining somewhere" is engine oil returning to the oil pan.

As I've mentioned, I'm not concerned about water from the exhaust system. Steam is more alarming. But steam could be coming from many places on the engine other than a head gasket.

The check engine light may be simply telling you that there is a misfire. It could also tell you if sensor readings are not within the correct parameters. You need to have the codes in the computer's memory retrieved by someone who knows what to do with the information they obtain. Simply having an oxygen sensor code does not necessarily mean that the sensor is bad. In other words, beware having the codes retrieved at an auto parts store. It's better to have a qualified technician allowed to take two hours to diagnose the problem.

The burning smell may be unrelated to the erratic idling issue.