'98 Jeep Grand Cherokee Suddenly misfiring

jeep

#1

Hi all,

I was driving my '98 Jeep Grand Cherokee Laredo (6cyl 4.0l 4 wheel drive) on the freeway when it, very suddenly, started shuddering badly. The check engine light came on and then started blinking. I pulled right over and shut it off. I stared it back up and the engine is misfiring badly. I had a code reader with me and it’s showing three codes. A random misfire, a cyl #5 misfire, and a Cyl#6 misfire. It will sit and idle (very roughly obviously).

There was no drop in RPMs, oil pressure, voltage or anything when it happened.

I got it home and replaced the distributor cap/rotor, all six spark plugs, and the plug wires but there is no improvement. I cleared the Codes and re-read them and got the same errors again.

Any suggestions from those wiser than I (that’s pretty much all of you here) on what it might be or what to check next?

Thanks, Jeff


#2

Check compression. I wouldn’t be suprised if you had a blown head gasket between cylinders 5 & 6. If you don’t have a compression tester, it’ll cost about $20.


#3

I think I do have a compression tester around someplace. I’ll add that to the list of things to check. Thanks!


#4

To have the trouble happen so quickly I would guess the trouble is due to either a fuel problem or a valve timing issue. I’m not sure if this engine uses a timing belt or chain. If the compression numbers show up low I would check the valve timing.


#5

Followup: Cylinder #5 indeed had no compression so, sounding like something way above my DIY repairs paygrade, off to the experts it went. Turns out it had a broken valve spring on #5. The misfire code on #6 was simply a ghost. I had the spring replaced and it runs better now than it has since I’ve owned it.

Thanks to the CT community once again for all your help.

Jeff