98 ZJ engine missing out

[ksjeepzj]

Hi, I am new to the Jeep world. I have a 98 Zj with a 4.0. between 65 and 70 MPH the engine misses or the tranny is searching it is hard to tell. can anyone shed any light on this problem? Thanks.

[Yucca-man]

Automatic or manual? The OD may be locking/unlocking on you...if it's a manual you should see the same behavior at about the sme RPM no matter what gear you are in.

[ksjeepzj]

Thanks, Yucca man, it is an automatic. Sorry, i forgot to tell ya that.

[TOOLman]

Does it only do this in this narrow speed interval? Have you noticed any other circumstances that affect the behavior, such as load (going up-hill)?

If the engine is missing, there are basically three things that can be the culprit: Electricity, fuel, or air.

I would start by looking at the battery connection, the spark plugs, ignition wires, cap & rotor, and ignition coil (in that order). If you don't find anything there, check the fuel filter and the air filter.

I had severe problems with my '95 4.0 missing this summer, which turned out to be a bad connection between the battery poles and the terminals. Mine behaved quite differently, though. It could start missing at any speed, under load or without load, etc. Sometimes it would hardly run at idle. Your problem sounds a bit different, but mine began in approximately the same way.

HTH.

[ksjeepzj]

Thanks, Tool man. It only does it between 65 and 70. I have had this problem with the cruise on and off. And it does seem to happen under a load ,like going up an incline. Thanks to everyone who has replied to my post. I have posted on other sights and no one replied.

[Yucca-man]

I think we have the same tranny. Mine constantly locks/unlocks in the same range, 65-70mph or about 2300 rpm when I go up slight hills on the freeway. You can either go faster or slow down, but you're right on the edge right now for the OD to unlock everytime the brain thinks it needs t put more power to the tires.

Speaking of tires, add a larger tire without regearing and you'll see the OD unlock a LOT more often. Believe me...just put 30s on the XJ and I unlock in the 75-80mph range right now.

[Jerry Falletta]

Some ZJ's had a problem with the overdrive solenoid going bad, but I have not heard of any 1998's doing this - mostly earlier models. The dealer's DRB box will probably show what is going on.

My former (1996) ZJ had that problem and it turned out to be some weak valve springs which were not too expensive to replace. That problem was reportedly corrected in the later 1996 or early 1997 engines, though. It drove me nuts for a while, though because it would only happen while under load at about 3100 RPM, and it always happened on the same long hill when driving home from work at about the same time in the morning - real Twilight Zone stuff :eek:. The hill, by the way, is across the lake and a bit south of where Rod Serling had once lived :D.

[ksjeepzj]

Thanks, Jerry. Glad I have an extended warranty. At least now I have some idea when I go the the dealership and won't look like an idiot. thanks, again. Jim :cool: