Need help. 98 "bucks" while crusing

Long story short. If staying at one speed 35, 45, 65, ect dosent matter what speed the jeep bucks and surges. It is reall pretty bad. But if you drop the hammer the thing runs fine and makes power.

It had a map sensor voltage low out of range code in it.

I have since replaced the following with new.

High quality borg warrner cap, rotor, wires. Champ copper plugs, Bosch front O2 sensor, Jeep MAP sensor, Jeep TPS, Jeep IAC.

I know there are no vaccum leaks I have caped everything off and checked the manifold for leaks. It pulls almost 18in of vaccume.

I have swapped computers with a friends 98 and it still does it and his ran fine with mine.

I will try to get a video up of what it is doing.

Any ideas? I am really tired of replacing parts. Only sensors I have not touched yet are the rear O2, CPS, Temp. I mean come on.

Thanks

Have you checked a really simple thing that i had happen on a jeep i owned a few years back......when under a load at any cruising speed it would "buck" like your describing. I fixed it by cleaning the air intake....it usually gets pretty dirty and once i cleaned it, it would fix the problem completely. I hope thats all it is for you!

I had a similar problem with my 98. I knew it was sensor related because it ran great at WOT, when many sensors are ignored. It turned out to be my upstream O2 sensor. You say you've changed that, however. What I found out later on that caused it to fail was my Coolant temp sensor. Turns out the wiring harness that passes between the fuel rail and the firewall, right underneath the big block ground, had been rubbing and chewed into a couple wires. Chased it for over a year, until it got through enough to give me a persistant problem. Check out your wiring in that area, just in case.

Mine would do the same thing, but it ended up being a faulty plug wire. Since you have already changed wires, I am not sure what to tell you....

Here's a sretch but I had a similar problem back with my first car. I dropped a plug when I was changing them and it had a chip in the ceramic part. I never caught it and mine ran like crap for a month or so until Ipulled the plugs to check the gap of each one. The i noticed the chip. Replaced` it and it ran fine.

Check the O2 Sensors! That and maybe TPS out of adjustment. Thats what it was on my 88

I forgot to mention I did an intake, TB cleaning on it. I will check the wires to the sensors but it is unlikely.

I inspected and gapped the plugs before I put them in. It was still doing it on the almost new old plugsand wires.

Really think the rear O2 would cause this? TPS is adjusted.


Thanks

Yes the rear will do this. I have seen it on a couple of Jeeps, a 89 chrysler and a 91 Olds Cutlass. All of them changed the O2 sensor and it fixed the problem. My 88 was only the TPS, when I adjusted it the problem went away.

BassnTruck said:

Really think the rear O2 would cause this?

Click to expand...

Dunno what "rear" means based on the quad(?) sensor setup of late model XJ's, but the O2 sensor at the catalytic convertor has no effect on performance, so it's not that one.

A 98 should only have 2 sensors, one precat and 1 after cat. The "rear" after cat sensor should only be checking if the cat works.