Bought my first XJ, pics inside.

Well I finally gave in and bought a XJ, I've wanted one for a long time, and this one was too good to pass up.

It's a 1998, 4.0L, 4x4, and auto trans. It was a police issue vehicle, so I'm having a hard time finding out about which trim it has.

I'd like to know as much about it as possible, I've got quite a few pictures already.

Only one problem with the Jeep I can find... For some reason it's got a rough idle, and when the RPMs drop under load it's rough also, for instance, 4th gear at a low speed, it really runs rough. Jeep has new plugs, wires, rotor, and a cap. There is no CEL in the Jeep so I wasn't really sure where to start on this.

















First time "off the road" with it this morning. :laugh:

Nice, clean find. A good basis for a project! I think I see a Chyrsler 8.25 rear axle under there.. so that's good.

For idling problems always check for vacuum leaks. Start with the hoses that come off the air box and go into the valve cover. It really helps to have a vacuum diagram (sorry I don't have one). Listen for hissing sounds when the engine is running.. they are usually easier to hear when you rev it up a bit.

If that fails, check/clean your IAC (idle air control valve).

Start there and see where it goes.

Have fun!

I went through the vacuum lines coming off the intake manifold, they all seemed good. I'll check out the IAT, I'd been reading and hearing about the TPS causing issues, or low fuel pressure, but it runs great at WOT.

I'm ready to start doing some off reading in it, I got it with brand new tires, I'll probably wear those down before I go for any lift.

Most fleet Jeeps were "SE" trim level (read base model).

Yours has steelies and no tach, so I would definitely say its an SE.

being and ex fleet vehicle I'm surprised it doesn't have the vinyl carpeting.

Its also got a skid plate on the diff and fuel tank, a long with power locks and windows.

Is it leaking fluid? Drivers side undercarriage looks suspect?

Looks like a nice find!

If it has the skid plates then most likely it have the limited slip rear! Check the glove box and somewhere in there you might find a sticker warning to be careful when jacking it up to put on a spare tire not to put it in gear, duh, but if you have that sticker then you definitely have it. Usually the limited slip was part of the UpCountry Suspension package which included the skid plates and heavier duty springs that sat an inch taller than regular XJs and it has factory nitrogen charged shocks. They also included a full size spare with it too since they had a few XJs catch on fire with the little doughnut spares and the limited slip diff because the different size tires would cause the clutches to fight to equalize the wheels and get hot.

Looks alot better than my 99 5speed rust bucket i want to dump. Good find, much fun to be had!

Nice Jeep, I hope you are able to work though the rough idle issue.

VIN Decoder tells me that it started as a SE trim.

However, there was a "Police Package" that included a number of options that were available only in different packages. So it does not surprise me that it has skid plates, a tow package, and a full sized spare.

As for the possibility that it has a limited slip or a "UpCountry" package?
I don't know.

Well it does have limited slip, its got the sticker in the glove box

I have an ex police '95. Check your wiring even if it has nothing to do with your problem. They aren't gentle taking their stuff out. Stuff hacked and spliced everywhere.

westvirginia24976 said:

I have an ex police '95. Check your wiring even if it has nothing to do with your problem. They aren't gentle taking their stuff out. Stuff hacked and spliced everywhere.

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That brings me to another question. The back windows will only go up and down from driver controls, you think they disconnected the wires in the doors?

Perhaps. If they didn't want "perps" to get out. Do the door locks work back there? Might give you a clue.

efrie004 said:

Well it does have limited slip, its got the sticker in the glove box

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Well that is fairly rare so consider yourself lucky! I have the limited slip and can tell you it does help and make a difference. I have struggled less through obstacles that my equal setup open differential counterparts had difficulty will.

For future maintenance, make sure when you change the rear differential fluid that you add the proper fiction modifier additive in with the gear oil or you will burn up what is left of those clutch disc in the limited slip real fast! Some gear oils have the friction modifier added already like Royal Purple.

I changed the front pads out, even though they weren't really worn. I get a little noise when I get on the brakes, it's coming from the front, and I'm pretty sure it's the booster leaking vacuum. My question is, do you think the booster could leak enough that it would cause a rough idle? I already replaced the check valve and grommet, that didn't solve anything. Replaced the TPS and cleaned IAC, I also checked the fuel pressure several different times, it's a perfect 49 PSI.

I've scanned for codes, there aren't any. It's got to be vacuum, but there are only 5-6 lines on this 98 4.0L. I can't find a leak. The brakes are awfully mushy though, and the rear drums are out, so they're fine, no fluid leaks, I'm really thinking the booster might be the culprit.

It's the roughest right before you come to a stop, the thing really lopes and runs rough, then once you're stopped and there is no more forward motion it stops. If you put it in park it's even better, but stopped in drive with the brakes engaged it's minimal. Once you accelerate it's gone, until maybe 4th gear and low RPM's again. I'm really not scared of tracking down problems, specifically vacuum issues... I owned a diesel W123 Mercedes, nothing can be that bad. :laugh: