1998 XJ - misfire, but no codes

Hey guys,

I just picked up a '98 XJ last night as a project vehicle... When I first looked at it, it was running on 3 cylinders and wouldn't idle without a foot on the gas pedal. After dicking with the wires to figure out what cylinders were (and weren't) working, I managed to get it running on 5 cylinders and idling on its own... But cylinder 2 seems to still be out (and the exhaust reeks of unburned gasoline).

Odd thing is that the car isn't throwing any codes or a CEL. Anyone familiar with the 1998-era ECU that can give some insight into why this might be the case? The thing had been sitting for a while so the battery was dead, but after jumping it and unloading it from the trailer last night it showed signs of holding a charge... So it's been sitting on a 2A trickle charge for about 12 hours now in the hopes of getting the computer to retain some data.

I'm definitely open to suggestions on the CEL/code issue so please let me know what you understand of this era. My 2001 will throw a misfire code in less than 60 seconds of runtime after a full power drain (or battery disconnection) so I'm a little perplexed.

Oh, and the CEL does have a good bulb on the '98 (it turns on when the ignition is first turned to "On").

New project, start by verifying mechanicals worth messing with. Check compression. If a valve is burnt, or cylinder wall severly scarred, etc., lowering compression below 120 or so, you are just waiting time until you take care of that.

From your description of having to futz with the wires, I would start with both a compression test as winterbeater suggested and if that checks out, (120-150 psi with no more than a 30 psi variation between cylinders) then perform a full tuneup.

That would consist of Champion copper plugs gapped to .035, quality plug wires, distributor cap and rotor. A tuneup may likely resolve your symptoms.

Also be sure that the battery you have checks out. By that I don't mean just charged, I mean that it passes a "load test". Marginal batteries can cause many symptoms on the 4.0 engine as the engine management system is not happy. Any parts store will load test your battery for you for free.

Good luck and keep us posted!

Yeah, good points - compression testing is definitely the next step given that the PO had the vehicle diagnosed as having a bad head gasket... I've just been hoping that it was a misdiagnosis. This thread was focused primarily on ECU and CEL behavior, as it's definitely different than my 2001.

Picking up a compression tester and whatnot on my way home from work so I'll get the diag done tonight and post up the results.

Since you will be removing the plugs anyway, take a look at those.
And if you can see into the bore with a flashlight, and #5 is a lot cleaner? That's a bad thing.

A friend has a wall inspection scope that's small enough to function as a bore scope, so I'll use that if I do any more diag before I pull the head...

But, after checking the oil level I noticed that it was extremely high, but an odd viscosity. I did a partial drain and shined a bright light through the oil as it flowed, and there was definitely a green hue... And as it ran down the pan, it did separate into two distinct bands (the outer/higher one being green).

Fairly certain it's the headgasket at this point. Doing a compression test tonight and narrowing down what cylinders are affected so I can have a better idea of what I'm looking at upon pulling the head off.

Head gasket? You hope!
could also be head and / or block.
Pull the head, look at the gasket for signs of breach around the affected cylinders, have the head magna fluxed / checked for cracks. If the head is real bad, you might even check the block. If the head is fine... almost no way the block is bad.

Right on. I'll definitely be taking the head to a shop to have them check everything... Shouldn't be too expensive.

Last night I started doing the compression test after an oil change and cooling system flush. I used this wretched little piece of crap to do it. Why is it wretched, you ask? Well, the f***ing M14 adapter has no hex head on it (only texturing for finger-tightening), and it was an incredible pain in the ass to get threaded into each cylinder. I ultimately had to put it on the hose, start twisting the hose hoping to get the threads to bite, then twist it as tight as I could hoping to get a good seal (via the rubber hose).

After a lot of struggling, I managed to get it into cylinder 1... 34 psi. I figured it might be because I didn't get it in there tight enough. Oh well, on to cylinder 2... 28 psi. Same deal. Figured it was due to the wretched design of the thing and my inability to tighten it.

Then came cylinder 3. Came in at 112 psi, at the same tightness I achieved on the other cylinders. Once I hit this number I said screw it and just changed the remaining plugs and ran the car for a bit to re-charge the battery. No change in behavior, so it's definitely low compression on those cylinders.

Then my roommate came home and showed me his compression tester, which had an M14 adapter that was 3x longer, with the added bonus of a hex head at the hose end. Dammit.

At this point, the car is drivable, and I close on my first house by the end of the month... So I'm just going to get it inspected and registered for the time being, as I'd like to keep it mobile until I can give myself a couple weeks to work on it (I know how slow I am with some of these things and don't want to hire a wrecker to move it). Not to mention this house will be the first 2-car garage I've ever had entirely to myself, so it'll be way nicer to have adequate space to work on it.

Sounds good. Limp it into that nice big 2-car garage and wear a big, sloppy grin while you work in it.

yossarian19 said:

Sounds good. Limp it into that nice big 2-car garage and wear a big, sloppy grin while you work in it.

Click to expand...

Adult beverages can help too, but not too many! :cheers:

Keep us posted.....