1999 XJ 4.0L Automatic 4WD, 357,000 miles

So, this is a combination of several issues over time. Used to not blow blue smoke, just would idle rough (and engine would shake) on startup and smooth out after a minute or so. That stopped after a few months, and it was fine for a while. It's been burning and leaking oil for years now, about a quart a week at this point. Occasionally it would die when I'd let other people drive it, and I'd show up and start it up no problem. Now, I've only had it for 4 years now. I really don't know what it should sound like at idle, and compared to other people's Cherokee's mine sounds pretty gnarly. But for how I've seen it run, it seems to go pretty good most of the time.

It has been blowing a lot of blue smoke from the exhaust consistently for about 8 months now, hot and cold. Enough to make clouds the size of itself. Recently, it's been giving clogged fuel filter symptoms in the first mile or so of driving-- as in not much throttle response and then all of a sudden it will clear up. Last week, it died on me suddenly while I had been off-roading at low speed for a few hours. I cranked it on and off for a minute or two, then took a hike for an hour. When I got back, it started right up on the second cranking attempt. Two days ago, it barely started back up after idling for a while in a drive-thru line. I got to the window, turned it off, and when I cranked; it fired up immediately but then went into a horrible rough misfiring idle. I got it to crawl out of line, and coughed and sputtered into the middle lane. I had to feather the throttle and shift between neutral and drive to get it there, all the while it was just about to stall out and die for who knows how long. I hated doing it, but I managed to get the RPM's up to 1800 and shifted to drive; it bogged down for a few seconds but then all of the sudden it cleared up and ran just fine. Turned it off and on a few times when I got home, then left it off for an hour. Went back and turned it back on; drove it around that day as well as today. My Craftsman OBD-2 reader showed no codes despite the check engine light being on consistently now (used to go off and on), and the NAPA reader also said nothing. O'Reilly's reader told me I need to replace my catalytic converter.

I have been chasing a vibration issue with it as well; I know before I got the XJ the previous owner must have driven it with a bad vibration till it died on him. I've done a decent bit with it; and reduced the vibration significantly. Have more plans to fix that, but that's beside the point.

I've given tune up's to a lot of friends vehicles, my work trucks, and other equipment and vehicles I have. Just never took the time to do it to the XJ, so I'm thinking it's time for it to get one as well. I do have a remanufactured engine to put in it, but I really don't feel like doing that just yet. So I figured I'd list out my ideas and hopefully get some from you guys as well. I also do have the full Chrysler set of literature for this model and year (Factory Service Manual, transmission manual, body manual) so tomorrow I'm probably gonna do some reading.

1. It probably runs rich. So I think first I'm gonna check the fuel pressure, do a volume test for the fuel pump, and then drop the tank and replace the fuel filter. I should probably clean the injectors too.
2. Clean throttle body and check TPS, Mass airflow, O2 sensor (the first one in line?), IAC valve
3. Maybe there's a vacuum leak? I've heard to check for that you spray brake cleaner at it and listen for an RPM change
4. Maybe there's a leaky injector? I don't know how to test that
5. Probably should replace spark plugs, wires, distributor cap & rotor
6. Replace air filter. It's looked 'fine' for 4 years now; maybe it's not

 

Too many issues to form a reply 😕. Tune up, good start. Compression test definitely. Fuel diagnosis for sure.375k is up there bro.

 

Compression test for sure. I'd do an oil analysis (take sample, send to lab) as well. No sense spending a lot of time and money on an engine that maybe a goner (or a good platform for a stroker).

Excessive oil consumption can (and likely did) wreck your cat.

 

I definitely agree; tons of miles and there's plenty of issues. I also know that the PO sunk it in a river, twice Lol. I've been having fun seeing how many miles I can eke out of this engine before putting the next one in; but it might be time.

I'll go ahead with giving it a tune up; since I'm gonna need to get new parts and clean up for when I drop in the reman engine anyways. Compression test is a pretty good idea; sounds like you guys think this thing's toast. I've never heard of doing an oil analysis, but I'll look into finding a place that I can mail a sample to. Makes sense that oil consumption would wreck the cat. Would you replace it? I know I should at least wait to do that until it has the new engine.

I'll keep this post updated if you guys are curious as to how a neglected almost 400,000 mile engine holds up. Thanks for the replies!

 

I agree - do a compression test FIRST - if the numbers are low or inconsistent look for a rebuilt engine or a good re-builder in your area. If the numbers are good, then spend your time testing sensors, wiring, injectors etc...

 

So, got a few updates. I followed the factory service manual to test the compression, and I was moderately impressed. I repeated the test 3 times over, cranking 3 revolutions for each cylinder. Here's what I found:

Engine temp: 98 degrees
Cylinder 6: 150 PSI, 154 PSI, 155 PSI
Cylinder 5: 153 PSI, 154 PSI, 153 PSI
Cylinder 4: 160 PSI, 158 PSI, 160 PSI
Cylinder 3: 145 PSI, 149 PSI, 149 PSI
Cylinder 2: 141 PSI, 137 PSI, 139 PSI
Cylinder 1: 125 PSI, 125 PSI, 125 PSI (131 PSI at 7 cranks)

These numbers don't seem too bad to me(?), since the acceptable range is 120-150 PSI, with a max difference of 30 PSI between cylinders. Cylinder 4 being 160 does put it out of spec though.

I went ahead and replaced the spark plugs and spark plug cables since I was already there. The old spark plugs were really burned, all white. That actually did wonders; (what a surprise). The engine idles a lot better, there's way less vibration and noise in the cab, and the blue smoke is pretty much gone. I've been driving it around the past few days and looking at the exhaust smoke hot and cold; it's pretty much back to normal and invisible. I also cleared the check engine light and that hasn't come back on. However, it still loses power occasionally after startup, so I'm gonna work to find what's making it stall and keep going through with the tune up as well. I suspect I may have a leaky injector. I am gonna put the new engine I have for it in sometime this year hopefully.

What I've got planned:
1. Test fuel pressure, volume test, and leakdown test. I noticed it had the exact same stall symptoms when I disabled the fuel pump.
2. Replace distributor rotor, check distributor shaft, and test ignition coil
3. Clean throttle body, check IAC, and test TPS
4. Clean injectors
5. Check PCV and EGR valve

 

No idea how old these plugs are

Probably should try to figure out why they got so hot