XJ Performance Issues

chris

chris

cltdba
Moderator
Joined
Sep 28, 2009
Location
Concord, NC
I'm having problems with the XJ that I can't get figured out. It runs great for several hours and then begins having problems where it spits and sputters. At WOT you can hear it popping/spitting from the intake and doesn't rev higher than 4k. It almost seems like a timing issue, as if the fuel is being sprayed too early or late. If I turn the ignition off and restart it the problem goes away for a little while. Cycling the engine always fixes the problem and it runs great after a cold start. This problem existed prior to the engine mods I've listed below. It threw an O2 code after I changed the exhaust, but is no longer throwing any codes.

My next steps are to replace MAP sensor, pull and clean fuel injectors, check timing, replace distributor, and replace ignition coil. Does this seem like a good route? Does this thing have an ignition control module or is that part of the PCM?

What else can I try?

1991 XJ Laredo, 4.0 HO
---------------------------------
Engine/Exhaust Mods:
- Cone filter/air box gone
- AC bypassed/No AC parts remain
- Cat removed
- Cylinder muffler, drops off just above rear axle

Parts replaced:
- PCM/ECM (came from 1994 XJ)
- crank position sensor
- fuel filter
- radiator, thermostat, tstat housing
- temperature sensor
 
I had the same problem for almost a year, I changed everything, plugs, wires, ignition coil, and distributor cap nothing helped. The last thing that I did was change the O2 sensor and that seemed to solve the problem. That was over 4 years ago. Have you changed your O2 sensor yet, that would be the first thing I would do.

Not to turn you away from this site but www.naxja.org is a XJ/MJ web site that has covered every XJ/MJ problem you can imagine. Try using the advanced search option, and search titles only.
 
I wouldn't throw parts at it until you know whats wrong. It's OBDI so it should be pretty simple to diagnose. It may not through codes, but should have stored codes in it.
 
I think it needs a 4.6 stroker!
But I have nothing else useful to add. I was going to recommend crank position sensor because that's what my TJ did.
 
I've replaced the PCM and the crank sensor already. Have not tried the O2 sensor yet. Prior to changing the PCM, I hooked it up to one of those expensive ass OBDI readers and there were no codes stored other than the O2 sensor code. The O2 sensor code was thrown after taking the cat off so I assumed that was the problem.

I'll hook it up to the computer again and see if there's anything new. Otherwise, I think I'll replace the O2 and the MAP sensors and go from there.
 
I have a 99 XJ ( 4.0 )

I dont know if this is anything close to your problems but, I also do not have a cat. ( Have a pre-cat thought )

My CEL will come on and it reads something like bank 2 sensor below thresehold ( O2 Sensor ). It also spits and sputters like your talking about. I use my computer to reset the PCM and its fine.. Mine only does it every now and then so i dont worry about it.

I'm woundering if its the same thing. but with yours not being
OBD-2 its not showing up?..

Just a Long shot, hope this Helps if not Bump.
 
Quite possible. I can try disconnecting the O2 sensor and see if it recreates the issue or makes it better. Worth a shot, thanks!
 
This is a long shot, but it happened on my buddy's TJ. He had a wire that was barely chafed going to the CPS. It would find ground every now and then and all hell would break loose, i.e. it would barely run. Check it out.
 
Sounds like an o2 sensor to me also. If you have no cat it wont work right because it will never hit the proper temps. Its obd1 though. Just unplug it. For some reason obd1 computers seem to work better with no 02 than a bad or misfunctioning 02
 
I know this gonna sound stupid, and I am definately not being a smarty pants, but..When is the last time you changed your air filter, or cleaned it if it's a K&N?


It sounds like the same thing mine was doing back when it snowed. I had cleaned the filter 3 months earlier, and only rode a few times but when I took it out and checked it...after 3 months, it was awful. I cleaned it and problem solved.

easy fix..I hope it's that simple for ya.
 
willness33 said:
This is a long shot, but it happened on my buddy's TJ. He had a wire that was barely chafed going to the CPS. It would find ground every now and then and all hell would break loose, i.e. it would barely run. Check it out.
Click to expand...


I had a 97 tj that did this. Its a cool story. My tj would start running like crap and even cut off with out cranking back for several hours. Left me stranded a few times in one week.

I called Sheldon G. and he said ''Its a long shot but..'' Then he told me to see if the o2 sensor wire is too long and doubled back on itself and the exaust pipe( melted)..sure enough, it was. I fixed that and she was good to go.
 
Filter is brand new. First run was last weekend. :) it's actually one of those spectre filters. Similar to k&n. I think it must be the o2 or the map sensor. Unfortunatly the problem takes so long to present itself I won't know until the next wheeling trip which isn't until aug 7th unless I get the motor mount fixed in time for the flats on the 24th.
 
I do believe their are 2 o2 sensors. It may be the one in the back by the muffler. Do not know if this would help. Good luck!!
 
Dylan W. said:
I had a 97 tj that did this. Its a cool story. My tj would start running like crap and even cut off with out cranking back for several hours. Left me stranded a few times in one week.
I called Sheldon G. and he said ''Its a long shot but..'' Then he told me to see if the o2 sensor wire is too long and doubled back on itself and the exaust pipe( melted)..sure enough, it was. I fixed that and she was good to go.
Click to expand...
Yep, my friend and I scratched our heads forever on his issue. We swapped out EVERYTHING related to fuel and spark management including the ECU. It helped that he had a perfect running '97 XJ (same year as his TJ) to steal parts from to troubleshoot. That little chafed wire was a lucky find. You know, as I sit here and try to remember exactly what it was, I can's be certain it wasn't the O2 sensor and not the CPS, but it's one of those things that you think "nah, it can't be that". It happens.
 
Welp, took the XJ to the flats and was highly disappointed in it. It's still having the problem and it seems it's getting worse.

1. I unplugged the O2 sensor, started having issues after about 20 minutes.
2. Replaced the ignition coil, still had issues, but did seem a little stronger at first.
3. Replaced the Coolant Temp Sensor on the back of the head. Still having problems.

I have a MAP sensor I could try replacing, but I'm thinking this may not even be sensor related. Amajeepman mentioned a possible burnt valve. It is popping/backfiring through the intake when it begins having these issues. Now after turning off the jeep and cranking it back up it only fixes the problem for about 5 minutes.

Anyone got any more ideas? I'm about fed up with this thing and am contemplating parking it and building the yota, but I hate not having something to wheel.



PinkyXJ said:
I do believe their are 2 o2 sensors. It may be the one in the back by the muffler. Do not know if this would help. Good luck!!
Click to expand...

There's only one sensor on my XJ. It's right before the cat..cept I have no cat anymore.. :) There never was a second one after the cat anywhere. The tail pipe is gone and the exhaust dumps off right above the rear axle. Running a cylinder style muffler.
 
my wifes started sputtering yesterday and triggered the cel. got to looking around and I had a busted plug boot on #4 and it was arching to the block. It wouldnt do it when you first started it only after it ran for a while. Im guessing the heat made the boot expand letting out the arch. When it arched it had a ticking noise that sounded like a manifold leak.. new plug wires and it hasnt done it yet....
 
cltdba said:
Checked my boots yesterday as well and they're still in good shape. :(
Click to expand...

maybe the problem was you letting Michael drive it the last time....:lol::shaking:
 
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