UPDATE: The issue has been resolved. Please see the list below.

Hi all

I have a 1991 Cherokee XJ Limited. When driving (accelerating, or applying the throttle to maintain speed) it shakes. Sometimes it's a a small shimmy that is barely noticeable. Sometimes it is quite hard shake to the point where you can hear something (I think exhaust) shake and clank. RPMs on the gauge are steady, but you can tell the engine is shaking. This does not happen at any specific speeds, loads or RPMs. It seems to be worse when cold but still happens when warm. It happens every time we drive it.

The Jeep starts up pretty easily. Only have to crank a second or two.

It's a 1991, so it's OBD1. I used the key trick and I don't get any codes (only the battery disconnect one.. which is obvious since I've disconnected the battery to work on the Jeep..).

I am interpreting this as a misfire - does this sound right?

I'm trying to plan out what I do to fix it. I am hoping the forum members could pitch in and let me know if I am missing anything, give suggestions or tell me if I am off track.

It's a complicated history, so I've tried to list everything out below that's relevant. I am sorry this got to be quite long... but I think it's relevant..

History:
Had the XJ since June 2016. The PO let the thing sit for years, and it was pretty noticeable that it had water damage (interior mouldy, starter was rusty and toast). No body rust but it had clearly been sitting.

We brought it to a shop for inspection and it was given an all clear (whatever that means).

We did some maintenance, fixed some wiring, cleaned the interior. New battery. New fluids and fuel (plus fuel stabilizer). We had no issues driving it. However on our first trip it starting bucking, RPMs dropping to zero and stalling. We stumbled home from that trip successfully (yay Jeep!). Engine ran pretty cool - temp gauge always in the middle even in the heat of the summer.

First trip to Mechanic:
We brought it into a shop and they replaced the crankshaft position sensor, with no improvement. They then replaced the distributor. We were left with less power, but no more issue with stumbling. I figured they set the distributor right and I figured the timing may have been too advanced earlier and that it should be that low in power. We only drove it on flat land after that, didn't need to do any heavy highway driving so I just thought we had a small loss in power.

Working on it over the Winter:

The starter died and so I replaced it. Then over the fall and winter I kept up with some maintenance:
- Fuel filter
- Oil filter
- Improve grounds and new battery terminals
- Repair wiring
- Cosmetic improvements & cleaning up interior, improve wiring robustness, etc
- Replaced the IAC
- Replaced the coolant temperature sensor (old one measured out of spec)
- Rear shocks
- Diff oil and seals (front and rear)
- CAT back exhaust

After all this, with the new starter it started quicker than when we first bought it.. but still not instantly.

Did more... but this isn't a build thread so just listing out the big stuff/ things that might be relevant.

We then took it for a hiking trip in early summer 2017 and the Jeep overheated...burst a hose so towed it back into town:
- Replaced coolant hoses (needed it anyways)
- Replaced fan clutch (was dead)
- Bought a spare electric aux fan - old one works so new one was not installed at this time.

This was unusual because the Jeep ran so cool the previous summer.

Second Trip to Mechanic:
Drove it on the highway after the repairs and it kept getting much hotter than before, and very low power. The power/ torque was so low that it was very obviously not supposed to be like that. You don't notice the low power when driving on flat land, but when going up the mountain on a highway it's night/ day. However...no misfires, no stumbling, just hot and low power. I realized this looked like a timing issue so brought it back into the shop and told them to check the setting on the distributor.

The shop said, yea, distributor was set wrong. They fixed it but then started acting flaky. The rest is hard to get out of them but I know:

• They said the car was running rough again, and described it as the stumbling we had before.
• They tried replacing the ignition coil and it did nothing, so they said they put the old one back in (I have confirmed it does look like the old one)
• They mentioned the crankshaft position sensor again, but didn't actually say they changed it
• They told me after having it a few days of troubleshooting and not telling me what they did (all labour under warranty) that they found the issue to be the timing chain stretching. They replaced the timing chain.
• After I was there to pick up the XJ they told me they gutted the cat because "it was still a little sluggish". I was a little PO'd about that.. I knew it needed replacement and I was getting ready to put a new one in. So now I need to put a new CAT in.. but after I fix the misfire so I don't kill the new CAT...

We picked up the Jeep. Power was back. Snappy, but driving it home is started shaking a bit which seems like a misfire. HOWEVER the engine runs much cooler now (like it did when we first bought it).

Things I did after Mechanic:
I don't know what the shop did, and they weren't very transparent with me about what they actually troubleshot, what they replaced and what they did on the Jeep. So I decided to take a cut at the easy stuff myself. Before I started all of this, the symptom existed on the Jeep. It seems like a misfire to me but I describe it at the top of my post. Again, the RPMs are steady this time around so the original issue seems to be gone but replaced with this issue.

So far I have:

• Replaced spark plugs. Old plugs are clean and not soiled. They are worn, so needed replacement at some point soon anyways. I replaced with Champions gapped to 0.035+/-0.002 using feeler gauges.
• Replaced ignition wires with NGK replacements. Old wires were a little loose when I swapped the plugs. I could easy have pulled Cyl 4 off. New wires click into place and are clearly engaged.
• Checked vacuum hoses visually. I don't see any issues but I haven't checked vacuum.
• I checked fuel pressure about 2 months ago (before we brought it to the mechanic the last time). Looked to be in spec. We idled the engine and fuel pressure was in spec.
• Checked the O2 sensor wiring. The harness was getting close to the exhaust and the conduit melted, but the wires in tact. Harness is secured out of the way of the exhaust manifold now with new conduit.
• Checked fuel injectors to make sure the shop didn't swap them around. I didn't peel back the wire conduit to check wire colours, but the injectors and harnesses looked untouched.
• Checked to confirm the distributor is torqued down fully. I didn't take the cap off, but wanted to make sure all bolts were tight (the shop forgot to tighten a few things down the last time I went to them...)
• Checked to make sure the CPS, TPS and Map sensor are all plugged in properly. Connections are all good.

After doing this (which is admittedly not much) the issue still persists. It has not gotten better or worse.

EDIT: I'm revising the plan below as I get feedback. Thanks everyone!

My current plan:

• Replace ignition coil. Again, check if it makes a difference. Clean grounds, make everything is tight. This should finish the spark tuneup. --- [DONE; test drive complete. No effect (good or bad)]
• Test throttle position sensor resistance. Check resistance at zero throttle and check to ensure it is smooth gain as throttle is applied. --- [DONE; smooth gain & in spec]
• Check torque on intake manifold bolts as per cruiser54's recommendation
• Replace Crankshaft Position Sensor, OEM spec with my spare. I could not find Mopar but I found a Blue Streak one and it seemed the best out of my options. Even if Blue Streak is not the best I will swap it to see if it makes a difference before I invest in another one.
• Replace the O2 sensor. I have a Bosch one I found was recommended on several forums and is an OEM replacement type (not generic). --- [DONE; test drive complete. Idle seems smoother and less cyclic. Misfiring / sputtering issue persists though.]
• Replace MAP sensor - old one is corroded from leaking cowl seal [DONE; Test drive complete. No effect (good or bad)]
• Clean and verify electrical connections [DONE; test drive pending]
• Remove, clean and reinstall throttle body (with new gasket) [DONE; Test drive complete. No effect (good or bad)]
• Verify timing as per feedback from cruiser54 and '90Cherokee [CONFIRMED TO BE THE CAUSE. Timing chain was set wrong, to valve timing was bad. Distributor was also set wrong so crank/cam not synced. Correcting both the timing chain and the distributor has fixed the issue.]
• Verify fuel pressure again, under load as per '90Cherokee recommendation. I'll get a hand from my wife to do this (not enough hands/ feet to coordinate it all myself!) [Shop did this as part of their troubleshooting and confirm the fuel pressure is good]

This is as far as I got. Any other ideas? Is is possible that the shop still has the timing set up wrong somehow? Should I be worried about anything else?

Once this is all done I will install a new CAT, but I don't want to put a new CAT on a car that's misfiring.

Your ideas are appreciated. Thanks in advance!

 

I'm not focussed enough to be of much help about the problem, but any shop that would gut the cat, especially without consulting you first, is extremely suspect. It's illegal to do that and not right to destroy a customer's part without a conversation/permission.

 

Thanks for the reply '90Cherokee. I agree. That really tipped me over the edge with them. They are VERY reputable in my area, but I really don't like how they have handled things with us at all. I'm looking for another shop (I posted another thread in Cherokee Chat reaching out for recommended shops in my area...).

I am especially frustrated by their methods in solving the problem(s) we have brought the XJ in for. Anyone replace parts randomly after a google search, I am bringing it to a shop for their expertise. I much prefer someone to troubleshoot a problem over just swapping parts out. This is why I am reviewing everything they have done (within reason) and confirming what has been replaced/ what has not been replaced and hoping to pick up on some of the troubleshooting myself before handing it over to another shop..

 

Every once in a while I get stumped with a vehicle. When I do I tell the customer "I think it's 'X' but not sure 'till I fix that"; do you want me to try that or do you wanna take it somewhere else? Because of my reputation they always say yes, but I won't make assumptions with most of them just to be safe.

If a mechanic tells you that your problem is 'X' and it wasn't he shouldn't charge for that repair. Anytime a mechanic tells you that you need more than one part/repair for one problem be suspicious.

 

I've had lots of issues with Champion plugs causing misfires, especially the ones with a smooth insulator. Other than where they are the exact OE spec number I won't use any Champ plug due to frequent issues.

If you can verify that the timing is right that's something easy to eliminate from the possibilities. If you can verify fuel pressure under load where it's misfiring it would be nice to rule that out too.

 

Lots of good advice here.

Couple things.

Make sure your intake manifold bolts aren't loose.

I am also not a fan of Champion plugs. I use NGK ZFR5Ns in all my 4.0s.

I'm suspicious of their dinking with the distributor.

I'm attaching a link to a tutorial on indexing it yourself.

I only use NGK or NTK oxygen sensors. Not a fan of Bosch.

http://www.angelfire.com/my/fan/dist_index.html

 

Thanks for the feedback! I heard a lot of mixed feedback on Champions. I picked up the ones referenced on the Emissions label under the hood. I did notice the PO had NGKs installed though. Regardless, there was no change after I replaced them making me think it was not the plugs.

Do you have a recommendation on how to check/ verify timing? I see cruiser54's recommendation below (which I like) but I'm open to alternative approaches!

Thanks! I've added these items to my to do list and revised my original post.

I agree about the distributor. I don't know if you caught it, but the shop also changed the timing chain. Do you think I'd see a similar symptom if the timing chain was set wrong? Are there any recommendations on how to verify that without taking too much apart?

I read mixed feedback on the O2 sensors. What kind of issues have you had with them?

 

Yikes, I typed out a reply but must have dropped it before I could finish posting. Here is an alternative version..

I just wanted to thank you guys for your feedback. I've updated my original post and my plan to incorporate your feedback. Hoping to get to some of it in the next couple days, and try to knock off most of the list before the end of the weekend.

I went with the Champion plugs that share the same PN as listed on the emissions label under the hood. They aren't the smooth ones. I didn't see any change (at all, neither good nor bad) after replacing them so think it's reasonably safe to assume (for now) it's not the plugs. However I did notice the PO used NGK plugs. Worth a thought.. maybe this Jeep prefers NGK..

I've got my Haynes open now looking at the distributor installation procedure. I like the link cruiser54 sent..

Should I check anything with the timing chain? Would that cause similar symptoms as I am seeing? I agree about the distributor but don't want to assume the timing chain was set right. Any way to verify that without too much work or disassembly?

I got the Bosch O2 sensor based on recommendations online but noticed some contradictory feedback online. Cruiser54, you say you have issues with Bosch O2 sensors on the 4.0. What symptoms do they show? I'd like to know if an uncooperative O2 sensor would make the engine behave any differently than a bad/ worn/ carboned up one.

Thanks again!

 

NGK and NTK.

 

I had the day off, so I'm updating this just to keep track of where I am in the plan and document it.

Ignition Coil
I replaced the ignition coil. Took a little longer than expected, but I was being careful and only had my deep sockets with me (which made tool clearance tighter than it should have). Removed the bracket, cleaned the grounds and replaced the ignition coil on the bracket, then re-installed everything. Everything went fairly smoothly as it should have.

Throttle Position Sensor
While I was under the hood and the battery was disconnected, I checked the resistance of the throttle position sensor.

Rather than checking voltage (which tests not only the TPS but the resistance of the cable going to it) I just unplugged the TPS cable and probed the sensor with my multimeter and measured resistance across the sensor.

At zero throttle position the resistance was 4.52 ohms. I can't remember which pins I measured between, but I was mostly testing to make sure resistance transitioned smoothly and did not drop out or spike.

When I pulled the throttle cable as far as I could, I got the resistance down to 1.54 ohms. Not sure if I pulled hard enough, but the issue we are seeing isn't at full throttle so I think this is safe to stop there. I also couldn't find my alligator clips so I had to carefully hold the multimeter on the pins with one hand, and pull the throttle cable with the other..

I gently and smoothly pulled the throttle cable multiple times going from zero throttle to full throttle, and released it back down. The resistance transitioned smoothly on the full range of the throttle. I did this about 5 times each way and am confident in the results.

I've read on another forum an instruction on how to do this with the TPS removed (use a screwdriver instead of pulling the throttle cable) and it is supposed to range between 0-5 ohms, but it could be a lower range than that (say 1-4.5 ohms). This was on the same design TPS as the '91 XJ has, so I feel pretty comfortable that not only is the TPS in spec at zero and full throttle, it also is not causing any erratic throttle signals during acceleration. I'll cross this off the list.

Intake Manifold Bolt Torque
I started checking this and had my torque wrench with me (and my Haynes describing the torque pattern) but I misplaced a socket extension that I needed. I packed up and made lunch and got caught up doing other stuff.

Since I did the work in the garage of my apartment, I cleaned up right away and haven't been able to go back down and start the XJ yet. I am now caught up with house chores. Since this is my wife's XJ, I will wait for her to get home from work in a few hours before we start it and take it for a test drive. If I do laundry and other house stuff, she will be more willing to go on the test drive and let me keep working on it tomorrow.

I'm off work tomorrow as well so I plan on tackling other items off the list then as well.

 

I think I'm just updating this for myself really...

Test Drive after Ignition Coil
After replacing the ignition coil we took the XJ for a test drive last weekend. As I expected, it did nothing to fix the problem. It didn't make anything worse either (phew). So I was able to cross that off my list.

O2 Sensor
Next on the list was O2 sensor. I went to do it last Saturday. I had an O2 sensor socket that I bought on Saturday morning, but when I went to pull the old O2 sensor out I found I didn't have the right adapters to fit anything I had other than my long 1/2" drive breaker bar. It was either that or a short adjustable wrench. The breaker bar was too long to actually use and the adjustable wrench was too short. I stopped what I was doing - I didn't want to round the nut with the adjustable wrench.

So this was an excuse to buy a 15" long breaker bar with 1/2" drive.

I bought the new breaker bar last weekend on Sunday morning and was going to finish the O2 sensor swap but fell sick for Sunday afternoon/ Monday and couldn't finish the job.

I'm feeling better now so this morning I went down with my new breaker bar and was able to remove the old O2 sensor in minutes. No heat needed. It took me maybe 5 minutes to remove it. Took me longer getting into position under the Jeep than it did to actually remove it. The O2 sensor looked... possibly original. I'm very thankful it was so easy to remove.

New one is now installed and torqued up. I started the XJ up and cold it seemed to idle fine, then I let it warm up. Idle is fairly smooth (idle been cycling before, so I take this as a good sign) and I could rev the engine without any misfires happening. I don't see any exhaust leaks but I'd like to check again.

I am hoping to go for a test drive with the wife tonight. She's the one that drives the Jeep, so I want to make sure she drives so we can continue to replicate the issue.

I'll update again after the test drive this weekend.

 

Thanks for the updates!!

 

O2 Sensor Test Drive Results
We took it for a test drive up the street today and the issue is still there. It sputtered up the driveway like usual. It did not shake violently this time (no clanking) but my wife said it was running like usual. I'm not sure if she's learned to compensate or if it has improved a bit.

Generally I think it's running a little smoother than before but I might just be thinking / hoping that.


Next Steps
I'm going to keep working through the list this week. I have this upcoming Friday off work again. Technically tomorrow is a stat holiday in Canada as well but I'm not sure I'll get a chance to work on the Jeep for the rest of the weekend. I'll probably check intake manifold torque next, and replace the CPS.

I'll probably buy a valve cover gasket this weekend so I am ready with a new gasket for when I pull the valve cover to check the timing. Needs a new gasket anyways.

Question for you all ...
I have a new MAP sensor that I bought when we first got the XJ. The map sensor on the Jeep is corroded a bit, and there was clearly water ingress on the firewall from the cowl seal. I was planning on eventually swapping out the MAP sensor (even if it is working OK) once I had this issue resolved just because I am suspicious of the corrosion. I haven't tested the MAP sensor yet but I was wondering if it makes sense to throw it in quickly to see? It's probably the easiest sensor to replace, IMO.

 

I would chuck it in there.

Ever done a connector refreshing in the engine bay? http://cruiser54.com/?p=35

 

Thanks! I'll add the MAP sensor to the list.

I also realized I should pull the throttle body to clean it. Since the PO had the Jeep sitting for years, there was a lot of debris in the airbox when we got it (I think there were rodents living in the air box, actually). I cleaned all of that out but haven't cleaned the throttle body yet. I'll do that for peace of mind - just in case the butterfly is gunked up and sticking.

I refresh and clean all contacts every time I touch something. I've refreshed all of the grounds (new cables and I've sanded all of the contacts) and for other connectors.. if it's a large enough connector I usually polish it and mechanically remove any corrosion with a scotchbrite pad or emery cloth.

I'll step it up a bit and get some more contact cleaner and spray all of the sensor contacts as well. I actually have a replacement MAP sensor connector that I can solder in, but I was originally holding off on doing that. I'll swap the MAP sensor first, clean the contacts as per your guide, then solder the new connector in later.