Hey all, my '98 4.0L recently started making a metallic knocking noise. I pretty quickly diagnosed it to be coming from the lower end bellhousing/oil pan area. I haven't put a stethoscope to it to isolate it farther since i don't have one, but a few other things are pointing me to the flexplate.

-the noise tracks with engine RPM, is noticeably louder at cold idle but never fully goes away now. It also briefly stops when i shift gears, before starting back up once in the desired gear, I haven't worked out if this means anything but it seems relevant
-previous owner did an engine swap 5k miles ago and the driver side bellhousing to engine bolt is all the way backed out, leading to a noticeable gap between the engine and trans on that side. my guess is it's been running like this for the whole 5k. I just recently took it for it's first couple hundred mile trip so i'm thinking the fatigue from more than just a daily drive may have accelerated the failure.
-i have noticed lately since the noise has started it has started to drive a lot worse and seems to have less power, it always shuddered a bit on accel and wasn't the smoothest jeep but i assumed this was due to the lift and tires, etc. probably not the case. (currently getting 11-12 mpg daily)
-recently popped a code for the trans (likely 2 but i'm an idiot...) I saw P0700, but the screen on my reader only shows 1 at a time and for some reason i didn't think to look for a second. (i've read P0700 is usually accompanied by a second code). i cleared it and drove it home with no issues, and also no physical issues when the code popped, it was driving fine.
-Finally, what i'm assuming is the actual crack, but it's tough to tell because i couldn't get the dust guard all the way off due to a backwards bolt not clearing the exhaust.
I'm planning to use the long weekend to drop the trans and replace the flexplate, my main question is, should I be worried about anything else while I'm in there? Or will the flexplate have done it's job pretty well of absorbing all the bend from the loose bellhousing bolt and spared any damage to other things like the TC or engine bearings?

Also looking for suggestions or feedback if there is anything else I can check or if this is as definitive as i think it is. i've seen exhaust leak and evap solenoids mentioned, neither of those seem to be the issue (just based on proximity and volume of the noise to the bellhousing area)

Thanks!

 

pic didnt upload right in the first post

 

From Experience.....Years back I had a 90 XJ that developed a cracked flex plate....Miserable job, bit the bullet & changed it....About a year later the flex plate cracked again.....This time I did some homework.....I learned that there was either too much thrust from the crank shaft, or the front pump on the transmission......After some determination the crankshaft was shimmed & the flex plate replaced.....about another year later....cracked flex plate again.....this time the XJ was retired.....The point that is hardly ever considered is how did the flex plate crack in the first place???

 

UPDATE: I got started tearing into it tonight and got a better look at the flexplate in my garage, definitely cracked so nothing to do now but crank through it.

yeah marauder i'm fairly certain the cause is the gap between the trans and engine, this bolt (driver side) is completely loose causing a gap between the two, putting a ton of extra stress on the plate.


starter teeth look OK, no obvious signs of contact or fresh metal but more fun finds! the top bolt that mounts the starter was completely missing...stay tuned to find out what i find missing next!

also got eyes on the starter side of the flexplate teeth, they look relatively normal as well.

 

Great news on your finds, that gap would certainly cause a stress situation.....Now you have an answer why the flex plate cracked....and the fun begins....Good Luck with your project....

 

Be aware the starter uses one metric bolt and one SAE bolt.
I used to have a diagram but I can't find it now.

 

Gotcha, yeah thanks for the heads up. I'll have to do some more digging around to figure out what the right replacement is, I think I saw a diagram in one of the flexplate replacement threads but there's so many...haha.

Somewhat related but I may replace my trans cooler lines while im in there, the lines have been leaking for a while and now seems as good a time as any to get em done. Are there any recommendations of replacements to get or avoid? I haven't had any issues with Rockauto parts so far and was thinking that, assuming they have them

 

update here, cracked all the way around. I got the new one on and am in the process of bolting it all back together. Thanks to all on this forum for all the posts and feedback from vets. (from a newbie perspective I know it might be annoying to see the same question pop up all the time but I personally pull a little tidbit from each post and it's worth rereading 90% of the time). I'll post some of my lessons learned once i get it back together and know i didn't mess anything up XD

 

Be aware of this:
https://www.cherokeeforum.com/showth...7&goto=newpost

 

yep, I measured my OEM right at 1", I couldn't get a super clean measurement on the new once since I read about this after I had everything bolted up but I also got the ATP plate. My crude measurement through the starter window came out at right around 1" though. Plus no grinding or rubbing when everything is tightened down, everything is nice and smooth.

HOWEVER, I got everything all hooked up and double triple checked all my connectors, sensors, etc and on first start up it sputtered and ran like absolute crap...
my first thought was after almost a week sitting, fuel drained from the rail and it just needed a prime so I primed it a few times and tried again.

it seemed to run 'better' but only barely, it will run for a few seconds with what sounds like a very consistent sounding miss, maybe only 1 dead hole, and then after a few seconds it will fall on its face and any throttle or attempt to save it will not help. I didn't get it to completely stall, but never smooth running.

one thing to note is it popped a p1391, interm CKP or CMP and after being cleared this came back pending again on the next cycle. Something to note here about the crank sensor, it was running fine with only the top mounting bolt since I got it, I took this opportunity to finally reinstall the bottom sensor mount bolt, this seems counter intuitive but could this change have caused issues?

the smooth-ish running for a few seconds makes me hopeful that nothing with the flexplate or trans is messed up but could it just be the removal and all that finally killed the Crank sensor? Any help is greatly appreciated!

I'll be doing some more digging tomorrow but I've had enough for tonight...

 

After some more reading around, the first obvious step will be a wiring check and connector cleanup to make sure i'm getting good contact.

I'm also planning to pull the starter back off and take a peek at the flex plate to see if 1) anything is grinding or showing signs of fresh wear and 2) to try and count teeth and window spacing based on the concerns about ATP's manufacturing from keyXJ (https://www.cherokeeforum.com/f2/pro...-noise-269417/).

IF I get to the point of replacing the CPS (i have no idea on the history of this one or if it is even OEM), where is a good spot to get an OEM replacement? A lot of threads i read are pretty dated and i've struggled a lot lately to find mopar replacements for other things. I did find 56027866AC on eBay, genuine MOPAR, but my parts manual calls for 56027866AB, is AC backwards compatible?

 

I disassembled and cleaned all grounds, shoutout to CCKen for the writeup with images on ground locations. None of these looked terrible but was good to do regardless and didn't fix the issue unfortunately. I took a closer look at the CPS connector and everything seemed in good shape, no obvious damage or bent pins. Threw some dielectric grease on it and hooked it back up. I tried backprobing with a safety pin but I couldn't get a 5V power out of any of the 3 wires when keyed on (reference to battery negative terminal). Is this an issue/should I try again? this method has worked for me on other sensors. If i should be getting 5V on one of the pins i'll give it another go and try to get a better connection. A lot of the CPS troubleshooting threads are scattered and somewhat inconsistent.

I ordered a 56027866AC crank sensor off of eBay, genuine MOPAR, with hopes that it will help but will continue troubleshooting while i wait for this in the mail. Gonna pull the starter off today and take a peek in there.

 

Update: I unplugged the injectors to get it to crank and make sure the noise I am hearing is from irregular combustion and not from something mechanically out of whack. With no fuel, it cranks over fine and sounds normal, which is a huge relief, even if only a partial relief.

After some more reading I am seeing some stuff related to gauges acting up with relation to CPS failure. Some things i've noticed recently but chalked up to a cleaning needed in the cluster: speedo has dropped out on occasion in combo with the airbag light coming on (a swift tap on the dash woke it back up) Once in the week leading up to the flexplate swap I noticed my fuel gauge was dead, stopped to throw a few gallons in it and after firing back up it read fine. Definitely looking more and more like the CPS.

 

New crank sensor installed, MOPAR 56027866AC, and IT LIVES!!! Runs nice and smooth and starts up great. $180 at the stealership for it but they are the only ones in the state that have it and I was itching to be done, and to get out this weekend so it is what it is.

 

To put a bow on this and close it out, I took it out this weekend and put about 100 miles on it, so far so good. Some things i picked up on that I didn't find thread surfing initially, hopefully this helps the next person out:

NOTE: my replacement was the ATP Z337 from Rockauto, this worked for me but others recently have noted tolerance issues (see https://www.cherokeeforum.com/f2/pro...-noise-269417/ and https://www.cherokeeforum.com/f2/fle...arting-266340/ )

-This fix is not as intimidating as it sounds, be careful and have some common sense but if you're comfortable with what you're reading and have a safe trans jack, you can do it. This job significantly increased my level of confidence in what i'm capable of fixing on this rig.
- I did this in the garage, front wheels on ramps, in Park, with the rear wheels chocked and the E brake on. (4.5" lift on my rig also helped a lot with maneuverability and breathing room to work) I supported the engine with a small jack while i removed the trans.
-It would be helpful to separate the exhaust just downstream of the cat, but not required. I didn't have the tools/means to disassemble and re assemble everything so I chose to drop the whole exhaust from each hanger and wiggle it around to get the room i needed. I was wrestling with my arms and legs under it at times but it can be done.
-If you can unbolt the exhaust bracket from the trans, that would also help, I couldn't get these bolts loose. QTY 2, 18 or 19mm i believe
-an impact driver got the flexplate to engine bolts out no problem, i only had a ~16" breaker bar but i couldn't get them loose by hand without yanking the engine around too much.
-Get the trans jack as close to the cross member as you can, this would help with the angle and make it easier to bolt back up to the engine.
-when bolting back up, I put the 2 (16? 18? mm) bolts in first that join engine and bellhousing. the biggest beefy ones out on the sides, i can't remember what size. i drew these tight to draw the engine and trans together and then lowered the whole assembly back down to gain access to the E12 bolts up top.
-USE LOCTITE! Can't stress this enough. The previous owner didn't and that's what got me in this mess to start with
- spin everything over by hand once you get it all bolted back up, should sound nice and smooth, no rubbing or grinding.
-also noting that 56027866AC crank sensor worked for my 98 (parts manual calls for AB OEM part, I wasn't sure if the suffix was a dealbreaker but it connects up fine)
-TAKE NOTES, and stay organized. I ziploc and label all of my bolts so I remember which are which. this will help also, a lot comes apart so good to review and make sure you didn't miss a connector or breather or bolt.

Feel free to PM me if you have any questions, this forum and threads helped me a ton so I'm happy to pass on what I can to the next person.