1987 Cherokee Renix 4.0 - rough Idle/misfire

So as u know I am no expert and could be completely wrong, but if a lifter was bad, would it depress all the way? Causing the valve to stay closed? Or stay closed longer than it should? And a sticky lifter would be stuck open meaning the rocker would be pushing the valve open more than it should be open? I feel like the ladder is what is going on. If u look at the back of the rocker while the engine is running you can see the highest point of the stroke on the other rocker is where the rocker in question is resting... So could the lifter be stuck? Not compressing at it should? Or is that not how it works?

I have read where people can use wd 40 or matter motor oil to poor it down the pushrod hole and work the lifter back to life, am I thinking of something else? Any experience with something like that?
 
The way the rocker is moving and the noise you have indicated a collapsed lifter. A few causes for that. Blocked oil passage so your not getting the oil pressure to the lifter to keep it "pumped" up. It could be stuck in the collapsed position. It could not be sealing in its cavity so the oil pressure is ineffective.
 
You could try and run a quart of marvel mystery oil in with the engine oil. I hope some one else can chime in and give you some options or ideas.
 
The lifters purpose is to keep the valve lash down. It's unlikely to affect how it runs, but it may cause increase wear on the rocker arm and pushrod.

i'd probably put some marvel in it, drive it for a a hundred miles and see if the lifter tick/failure goes away. you might get lucky.

FWIW I've driven a 4.0 for a long time with a low speed lifter tick. So as long as it's running well I'd probably just leave it be and live with the noise.
 
Well, sorry I have been MIA for a few days, but I decided to take a break of a couple days from working on the Jeep. I did some additional testing and found that it could really only be the spring, or the lifter... I tested the spring pressure the old school way, i got up in the engin bay and pushed down as hard as I could and the intake valve spring just barely compressed, and the same exact thing happened on the exhaust spring. I know that is a terrible test, but I was looking for big differences which clearly were not present. With that being said, it certainly had enough spring strength to where it should run decent enough so I am leaning more toward the lifter being an issue.

Since the rocker arm seems to be sticking the valve open, I would have to assume that the lifter is stuck open. I am not an expert, but to me it makes sense. If the lifter was collapsed, I would be more of an issue of the exhaust valve not opening enough and maybe backfiring through the intake?

Either way... it doesn't matter. I decided to tighten all of the rockers to the spec torque and put the valve cover back on. I basically figured that the next step is going to be removing the head so that I can replace the lifters and while I was at it, i was going to order a re manufactured head to throw in there just because, why not... I am already in there.

After putting the valve cover back on... I knew that I lost probably a good quart of oil, onto the engine block and the cement under the truck (that was fun to clean up), so I needed to add a quart. I figured... hell... i think it is time to try the Mystery Motor Oil here becuase if it is a stuck lifter, or an intermittently stuck lifter, maybe this stuff will sit in there and break up whatever is causing the sticking. I drove the sputtering jeep up to the AutoZone, everytime i hit a stop sign or light, the car was shaking due to the miss... I grabbed a quart of MMO and threw it in.

I then started it up and decided I wanted to circulate the MMO and get the engine nice and hot for a while, I drove to a small mountain by my house and drove up and down it for about 40 minutes, making sure my RPMs were getting high enough to make the engine work. I started to feel the engine get full power under acceleration and when I stopped at lights and stop signs, all of a sudden, the misfire was a little bit less frequent, maybe the engine was shaking and making that misfire noise every 5 seconds instead of every 2 seconds... I though, heck, we may be onto something here...

I drove for a while and the engine stayed the same, sputtering every 5 seconds or so, but it was getting late so I went home and parked her. Definitely an improvement, but still misfiring.

Yesterday, I got home from work and it was dark and a bit chilly. It was maybe 55 degrees so basically the engine was as cold as it had been since i got it. The MMO soaked in there all night and I told myself I was going to start this thing up and drive it everyday for a week and I would see if any additional improvement was made.

I started the jeep up and the idle was perfect. Not missing a beat, not even a single misfire or shake, purred like a kitten... I thought to myself not to get excited, because it was probably due to the cold start and wanted to let it warm up to operating temperature to see if it would develop a slight misfire like always. 15 minutes later she is up to temp and still not a single misfire. I revved it up and still no misfire. Now i was a bit excited... so I jumped in the jeep and took her for a good 15 minute spin, pushing the engine, getting the RPMs up from time to time and still... no misfire. Idle is right around 850RPM and ZERO shake at idle. No pause before revving, no misfire, just 100% perfect. I simply could not believe it!

Needless to say, I have been hurt before :) so I am not getting my hopes up completely yet... but it has NEVER run so good, even for a span of 10 seconds before. Yesterday it ran absolutely perfect for 40 minutes or so.

I do think i may need to adjust the Transmission side of the TPS as it does seem to shift a bit early... the Power Trans light isn't working so maybe a fuse needs to be replaced there too. I want to change the oil next week after letting this MMO run in there for another hundred miles or so and then put in fresh oil with another quart of MMO for another couple hundred miles and reassess. I need to double check all fluids and go through the engine bay to ensure everything is zipped up tight.

I will keep you all posted on this! If anyone has any questions at all about my process or what i had done to get this thing to where it is now, let me know. Fingers crossed, I am hoping I get home tonight, start it up and get the same results!

Once again, thank you all! And thank you Cruiser54 for the work you put into helping others with your RENIX maintenance steps, I will use those for years to come.
 
Thanks for reading that book in the post above by the way... wow that was long! I just really wanted to be thorough as every detail could mean something to someone. I will be back soon with more updates.
 
Haha, I am very happy! But just trying to keep my excitement in check... seems too good to be true... usually things that are too good to be true, ARE! hahaha. But yea man, excellent call on that Mystery Motor Oil! I think I am going to make that stuff a part of my oil change, all the time. I will just use half a quart or so rather than the whole thing as a substitution... wow...
 
Here is the latest update. So i was not wrong to hold my emotion in check... haha. The thing starts and runs absolutely perfectly, drives perfectly no engine misfire or shaking, but all of a sudden, typically when the engine gets hot, the misfire comes back a little bit. I don't think it is as serious as it used to be, it seems to be more intermittent and few and far between, but I am going to give it some more time and keep you all posted. The video is below so you can see how it is... crazy difference, seriously.

https://youtu.be/VTUv6TL3ywI
 
My Question is... How hard is to the pull the head? If I seriously just wanted to get at the lifters and replace them, I don't want to change the CAM which I know isn't the best way to do it, but it should work just fine, is there a way that I can unbolt the intake/exhaust manifold and let it sit there while I lift the head out? Or do I need to completely disconnect everything and remove the entire intake manifold to get the head out to replace the lifters? Just wondering if anyone has experience on that. Thanks guys.
 
if you have a cherry picker you can pull the head with the manifolds attached. Or at least some friends to come over and help you lift it out. It's heavy and awkward with the manifolds attached, but it's easier to get them off while it's on the bench.

Otherwise you unbolt the manifolds and lay them to the side if you don't want to disconnect everything.
pulling the head isn't a big deal if you've got a torque wrench to put it back on with.
Obviously you'll be doing the head gasket job, so get that stuff. The book will tell you not to reuse the bolts, but I have without issue.
be prepared to break an exhaust manifold stud/bolt and to deal with the resulting extraction. sometimes you get lucky, but probably not.
don't forget to put sealant on the one that goes into the water jacket, can't remember which one it is.
 
I agree and if he had a real mechanical lifter failure MMO would not have fixed it so dramatically.

The lifter is not the droid he is looking for, or in other words, pulling the head is a waste of money. Just run the engine in park at 4000 rpm every start up for 60 seconds, keep the MMO-Oil changes up and drive it is my answer.

Part of my problem was loose valve guides and bad valve seals and loose rockers that slide sideways on the valve stems. Bought myself some time with better spark plugs, NGK, and new valve seals which is a snap to do, no need to pull the head. I just lined the rockers back up (they are easy to bend).

87manche said:
The lifters purpose is to keep the valve lash down. It's unlikely to affect how it runs, but it may cause increase wear on the rocker arm and pushrod.

i'd probably put some marvel in it, drive it for a a hundred miles and see if the lifter tick/failure goes away. you might get lucky.

FWIW I've driven a 4.0 for a long time with a low speed lifter tick. So as long as it's running well I'd probably just leave it be and live with the noise.
Click to expand...
 
My MJ is having a low idle where it almost wants to stall sometimes so I feel your pain. MPG is ok considering 33s and stock gears, but I cant figure it out either. I have done so much and no luck. Ill keep trying though.
 
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