87MJTIM

On the Renix, ANY ground is a critical ground.

I did the swap a couple years ago to an AX15 with an external slave cylinder. I left the PP from the BA10 in place. It just didn't feel right when shifting. I researched part number change for manual trans Jeeps on RockAuto. The LUK clutch kits changed when the Jeeps switched from internal to external slaves, not just the change from the BA10 to an internal slave AX15. Searching the individual components, besides the slave cyl/throughout bearing changing to a separate throughout bearing, the clutch disk remained the same for all years MJ/XJs through 2001. The pressure plate changed when the slave cyl switched from internal to external. This why I recommend changing the PP when you switch trans with an external slave. That background given, I don't think the PP is your problem. I think the problem is electrical. You state it only happens when you release the clutch. That suggests that the clutch pedal is contacting an open wire under the dash. Get under the dash with a light and depress the clutch. See if it contacts or moves some wires.

Try squeezing the lower hose (when it's cool). If it is mushy, you should replace it. While it's running, open the throttle and see what the hose does at higher RPMs.

My first thoughts. The water pump may be pulling enough to collapse the lower hose. How old are the hoses?

I was asked more than once "when will you/why didn't you turn it in for 'cash-for-clunkers'."

I can one-up that. While in an auto parts store, a guy ask me about my truck. He finished the conversation with "my grandfather had one."

I used EvapoRust in a rusty 4.0. The PO parked it with water in the block. I let sit a day or two, then drained, and rinsed it. It cleaned up the internals nicely. I then ran distilled water and vinegar for a few days while letting the engine idle. I didn't drive it with that in it, just idled.

I have a few full cluster from XJs. I am just up the road in New Market!

Could it be a T4 from a CJ? It would bolt up to a 4.0.

Was that a factory option or dealer installed?

An example of government in action or government inaction

I don’t need Easter to watch it. I just need a day that ends with Y.

sounds like someone did some "deep water" driving with it.

Would those bellhousing bolt up to a 4.0?

There are no bell housings for a BA10 to go external. Your options are to keep swapping slave cylinders or swap transmissions. Ask me how I know.

I think I've watched them three or four times, especially the rebuild portions.

A youtube presenter has a tear-apart and rebuild of an AX15 I followed this to open up an AX15. There is also Robinsonautomotive on youtube where he breaks down and rebuilds an AX15. This one is a little slower and the lighting is not as good.

A guy on youtube has several videos on tearing apart and rebuilding an AX15. I watched all these before I took apart one.

I have not tried a 12 point. Previously when I removed those bolts I throw them away and get hex head bolts

E20 is the type and size (or E12) I don’t remember

No offense intended. Most fuel senders advertised on the internet will not fit the MJ. Most are XJ senders. The sellers don't know that the two vehicles are different. Also, as mentioned, the Renix and HO senders operate on different ohm scales and in reverse direction.

Does the 2.5 have an IAC? I had the same problem with my 4.0 in my CJ. It would start up but died once I let off the gas. I took the old IAC out and cleaned it (ended up replacing it). It runs fine afterwards. (Mine is a 93 4.0 HO. )

ditto

If you haven't done so already, download the 88 electrical service manual. Search the DIY section. The efan wiring is the same for 87 and 88. I think for all Renix years. There is an entire page on the efan wiring.