engine swap question

I have an 88 xj (4.0 L) with a bad cylinder that I need to replace the engine on. I can get a 91 xj 4.0 (the whole jeep ) for nothing (it was wrecked). What is the difference in the engines between the 88 & the 91 ? What all would I need to steal from the 91 to make the engine work in the 88 ?

Im far from an expert but I bet if you took out all the electronics, intake, throttle body, exhaust, it should fit. What tranny? At least it's not gonna cost you anything! I would just take everything and then worry about it later.

There are some significant differences.

Control system electronics were change for the 1991 model year, from RENIX to ChryCo. The "best" way to do the swap is to change everything from the firewall forward at least - taking it off the donor vehicle and moving it over. However, you probably didn't want to hear that...

Second best? The knock sensor was deleted for 1991, but the cast boss should still be in place. Measure the threads on the RENIX knock sensor, and drill and tap a blind hole in the same place. Keep the RENIX head, intake, and exhaust manifolds, and bolt it onto the 1991 block. This will allow you to easily keep the RENIX sensor - especially the TPS, and especially if you have an automatic (which also gets a signal from the TPS, and has a separate control system.) The heads will swap easily - the differences are mainly internal, not including the change to the manifold mounts (you can make them work, but it takes WORK.)

Apart from that, and the control electronics, there are no significant differences between the RENIX and 1991 ChryCo blocks - so you should have no trouble adapting the new engine to work with the current electronics.

If you have anything left from the donor, I'd like to talk to you about electronics and wiring after you're done - I'm working on a RENIX simulator, and I've just had a flash to make it compatible with OBI-I/II - or just figure out how to adapt everything once and for all...

5-90

Yeah, after searching here and other forums, I think I will pull the head off of my dead 88 4.0 and see what it looks like. If it is good, I will just put it on the 91 block, and drill and tap the hole for the knock sensor. Since it is my wife's dd, and she wants to get another vehicle later this year, I aint about to go crazy with it, just the cheapest and easiest. It's either that, or get a junk yard motor for 300 bucks and drop it in without having to do anything else.
Are the head gaskets the same from 88 and 91 on the 4.0's ? I know my 86 to 92 4 banger gaskets were different, although I dont know why, since I kept my rebuilt 86 head and put it on a 92 block
What about oil pumps ?
Should I steal the distributor from my 88 and put it on the 91 ?
Accessory brackets the same ?
I assume I need the flex plate from the 88 to work the cps ?
Basically just keep the 91 block and put all the 88 stuff on it?

I don't recall, but I think the differences between the two gaskets are minor. You can probably use the HO gasket with the HO block and the RENIX head. Besides, the Fel-Pro 9076PT-1 I've got (measuring for a torque plate project) is listed as working for 1987-2001...

Yes, take your distributor off. The later distributor, as I recall, won't work with the earlier electronics (you could probably get away with OBD-I/OBD-II swapping, but most of the RENIX stuff won't get along with ChryCo.)

Oil pumps? If you run a priming rod down the distributor hole and you note good oil pressure, it's not even worth dropping the pan unless you've got a leak. I think the oil pumps were also the same all the way up - but I don't have those notes handy.

Accessory brackets are, also, probably the same - but if you take the RENIX head and put it on the HO block, you've eliminated that problem anyhow.

Did I miss anything?

5-90

Well, I am gonna see about getting the donor 91 tomorrow and doing a compression check and pulling the head off of it, and then pulling the head from my 88 to see what shape it is in. If all is well with the block from the 91 and the head from the 88, I will do it that way, if not, I will just pick up a junk yard motor for 300 and either sell the 91 for parts or keep it to steal parts from for my 86 & 88 xj's
I was just talking to the guy who owns it, and he said I can have it if I want, I just need to talk to the guy who towed it, to pay him for the towing. He even told me the title was laying on the seat, and that it ran good, just had high mileage, and the transfer case was bad, didnt want to work in 4 high, but I figure 4 wheels with tires alone is worth the towing bill.

My wife's 88 xj - here goes.
Was running like crap, decided to change plugs, cap, rotor, wires etc. since was overdue for them - still running like crap. pulled plug wires as engine was running to see if bad cylinder - #4 no difference, ran crappy, all others , difference ran crappier - zero compression on #4 cylinder, didnt bother doing the rest, as I knew there was a major problem, blew air into #4 cylinder (dont knopw if it was at tdc or not), air came out dipstick tube and oil cap, so figured bad piston, or rings were gone. Can watch oil press gage go way up, as when the piston goes to compress, the compressed air/fuel mixture goes into the crankcase. No water in the oil, but it does burn a lot of oil at the present time. Am I wrong in figuring bad piston, or could it be something as simple as a head gasket ? Any way to check,without pulling the head?

sounds like you're right about something majorbeing wrong, i would guess piston or rings, not head gasket, but i dont know that much to say really. i swapped a 91 ho engine into my 90 xj. auto in both got the rolled 91 for 300. the 90 had been overheated repeatedly and didnt like to keep coolant in it anymore, so i assumed head was bad. swapped all the renix sensors off the 90 engine to the 91, knock sensor hole was already there, and threaded i think, needed cleaning out. had to swap some acc. brackets, and the flexplate. i had the whole donor xj so i had the tranny cables and everything i needed. its explained fairly well at cherokee america's site

http://www.off-road.com/jeep/cherokee/99/09_sept/engswap/engswap.html

i also used the 91's cooling system, rad. and overflow, since my old tank was cracked and i liked the open system better. went fairly well. had some trouble getting the tps figured out, but it works now

Yea don't mess with swapping the wires, I used all the renix electronics, and it works fine. Just gotta swap ALL the sensors. Mine was a 87/93 but it's the same deal. YES, you need the old flexplate, it won't run without it (I installed the motor with the 93 flexplate and had to pull the motor again to swap it after a week of head-scratching - OOPS)

Although people say it works fine with the old intake, I chose to do a little more work to use the newer intake/throttle body/injectors, the newer design is better and the TB is a lot bigger - so it will give you a little more "balls". The only extra work involved in this is mating the fuel lines, and adapting the old throttle sensor to work with the new TB, there's several ways to do this, and it becomes obvious when you look at it.

Here's a link to some pics of my TPS adaptor, if you're interested, I did ugly work but it works flawlessly.

I decided to just get an engine from the junk yard, 300 bucks, being delivered tomorrow, already out of the xj, Costs a little more, but I wont have to worry about swapping my head (which I am unsure of the condition now) or any sensors, or drilling and tapping holes, or adapting tps or ?? and it will be plug and play. I plan on getting rid of this xj in a few months anyway, wife wants something different, and I just swapped the engine in mine about 2 months ago, and switched heads, and stole from one to put on the other, and just dont feel like going thru the extra work with this one, since it will be gone shortly. Just fixin it to drive for a little while, till taxes come back, and can put cash and this jeep down on something else.
I will pull the head after it is out, just to see if it was the rings or a hole in the piston