Well, its all about the entire intake, exhaust, fuel injectors, sensors, distributor, and also, do you have a v-belt? If so, that is different than the serpentine belt. These things have to be switched from your engine, onto the newer 97 block. The bare 2.5 block is basically the same, and will work, but there may be other small things to address such as these things as sensors etc from your old engine.

 

I did that swap.

The main difference is that the early 2.5L YJ motors were a throttle body injected. The TJ 2.5's are Multi-port fuel injected, therefore requiring a different psi coming from the fuel pump.

I went from a '90 TBI to a '97 MPFI. Ended up being a fairly extensive swap because I had to use an external fuel pump as the fuel delivery system on a 97+ requires more psi and needed to keep all of the O2 sensors in order for the computer to run right. As an aside, my '87 YJ has no 'check engine' light and any code the computer may throw has to be diagnosed by an OBD II scanner.

I'll take some pics this afternoon of the swap and post them up.

 

Got ya. Good info hub. So no yj 4 bangers had mpfi? What pump did you end up going with? Theoretically, couldnt you just use a tj pump?

I'd greatly appreciate some pictures!

 

Got ya. Good info hub. So no yj 4 bangers had mpfi? What pump did you end up going with? Theoretically, couldnt you just use a tj pump?

I'd greatly appreciate some pictures!

I guess you could use a TJ pump. Mine is inline and outside of the fuel tank. I mounted it on the crossmember in front of the tank. I used a Hesco pump.

Iirc, the TJ pump would not fit into the tank. . . .

 

i have a 94 2.5 mpfi. i think 91 was the first year for mpfi

 

I was under that impression, as well. Glad I'm not the only who thought that.

From an 87, if you wish to convert to mpfi, I can see how it would be more complex. I think he already has mpfi on his 91, and he may as well switch over the intake from his old engine. Guess I am trying to figure out why this swap should not be pretty easy if he just changes over the entire intake, exaust manifold, distrubutor, sensors, etc, onto the new block. (unless you are dead set on using all the intake/sensors, etc from the 97..)

No, I'm not dead set on using anything - I just want to get it up and going. It's just going to take a lot of pictures, labeling of harness wires, sensors, etc., and try to find a home for everything.

I did this swap in mine before I did the 4.0 swap.

The engine itself is a direct swap if you use all the accessories, manifolds, etc off your 91. The only thing I ran into was the temp sensor in the 91 is in the head. The 97 head will not have a hole or boss for it. I just drilled and tapped a 1/8" pipe hole in the thermostat housing and extended the wire for the senso to the front of the engine.

Good to know, I'll look for that - thanks!

Alright so I just wanted to make sure this was what I'm looking to do - I'm going to go grab the motor in the next few days, and start on it next weekend

Any more hiccups I might be expecting would be appreciated

 

From an 87, if you wish to convert to mpfi, I can see how it would be more complex. I think he already has mpfi on his 91, and he may as well switch over the intake from his old engine. Guess I am trying to figure out why this swap should not be pretty easy if he just changes over the entire intake, exaust manifold, distrubutor, sensors, etc, onto the new block. (unless you are dead set on using all the intake/sensors, etc from the 97..)

 

I did this swap in mine before I did the 4.0 swap.

The engine itself is a direct swap if you use all the accessories, manifolds, etc off your 91. The only thing I ran into was the temp sensor in the 91 is in the head. The 97 head will not have a hole or boss for it. I just drilled and tapped a 1/8" pipe hole in the thermostat housing and extended the wire for the senso to the front of the engine.

 

Double post

 

So I pulled the motor out of the 97 last week, and am going to pull mine out of my 91 tomorrow and throw in the 97. I've got the entire motor, tranny, and accessories from the 97 2.5L. However, I didn't get the ECU. I'm hoping it's going to swap over - hah I guess that we'll see tomorrow. Everything from the 97 motor looks about the same as my old motor.

Any tips, more advice before I finally delve into this? Odds are this'll get pretty picture heavy tomorrow WHEN I run into problems

 

Anyone?

 

Other than what I told you already....direct swap! :cheers2:

Get R done and go wheelin'!

 

So a few hang-ups...

1) Right side motor mount was completely seperated from the bracket - sheared off. Basically, just the weight of the engine was holding it in place! I took it to a local 4x4 shop on the island that I frequent, and they welded up a piece of 1/4" thick metal for me to patch it up. $45 and probably saved me a month of shipping time (I live on Oahu) - real nice guys.

2) I was originally planning on using the 97's 5-speed. However, on 93+, the hydraulic clutch line is in a completely different location than 93 and before. Therefore, I decided to just mate my original tranny, which is in great condition still, to the new motor. I'll keep the 97's 5-speed in my garage as a back-up

I'm just going to use all my old accessories, and, once again, keep all the new stuff for back-ups for when my older ones wear out. Kind of a nice feeling to have a back-up for everything in my engine bay...

I did have a question for you guys:

The 97's motor had power steering, so I may swap that over at another time. I went ahead and put the bracket on for it - only because it bolts on with the motor mounts brackets, and I didn't feel like pulling the motor off again if I wanted to convert it down the line.

Yes, I took a bunch of pics - I'll post them later today

 

Oh, and as of right now (Sunday AM), old motor's out, new motor's in, re-connecting everything! Whoo!

 

Got my attention here. Getting the engine in is of course the major part, that's done, good deal.

 

Great work Jedi!

Note new engine has a new belt and routing.

I just ordered the brackets and P/S pump last week to do the 2000+ intake swap on the 4.0. After I had everything installed, I was looking for some bolts upstairs and found the leftover TJ 4 cylinder P/S pump, brackets, and bolts.Doh! I had all the parts needed all along as they are the same.:cheers2:

 

I'm having a little bit of a hard time finding a serpentine for a 97 2.5L that has no power steering or a/c. The one I just put in originally had power steering, but I took it off because my 91 doesn't have the steering box for it, and I don't find it a necessity right now.

The only one I found is on Quadratec and I don't feel like waiting for shipping! Was no p/s, no a/c rare on TJ's? I'm assuming so!

 

Napa 25-060775 is what is shown on my Prolink site.

I guess it will depend on what brackets and accessories you used. Did you use everything minus the P/S pump off the 97?

 

Ahhh yeah good find, I don't know why I couldn't find that before! Yeah it's just a normal 97 2.5L with no p/s no a/c. I still haven't gotten used to searching for 97 stuff when it comes to the motor.

I swear my camera transfer cord loves hiding from me. I'll put em up tomorrow I promise.

 

Alright, got a lot more button'ed up. I'm an every-saturday-for-a-few-hours-while-my-wife-watches-the-kids mechanic, so I apologize for the slow progress! I've taken tons of pics, but am yet to find my transfer cord, so those'll have to wait for now.

Also started stripping the tub out because the guy who had the YJ before me laid down rhino-liner without cleaning or taking up the paint, so it started rusting underneath and bubbling up. I started out with wire wheel/grinder, then saw the light and moved to chemical stripper! My buddy enlightened me to some aircraft-stripper-type chemical they use to take paint off of concrete and wood, and it eats right through the herculiner. Let that sit in the sun for 5 minutes, and it just peels off with a scraper.

But to the motor! Here's a little list of what I used from which year motor...

97
---

Block
Alternator
Distributor, wires
Fan shroud
Radiator

91
---

ECU - all sensors
Tranny
Tensioner pulley
Exhaust manifold
Intake manifold
Motor mounts (had to re-build one, just welded a new 1/4" plate to the bottom, was rusted and sheared off)
Fuel rail - injectors, etc.
Intake/airbox


Had it all tacked up minus cooling system and just wanted to try and crank it - wouldn't even try to crank. Started motor was clickin away at it, but no action from the motor. I honestly wasn't expecting it to crank up first time - that'd be too easy!

I'll try to get some more time on it tonight - if not, it'll continue next Friday/Saturday! And I'll continue my search for camera wire...

 

Hey to anyone who's done a swap like this - how'd the crankshaft position sensor cross over? Any problems? I can't get it to start yet, and that's the next problem I'll be tackling.

 

Sensor goes in the trans bell housing, so I just reused my old one that was already in it.

 

There's a sensor directly in front of the distributor cap that's different from the 97 2.5L to the 91 2.5L. The 97's block has a two prong female end, but the 91's block has a one prong male end. Additionally, I'm using my 91's computer, so I need to switch them out so it'll mate up with my harness, right?

 

Okay so I just figured out that it's the oil pressure sending unit. I should just be able to throw in my old YJ one into the TJ block, correct? We're trouble-shooting because it won't turn over and I'm hoping that this is the cause.

 

Yep, just swap.

I was sitting here trying to figure out what was in front of the dist cap. The oil sender is to the rear of the dist.

 

Would that keep it from starting?

 

Awesome. Successfully broke the actual sensor from the threaded nut that holds it into the block. whoo hoooo.