Swap XJ 2.8 into 2.5 MJ?

[lil_loco]

I blew out my speedometer gear on my 86's NP207 and after waiting 2 weeks for the part i got a nice memo from the supplier that it was backordered indefinately... gee thanks. In the meantime I have been searching for a compatible auto transmission (TF-904/909) to replace my AX-4...today I found both in a perfectly priced 86 XJ running a 2.8l V6.

 

Since the 86 MJ is running 2.5l and can't keep up with the other cars in the slow lane on the roads I use and won't like the weight I am going to toss on it with mods and the need to tow (reinforcing frame is going to be done), I was planning on going to a larger engine or something with tons of power and I read that HT 3.4 is a bolt in replacement for the 2.8l V6... which is quite interesting and will save me tons of money as well as open the door to much bigger options.

 

But now the real question is how hard is it to swap the 2.8 from the XJ into my MJ?

[JeepcoMJ]

I blew out my speedometer gear on my 86's NP207 and after waiting 2 weeks for the part i got a nice memo from the supplier that it was backordered indefinately... gee thanks. In the meantime I have been searching for a compatible auto transmission (TF-904/909) to replace my AX-4...today I found both in a perfectly priced 86 XJ running a 2.8l V6.

 

Since the 86 MJ is running 2.5l and can't keep up with the other cars in the slow lane on the roads I use and won't like the weight I am going to toss on it with mods and the need to tow (reinforcing frame is going to be done), I was planning on going to a larger engine or something with tons of power and I read that HT 3.4 is a bolt in replacement for the 2.8l V6... which is quite interesting and will save me tons of money as well as open the door to much bigger options.

 

But now the real question is how hard is it to swap the 2.8 from the XJ into my MJ?

 

DON'T do it, DON'T even consider it.

 

the 2.8 has less power than the 2.5, and is even more of a dog.

 

you'd be wasting your time on that swap, it's a completely worthless idea...if you want a nice upgrade, get a 3.4 right off the bat

[lil_loco]

but is it still bolt-on with the 2.5?

[Pete M]

The trans might be, but the exhaust, electronics, and everything else associated with the engine is not. The 2.5L and it's fuel injection are better than the 2.8L by far. Is the 2.5 better than a carbed 3.4L? I don't know. If you've got a 4speed manual trans, than you're really being hurt by the crappy 3.55 gear ratio. that is the biggest cause of your truck's sucky performance. I would recommend focusing on getting axles with 4.10s in them rather than an engine swap. :thumbsup:

[JeepcoMJ]

but is it still bolt-on with the 2.5?

 

somewhat-kindof-ish

 

you'd still have to do a complete wiring swap, you'd need to swap to the auto, you'd need to swap fuel lines, remove the MJ sending unit and find a 2.8 MJ sending unit, then swap the engine bay accessories to the 2.8 ones, and you'd have to splice tail lights.

 

I will not ever give you advice to do this swap...all of my advice is against it.

 

get an auto transmission with a 60 degree gm bellhousing that's 4wd, then go get a camaro or firebird 3.4 liter v6 and drop the camaro motor into your jeep. take the un-necessary parts out of the camaro wiring (headlight wiring, abs wiring, etc.) and piggy-back it to your current harness. this will give you multi-port fuel injection

 

then you just need a 4.0 MJ sending unit for the gas tank, automatic brake pedals, and transmission shifter for the auto.

 

the 2.5 oil pressure and coolant temp. sending units will pretty much bolt on to the 3.4 , so you won't even have to swap out gauges. this leaves little to no interior work to be done.

 

I recommend spending your $$$ on a camaro or firebird 3.4 complete with engine wiring (and dash if you can get it), then stripping the wiring harness of all unnecessary electronics, then getting a VATS bypass module made by Bakerelectronix so that you won't need to run with the coded gm key in your ignition. the entire swap will only cost you a thousand bucks, if that, and you will net around 145 hp with 17 to 22 mpg, and a great towing capacity.

[lil_loco]

Hypothetically.... If I were to keep my 2.5l (which only has 10k or so - reman) would swapping to auto transmission alone (3spd) make a noticeable difference? or do I also need to find 4.10s (a rare find around here, rarer than a 3.55/3.07 D44 rear)?

 

If that is the case then I can save $$$ as I wait until the weather is friendlier or to pay someone to do my swap and find decent 3.4 MFI engine...hmmmm

 

get an auto transmission with a 60 degree gm bellhousing that's 4wd, then go get a camaro or firebird 3.4 liter v6 and drop the camaro motor into your jeep. take the un-necessary parts out of the camaro wiring (headlight wiring, abs wiring, etc.) and piggy-back it to your current harness. this will give you multi-port fuel injection

 

then you just need a 4.0 MJ sending unit for the gas tank, automatic brake pedals, and transmission shifter for the auto.

 

the 2.5 oil pressure and coolant temp. sending units will pretty much bolt on to the 3.4 , so you won't even have to swap out gauges. this leaves little to no interior work to be done.

 

I have the whole running 86 XJ (4x4 Auto 2.8, unknown axles but tow-package) coming my way anyhow since it cost the same as the NP207 part I need to replace on my MJ. How do I know if the Torqueflight 904/909 auto tranny (GM) is 60 degree? I just know it is what is used in place of my AX-4 on either engine (2.5 or 2.8 ) and the shifter and peddles will match since they are both 86s.

 

so the 3.4 would bolt on to the rest so long as my TF-904/909 is a 60 degree? Is there any machining or spacers or such that need to be used? I know some engines match angles but use a different bolt pattern...

 

Are 4.0MJ fuel sending units available at NAPA or such places? 4.0 MJs are not easy finds around here, let alone any MJs that people are willing to part with or not stripped and rotten to death...

 

 

I recommend spending your $$$ on a camaro or firebird 3.4 complete with engine wiring (and dash if you can get it), then stripping the wiring harness of all unnecessary electronics, then getting a VATS bypass module made by Bakerelectronix so that you won't need to run with the coded gm key in your ignition. the entire swap will only cost you a thousand bucks, if that, and you will net around 145 hp with 17 to 22 mpg, and a great towing capacity.

 

so with the :Canadaflag: exchange rate I am looking at almost 3k eh? LOL ;)

 

 

Are there any good write ups for first timers about this 2.5 straight to 3.4 swap (i like pictures)? Particular the wiring thing?

[JeepcoMJ]

first.

 

wiring, that's easy...I have all of the diagrams, or can get them from alldata.

 

second.

swapping to auto will make it worse. it will become even more of a dog than it is, you lose a gear, and your gas mileage will likely decrease. you'll want to swap to 4.56's with that combo most likely.

 

third.

the transmission in the xj will bolt right up to the 4 cylinder, and to a 2.8, since they both use 60 degree gm bellhousings.

you may have to re-drill the flexplate to get the torque converter to match up, and you'll probably have to get a different TV drop-down cable for the transmission.

 

fourth.

yes, the pedals and shifters are interchangeable between the vehicles.

 

fifth.

you'll be able to find an MJ 4.0 sender from someone on the club here, if you can't at a parts store.

 

 

as far as write-ups, I don't know of anyone who has opted to upgrade the 2.5 to a 3.4...the 2.5 is generally just fine for a DD, and does well off-road too. the 2.8 is what is usually upgraded because of how bad it sucks.

 

it would be fundamentally the same swap though. just do yourself a favour and make sure you keep the camaro F.I....don't put a 2.8 carb and such on it, that's worthless and is half of the 2.8's problem anyways. the other half is that it's just a $#!&ty motor to begin with.

[lil_loco]

too bad I can't drive standard to save my life... so I have to swap out the AX-4 to auto before I hurt it anyhow. Is there a better auto option then that would be happy to work with both the 2.5 and the short future engine upgrade? I think most of my bogging problem is that I can't find good shifting points and I am too scared to hurt the transmission.

 

Going 4.56 will cost me 2k alone in regearing :(

 

 

So to clarify: redrilling the flexplate for t-converters is for the swap to the 3.4 or just the transmission swap? TV drop-down cable same deal?

 

Never fear... I plan on staying far away from carbs unless we are dealing with my Ninja, my initial plan was to get a crate FI or modify it to take on FI.

[JeepcoMJ]

too bad I can't drive standard to save my life... so I have to swap out the AX-4 to auto before I hurt it anyhow. Is there a better auto option then that would be happy to work with both the 2.5 and the short future engine upgrade? I think most of my bogging problem is that I can't find good shifting points and I am too scared to hurt the transmission.

 

I'm no expert on auto transmissions so, idk :dunno:. I'd suggest finding someone to help teach you to drive standard a little better...it is very hard to get at first

 

Going 4.56 will cost me 2k alone in regearing :(

 

not necessarily. find a local 4x4 club to help with the install, gears won't run more than $600 USD

 

So to clarify: redrilling the flexplate for t-converters is for the swap to the 3.4 or just the transmission swap? TV drop-down cable same deal?

 

for either swap, it may be necessary...idk if it will be or not, that's something you will discover when you get to that point. be aware though, that if you put the 2.8 flexplate on the 3.4, you need to have a machine shop neutrally balance the flexplate. so, try and get a 3.4 from an auto camaro/firebird to keep costs even lower

 

Never fear... I plan on staying far away from carbs unless we are dealing with my Ninja, my initial plan was to get a crate FI or modify it to take on FI.

 

good plan

 

[Eagle]

But now the real question is how hard is it to swap the 2.8 from the XJ into my MJ?

It's not impossible -- it will be a bolt-in swap, but you'll be changing all the underhood wiring, and you'll have to find a gas tank that's set up to work with the V6 mechanical fuel pump.

 

The big things is, the 2.8L won't get out of its own way any faster than the 2.5L. Personally, I'd prefer the 2.5L over the V6 any day. The 2.8L V6 was badly under-powered in the Chevy S10, and it was badly underpowered in the Jeep Comanche. If you look at the actual torque and horsepower ratings, you'll be doing a LOT of work for effectively zero gain.

[Pete M]

I stand by my statement that gearing is the problem and gearing is the solution. If you've got bigger than stock tires you will want to do that regardless of what engine you have. 3.07 and 3.55 ratios should never have been offered in Jeeps. :(

 

But if you're dead set on swapping drivetrains, go buy a 4.0L XJ that has a good drivetrain and start swapping over everything (and I mean everything, including the hood, radiator support and radiator). You'll have more power than the 3.4 and most everything will bolt-in. And then you'll still not have enough gearing. It'll be better with the added power, but still not ideal if you've got bigger tires.

[JeepcoMJ]

I stand by my statement that gearing is the problem and gearing is the solution. If you've got bigger than stock tires you will want to do that regardless of what engine you have. 3.07 and 3.55 ratios should never have been offered in Jeeps. :(

 

But if you're dead set on swapping drivetrains, go buy a 4.0L XJ that has a good drivetrain and start swapping over everything (and I mean everything, including the hood, radiator support and radiator). You'll have more power than the 3.4 and most everything will bolt-in. And then you'll still not have enough gearing. It'll be better with the added power, but still not ideal if you've got bigger tires.

 

 

I agree with your position on gearing...to a point. the phrase "there's no replacement for displacement" does also apply, except in the case of the 2.8 liter.

 

as for the 4.0 swap, don't forget that the 86 models use a completely different radiator support, all the way to the inner fenders, a different front crossmember, and a different hood. that would all have to be swapped...and that's fab work to do it (not easy either if you don't know what you're doing with a spot weld drill bit)

[lil_loco]

ya I am not feeling the love for the 4.0l, kinda want to keep the All Makes Combined ratio on my 86 and stick to something GM under the hood and NOT lose my front-end in the process. Also not liking how the 4.0l sucks my wallet dry in the XJ I use a DD... I confess I have a heavy foot on the gas and average 130kmph.

 

I have now heard equally bad and good things about the 2.8l. I do see a lot of tub jeeps hosting a 2.5l running 35s on stock gearing and not having trouble breaking 100 (kmph)??

 

Other engine options other than the 3.4 MFI that will max towing and not drink my wallet dry? Of course I don't want to modify the body whatsoever (rad swapping and mounts are unavoidable).

 

Would the fuel sender from the XJ tank work for any of the swaps suggested? Id like to us as many parts from this donor Jeep as possible since scrap prices are le crap right now.

 

I need a better engine... the 2.5 needs a rebuild but I can't lose my truck for too long.

 

cheers!

[Kenosha Warrior]

I was hoping you'd swing over this way, listen to these guys. They know their stuff. :clapping:

[Pete M]

Also not liking how the 4.0l sucks my wallet dry in the XJ I use a DD... I confess I have a heavy foot on the gas and average 130kmph.

That's kinda harsh man. Flying a brick down the freeway at top speed and then complaining it sucks too much gas? :(

 

I do see a lot of tub jeeps hosting a 2.5l running 35s on stock gearing and not having trouble breaking 100 (kmph)??

Those Jeeps are likely running 4.10s. You've likely got 3.55s. That's a huge difference.

[Car RamRod]

ya I am not feeling the love for the 4.0l, kinda want to keep the All Makes Combined ratio on my 86 and stick to something GM under the hood and NOT lose my front-end in the process. Also not liking how the 4.0l sucks my wallet dry in the XJ I use a DD... I confess I have a heavy foot on the gas and average 130kmph.

 

I can't not post here, due to past experience.

 

Completely wash the 2.8l idea from your head. It's a complete boat anchor of an engine, that's wieghed down even worse with extensive emissions work. Something HAD to be done, I couldn't keep up with traffic on hills, and it sucked gas horrendously.

 

I was all set to start collecting up parts for a 3.4 swap, when I found an 87 with a 4.0/5speed for $300. The engine was shot, but the trans was mint, so I went for it (also had a black interior :brows: ). I spent somewhere in the upper hundred for a reman 4.0, and besides that it was just a good deal of time that it took to swap everything over.

 

Having driven the truck almost a year, I have absolutely ZERO regrets with the path I took. It's got plenty of power and on the highway I get well over 20mpg. I've even done so well as 24.5 a few times, and 25 on one road trip.

 

So if you can find a good donor vehicle, that's a great swap. If not, I've heard good things about a 3.4 swap as well. Just stay away from the 2.8.

[lil_loco]

ok so a 4.0 out of an 89 MJ will do the trick? what if it is 2wd?

I just located one that has a D44 3.07 and black interior and he wants 400$ cdn...

[Kenosha Warrior]

ok so a 4.0 out of an 89 MJ will do the trick? what if it is 2wd?

I just located one that has a D44 3.07 and black interior and he wants 400$ cdn...

 

 

Yeah, that'll work. If you're taking the trans too, just find an AW-4/NP231 out of an XJ or something like that and stick it in. Driveshaft mods ARE going to be nessesary.

 

But before you pull the trigger on that deal, check your Jeepkings PM plz.

[Pete M]

And a word of warning. 3.07 gears suck, even with a 4.0 in front of them. But the Dana 44 is a good place to invest your money and that price sounds good if everything you need is in decent shape. Be prepared that you will have to swap over just about everything so make sure everything is in order.

 

If it were me, I'd probably keep looking for an XJ donor that already has the engine/trans/t-case you're looking for (all-wheel-drive is out there if you find one with a 242 t-case). It'll make for a much smoother swap (there are some wiring differences between 4.0/stick and 4.0/autos).

[lil_loco]

Yeah, that'll work. If you're taking the trans too, just find an AW-4/NP231 out of an XJ or something like that and stick it in. Driveshaft mods ARE going to be nessesary.

 

Id be taking the whole truck... It is on the road....

 

so clarification:

to go 4.0l while keeping as true to the Comanche as possible and using my 86 as base, guess ill lose the GM percentage but still NEVER DO EMISSIONS AGAIN!! I would need a front end/hood off another Comanche that originally had 4.0l so I don't have to mess with modifying the firewall as well as the wiring and senders so...

 

Using the 86 as a base:

Id put the 89 front end and engine into the 86, put the 89 wiring and senders into the 86, have some fun and toss the 89 interior into the 86 (yay! no tan and a decent wiring harness for stereo), maybe the doors too, but for the 4wd what part of the drive train needs what? I have a NP242 from a 91XJ lying around needing a home (I prefer the ft-4wd anyhow) so that out of the way then I can toss in an AW-4 as bolt-on? or do I still need mods? Can't I keep my current drive shaft from the 86?

 

I also have a D44 3.55 lying around so I could sell that 3.07 to someone who wants to regear. This route, if I am not overlooking anything would be easier for me to do and all I would need is an auto transmission which I was planning to buy anyhow.... right?

[JeepcoMJ]

correct.

 

but it's not actually the front clip (the grille) that needs to be swapped.

 

it's the part underneath, which supports the radiator and goes from between the fenders all the way across, and the front crossmember.

 

these are not bolt-on parts, so you will have to do some fabrication.

[JeepcoMJ]

and why not just convert the 89 over to 4wd, and either keep the 86, or sell it?

[lil_loco]

Here anything 1988 or newer needs regular emissions testing and I like to avoid those like the plague... Also the 86 is already plated and insured and if I go to an 89 insurance jumps significantly. :shake:

 

I worry that I might end up not wanting to kill the 89 although the body is a bit banged up towards the back... the 86 was supposed to be a donor as well but then I found the engine was re manufactured with only had 10,000kms on it, the interior was next to perfect and the truck was more solid than my 88. :wall: I am not allowed to harbor any more Jeeps they are already being scattered all over the province.

 

so the whole front end can't just be swapped without fabrication? I mean everything from firewall forward, fenders, hood, front, the whole deal? and then I keep my chrome front clip? Is it a hard job to do?

 

... gotta brush up on my terms I guess....

[Car RamRod]

but it's not actually the front clip (the grille) that needs to be swapped.

 

it's the part underneath, which supports the radiator and goes from between the fenders all the way across, and the front crossmember.

 

these are not bolt-on parts, so you will have to do some fabrication.

 

This is a good point, and 100% correct.

Mine didn't take long to do, but I also have a plasma cutter and a welder so that made life alot easier.

 

Don't let my post mislead you..... it was ALOT of work. I transfered a 4.0/5speed into a formerly carbed/auto truck, along with the full 4.0 harness and a whole interior swap. It took me roughly a month of a few nights a week and an occasional saturday. But like I said earlier, I took my time and did it right, and now I'm

[mvusse]

Also not liking how the 4.0l sucks my wallet dry in the XJ I use a DD... I confess I have a heavy foot on the gas and average 130kmph.

That's kinda harsh man. Flying a brick down the freeway at top speed and then complaining it sucks too much gas? :(

 

There's no way 130km/h (80 mph) is anywhere near top speed. I have no clue what the top speed of my MJ is (4.0/AW4 4x4), but I've had it to 85mph with lots of power left during an uphill pass. I'm guessing top end to be a bit over 100.