Swapping a 3.5 into a 94 LS Montero with 5 speed

Cosmos99

Member
Posted this on the ADD forum too but wanted to cover my bases and hope people can chime in.

I have had 3 Montero's. Gen1 2.6, My 94 LS 3.0 and a 99 Gen 2.5. I LOVE my 94 since it was a 3 owner gem with 70k miles ( all records from new ) when I bought it 3 years ago. It now has a tad over 100k and could pass for having on 40k since she is so clean. My only gripe is the anemic 3.0 12v when driving over mountain passes on the highway. I am either at 4500-5000 rpm screaming or bogging and loosing speed. My base altitude is 5300ft and I spend a considerable amount of time at 10k and above so it gets worse.

I was chatting with Josh and instead of selling her he mentioned doing a 3.5 swap and 4.90 gears. This is very appealing and I would love to have it in my narrow body 94 with a manual. After a brief search there does not seem to be much info on swapping a 3.5 into a 3.0 Monty. I am faced with selling her and getting a more powerful ( 95 or 96 SR or a 3.5 Monty all of which will not be near as clean and rust free as mine ) or adding more power. I am perfectly capable of the mechanical and fab work but I am not sure about what to do with engine management. Should I find a 3.5 Sport and swap over engine and harness and ECU? It would be an added bonus to make it an OBDII compliant swap so I could run my bluetooth diagnostic tool and run real time data. I should also mention my area is a ********** with emissions so it has to run clean.

My question to the collective of montero experts is what should we expect and look for in doing this swap? Any info or insights or even links to info would be greatly appreciated.

Thanks!

-Ed
 
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nwoods

Expedition Leader
Might get better help on this topic on the SoCal Montero group on Facebook, or the Adventure Driven Design forum. The ADD forum has more guys who've probably done it, but they are the silent type and don't share much. The Facebook group is a mix of quiet knowlable guys, a few outspoken well-meaning guys, and your normal mixed bag of deplorable like me that would love to know the answer too.

I wanted to jump from a 3.5 SOHC to a 3.8 in my 2002 3rd Gen, but was concerned about the ECU stuff. The engines are all quite similar at the block level, but on my '98 3.5 SOHC, the front end was significantly different than my 2002 3.5 SOHC. Went from 3 belts to one serpentine belt, and the accessory mounts were in similar locations, but mounted differently on a significantly different front plate/bracket. The top end seemed quite similar though, with regards to the intake manifold, but the throttle bodies where quite different.
 

Cosmos99

Member
Might get better help on this topic on the SoCal Montero group on Facebook, or the Adventure Driven Design forum. The ADD forum has more guys who've probably done it, but they are the silent type and don't share much. The Facebook group is a mix of quiet knowlable guys, a few outspoken well-meaning guys, and your normal mixed bag of deplorable like me that would love to know the answer too.

I wanted to jump from a 3.5 SOHC to a 3.8 in my 2002 3rd Gen, but was concerned about the ECU stuff. The engines are all quite similar at the block level, but on my '98 3.5 SOHC, the front end was significantly different than my 2002 3.5 SOHC. Went from 3 belts to one serpentine belt, and the accessory mounts were in similar locations, but mounted differently on a significantly different front plate/bracket. The top end seemed quite similar though, with regards to the intake manifold, but the throttle bodies where quite different.
I posted there too just to make sure. Josh from ADD and I have been chatting and we are going to try and see what is all needed.
 

Toasty

Looking for that thing i just had in my hand...
As we already discussed, you have a 12v 3.0 so your swap will be really involved. I would do 5.29's and be done, just enjoy the low milage machine and keep up on it's maintenance. If you really need power might as well swap in a more modern engine that will be supported for years to come because let's face it there are no more 6G engines being sold in the US and haven't been in a while.
 

Toasty

Looking for that thing i just had in my hand...
If you swapped an entire harness from a late er Gen 2 including gauges the 3.5 swap wouldn't be bad but that's a lot of work for more really old parts that may become damaged in the swap process. When I've done harnesses in the past i unloom the whole thing, inspect, repair and reloom. Get the tool and connecters ahead of time to make those repairs.
 

Cosmos99

Member
If you swapped an entire harness from a late er Gen 2 including gauges the 3.5 swap wouldn't be bad but that's a lot of work for more really old parts that may become damaged in the swap process. When I've done harnesses in the past i unloom the whole thing, inspect, repair and reloom. Get the tool and connecters ahead of time to make those repairs.
Yeah that's what I planned on doing. Josh got me all excited on a 3.5 and 4.90's. Might just do the 5.29's since the engine swap while not impossible is a little more involved than what I wanted.
 

IncorpoRatedX

Explorer
The suggestion I made was to look into a resto-mod, assuming working space is available, fair downtime expected and significant R&D was done prior to start; It could be a really good chance to do maintence and get upgrades. However, the cross-over data between the 6G engines is minimal, and mostly what does exist, is fragmented in the brains of everyone around. I mentioned here and the ADD forum being a good place to explore the idea, it also gave me a place to park the conversation, so I could easily return to it.

My thoughts were as follows: buy 4.90 and 3.5 equipped sport, rob the 4.90's and applicable suspension parts, refurb what can be done in advance (some montero parts would have to be reused since sport suspension isnt indentical to the full size) Then use the 94's 3.0 engine management on the sport 3.5 engine, (modification surely required, but, how much?) Back the increases displacement up by running premium fuel, piggy back that with an safc if needed. The engine would be a 16% increase in displacement, the ECU's injector duty cycle control 'should' be able to handle that after an octane reset, I would think, especially on premium.

Regarding the wiring; would not consider swapping any of that or trying to use the sport ecu, harness or whole system from the donor vehicle, that would be way too much work, especially in the dash area, wiring there turns into a nightmare of connectors, as toasty mentioned, at that point you want to strip it all back and do it right, but that would be heavily involved.

we have got the following engines on stands in the shop.
94 sohc 12v 3.0
98 sohc 24v 3.5
05 sohc 24v 3.8

Spent about 15 total minutes comparing the three, so inspection has not been that close, but the 94 and 98 look a lot alike the front accessory plate, intake manifold and electrics could transfer over.

Both use hall effect cam/crank sensors, both use waste spark ignition on 3 coils, didn't see any immediate reasons you couldnt take the donor 3.5, strip it down to long block, take the original 3.0 and swap over all the external engine parts, etc and plant that in the 94 chassis using the 94 management.

One thing to consider regarding sensors; this doesnt necessarily apply here but, there's a difference in 3.8 and 3.5 cam sensors, they use a slightly different cam position sensor and wheel, so comparison of working values and sensor types is needed in that area to ensure the 3.5 gear would work with 3.0 sensor, or maybe both can be moved over.

Basically, if the long block can't be shoved in there, this project would not be worth the effort imo. However, if 3.5/3.8 long blocks can shoehorn into LS model gen 2's easily, there's a lot of great 'bare bones' chassis' out there that would be good to build up on a budget. I myself prefer the lack of extra cladding on the LS.
 

Toasty

Looking for that thing i just had in my hand...
You have a 12v? I thought your '94 engine was a 24v, his is a 12v, he has a dizzy, one coil and the old MPI. Basically a Gen 1 engine, I've owned 4 94's one of each engine and 2 3.5 DOHC. If you have a 12v i may be interested in it.
 

IncorpoRatedX

Explorer
oops, my bad, I have a 24v, I typo'd that, had 12v 3 liters on my mind. I've got the entire harness and ECU as well. Was gonna stab it into my Gen 1 but went with the turbo diesel. It's the engine I offered to you not long ago for your Gen 1. The oil pump needs to be swapped to the dohc (got one from kevin) before it can bolt in, or an external oil filter mount to keep the oil filter off the diff. You're welcome to it if you wanna go that route. Clay's son needed the coil pack ignitor and I've taken the timing belt off and began taking the oil pump off to swap.


Has Ed confirmed he has a dizzy? My engine is also of a 94 and there is absolutely no distributor, Rock auto shows a distributor cap listed for the 3.0 all the way up to 1996, but only in 94 it actually lists a distributor. I pulled up ASA and 3 different intake/ingition set-ups are shown for the 3.0. This is what my 94 3.0 has for ignition

*Edit - Just talked to Ed, he does have a dizzy, I'd shoot this project down from a time and materials stand-point.
-Had it been a sohc 24v 3 liter, i'd push to explore this. Maybe we've got other 3 liter LS owners that will pick this little project up.

94 24v ignition.jpg

I wonder if this is one of the cases of using whatever inventory they had before shipping the stuff overseas, as things end up delayed by 6-8 months, he could technically have a built in a 93 model 94.

I wonder if removing the dizzy and replacing it with CAS and waste-spark can be done on the v6 engines as it can on the 4 cyl engines.
 
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Toasty

Looking for that thing i just had in my hand...
I had a late '94 with a 12v it came from Puerto Rico and i I've also had a late '93 with a 24v DOHC. Mitsubishi has thrown out some wild cards.
 

Swift_45a

Observer
Posted this on the ADD forum too but wanted to cover my bases and hope people can chime in.

I have had 3 Montero's. Gen1 2.6, My 94 LS 3.0 and a 99 Gen 2.5. I LOVE my 94 since it was a 3 owner gem with 70k miles ( all records from new ) when I bought it 3 years ago. It now has a tad over 100k and could pass for having on 40k since she is so clean. My only gripe is the anemic 3.0 12v when driving over mountain passes on the highway. I am either at 4500-5000 rpm screaming or bogging and loosing speed. My base altitude is 5300ft and I spend a considerable amount of time at 10k and above so it gets worse.


-Ed
Colorado?

I might be willing to part with my 96 SR ( I don't think I can keep her idle any longer and not feel incredibly guilty, I have too many cars and motorcycles as is) if she will go to such a project, she is in SoCal. She has battle scars, and crossed 200k on my last surf trip. Let me know if you want to discuss details. Everything on her is stock and solid aside from the tired and worn suspension and the dreaded valve stem seals smoke started on my way back. That way you can have everything you need to swap everything over. I miss those gears going up the hills, my 3.5 SOHC 2.5 feels puny by comparison on OEM wheels/tires!

I daily my 2.5 so I'd rather the SR get another shot at life than wait for me to finish 2-3 other projects before I can get aroudn to her. I'd be sad to see it go, but everytime I post here (that's her in my avatar) I'm reminded how I never have time to work on it.
 
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