Diesel Comanche build


Hello Expedition jeepers, It's time now for my '86 Comanche to get it's own thread, can't keep hijacking my '92.

The build started unexpectedly when I found a nice rust free '86 longbed with a GM 2.8 V6 and a split crankshaft for $300, then an AX-15 came along. So I started thinking about how I'm tired of waiting for Jeep to come out with a diesel. I'll just build my own. I found a 1978 OM617 with 106k miles and everything is coming together. The adapter from Koch Enterprises is on it's way and then it's game on.

Here are some pics of what I have so far.







Automotive Artist
I'm looking forward to this thread. You do good work so this swap shouldn't end up being the typical young Jeeper hack job engine swap and us fussy old farts should be able to get something out of it. :)

I don't suppose you've been tracking your mpg with the tan MJ on fuelly.com or similar? It would be great to get some real world mpg numbers to compare between the two Jeeps with the same driver.

Dr. Marneaus

Station Wagoneer
awesome, I'll be watching though i likely wont have much to offer, knowing nothing about diesels or Comanches haha.


Reece, I haven't tracked it on any specific tracker but I'll look into it. I calculate the mpgs on my tan one every time I fill up. There's a gas station here in Libby that carries non-ethanol gas and the mpg are better. I have gotten 18.5 mpg in the tan one with combined city/highway being easy on it. And 13.5 mpg towing max load across the country. I'm hoping to get higher than 25 on the diesel.
Thanks Mbogo and Dr M. I almost bought an '86 factory diesel cherokee with the 2.1l to swap in the comanche, but I think the Mercedes will be much better. I will try to provide as much information on here as possible bc I'm hunting around threads like you wouldn't believe trying to learn about this om617.


Automotive Artist
Please share your engine build up plans once you get it sorted out. I have heard/read that he OM617 is relatively easy to build into a 200 hp / 300 tq engine while being reliable. That's in the ball park of ~4.x stroker with twice the fuel economy. It would be great to see a good builder take it on to see if it lives up to expectations.


Hey guys I'm not trying to ruin dreams here, but most of the Mercs are getting 28mpg max..most around 25mpg and those guys are doing the few performance mods as well. Now in a jeep theres pros & cons...1 being the 5speed vs auto, the few performance mods, (3" Dp, long runner intake ect ect) & possibly weight & gearing..cons would be we are like a brick in the wind lol.

As long as you kept it around 65-68mph..and can keep the rpms around 2400-2600rpms it should get 25mpg, but not much more! The plus side is you can run bio fuel...50/50 atf & diesel ect ect..you can do alot which will keep gas costs way way down, so the slight gain in mileage plus lower gas cost is where the benefit comes from! If your going to run straight diesel, it won't be a huge gain!
So please think about fuel lines & filters & such when doing this..running used motor oil, or ATF or veggie will benefit you greatly in the cost department..just plan ahead! Some people run 100% bio...I've read enough to where I would as long as precautions are taken..filters & lines!


Expedition Leader
And temps... Bio doesn't care for really cold weather and likes to gel. We can put people on other planets but can't figure how to fix that one... go figure. :( But I can't wait to see how this turns out. Do you have a link to the adapter folks?

Black Dog

Makin' Beer.
And temps... Bio doesn't care for really cold weather and likes to gel. We can put people on other planets but can't figure how to fix that one... go figure. :( But I can't wait to see how this turns out. Do you have a link to the adapter folks?

We put robots on mars and heaters in biodiesel tanks, maybe when people actually step foot on mars they'll have a monkey touch the monolith moment and figure out how to not make oils gel at cooler temperatures. While they're at it they might accidentally come up with a way to prevent water from freezing too.


Automotive Artist
Factory VM engined Cherokee diesels got ~28 mpg (Imp. gal.). That's with a semi-modern diesel installed to production specifications.

I don't see why a warmed over OM617 built with an eye to torque and efficiency can't get within a few mpg of the same. Taking a holistic approach to Jeep building works wonders to efficiency.

Gaucho, decided on gearing? Done the maths?

I'd be inclined to leave factory-ish 3.55 gears and work with the completed truck before deciding whether gears are required. Your early rig might even have higher gears like 3.07s or so. Run 'em initially I say. Diesels don't like to spin at high RPMs.

FWIW, my Jeep consistently got 22-24 mpg when it was stock (4.0/AW4). Now that it is built I get 16-17 (18-19 with the Starcraft in tow - ******?!). If I could get 25 mpg built that would be fantabulous.



The MJ has 4.10 gears stock, I want to put 31" tires on it, either a BFG AT or Goodyear MT/R. I think the 31's and 4.10's will work best with the OM617, from what I've read the OM617 has a similar powerband to the 4.0, just not as powerful. My 4.0 has 32" Rubi tires and 4.10's and I really like the combination. If I can get 25 mpg on 31's I'll be more than happy. Now I don't plan on making any huge gains in power with this motor, I'm gonna keep it stock at first. Then add the long runner intake, an intercooler, and crank up the fuel a bit. And neither am I going to make it as detailed as my '92 yet bc I just don't have the money right now. I may make my own long arms for it, flatbed, and a behind the cab stainless snorkel like the isuzu NPR trucks have. My point is this truck will be built on a tight budget, and most everything made at home.


Pulled the 2.8/AX-5/NP207


The '86 speedo is cable driven, I wonder how i could adapt the '98 t-case to cable speedo
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Automotive Artist
IIRC the 91 (92?) YJ used a t-case sender that was both electric and mechanical. It fits in the later transfer cases - maybe. I may be muddling things but Spidey-sense says it might work for your setup.

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