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2.5L engine replacement options


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Hey there. So I am trying to get my 89 rwd 2.5L engine comanche on the road. The engine I have in it is the original 2.5L, I am pretty sure its the AMC I4 with the automatic aw4 transmission.

 

I took it to a jeep dealer today to see if they could diagnose the problem but they didn't have the eqipment to do it. The mechanic I originally took it to to said it had a psi of 30 and probably needed replacing. Since I can't find someone who can tell me if I just need to re build the top end or the whole thing. It looks like I will be replacing it.

 

This isn't the same 2.5L engine that was used in other jeeps well into the 90's is it? I'm guessing that it isn't otherwise the jeep tech's should be able to analyze it. Will a newer 2.5L bolt up to my transmission? What are my options? Thanks.

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Yeah, 30 PSI is no good. Normal should be... 120-150ish, I think.

 

The experts over at Wikipedia say that the auto behind the 2.5 was a Chrysler A904, not an AW4.

 

If you read this article over at allpar, it sounds like the 2.5 was carried on for quite a while, albeit with different fuel-delivery systems. http://www.allpar.com/mopar/amc-25.html

 

The problem they may have with diagnosis is that your Jeep uses Renix electronics, which are reasonably simple to diagnose, if one is handy with a multimeter and wiring diagrams. However, if your mechanic's idea of diagnosis is plugging in a machine and replacing the part it tells him to replace, your truck will be a mystery to him.

 

Someone who's done it will chime in with the best idea for your situation, but given the number of vehicles produced with that engine, I can't imagine a rebuild would be worth it.

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This isn't the same 2.5L engine that was used in other jeeps well into the 90's is it? I'm guessing that it isn't otherwise the jeep tech's should be able to analyze it. Will a newer 2.5L bolt up to my transmission? What are my options? Thanks.

The basic engine is the same, but your '89 has throttle body injection and an ignition system from a consortium of Renault and Bendix in Europe. In 1991 Jeep switched over to using a Chrysler-engineered multi-port injection system on the 2.5L engines.

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This isn't the same 2.5L engine that was used in other jeeps well into the 90's is it? I'm guessing that it isn't otherwise the jeep tech's should be able to analyze it. Will a newer 2.5L bolt up to my transmission? What are my options? Thanks.

The basic engine is the same, but your '89 has throttle body injection and an ignition system from a consortium of Renault and Bendix in Europe. In 1991 Jeep switched over to using a Chrysler-engineered multi-port injection system on the 2.5L engines.

 

Do you happen to know if the MPI system is adjustable? I think a 2.7 stroker would be fun, but not with the TBI.

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Yeah, 30 PSI is no good. Normal should be... 120-150ish, I think.

 

The experts over at Wikipedia say that the auto behind the 2.5 was a Chrysler A904, not an AW4.

 

 

 

Someone who's done it will chime in with the best idea for your situation, but given the number of vehicles produced with that engine, I can't imagine a rebuild would be worth it.

 

I had an 87 with the 2.5/AW4 and 4.56's. It was a fairly rare bird, but they're out there.

 

I had my 2.5 rebuilt .030 over and used a set of Yella Terra roller rockers to give me a little more lift. Electric fan, cone air intake, and it goes fine. No downshifting on hills on the highway, no problems getting going at all. Biggest difference is when you try to haul something. Though recently I towed another MJ on a tow dolly straight up a gravel hill on a guy's property. First time I'd really used 4WD Lo....I felt like I had a V8 pulling up that hill!

 

OP: Don't listen to anyone who tells you the 2.5L isn't worth it. It's a damn fine engine; if you don't want to go through the extra expense and time of shoe-horning a 4.0L in, it's the easiest way to go..

 

Tom

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As far as I know, any year 2.5 SHOULD bolt in to your truck as long as you swap over the intake and all electronics. The only difference in the exhaust manifolds is the EGR port. New manifolds come with a plug for that port if you don't use if for the MPI style. The head ports and accessory bolt up should be the same between all years as there is no mention of a cylinder head redesign for the 2.5 like there was for the 4.0 when Chysler installed their system.

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