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Unread 05-01-2011, 02:55 PM   #1
Schaef81
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1990 YJ Wrangler 
 
Join Date: Mar 2010
Location: Lititz, Pennsylvania
Posts: 318
90 to 91 Engine Swap

Ok guys here's the scoop. I have a 1990 yj with the 2.5 TBI engine. Basically the engine blew and I found a 91 mpi engine for 300 bucks. Bought the 91 engine with the plan of keeping it a tbi by swapping intake/manifold and all other accessories.

Over easter weekend when I was home from school I successfully got the old engine (90) out and the new engine (91) in. The only thing I kept on the 91 engine was the flywheel which to my understanding needs to be done. Now that the engine is in and everything component is hooked up it cranks but doesn't turn over.

My hunch is that the flywheel from the 90 engine needs to replace the 91 flywheel because the cps isn't picking up the 91 flywheel because it is made for 87-90 2.5l TBI engines. Is this a wrong assumption or could it be something else? As for everything else goes we carefully marked the distributor from the 90 and replaced the 91s distributor from that of the 90 to the correct position.

Any help is appreciated since I very much want to get my jeep on the road with summer coming up.

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Unread 05-01-2011, 03:08 PM   #2
minimudder
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1987 YJ Wrangler 
 
Join Date: Mar 2008
Location: Burton, OH
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I feel for ya man. My 87 to 91 swap has been an ongoing battle for 3 years. I work a little And get mad and outta money and stop but I finally have it running. I didnt stay with tbi and I forget
Why now. But it was probably a big mistake. I have so many little gremlins it took forever to figure out. So I would suggest calling a parts store and seeing what the difference is between the two flywheels. No CPS will def not let her run. Just double check all the major things for it to run gas air spark. And after that the flywheel would be a good place to start if you have it already. Seems like a good idea. Maybe someone on here knows a way to bypass the CPS just to get spark to figure out if the CPS is the reason you aren't getting it. Sorry I just rambled on and didn't probably help
Much but best of luck to ya!

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Unread 05-10-2011, 07:46 PM   #3
Schaef81
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1990 YJ Wrangler 
 
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Location: Lititz, Pennsylvania
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Ok for all that are interested. I swapped the flywheel from the 90 and adjusted the timing and the engine fired right up. So for future references you must keep the flywheel with the fuel system you are keeping. TBI 87-90 flywheel and MPI 91-95 for the 2.5 liter. Thanks to all who have helped me. Its good to finally have the jeep on the road!
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Unread 05-10-2011, 08:59 PM   #4
MoparFreak69
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1990 YJ Wrangler 
 
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Just so you know, there isnt any sensor in the distributors of the 4 bangers, they are simply a way to direct the spark. All timing is handled by the CPS and the ignition module, turning the distributor will do nothing. Glad to hear you found the problem, I was going to suggest swapping the correct flywheel onto the motor. 2 completely different systems, TBI is old school Bendix while MPI is Chrysler. Entirely different signals between the 2 systems.
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Unread 05-10-2011, 09:03 PM   #5
Schaef81
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Quote:
Originally Posted by MoparFreak69 View Post
Just so you know, there isnt any sensor in the distributors of the 4 bangers, they are simply a way to direct the spark. All timing is handled by the CPS and the ignition module, turning the distributor will do nothing. Glad to hear you found the problem, I was going to suggest swapping the correct flywheel onto the motor. 2 completely different systems, TBI is old school Bendix while MPI is Chrysler. Entirely different signals between the 2 systems.
Yeah man, made a ton more work for myself not switching flywheels when the engine was out of the jeep. Took the most part of 2 days to get everything together along with figuring out the nippodenso alternator setup with the renix. Needless to say though I'm extremely happy with the swap.
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Unread 05-10-2011, 11:03 PM   #6
lclark2074
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1990 YJ Wrangler 
 
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Location: RI
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the extra senser that comb on a 6 banger is for injectors not for ignition
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Unread 05-07-2013, 09:10 PM   #7
shnitzle
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1988 YJ Wrangler 
 
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different flywheels

in the bottom picture the left one is from an 88 the right from a 92
photo-11.jpg   photo-22.jpg  
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