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91 4.0 in a 87 comanche


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search "H.O. conversion" using the search feature. this has been done many times.

 

I did it, fairly straight forward. but you'll need to swap all electrical, fuel sending unit, gauges, all electrical components to make it work like a H.O.

 

 

you can adapt a renix (87-90) throttle position sensor to fit on a H.O. (91+) throttle body, and put a renix distributor, fuel rail, fuel injectors, and CPS with the motor and it will run, but you'll have to do an EGR delete on it and it will no longer have a knock sensor. this may effect your check engine light, and you may not make it through emissions (if you even have to) w/o the egr.

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the motor thats in in dose nt run right when takes off it falls on it face but slowly picks up and gose normal after about 45mph so i just want to swap it for the power!!!! of the HO

 

 

that's really not a good reason. the power differences are minimal (like 5hp if that).

 

 

if you're wanting true HO, you're gonna need a complete donor vehicle.

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i have the 91 motor/ wire harness/ tranny what else would i need then?

 

 

do you have the complete engine bay AND interior harness? gauge cluster? all other little odds and ends electrical related for the inside?

 

do you have the open cooling radiator? cooling lines? vacuum harness? engine computer, all sensors on engine and trans, etc. including speedo sensor?

 

do you have the transfercase for the 91? those are different input spline (23 spline), so your old one (21 spline) won't work

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Could be fuel pressure, or flow capacity. Can't hurt to change out the filter and the sock on the pump. Sounds more like an ignition issue, though. Are you sure you're firing on all cylinders? When was the last time you changed distributor cap, rotor, wires and spark plugs?

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I would try to figure out why Your Renix Engine is Not performing before going into a engine swap...

 

The Renix 4.0L Engine is said to be 170HP and the 4.0L HO is said to be 190HP...

 

I did the HO swap in my 89 MJ and it was a HUGE seat of your pants difference when compaired to the Renix 4.0L and Both engines had roughly the same KM on them... However I did add a Few extra goodies to my HO swap...

 

By NO means do you need to change out the complete wiring harness, You Can use the HO Engine harness and Just splice it into your Body Harness and If you were to use the complete XJ Harness including the Dash/Gauges then you will have to splice into the Tail light harness or search the Junkyard for a 91-92 MJ rear Tail light harness because it will be different and I know First hand since I had to do Just that which do able but a Pain...

 

And As stated you will require a New sender which your not going to get new so that means you need to find a Junk yard sender or do as I did and buy the New XJ sender and Modify it to become and MJ sender...

 

When Doing a 4.0L engine harness swap there is only a few wires that need to be spliced in allthough it will take you longer to weed out the Wiring that you will not use then splicing in the ones you do use...

 

The wire splicing is not a very hard thing to do unless wiring scares you and if it does I would suggest Just fixing what you have now...

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