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Part Interchangeability Between a 1990 4.2 and 1991 4.0

Swaping 258 to 4.0, 4.0 parts to 258 etc!
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Sailboy42
I think I'll order a "tab"
I think I'll order a "tab"
Posts: 45
Joined: July 31st, 2020, 2:45 pm
Vehicle Year: 1990
Vehicle Make: Jeep
Vehicle Model: YJ

Part Interchangeability Between a 1990 4.2 and 1991 4.0

Post by Sailboy42 » December 28th, 2020, 11:35 am

I am currently buying parts for my 4.0 stroker build. I would like to know what parts I can take from the 4.2 YJ and use for the 4.0 build
Info on Jeep:
Mopar EFI conversion kit installed
BeCool Rad
-electric fan
- HV alternator
-premier power welder
-ARB air compressor

The rest of the engine bay is stock, from my knowledge.
A big question I have is if the conversion kit wiring harness will work on 4.0
Examples of Info I want to know:
- sensors
-dizzy
- oil pan
-valve cover
-etc

brief info on stroker build:
-4.0 rods
-crank from 4.2
-custom piston
-custom cam
-24lb accel injectors

I don't know the state of a lot of the parts on the 4.0. I so I want to use as much of what I have.

Sailboy42
I think I'll order a "tab"
I think I'll order a "tab"
Posts: 45
Joined: July 31st, 2020, 2:45 pm
Vehicle Year: 1990
Vehicle Make: Jeep
Vehicle Model: YJ

Re: Part Interchangeability Between a 1990 4.2 and 1991 4.0

Post by Sailboy42 » December 31st, 2020, 8:21 pm

Determined the distributors for the 4.2 and 4.0 are dimensional the same. So as long as you have the proper electronics for that kind of dizzy, you're good to go.

Learned headers are not compatible.

You can put a 4.0 intake on a 4.2 but not a 4.2 intake on a 4.0.

Most of the MPI kit items are taken from a late model YJ. This means a lot of the components I have can be reused. Sensor and such. However still not 100% that the harness itself will completely work.

Trying to figure out now about the accessories brackets. I plan on buying a new water pump. However, what about the other items. PS, alt, compressor, plus brackets.

Sailboy42
I think I'll order a "tab"
I think I'll order a "tab"
Posts: 45
Joined: July 31st, 2020, 2:45 pm
Vehicle Year: 1990
Vehicle Make: Jeep
Vehicle Model: YJ

Re: Part Interchangeability Between a 1990 4.2 and 1991 4.0

Post by Sailboy42 » January 11th, 2021, 7:35 am

So far the senor connectors seem to be the same. The modules on the throttle body appear different but have the same connectors. I am also worried about the tunning of the ECM.

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