smtippin

Hey all, I've got an 89 MJ with a rinky dink little motor in it and have a donor yj (don't recall the year) that is sporting the Inline 6. It had some rear end damage so all the motor, tranny, transfer case, and front axle are in great condition. Can I swap the heart from the JY and slap it into the MJ? What issues will I run into?

Thanks,
s

mocXI

depends which motor, YJ's came with the 4.2 inline for a while, and then 4.0 so depends on year.

5-90

1975-up 6-258 engines were "wide deck" - and would also accept the 6-242 cylinder head.

However, the 258 wasn't equal to the 242 in terms of performance.

I do believe that the XJ/MJ and YJ share common engine mounting setups - it's the ZJ that differs. So, it probably will swap.

The YJ got the 258ci through MY1990, then it got the 242ci with Chrysler OBD-I fuel injection and engine management (the 6-258 through 1990 was considered "pre-OBD" and sucked fuel through a 2V carburettor.)

The 258 should net you something of a performance boost over the 4-150ci engine (also AMC,) but not enough to crow about overall. However, you should pick up low-end torque - which is what you want anyhow (the AMC six was known for having 80% or better of peak torque available off-idle to 5000rpm!) If it's a 1991-up, you'll have to move the electronics over to accommodate the 242ci six.

Either way, I'd want the whole donor vehicle handy while working on the swap, so you have any parts you might suddenly find you need...