Will a 1998 jeep 4L 2.5 motor work in a 1991 jeep wrangler?

check timing

which engine, Nat.? 2.5L or 4.0L? in the XJ/MJ pickup.
1986 is the first, AMC EFI, used, in Jeeps.
this is the RENIX system (French, EFI injection)
sorry, no ASD then, not until 1991 .with real Chrysler EFI.
the ECU powers the fuel pump relay directly.
if the ECU has power, it will energize this relay, does it?


4.0L here.86-88 (same is true up to 1991)
the ASD was introduced on the 1991 Wrangler but only 4L
the XJ/MJ same year but to both engines, 2.5 and 4L
both have ASD in 1991,
The MJ Comanche Pickup is a XJ cut down at the rear. and has same unibody base.
The engine book for XJ/MJ are the same blue book.

Check out ebay and see if you can get the part there. U can also check your local junkie for a good, used working part.

If the blower works check for coolant in the cooling system. Test operation of thermostat. Check heater control valve for proper operation if equipped. Pressure test cooling system to ensure system holds pressure (this will help you identify a leak, if any. If car does not over heat and cooling system is in good working order, then the heater core is clogged.
If the blower does not work Check fuse, relay, wiring for short to ground, apply direct battery voltage to blower motor. If blower motor turns on and fuse/relay and wiring are ok replace the switch.

Go the other direction. It takes a breaker bar to move the tension arm.

check the shift motor on the axle for holes. sometimes the rust through. i've fixed holes before with dura-glass body filler. if there are know holes,remove the shift motor to check and be sure the shift fork is not broken.

4 wheel drive is vacuum activated. Check vac motor 1st as it is probably the reason for it not engaging. I had a 88 cherokee w/ bad vac motor which caused exact problem you describe.

Take it to the Jeep dealer . It's still under warranty. Won't cost you a penny. Good luck.

Check transfer case wiring, possible loose wiring/open circuit. If your other lights in dashboard work such brake light, seat belt lights, engine light than it is not a fuse. raise all for tires from the ground and engage the four wheel drive remember to have in neutral and put in gear either 4L or 4H and see if the wheels in front move.

you could have vacumm problems making it seem like the timing is off, but the other guys are right on the timing!!!! it could be throw-body problems, like crack manifold problems. This year has thhis type of problem sometime. Try spraying WD-40 around the vacuum hoses, & manifold to see if the motor changes rpm????