Rough Running After Motor Swap

[carnuck]

My son swapped an HO 2.5 with 30K on it into a Renix MPFI '89 MJ. For some reason it backfires when revved and shakes. It ran perfect before the swap but the old motor ran about the same as this one does now. Flywheel and everything external are off the old motor. No manifold leaks. Sensors test within spec. At a loss because of the flu and I'm not there to help.

[onlyinajeep726]

Did you make sure the MAP sensor is getting proper vacuum?  That was my issue when I fired up my engine after a swap.
 

Also, Renix 2.5's are TBI, not MPFI, so I'm a little confused when you say '89 Renix MPFI 2.5L...
 

[cruiser54]

Dizzy is in wrong.

[Megadan]

I second the Distributor idea.  Check the timing.

[Jeep Driver]

My son swapped an HO 2.5 with 30K on it into a Renix MPFI '89 MJ. For some reason it backfires when revved and shakes. It ran perfect before the swap but the old motor ran about the same as this one does now. Flywheel and everything external are off the old motor. No manifold leaks. Sensors test within spec. At a loss because of the flu and I'm not there to help.

 

 

Is it Renix now?

[JeepcoMJ]

Swapped entire distributor as well as indexed?

[cruiser54]

Too many variables here. And, room for error as far as parts used in the swap. Seems it's the dizzy being installed wrong in 99% of these swaps. Carnuck, you need to go to the kid's place and exercise your expert assistance. 

 

Pretend he's a guy posting on here asking for advice. Give him some. 

[HOrnbrod]

It ran perfect before the swap but the old motor ran about the same as this one does now.

 

It's something external - most likely a bad dizzy. Stick a timing light on it and see if the light is steady on the marks. 

[carnuck]

I'm hoping to get to it this weekend. We had a "Wizard of Oz" moment this past week. 75 mph gusts that lifted our car port and turned it into a sail, lifting one side of our home sunday night (right as the end credits for Walking Dead were rolling). Luckily it dropped back into place but our roof and one wall was damaged as well as cold air blowing from the furnace vents with nothing running.

   It's a Renix MPFI 4 cyl (It's also in Canada) which has 4 separate injectors #53003956 like the 4.0L has. Turned out the TPS was buggered up. A new one for 4.0L and it was rolling again. It has the AW4 behind it.

[JeepcoMJ]

Renix didn't have. MPFI...it was tbi.

[onlyinajeep726]

I agree with JeepcoMJ... Unless you have something rare that no one here has heard of.  Can you get some good pictures of the engine in question?  I'd really like to see what it is.