TBI 2.5L (MJ) replaced with 4.0L (XJ), fuel pump differences?

The only thing worrying me about putting an XJ 4.0L drivetrain in a 2.5L MJ is the gas tank. (well, rear driveshaft too, but that's no biggie)

the donor XJ is an 87, the MJ is an 87.

will the XJ sending unit fit in the MJ's tank? Do I even have to worry about it?

Haven't really started tearing into it, just want to have an idea of what I'll have to deal with before I even start.

Different?

Ryan - I don't know if they are different; but I will have a pump from a 4.0 89 MJ out in a couple of weeks (pulling tank - using fuel cell)

Don't know about the assembly fitting into the tank, but the pump itself is different. The TBI pump for the 2.5L runs lower pressure than the MPI 4.0L...another guy on this board swapped a 2.5L pump in for a 4.0L one and it did work, but he didn't full-throttle it. Don't know if you'd end up starving the injectors or not (???).
You "could" swap the 4.0 pump into the MJ's pump harness, but they are different dimensions. I tried once when my pump went bad because the parts dork gave me the wrong pump. It wasn't a direct fit, but I made it work. Ended up feeling too uncomfortable about putting it into a tank of fuel so I returned it for the correct pump.
From pulling several units from both XJ's and MJ's in the boneyard, I don't think they will swap...the MJ unit is shorter and I don't think you could get the XJ unit to seal to the tank.
I'd look for a 4.0 MJ assembly from a yard (minus the pump) and just use the pump you have from the XJ.
HTH,
Jeff

Re: Different?

rsalemi said:

Ryan - I don't know if they are different; but I will have a pump from a 4.0 89 MJ out in a couple of weeks (pulling tank - using fuel cell)

Click to expand...

if I don't get something to work... I'll let ya know