Fuel Pump Question

[thbertson]

I have a 89 MJ 4.0 that I have stripped down the cab to the shell. I am replacing almost everything in and on it with the parts from a 95 XJ 4.0 donor. I am getting ready to drop the drive train in and I want to get my fuel system worked out first.

From looking at Autozone I see that the 92 MJ 4.0 and 89 MJ 4.0 use the same fuel pump since the 92 is a HO motor my original fuel pump from the 89 should work for the 95 motor. I should just be able to change the fuel lines or splice them in from the filter on.

I am not too sure about the fuel gauge sending unit from the 89 working with the 95 gauge cluster.

I was wondering what I need to do to get everything working correctly.

I have not removed either one of the fuel tanks yet.

Can I just swap the tanks? Or will the pump and sending unit from the 95 XJ fit in the 89 MJ tank. I know that the locking rings are the same.

Even if I have to go with a 92 pump and sending unit it will only set me back $102.

 

Any suggestions or ideas of what will work?

[mvusse]

XJ tank will not fit in an MJ. XJ sending unit will not fit in a stock MJ tank, but may fit in an after market tank without a pan. Renix sending unit will hook up to a a HO cluster, but full will read somewhere near empty (but not exactly) and empty will read somewhere near full (but again, not exactly).

 

Besides what the AZ site says, I'm not sure the Renix and HO use the same pump, but I don't see why your old pump would not work as the pressure and volume should be about the same.

[thbertson]

Thanks. I will check and see if I can change the ohm setting on the Comanche sending unit. I might be able to switch the wires on the XJ unit if there are two of them. If not I may be able to combine the XJ and MJ unit. Who knows maybe the 92 unit from AZ will work with XJ gauges.

[utah_redneck]

Your old stock fuel pump will work just fine. The fuel pressure output is going to be the same. If you are upgrading the motor to an H.O. the differences are the head (valve size), exh./int. ports are larger on the H.O., throttle body size, fuel injectors are larger. Because this stuff is bigger it really means more EFFIECENCY and some power increase. If I were doing an H.O. upgrade just do the head assembly, int./exh. manifolds, and all the stuff that goes on the int. manifold...i.e. throttle body, injectors, fuel rail, just to be certain it all matches up. But to also verify that just cross reference the "old" gaskets to the "new" gaskets from your current Jeep to the donor. Hope this helps.

[mvusse]

Thanks. I will check and see if I can change the ohm setting on the Comanche sending unit. I might be able to switch the wires on the XJ unit if there are two of them. If not I may be able to combine the XJ and MJ unit. Who knows maybe the 92 unit from AZ will work with XJ gauges.

 

No parts store sells Comanche sending units. They think they do, but they are Cherokee ones, which DO NOT INTERCHANGE, even though the parts stores think they do. The Cherokee one is mirror image from the Comanche one. If you have an after market tank without the pan inside, a Cherokee one MIGHT fit, but in a stock tank the pan inside the tank is in the way.

 

The problem with the gauges is not Comanche versus Cherokee. It is Renix electronics versus Chrysler (HO) ones.

[thbertson]

Thanks Utah. I am installing the whole drivetrain and harness from the XJ. The MJ was setting for years and I didn't even attempt to get it running.

[thbertson]

Thanks mvusse for the heads up on the pump/sending unit. I may need a tank also. Too bad the 95 XJ one won't work in the MJ. At first glance I do not think you can switch fuel level gauge in the cluster. Kind of strange that they reversed the ohm settings once they stopped using Renix equipment. I found an article that stated the the early Renix era was 1 ohm empty and 88 ohms full. And the Chrysler era induction is 88 ohms empty and 1 ohm full. I am sure they changed them again in 96 once the went to OBD2.

[mjeff87]

I'm running an HO pump assembly in my 87, it works fine. I just have to remember that "F" on the gauge means close to empty, and "1/4" is actually full.

 

Jeff

[thbertson]

Did you get the pump assembly after market?

[HOrnbrod]

Thanks mvusse for the heads up on the pump/sending unit. I may need a tank also. Too bad the 95 XJ one won't work in the MJ. At first glance I do not think you can switch fuel level gauge in the cluster. Kind of strange that they reversed the ohm settings once they stopped using Renix equipment. I found an article that stated the the early Renix era was 1 ohm empty and 88 ohms full. And the Chrysler era induction is 88 ohms empty and 1 ohm full. I am sure they changed them again in 96 once the went to OBD2.

 

You can reverse the polarity of the Renix sender removing it from the tank, disconnecting the wire that connects to the end of the winding of the float potentiometer and resoldering on to the other end of the winding. Then your HO fuel gauge will indicate in the right direction. :cheers:

 

http://www.comancheclub.com/forums/viewtopic.php?f=2&t=15936&p=163162&hilit=polarity+fuel#p163162

[cody4359]

["utah_redneck"]Your old stock fuel pump will work just fine. The fuel pressure output is going to be the same. If you are upgrading the motor to an H.O. the differences are the head (valve size), exh./int. ports are larger on the H.O., throttle body size, fuel injectors are larger. Because this stuff is bigger it really means more EFFIECENCY and some power increase.

95 and 96 4.0 pumps have the same specs which are not the same as as the 4.0 mj, but some what close

 

I'm slowly in the middle of swapping in a 96 xj 4.0 into my previously 2.5 89 mj. according to autozone website the spec for the fuel pumps are:

89 4.0 mj/4.0 96 xj

max free flow (GPH) 45/55

max pres range (PSI) 110/100

min free flow (GPH) 45/40

min pres range (PSI) 90/70

 

i have my xj pump mocked up in the mj sending unit bracket, it fits differently but will work if need be. now the 2.5 and the 4.0 MJ pumps have the same shape desing and would require no mods to fit the bracket.

 

my question is does anybody know if the differences in pumps are big enough to affect performance/reliability or should i just run the with the xj pump and make it work?

 

sorry. had the number lined up in the msg but when it post's it moves them over