97+ fuel tank & pump/sending unit in a 96?

hot_rod_hooligans · Feb 3, 2021

Not entirely an XJ, but I'm not having much luck on the MJ side. Has anyone tried running a 97+ tank and pump in a 96? Theoretically it should work as the 96 and 97 are pretty close mechanically and emissions.

I have (most of) a 1989 2WD MJ which me and my step son are going to build as his first car, we have a 1996 XJ which we are using as a donor to make the MJ whole again. The MJ to my knowledge was parked some time in 01/02 and hasn't been driven/started since, I do not know why it was parked. The truck was missing the dog house, the engine compartment and bed were full of walnut shells, and there was a rodent nest in the glove box. It did not come with keys, and the battery is toast, so I haven't tried starting it. Rather than chase potential mechanical and electrical gremlins, I made the decision to do a full H.O. swap from a newer XJ, I let the kid decide if he wanted a 97 and newer, or 96 and older, he wanted 96 and older. I made the decision to use 96 for OBD2.

This weekend I went and picked up the donor 1996 XJ we will be using, I know most of the swap should be fairly straight forward, the exceptions being the rear brakes to delete the ride height proportioning valve, the wiring behind the seats for the lights and fuel pump, and with it being a 96, the fuel pressure regulator since the 96 has an in tank regulator. It has been a few years since I have owned an XJ, and even longer since I've dug in to anything this technical.

What are my options? Will the the 97+ fuel pump/sending unit with the 96 fuel system so I can mimic how the 97+ builds did their fuel tanks? Or will I have to use a 95 and older style regulator at the fuel rail? Will this interfere with the OBD2? I would like this be as OE fit/finish as possible.

Anak · Feb 4, 2021

Well, you have picked the most challenging year to work around...

I think it may be do-able though.

If you are trying to use a 97+ tank and pump then '96 is probably your best bet with regard to fuel lines. The '96 has no return line, and I believe the situation is the same for '97+.

I do not know how fuel pressure is regulated on a '97+, but I assume it is in the tank. Confirm that, and also confirm the 49psi fuel pressure level. I know that is what the '96 engine/ECM expect.

I think you may also be facing a challenge with the fuel gauge. Look into the ohms range for a '96 and compare that to '97+. IIRC they are different. However, there may be a fix for this. At one point it was possible to get the '96 variable resistor as a single part (this would be the piece on the fuel pump assembly which is swept by the rising/falling float for fuel level). I am aware of this part because I was looking into trying to run a Genright tank in my '96. IIRC this was going to be the biggest issue. My hope was that if I swapped the '96 variable resistor onto a '97+ pump assemble I could get the correct ohms range and make everything work correctly. I have no idea how feasible that idea actually is as I have never managed to lay my hands on all the pieces and ascertain the feasibility of the idea.

I don't have it handy, but I should be able to find the part number for the variable resistor if you cannot find that part number. What it will take to find the actual part is another matter entirely, although you could conceivably pull the one off the pump assembly that is in your donor vehicle. It seems a shame to break down one of those however. That is a one year only part, and has been hard to come by. I would take a good look at both pump assemblies and resistors and do all you can to be sure it can be swapped before tearing down the '96 unit.

hot_rod_hooligans · Feb 8, 2021

Anak said:
Well, you have picked the most challenging year to work around...

I think it may be do-able though.

If you are trying to use a 97+ tank and pump then '96 is probably your best bet with regard to fuel lines. The '96 has no return line, and I believe the situation is the same for '97+.

I do not know how fuel pressure is regulated on a '97+, but I assume it is in the tank. Confirm that, and also confirm the 49psi fuel pressure level. I know that is what the '96 engine/ECM expect.

I think you may also be facing a challenge with the fuel gauge. Look into the ohms range for a '96 and compare that to '97+. IIRC they are different. However, there may be a fix for this. At one point it was possible to get the '96 variable resistor as a single part (this would be the piece on the fuel pump assembly which is swept by the rising/falling float for fuel level). I am aware of this part because I was looking into trying to run a Genright tank in my '96. IIRC this was going to be the biggest issue. My hope was that if I swapped the '96 variable resistor onto a '97+ pump assemble I could get the correct ohms range and make everything work correctly. I have no idea how feasible that idea actually is as I have never managed to lay my hands on all the pieces and ascertain the feasibility of the idea.

I don't have it handy, but I should be able to find the part number for the variable resistor if you cannot find that part number. What it will take to find the actual part is another matter entirely, although you could conceivably pull the one off the pump assembly that is in your donor vehicle. It seems a shame to break down one of those however. That is a one year only part, and has been hard to come by. I would take a good look at both pump assemblies and resistors and do all you can to be sure it can be swapped before tearing down the '96 unit.

I think I’m going to try to retrofit the 97+ XJ pump into the MJ tank like I’ve seen a lot do, just figured asking if anyone had “upgraded” to a late model tank would be more direct

Anak · Feb 8, 2021

I see.

Issues should be the same, plus the adaptation of the tank.

For the use of a '96 fuel rail and computer you are probably on a reasonable track.

smokeyyank · Feb 8, 2021

Suggest checking comancheclub out and asking there. Crossover year is probably the worst for trying to swap anything, seriously either find a 98-99 go all in or keep the Renix.

97+ fuel tank & pump/sending unit in a 96?

hot_rod_hooligans

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Anak

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hot_rod_hooligans

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Anak

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smokeyyank

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