OBDII fuel module to OBDI harness
 

Hi All,

I am racking my brain with this problem/mod, but getting frustrated. I am attempting to install a poly fuel tank from a '97 donor XJ (4.0) into my son's '90 XJ (4.0). The '97 is OBDII. I have looked, and looked, and looked online for a pinout of the '97 fuel module plug. All I can verify is that black is ground! Can anyone help me? The '97 fuel module has 4 wires.

Thanks very much.

edit- here are a couple pics. They are the same with different background/lighting. I hope you can see them well enough. I *THINK* orange is pump power, black is ground, but I don't know what to do with the other two wires.

From a little research on google I have found that the fuel pump is grounded through the tank. Because the new tank is plastic, I believe the extra wire is a ground wire.

One will be 12V, one will be 5V, and one will be for the fuel gauge. Honestly, I can not tell you which is which because I was unable to find a definitive answer. Best I can say is take a volt meter and with the key on, measure each pin on the stock plug. This will tell you which is 12V, 5V, and the one without any supplied voltage should be the one for the gauge. As for the new plug, I would probably try to do the same thing if you have a 97+ to check with.

All the information above is from searching google. I can not verify that it is all completely correct but it sounds right. Hope this helps somewhat

Thanks Adam. The '97 is a salvage car and no way to test for voltage in that system.

I can't find anything definitive either. Not a good sign if you are unable!!

OBDII plug...
I think orange is 12V
I think black is ground
one is gauge
one is fuel pressure(?)

Would the fuel pressure be 5V?

I believe the 5v is sent for the fuel gauge. The float to my understanding is a potentiometer and if the computer knows 5v was sent and 4v came back, that then corilates with the floats position this giving the computer the fuel level in the tank.

I stared at the wiring diagram in my Haynes manual for an hour. Alternated between it and the module. Couldn't figure the wire colors to save my life! Then had a revelation. You know, a sudden comprehension. Like... I get it! And I cut the OBDII plug from the wiring harness of the donor XJ, and I brought it back to the shop. Colors make more sense now!

If I put 12V to the fuel module should I hear the pump wind up?

Yes you should.

alright... either my pump is bad, or I'm not doing it right! I did not hear the pump start. I will do it again.

I have finally IDed all the wires going to the fuel module. I should have used the vehicle side of the harness, rather than the fuel module side of the harness. Here is how the wire colors transfer from the vehicle harness to the fuel module.

I have to go to work. I will post up a pic of the vehicle harness plug later.

Here is a pic of the fuel module plug cut from the harness of a '97 XJ. The wiring diagram I used was from Morris 4X4 website. Maybe this will be useful to someone someday? :dunno: