YJ fuel pump used in cell fuel delivery issues

first things first...

I put a fuel cell in my 88 MJ, and i used a YJ square style fuel pump assembly. In order for it to fit inside the new cell, i had to modify the pump assembly and shorten it because it was too long.

Next, i went to hook up the two OEM fuel pump wires running to the rear end... and the wires arent delivering power to the fuel pump. The YJ pump works, i tested it by holding the wires to a battery after installation.

What would cause the two OEM pump wires to not be getting juice? The relay? The ceremic resistor on the fender? What else should i check?

Also, does the early 90s YJ fuel pump move fluid at the same pressure as a Renix fuel pump?

I really need to get this figured out.

You should get power to the pump wires for a few seconds as soon as you turn the key to run, the ECU does this just to prime the fuel rail. Then you get fuel again while the engine is cranking over, power to the fuel pump comes directly from the starter relay and bypasses the ballast resistor. Then the ECU closes the fuel pump relay as soon as it gets a good pulse from the CPS and you get fuel pump power through the ballast resistor (typically a couple of volts less than battery voltage).

You can unhook the starter solenoid wire from the starter relay and turn the key to start and you should be getting power to the pump as long as you hold the key on start.

You can also jump the orange wire with the black stripe at the start relay directly to a power source, like the main power lug on the starter relay. But this can be risky if you have a short somewhere you may melt something.

Best to test it with a volt meter or a trouble light before trying it for real.

Making sure you have a good ground is always advisable. Assuming the ground is good without ohm testing is a crap shoot.

I have no idea what the pump pressure of your pump is. Hopefully it is near the recommended OEM pressure, the ECU has no way of knowing what the fuel pressure is and assumes it is within specs when making fuel management decisions.

Should be a three wire connector, orange (sometimes purple) is fuel pump power, tan is for the fuel gauge sending unit, black is ground. You may want to research and double check the colors, I'm old as dirt and have occasional brain farts. There was a recent thread on power to the fuel pump, try search, there is even a schematic in that thread.http://naxja.org/forum/showthread.php?t=1100748&highlight=fuel+pump

Up through 1993 the YJ with a 4.0 used the same pump as the XJ with a 4.0; 1994+ it is a different pump rated at a higher PSI HOWEVER the fuel pressure regulator on the rail might/should be able to handle that problem.

ok thanks guys. Anybody else wanna chime in?

barillms said:

ok thanks guys. Anybody else wanna chime in?

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Moving your thread to the MOD forum.