No fuel pressure at the rail

[mike71800b]

The regulator for the fuel rail responds to changes in vacume when you change thorottle positions. I.E. it raises fuel pressure when you floor it. I don't think it would be bad.

 

[old_man]

Don't jump across the resistor, you may burn up the pump. Check the voltage across it, if it is burnt open it will have the full batery voltage b/t the terminals of the resistor. If it checks less than full voltage on its terminals then it is doing its job and there is a load on the pump end.
If you want to learn more D.C. tricks in this manner, google voltage drop in series circuits and read a while.
It's ok to jumper the relay to see if it has bad contacts or isn't being relayed on by the ecu.

Jumping across the resistor will not burn up your pump. It was a late mod to quiet down the motor. Many models did not have the resistor.

Now there is a very common problem that I didn't see addressed. There is a short hose from the pump to the mounting plate, inside the tank. They split or come loose. You will get just a trickle of gas in many cases. So I recommend you don't pull your new pump out of the box until you pull the assy out of the tank and take a look. That way you can return the costly pump. Now as to what pump to buy. I have only found two pumps to be worth the effort. If you read on here, there is a real trend that a new pump will only last a few months and then have to be replaced again. The two pumps I have seen good luck with are the OEM pump and the Holly pump. Remember to get a new strainer screen when you get your new pump. If you read the fine print, most warranties are void if you don't change the screen. Now on to what I think is the most important thing to do when changing a pump on an older vehicle. You should drop the tank and completely rinse out the tank to get rid of crud in the bottom. That crud will kill a new pump in a hurry.

 

[Flash]

I'd say it's about fifty-fifty, the guys that have swapped out the pump and fixed the problem and those who have swapped out the pump and then had to find the original problem.
When you turn the key to run, the fuel pump relay will close for a second or two (if you hold your finger on the relay you can feel it click), just as a prime, it doesn't really build much pressure. It builds enough pressure to get just a slight squirt if you depress the shradder valve. During start, the fuel pump relay closes and supplies power to the ballast resistor relay (the ECU closes the relay), which bypasses the ballast resistor for the start, then you get pressure. If the ballast resisitor is bad, it will start (likely) but won't run and will shut down as soon as you release the key. The ballast resisitor is bypassed (through the ballast resistor relay) when the key is in the start positon.
The dark green and black wire at the resistor, is the pump end of the resistor and should have power, for a second or two, when the key is turned to run and during start and with the key in the run posiston after the motor is running.
If the fuel pump relay isn't actuating, it's usually because the ECU refuses to actuate the relay, bad CPS, bad Cam posiiton sensor, maybe the MAP is getting no mean atmopheric pressure index signal and other stuff.
There is also the off chance that a connector is corroded (no power to the pump), a relay is flacky or the pickup tube on the pump is falling apart and there is a hole in it.
Or maybe a bad pump. Changing out a pump is a beatch. I'd sure as heck make sure I'm getting juice, before I went through the convulsions of changing one.
I've had fuel problems on three different XJ's (sometimes multiple problems with different causes, at different times) and haven't replaced a pump yet. It always turned out to be something else.

Thanks, that make a lot more sense about the Way the pump work and the ballast works!

Flash.

 

[jordo]

What exactly will jumping this do?

Bypassing the resistor will send more juice to the pump. The resistor simply reduces the voltage to the pump so it's not so noisy when it operates. The pump doesn't need to operate at full tilt to deliver the required fuel. If the resistor is failing the pump will not be recieving enough juice therefore not pumping enough fuel. However, as someone mentioned earlier make sure your wires/connections to the pump are in good condition first.

edit-whoops-looks like i missed a page and things were explained-my bad.

 

[gundog]

Bypassing the resistor will send more juice to the pump. The resistor simply reduces the voltage to the pump so it's not so noisy when it operates. The pump doesn't need to operate at full tilt to deliver the required fuel. If the resistor is failing the pump will not be recieving enough juice therefore not pumping enough fuel. However, as someone mentioned earlier make sure your wires/connections to the pump are in good condition first.

edit-whoops-looks like i missed a page and things were explained-my bad.

Any ideas on what kind of volts I should see at the connection to the pump (outside of the tank)?

 

[old_man]

With the resistor jumpered, you should get battery voltage. With the resistor, it should be somewhere between 6v and 10v.

 

[gundog]

I checked all of the connections and everything looks good. I have removed the fuel pump assebly from the tank (wasn't that bad as the tank stays put on a 1996). Does anyone know if I can plug the pump back in and try it while it is out of the tank? Also, there is a 5 pin connector where the fuel pump assembly plugs in (outside of tank). If I am checking for volts there, which two of the five pins do I check across (wire colors)?

Any other thoughts on where to buy a pump (besides dealer)?

 

[Flash]

I can't tell ya what colors are, they but if ya fallow the wires form the pump you will now with 2 that you need(power and ground to the pump are the one's the you need to trace back form pump to conector.............I thing it even Has (+) (-) on the pump.

Flash

 

[gundog]

I can't tell ya what colors are, they but if ya fallow the wires form the pump you will now with 2 that you need(power and ground to the pump are the one's the you need to trace back form pump to conector.............I thing it even Has (+) (-) on the pump.

Flash

Update: I checked the voltage at the connector to the pump and got 10 volts while cranking. Pump would still not turn so I will be ordering a new one. Anyone got any advice on where to get a decent pump for a decent price?
Thanks for all the help.

 

[blakebmxr3]

i got the expensive(dont remember what kind) fuel sending unit from auto zone, slapped it in and my jeep runs fine.....it was like $110 i think.