No fuel pressure at the rail

I believe I have a fuel delivery problem. Last week while driving on the highway, my XJ felt like it ran out of gas and died. Try to start it for about 30 mins and then it fired up. Yesterday, the thing would not start. I checked for fuel at the test port on the rail and there is barely enough pressure to cause a drip. I changed the fuel filter with no effect. I suspect the pump but would like to check the regulator first. Problem is I can't find the regulator. It isn't on the fuel rail like Haynes shows. Any clues? Pictures are worth a 100 words. Also, how would I check the fuel pump relay?

what year?

With my 89 i ran it out of gas(bad gauge) and even after i put 5 gal. in it it wouldn't start.
Checked the fuel flow at the schrader valve and there was vary little flow(pump works but no pressure)

banged the tank with a hammer while my buddy cranked it. after a fue sec of cranking it it fire right up and haven't had any problem with it sense!

talking to the previous owner was told that every time he ran it out of gas:confused1 that he would have to hold the shrader valve open while he cranked it till it stared spraying fuel every were or it wouldn't start!...?

I haven't ran it out of gas sense and don't plan on it to find out if it works?
the pump gets an air lock in it:dunno: or some thing!


Flash.

i had the same exact problem with my 1989 xj. first i changed the fuel filter and that made it run for like 200 more miles, then it died again. and again. and again on the trail. checked everything and there was barely pressure at my test rail, so i disconnected the connection(coming from the fuel sending unit) near the gas tank and turned the key on whilst i had the electric tester to tell me that there was in fact power oing to the fuel sending unit. So i for sure needed a fuel pump. Had some parts not matching problems and ended up ordering the whole new fuel sending unit. Sure enough it fixed it right away and my jeep hasn't died since. so i would say get a new fuel sending unit, it onl took me like 30 min. max on the trail.

oh ya don't forget to check for gas in the tank

Sorry, it's a 96 XJ 4.0 i6 4WD, 119,000 mi.

oh ya, the fuel pump relay is on the passenger side(under the hood) next to the coil, in a row of four relay's. the fuel pump relay is the third one back(standing from front looking into the engine compartment)

try the shrader(test port for a fuel pressure gauge) trick.........whats ya got to loose!..........and then the tank bang trick.

Flash.

blakebmxr3 said:

oh ya, the fuel pump relay is on the passenger side(under the hood) next to the coil, in a row of four relay's. the fuel pump relay is the third one back(standing from front looking into the engine compartment)

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thats a good idea, just swap the relay with one of the ethers ones. they or interchangeable!

If you're not getting proper power to the sending unit might want to check out the ballast resistor. quick and easy-jumper the two wires going to it and see if there is a difference.

or the ballast resistor might just be dirty. it is on the drivers side near the front of the fender, it is a little white (if its clean) rectangle thingy with only two wires going into it.

A few more questions:

On my 96, where is the fuel pressure regulator?

Where is the sending unit?

Where ss the ballast resistor for the sending unit exactly on a 96 XJ?

well i figured it would be close to the same on a 96' but i have an 89'

my fuel sending unit is in the gas tank. if you're lucky like me then it'll be on the side of the gas tank closest to the rear diff. and in my 89' the white ballast resistor is on the drivers side fender, close to the front next to the air filter, and its up high, like right below where the hood closes. as for the regulator, i never found it either, the fuel sending unit seemed to be the only thing i needed

Just a quick question, when you turn the key to the run position, does the "Check engine" light come on? Have you tried to run the Mil codes?
Reason I asked, is if the computer doesn't get the right info from some sensors, it will not turn on the fuel pump relay.
The fuel pump relay will click once to prime the rail, but then refuses to reengage and pump any real pressure.
Not something I'd try without a good diagram, but I've jumped the relay, to test the pump. But if you jump the wrong pins, you may possibly damage something in the computer. Not something I'd try, without some refernce material handy.
Many relays will have a diagram on the side, showing you the switch contacts and the acutator coil. Which pins do what.

Flash said:

what year?

With my 89 i ran it out of gas(bad gauge) and even after i put 5 gal. in it it wouldn't start.
Checked the fuel flow at the schrader valve and there was vary little flow(pump works but no pressure)

banged the tank with a hammer while my buddy cranked it. after a fue sec of cranking it it fire right up and haven't had any problem with it sense!

talking to the previous owner was told that every time he ran it out of gas:confused1 that he would have to hold the shrader valve open while he cranked it till it stared spraying fuel every were or it wouldn't start!...?

I haven't ran it out of gas sense and don't plan on it to find out if it works?
the pump gets an air lock in it:dunno: or some thing!


Flash.

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I had a similar problem as Flash but the banging finally woke my neighbor and he suggested I check the plug on the fuel pump wires. I did and sure enough they were corroded from driving through the mud and water in N. Georgia when I lived there. Electric contact cleaner and a small wire brush and no problems since that was over 2 years ago. Good Luck!!!

gundog said:

I believe I have a fuel delivery problem. Last week while driving on the highway, my XJ felt like it ran out of gas and died. Try to start it for about 30 mins and then it fired up. Yesterday, the thing would not start. I checked for fuel at the test port on the rail and there is barely enough pressure to cause a drip. I changed the fuel filter with no effect. I suspect the pump but would like to check the regulator first. Problem is I can't find the regulator. It isn't on the fuel rail like Haynes shows. Any clues? Pictures are worth a 100 words. Also, how would I check the fuel pump relay?

Click to expand...

I'd say it's almost certain your fuel pump has died. You could swap the fuel pump relay with the AC relay and see if it works, and you could also try jumping the two terminals of the ballast resistor on the driver's side inner fender next to the brake master cylinder. If those measures don't work, replace the ballast resistor (it's cheap). If you still have no joy, replace the fuel pump. The regulator is also in the tank and is part of the fuel pump assembly.

Dr. Dyno said:

I'd say it's almost certain your fuel pump has died. You could swap the fuel pump relay with the AC relay and see if it works, and you could also try jumping the two terminals of the ballast resistor on the driver's side inner fender next to the brake master cylinder. If those measures don't work, replace the ballast resistor (it's cheap). If you still have no joy, replace the fuel pump. The regulator is also in the tank and is part of the fuel pump assembly.

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Thanks Dr. So I get this straight, I jump the two terminals of the resistor and then check for pressure at the rail? What exactly will jumping this do?

Also, if I replace the pump, is it best to replace the whole assembly? My local dealer has a factory rebuilt pump only for $93 and a complete rebuilt assembly for $182. I would much rather go with one of these options. I assume with the assembly I would get a new regulator. I have read some bad posts about aftermarket pumps not lasting very long. Any thoughts?

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.

gundog said:

Thanks Dr. So I get this straight, I jump the two terminals of the resistor and then check for pressure at the rail? What exactly will jumping this do?

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i think he was suggesting a way to jump past the relay and prove whether or not your fuel pump will work..

if it pumps when you jump thru the relay plug then the relay or related sensor is the problem..

Having to hold open the schrader to pump up the system with fuel sounds more like a check valve in the pump, it only is seating properly when there is fuel on the pressure side of the valve in the line, this pressure reseats the valve firmly. Without the pressure mentioned, the fuel won't flow.
Bangin on the tank may help this valve reseat.
I'm not that familiar with the cherokee, but most FI systems switch on the pump and bring up to pressure before turning to crank. Switch it on and off and listen for pump whirr/buzz. Or backtrack to see if you have voltage, but it was running well until empty and others have had repriming probs.
I'd try holding the schrader open with a screwdriver with someone turning the key on off.

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.

gundog said:

Thanks Dr. So I get this straight, I jump the two terminals of the resistor and then check for pressure at the rail? What exactly will jumping this do?

Also, if I replace the pump, is it best to replace the whole assembly? My local dealer has a factory rebuilt pump only for $93 and a complete rebuilt assembly for $182. I would much rather go with one of these options. I assume with the assembly I would get a new regulator. I have read some bad posts about aftermarket pumps not lasting very long. Any thoughts?

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Thanks everyone. I will check these things out later tonight. Does anyone have any ideas on fuel pumps if mine turns out to be bad? Do I need the complete assembly or can I just replace the pump? What about the regulator on the assembly?

Thanks.