fuel delivery problem '90 4.0

I have spark and Jeep will fire with intake cleaner or the like sprayed into throttle body. Fuel pump comes on with key and runs for a few seconds and shuts off. Turn key back on and pump runs for shorter time and shuts off. Seems fine. I removed the fuel filter and it is not clogged and pump runs and pushes fuel out of the "out" side of filter when key is turned on. I still however have no pressure at the fuel rail and if I disconnect fuel line at the rear of fuel rail (which I think is the "in" side) no fuel comes out. Ideas? Oh, yeah...new CPS was my first part replaced when Jeep wouldn't start the first time.

I had a similar problem that turned out to be the fuel pump. It stumped me because it was running and getting fuel to the fuel rail, but it was not enough pressure to run the FI system. I changed the fuel pump and problem solved.

Good luck.

i have a 96 4.0 high output, and when i get down to a bit less than a quarter tank it gives me trouble starting sometimes...i thought it might be the fuel pump but i wasnt sure...i used to put starter fluid in the throttle body like you and it ran for a few...id let it sit for a while and somtimes it would turn over...if i couldnt get it goin id just add gas and it would go..so now i just treat it like a 1/4 tank is E...might be the fuel pump/floating gauge??treating 1/4 tank like E is cheaper than getting the pump fixed

I did fill it up about halfway just to be sure I didn't run it too low. The thing is when I turn the key on it will pump out of where the fuel filter is but it will not pump up to the fuel rail. I guess it just coming on doesn't mean it is working up to pressure. So answer this...is there anything that would command the pump not to pump when cranking? I just want to be sure it is the pump before I buy one. Any other tricks for checking it?

Have someone with a guage check the fuel pressure at the fuel rail. If it is low, then it's time for a new pump.

There is no pressure whatsoever at the rail. With the lines disconnected it will push fuel for a couple seconds but then stop. It however does not seem to be pumping when cranking. How does the pump know when it is up to pressure and when to stop. Basically what controls the operation of the pump, so I can check those parts before buying a pump.

I'm not sure. Confirming no gas comes out when you press on the small valve on the fuel rail (with the ignition in the "on" position)? If that's the case, then I don't know what else to check. The fuel filter is good, the lines are clear...It seems like the pump to me, but maybe someone else has other experiences that will point you elsewhere. As for the operation, the fuel system has a return (bypass) that returns excess fuel to the gas tank.


Good luck!

It's just really weird that it will pump and then shut off before it gets to pressure. Wish I knew more about it. Maybe I will hard wire the pump and then see if it will just run and not stop.

The rear line is the fuel return line, not the supply from the pump. The front line is the supply line. There is a fuel pressure regulator at the fuel rail inlet that could be bad or clogged up. There is a pressure, fuel flow reed valve test port on the drivers side of the fuel rail. If there is no flow or pressure at the test port it is either the pump or pressure regulator that is bad.

There is also a pressure relief valve and return check valve in the pump itself that is usually what kills a pumps output. When they go bad it is not repairable, requires replacement of the entire pump assy.

mattyjeep said:

I have spark and Jeep will fire with intake cleaner or the like sprayed into throttle body. Fuel pump comes on with key and runs for a few seconds and shuts off. Turn key back on and pump runs for shorter time and shuts off. Seems fine. I removed the fuel filter and it is not clogged and pump runs and pushes fuel out of the "out" side of filter when key is turned on. I still however have no pressure at the fuel rail and if I disconnect fuel line at the rear of fuel rail (which I think is the "in" side) no fuel comes out. Ideas? Oh, yeah...new CPS was my first part replaced when Jeep wouldn't start the first time.

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OK...think I have it narrowed down to fuel pump. I can make the pump run by using the connections under the relay to provide power directly to the pump from battery, but the pump will still not provide enough push to get the fuel to the engine compartment. I have checked all the lines and tubing and everything looks good. I have disconnected both lines at the fuel rail and still not enough power to push the fuel up to the front. The only thing I haven't done yet is check and see if compressed air will make it to the front to be sure the lines are clear. The filter has been checked and flows nicely and just to be 100% I replaced that also. So it looks as though the pump has enough power to push fuel out of the line when disconnected near the tank but not to get it all the way to the front. Is this possible or does it have to be clogged somewhere? Since the tank was as at least half full and I could turn on the pump at will I went ahead and used the pump to empty the tank a bit. While doing this I noticed that it took the pump about 5 minutes to push out about 3 gallons of fuel. Does that tell me anything?

Check the fuel line along the frame rail to make sure it is not pinched or dented that may block or slow fuel delivery.