Please HELP!! 4.6 Won't stay running...

[cigarluvr]

Ok more hints...If i jump the Fuel Pump Relay so that the pump stays on...I still get it to start,then it dies as if it runs out of gas...same issue...anyone have some insight? Also, I am not getting any codes.

[gradon]

If the fuel system is like the 91-95 XJ's, the pressure at idle is 31psi and if you disconnect the vacuum hose to the fuel pressure regulator on the front of the fuel rail, the pressure should rise to 39psi(correct me if I'm wrong).

[cigarluvr]

What if it's not running? Just with the key on?

[Cheromaniac]

What if it's not running? Just with the key on?

As long as the ignition is on you should still have ~30psi of fuel pressure even without the engine running. If the fuel pressure is very low, it means the fuel pump isn't priming the system.

[cigarluvr]

OK...so i finally had a chance to throw a fuel pressure guage on it.

0 psi when i turn the key on, and 0 when i jump the FP relay at the PD Panel. Fuel is moving tho...

So I'm thinking either the FP is not pumping hard enough or fast enough or that the FPR is just returning the fuel to the tank.

Thoughts?

[6TIME]

Sounds like the pump may be toast, can you hear it running when the ignition is on?

[cigarluvr]

I can hear it...that's what so frustrating.

[yuppiexj]

I can hear it...that's what so frustrating.

Fuel filter clogged?
Gas tank empty enough that it's sucking air?
Kinked/crushed.bent fuel supply line?

[SilverXJ]

Possibly disconnect line in the tank.

[cigarluvr]

I don't think it is any of those diagnoses...

If i remove the fuel line at the rail and jump the relay i get a steady stream of fuel...and if I press the shrader valve on the rail with the line attached, same thing, steady stream of fuel. Could my FPR be allowing the fuel to return back to the tank? Could the fuel pump be pushing fuel around the FPR?

[SilverXJ]

A steady stream of fuel does not mean there is any pressure behind it. If there is pressure and you open the schrader valve it would spray out.

[cigarluvr]

Yeah, right...so where is the pressure bleeding off at? Weak pump?

[yuppiexj]

It could be a split fuel line in the tank.

The pump ends up pumping spraying fuel around the inside of the tank. you may get some flow at the manifold but no real pressure.

you may be able to diagnose this by jumping the fuel pump relay and listening through the filler neck for tell tale sounds of spraying in addition to the sound of the pump running.

[SilverXJ]

x2. It could be any number of things. Failed regulator, regulator leaking into vac line, broken or disconnect hose in the tank, faulty pump, low voltage to pump, etc.

[Cheromaniac]

I don't think it is any of those diagnoses...

If i remove the fuel line at the rail and jump the relay i get a steady stream of fuel...and if I press the shrader valve on the rail with the line attached, same thing, steady stream of fuel. Could my FPR be allowing the fuel to return back to the tank? Could the fuel pump be pushing fuel around the FPR?

When you press on the Schrader valve the fuel should shoot up in the air like a fountain so you have very little fuel pressure. Your FPR could have a ruptured diaphragm but you'll need to check the fuel flow from the pump first before making that diagnosis. Disconnect the line that goes from the pump to the fuel filter and place a bucket underneath. Turn the ignition on to activate the pump for exactly one minute while a buddy makes sure that the fuel goes into the bucket. In that minute you should collect at least one liter of fuel. If it's much less or none at all, replace the pump.