'99 Exp. 4.0 SOHC 4X4 4 Dr

[Van]

Made in USA.

I began having starting trouble last week. Extensive cranking to get it to go.
Idle seems to be lower.
Of course I came here to try and diagnose the trouble.
Cycling the ignition a few time helps it start better.
Changed out the fuel filter with no change in symptoms.
Today, I had to floor it to move out into traffic. Check engine light came on.
AutoZone diagnosed it as both banks lean.

I suspect the fuel pump.
Just thought I'd pass it by the experts here first.
Thanks in advance.

 

[robertoa1a]

an you check the fuel pressure on a cold start? How does it run after starting?

 

[Van]

Haven't checked the fuel pressure.
It seems to run OK, just low idle and doesn't have the get up and go it should.

 

[jlsparky7]

Probably fuel delivery problem. Did it start after you filled up with gas or after the vehicle was sitting awhile?

Check the pressure at the fuel rail.

 

[Van]

Neither.
Just started out of the clear blue.

 

[Van]

Used a fuel pressure tester.
Key on, pressure is below 10 psi and drops off rapidly.

Once running, it's between 44-48 psi.
Shut off and the pressure drops rapidly.
I'm guessing bad check valve.

Opinions?

 

[robertoa1a]

Not enough fuel pressure on start up and a little high on run. I think that has something to do with the fuel pressure regulator vacuum line or evac system. Do you have rigging for measuring pressure at the filter?

You might have a small leak in the fuel line near one of the fittings.

 

[Van]

The book states pressure up to 65 psi.
No fuel leaks that can been seen or smelled.

 

[robertoa1a]

Maybe 65 without a regulator. More like 36-40 at the rail. Any how, 10 on start is way to low. Have you tried several key on, key offs before cranking.

 

[Opera House]

Pressure should be able to hold for 15 minutes so there is a leak. Forget the change over year, but either will have a pressure regulator or accumulator that has a hose connection to manifold vacuum. Remove vacuum line to it and see if you smell gas. If you need a longer test, engine will run fine if you block the vacuum hose. This kind of leak usually makes one side rich. Check valves and leaky injectors just cause starting problems not running lean. Pump seems to have enough pressure. There is likely a secondary cause and although the fuel is a real issue it is a red herring.

 

[Noslo351]

Did you figure out the problem with your fuel pressure issue? I'm having the same problem. I read a that there could be a leak on the connector hose in the gas tank. The hose connects the fuel pump to the regulator that is mounted to the pump/sending unit assy inside the gas tank.

 

[DW_810_Stock]

Hey Guys,

I also have a 99 SOHC 4dr 4x4 XLT with what I believe to be a fuel pump issue.

A few days back, driving along at normal speed, all the sudden lost power and within about 200yards the engine was stalled. Muscled it into a parking lot. Engine will fire or try to fire every time you try to start it, but will run for a maximum of 2-3seconds before dying out. If you goose the throttle it dies even quicker.

Quick rundown of what we've looked into:
- No CEL
- No Codes on our OBD II Scan tool
- Fuel pressure is less than 10psi at key or at start attempt. It was so low that after I measured it, I manually hit the schrader valve and the fuel just dribbled out, even with a few key-up cycles, confirming that the pressure is very low. (I didn't believe my gauge at first)
- You can hear the fuel pump run for about 1 second at key-up
- Fuel Pump was replaced 2yrs ago with an aftermarket version
- Fuel Filter is regularly changed (just got changed again for good measure)
- Fuel cutoff swich is not popped, plug seems tight
- Switched Fuel Pump Relay & checked Fuse
- Theft light does blink, but we've tried multiple keys with no change in result? I dont think a PATS issue could stall a running truck though, could it?
- IAC was removed and cleaned
- EGR was removed and cleaned...was working properly
- Battery voltage is about 11.9 before key-up, about 14 during the 2-seconds of running
- Vaccuum seems strong (not measured)
- MAF looks clean, has no effect if it is plugged in or not

Since we can hear the fuel pump, but the pressure is non-existent, there must be an internal leak in the fuel pump assembly? There are no other visible fuel leaks elsewhere in the system. It seems strange that the fuel pump would fail so quickly after being replaced only 2yrs and about 12,000 miles ago, but it is possible.

I just want to try and make sure we've checked everything else before we drop the tank or spend the money on a new fuel pump assembly.

Any thoughts, or do you agree that it's the fuel pump?

Are there any common fixes out there for this fuel pump, or will we need to replace it completely?

Any response is appreciated

 

[robertoa1a]

Try checking pressure at the filter to rule out the possibility of the fuel pressure regulator recirculating back to the tank. Years ago, on a first gen I had a rust hole in the line inside the tank (though highly unusual). Third, check the ground for leaks.

 

[DW_810_Stock]

Update: It was the fuel pump...we swapped it out last night and now it runs like new again...