twice this week my '94 2.3 has died right after starting. i got it to fire on either both times and eventually would run on its own. i bought a guage to see what the fuel pressure was running cause when i suspected it was a fuel issue i had put a small scewdriver in the fuel rail test port valve, expecting a spray of fuel and there was nothing. well with the guage on i had no pressure at first, engine wouldnt start, finnally for no reason i had pressure and it started, was running right at 30 psi. can drive down the road and seems to have no problems getting enough fuel, accelerates through the gears just like always. i dont know if theres a relay/electrical issue or a pump about to die completely. seems a pump should either work or not work, not be a intermittant problem. and its never happend once its running, its always been a start-up issue. im sure sometime its going to be completely dead in the water. any thoughts/ideas?

 

The pump could be wearing out, and the brushes failing to contact the armature immediately. The fuel pump relay could be failing, or the rollover switch may not be making good contact. The computer enables the pump for a short burst when you first turn the key to ON. Listen for the whirr/hum of the pump at that time. If you don't hear it try again. If you don't hear it, your truck likely won't start.
tom

 

1994 will use a Return fuel system with FPR(fuel pressure regulator) on the fuel rail on engine.

Fuel injection systems will hold pressure for MONTHS, not minutes, hours or days,......Months

There are 3 things that hold the pressure in the system
1. Fuel pump has a built-in Check Valve(back flow preventer), basically just a flap that is pushed open by flow when when pump is on then closes when pump is off

2. FPR, it is a spring loaded valve set for about 40psi, if pressure gets higher than 40psi then spring/valve is pushed open and sends "extra" fuel back to the tank

3. Fuel injectors, they, of course, should be closed when engine is off, if one is leaking you will have Rich running and very poor MPG, which you don't mention

You should attach fuel pressure gauge to engine
Pressure should be 15-20psi at the lowest, if engine has been sitting off for awhile
Cycle key on and off one time and check pressure
Each ON/OFF should add 10psi of pressure, and it should hold that added pressure up to 40psi then hold at about 40psi, 35psi is OK, that's the FPR working
If pressure still drops after key ON/OFF then FPR or Check Valve are leaking, you won't smell gas because it is leaking into the gas tank

You need about 20psi for the engine to start, so for now cycle key ON/OFF 3 times and then start engine.

To check FPR remove its Fuel Return hose, put a towel down under FPR
Cycle key ON/OFF, no gas should come out of FPR........until fuel pressure is above 40psi
If no gas comes out then Check Valve in fuel pump is the issue, it is not a separate part, new pump is needed.

If gas comes out of FPR with pressure under 30psi replace it

FPR also has a Vacuum Hose attached, this helps equalize fuel pressure when engine is running, when engine is idling Fuel use is low and Vacuum is high, so vacuum pulls against FPR spring to open it a little, when accelerating fuel use is high and vacuum is low so no vacuum assist against spring in FPR.
This helps keep fuel pressure between 30-35psi at the fuel injectors so no big swings in pressure that would give the computer problems in setting injector open time
FPR vacuum chamber can leak, this will cause gas to be sucked into the intake via the vacuum hose, which would cause Rich running and a drop in MPG