on startup, what should an electric fuel pump do?

i have the bed off my truck, and the lines on the fuel pump disconnected. when the key is turned to on (not start), some fuel will spurt out the pump, not much, and spraysabout a foot from the pump. then it stops. how much pressure is the pump supposed to put out?

I am trying to narrow down an on-going no-start problem that has gotten much worse over time. the truck used to run excellent, then would run poorly from time to time, then all the time, and now it wont start. i dont think i'm getting fuel to the rail, and i think my pump has been going bad over time.

1993 W150, 318magnum, auto, 70kmi

 

Not sure on that year system,but on the 1988 fi system it is 14.5 psi,and it should kick on for about a second to pressurize the system.

 

With your 318 mag Haynes says that with the regulator vaccum hose attached there should be 39 ro 41 psi of pressure. When yoi first turn the key to on without starting the pump kicks in for about 10 secs to prime the line and build pressure. After that it stops until you start the truck. Did it use to carnk like a bitch when cold but then start when it was warm. Like got up in morning and it would carnk but no start then if you came out about 3 or 4 o' clock it would start like new? If so this happened to mine too. It got bad enough that the battery would die before i had the thing started. While i cranked it the fuel pump and asd relays would tick then when they stopped it would start no problem. I replaced the whole fuel system almost, pump, relays, regulator, filter. Nothing, then took to guy and crank senor wire was bald and shorted the damn computer out and fried. Replaced computer and runs like a champ.

 

No starts and hard starts do not necessarily mean a fuel problem. The pressure can be measured at the rail with a cheep gauge (less than $20) and aid in T/S'ing a problem. As others had mentioned, the short pressurization is normal and the pressure is to act as a prime till the engine is running. I'd measure the pressure at the rail before I'd pull the bed and line because it could be as simple as a plugged fuel filter or line, but start at the engine, and if good, then look elsewhere. If bad, then work backwards to the pump etc.

 

Ya mine ran like crap under a 1/4 tank, so I hooked up a fuel pressure gauge to the rail and tested it. It would prime to 31 psi at start, but once I started driving around the lot it would drop to around 7. I had already replaced the filter, so I replaced the pump and it was good to go. If you already have your bed off, a pump change would be very easy.

 

yeah, the bed is already off, so any tank/pump work is easy.

My fuel pump does not run anywhere near 10 seconds when the key is first on, maybe 4 sec.

If i cant get the truck to start, which it does not do at the moment. how do you test pressure at the rail?

 

4 sec is should be fine...The presure guage screws onto the schrader (sp?) valve on the rail. It should have a cap, just like a tire valve cap. Just take the cap off and screw on the hose that comes with the gauge. Turn the key and read the pressure.

 

You suppoes to check with regualtor waccum hose on and off. like i said before with attached31 to33psi, disconnected- 39 to 41 suppose to raise with it off.If you don't get those figures then i would proably look towards the regualtor. But you are suppose to pinch the return line, and see what the pressure does. I fit rises sharply the regualtor is bad, if it doesn't rise then there is a leak or restriction or the pump is bad. But the line is stainles and if you pinch it then the line will mes up. So your supose to rig up a rubber fuel line from line to fuel rail.