truck died then would only crank

[JP_McCann]

title says it all. Was driving the truck home on the highway then all of the sudden i look down and realize that it died. got into the nearest parking lot and the car would just crank and crank, but not turn over. Had a very similar problem with my mustang and it was a bad wire in the fuel pump relay. what would the problem be in this case? Would it be a wire or fuel pump? is there any way to determine what is causing the problem. truck is a 1997 f150 super cab 5.4 4x4

[Monsta]

When you turn to key to ON without starting, you should be able to hear the fuel pump prime the line. If not, you can usually determine that the fuel pump, the fuse or associated wiring is bad.

You can purge the system of pressure by pushing in the Schrader valve on the fuel rail prior to listening for the pump.

You can also test the wires as close to the pump as you can get for power to help eliminate a bad wire as the culprit.

[JP_McCann]

couldn't hear the pump prime so that is another reasn i was leaning toward fuel pump

[JP_McCann]

what should the fuel pressure be when running? It was 30PSI. is that low?

[JP_McCann]

also in other news. The truck seems to run better when cold. Any ideas?

[pintopower8]

The fuel pressure spec is 30-45 psi with the vaccum line attached and 40-50 psi with the line detached. After 5 minutes the system should hold 30-40 psi. I would start by looking at freeze frame data on a scan tool, but if you don't have that resource try this. 1, check the inertia switch (under passenger kickpanel) 2, test the fuel pump relay and verify that fuel pressure is well with in the spec. Maybe time for a fuel filter? I'm not sure how familiar you are with testing devices, I use a Snap-On Vantage Pro and amp ramp the fuel pump. When the truck is running you should have 12.6 volts to 2 relay pins, and a ground to the other 2. If you have all that, hear the relay click, and still no prime check power and ground at motor, at that point you will probably already have the tank down anyway

[pintopower8]

Also your truck will almost always run better cold, the feedback system isn't online yet and the computer defaults to open loop rich.

[bc11]

There is a 15 amp fuse under the hood at the front of the fuse box that controls the fuel pump.

[JP_McCann]

so if the fuel presure is 30 PSi should i replace the fuel pump?

[JP_McCann]

finally got around to doing more work on the truck. tested the fuel pressures. 28-30 PSI with vac attached and 38-40 PSI with vac detatched. after 5 min hold it was at 38 PSI. does this seem like something should be replaced?

[Joe Finn]

Might want to check the crank position sensor.

[bc11]

here is a post from cmorningstar01 from another thread which may be something to think about. You might have some type of intermittant vacuum leak. It's from the thread on the squeel/hiss sound heard:

On the engine side of the power brake booster vac there is a part from the emissions system marked EVAP, there is a vacuum hose that runs from the underside front of the intake manifold to this EVAP, Check this, On my truck(97 F-150 4.2V6) this hose was dried out and very brittle and pourous, I did not get any codes from it but it was def leaking vacuum, The EVAP itself could also be malfunctioning and possibly causing this squeeling sound, I think it may have some type of diaphragm in it and this could possibly be leaking ., You can disconnect this hose and block it off (temporarilly) to see if this is the source of the sound, I believe this is part of the Evaporative emissions system and keeps a vacuum draw on the fuel tank to reduce vapor emissions.

Val