I have a 1996 F150 with a 4.9L 6 auto & dual tanks. The front tanks fuel pump went out over a year ago and I have been running on the rear tank with no problems for over 20,000 miles. Just a few days ago after parking it in the garage it would not restart. The engine cranks. You can hear the rear pump working when I turn the key on. I replaced the fuel filter. There is fuel at the relief valve. I took the ignition module to the auto parts shop and they tested it and said it was OK. The plugs are getting spark. I've checked for blown fuses and none were found. Any help to get my truck running will be greatly appreciated.

 

sounds like the other pump is going out/went out. if u hear it working, u need to wait for it to build enough pressure before itll start, u notice it when it stops humming.

 

I replaced the crankshaft position sensor and it still would just crank. I don't have a code tester or repair manuel. So I was looking on the engine and noticed that there is a vacuum valve under the intake manifold that is connected to the fuel line to the number 1 injector. I think it's called the fuel cutoff switch. I pulled the vacuum line off and squrited some WD-40 in the valve and put the hose back on, sprayed some gas into the air intake, and it started up. It's runned fine all day.

 

You found the fuel pressure regulator.

 

The problem of not wanting to start returned. So I replaced the regulator and that did not fix it. Everything seems fine but when the truck hasn't run for about an hour it will not restart. But when I spray some gas into the air intake it starts right up and runs fine. If you have any ideas I'd appreciate hearing them.

 

Sounds like the fuel pump to me. You really need to check your pressure. It's bleeding down somewhere.

 

There's not a lot to the fuel supply system: pumps, filter, regulator and injectors.

If the pump were shot t wouldn't keep running once you got it running.
You have a new filter and a new regulator and neither solved the problem. That leaves the injectors. What it sounds like is that you have a leaky injector. When you park it for a while, that gives it time to bleed down the pressure in the fuel rail. What I don't understand is why the pump doesn't restore pressure when you re-start.

 

Since the starting problem began I have driven over a thousand miles in my truck with no other problems. But when the truck is cold I have to squirt gasoline into the air intake to get it to start. If I stop and restart within 30 to 45 minutes it will restart on its own. Is there some part that primes the motor with fuel that is temperature sensitive? I'm glad that at least it runs but it is a problem that I'd like to solve.

 

All your symptoms point directly to a leaking injector. It functions more or less normally when running but will not hold pressure when shut off. This allows then fuel pressure in the rail to drop to zero over time. It is a slow leak so you can get an easy re-start if the truck has been off for only a few minutes.

When you turn the key to "on" you energize the fuel pump relay and the fuel pump starts; you should be able to hear it run. It should re-pressurize the fuel lines allowing the truck to start when you next move the key to 'start." That is AFAIK the only priming device involved.

What I do not understand is why the fuel lines are not re-pressurizing when you turn the key. Next time you go to start the truck, turn the key from off to on and wait about 15 seconds before moving the key to start. If this solves the problem, then you need to find the bad injector(s).

 

1995 f150 4.9L won't start, it cranks but not firing. I have checked the fuel pump, it is working, replaced fuel filter, and there is fuel pressure at the fuel rail. I have replaced the ICM, coil, distributor cap and rotor. the test light I bought shows no spark coming from the coil, but if I use starter fluid it will fire, so there has to be spark, light must not work. This problem started like this, truck would start and run, I would drive it and when I turned if off it would not start back until the next day, then it would start and I could drive it and the same thing over and over, but whatever was going out finally went out and it won't start at all now. Somebody help I'm spending everything I have trying to get this thing to run...Thanks for the help!

 

the fuel pump only stays energized for 3 seconds after you turn the key on, then stays on after the engine starts, could be the fuel return check valves in the fuel pump leaking the pressure down. try turning the key on and off several time then try starting it.

 

To William Ozment:
on the OBD I systems sometimes the Mass Airflow Sensor can short the Ign circuit, unplug the wire from the MAS and see if it starts. I have also heard that
if i will start with the PCM disconnected it is a bad PCM. Worth a try

 

Thanks I’ll try it

 

I unplugged the MAS still no start. From the check engine light I’m getting code 522 which is the neutral safety switch, but would that switch allow the engine to crank without starting?

 

Does your truck have a shrader valve on the fuel rail? If so, borrow/buy a gauge and check the fuel pressure. It could be low.

How many miles are on this truck? Does it have good compression?