Ok so long story short, we have an 87 F150 with an EFI i6 300 engine that was sitting for about 7-8 years on our farm, I got it running and driving and took it around the yard just fine. Then after letting it sit for a week it wouldnt start again. It cranked just fine and ran off starting fluid without issue. I then replaced the front gas tank, front fuel sending unit, and high pressure pump (as they were all rotted pretty bad) and the truck still wouldnt get fuel to start (no gas in fuel rail line). After then changing out the fuel pressure regulator (which was a PITO as its under the air intake) the darn thing still wouldnt get fuel to run (again no/little fuel in the fuel rail but would run just fine off starting fluid). Finally after manually bypassing the fuel selector switch I was able to force the pumps to supply sufficient, pressurized fuel to the fuel rail (as fuel now shot out of the pressure relief valve when depressed) and still the truck wouldnt start. However, at the first crank of the engine it would sputter for a second but then continue to crank/turn over without any signs/sounds of fuel being injected. My question is what should I go to next in fixing/replacing/diagnosing? I dont think the injectors are clogged as the truck was running just fine before this whole ordeal. Is there some way to check that the injectors are getting power? I read elsewhere that the injectors are grounded on the fender or something, what might this mean (I dont have much experience with EFI engines, mostly know about carbs)? Any help is greatly appreciated, thanks.

 

Who is to say that when you drove it for a few days that something between the filter and injectors didn’t clog them? Did the parts store give you the correct regulator for a 4.9L and not one for a V8? How much pressure do you have at the rail?


The low pressure pump in the tank keeps the reservoir full for the high pressure pump on the frame rail. How did bypassing the switch on the dashboard make the pump supply enough pressure to shoot out of the rail? A noid light will tell you if the computer is firing the injector(s). The injectors are ground side switched in the computer.

 

I haven't checked the pressure at the rail with a meter or anything yet, just looked at how much fuel was coming out of the pressure relief valve. Ill double check that the right fuel pressure regulator to make sure the right one was put in. To "build" pressure, I simply ran a wire from the positive terminal of the battery to the fuel selector switch plugin and alternating between powering the high and low pressure fuel pumps. Also how do i see if the "noid" light is on to check the injectors?

 

So are you saying the pumps do not run for a couple seconds when you turn the key from OFF to RUN?

Noid lights


Noid light installed


You will see the light flash if the computer is grounding the circuit.

 

Ok, so I have gotten around to working on this truck again (lots of projects and no time lol) and I was able to connect a noid light to the first injector. It "blinked" when cranking it. Next I checked the high pressure pump and it does appear to "whir" for a few seconds when the truck is starting. I double checked that the fuel pressure regulator is correct for the 4.9L I6 300. The fuel tank selector valve (on the frame) is leaking again so I know that the low pressure pump is working and it appears to be sending gas to to the high pressure pump. However, when I depress the fuel pressure valve (right behind the upper intake manifold) I all hear is a small hiss and no gas comes out.

This makes me think that the system is underpressurized still. My assumptions so far are that this could possibly be due to: the fuel pressure regulator is somehow not installed right; the high pressure pump is faulty somehow (it was "new in the box" but was in a garage for at least a decade), the leaking fuel tank selector valve is somehow causing this issue, or the fuel filter I bought is somehow clogged from the factory. Any idea on what to start looking at next?