I have an '88 F-150 5.8ltr with dual tanks. The truck was sitting, unstarted for about 6 years and i have recently done some work to get it going again. Everything was running great, but once i took it on a drive for longer than 30min it sputtered and died and wouldnt start back up. i let it sit for a couple minutes and it started again, but only ran for about a minute and did it again. If i leave it overnight and start it up in the morning, it runs for 20-30 minutes before it does it all over again.

The selector valve is working fine, we've replaced the fuel HP pump and filter.We put a fuel pressure gauge on the fuel rail and when the truck runs, it idles at 35psi, but after a bit it drops to 0, so i am convinced that it is a fuel issue. We are getting plenty of fuel pressure coming out from the fuel filter, and the line running from the filter to the fuel rail is not blocked.

At first we thought maybe there was some junk in the fuel line/rail that was blocking fuel flow, but i find it odd because the truck will run fine for a full 20-30 minutes before i lose pressure, if it was just blocked you'd think it would do it a lot sooner than a half hour of running. Fuel regulator on the return line is functioning properly as well. I'm out of possibilities, any ideas?

 

Interesting, you may want to verify your intank pumps are good as part of the troubleshooting process. Mine sat for a couple years before I bought it and it had the same problem except it would only run for about 5 minutes. Both intank pumps were bad.

You could disconnect the output line from the front of the dual reservoir that leads to the high pressure pump, uplug the high pressure pump so it doesn't run dry, connect a hose from the nipple to a bucket, ground out the test plug in the engine bay, turn the key on and make sure fuel comes out from each tank when you switch it. Of course observing safety precautions at all times with regards to fuel and open flames and sparks. This would give you a good indication if your intank pumps and reservoir is all functioning correctly.

If you had nothing coming out but still have power at the tank plugs, I'd say you were on to something. BTW, there are tons and tons of threads on fuel system troubleshooting, seems to be a common problem with these trucks. Search is your friend my friend.

 

Too add a little more info to this. When the truck dies and fuel pressure gauge goes to zero we can pull the line feeding the fuel rail from the pump and it pumps fuel fine. Fuel also shoots out of the fuel rail under pressure indicating a blockage. The problem is that is it so predictable I cannot believe a blockage could be that consistent with the time intervals of running and stalling. The incoming fuel line is on the passenger side fuel rail and the schrader valve is on the drivers side with a a rubber like tube connecting them. The tube does not look colapsed, but didn't want to remove the distributor and possibly the manifold to troubleshoot this without checking here first.

 

The engines runs for a short period when it has fuel, make sure the supply side is all functioning. Im guessing the high pressure pump is doing all it can to keep it running, but with out the low pressure (intank) pumps feeding it, it eventually cavitates. When that happens, its finished until enough fuel siphons its way back down there for the high pressure to pump it again.

If the supply side is all good, then you know you'll have to dig into the engine compartment.

 

II hear what your saying about the pumps. There are a couple reasons why I have have not gone that route. First the probability of both tanks having bad pumps makes it less likely although it is possible. The other thing is that as soon as the problem occurs I can pull the line going to the fuel rail and prime the HP pump and it shoots plenty of fuel. I will jam the fuel pressure gauge on it next time and see if I can get an actual pressure reading instead of just an inaccurate visual. Wont be able to look at it til next week, but will post back. Thanks

 

With that fuel system, something as simple as a restricted fuel return line or the wrong gas cap is on the tanks. If the return is blocked it only takes a short time to have the incoming (supply pressure) and return pressure to equalize and then no fuel will flow. The fuel cap can seal the tank from barometric pressure and the pump will not be able to maintain fuel supply.

 

I had actually though about the return equalizing, but as I stated earlier it blows fule out of the fuel rail when I take the supply line off. My son-in-law did just throw a couple new gas gaps on the tanks so we wouldn't have the old ones cause it to not pass emissions. Color me stupid, but I was not aware there were different types of gas caps. I will have him throw the old caps back on and see what happens.

 

With a little luck, it will work. The wrong cap can also effect an emmison test as you suggested. Please let me know if it works.

 

Yea it passed emission no problem. I just sent a text to my son-in-law to try the old caps. Hoping that is it even though I am going to feel real stupid. Thanks for the help so far

 

Apologies, I thought I posted the fix. Always hate it when I read a thread and the op never comes back with the fix and here I went and did it. Anyway, it turned out to be both in tank fuel pumps were not functioning. After the truck would sit it would fill the tank switching resevoir enough to allow the truck to run for a little while then die. We had discussed this early on, but I reasoned that the probabability of both pumps going out was too high. Hopefully this will help someone else out.