Switch or Valve?

[The--Tank]

Hey guys I'm new to the site and I have been trolling around looking for the answer to my question but can't seem to find it. I just bought my son an 86 4x4 the the PO replaced the 305 with a 350 and it runs and drives great, my only problem is when I'm running on the driver side tank around 70 it starts cutting out real bad like it is starving for fuel. I thought it might have been the carb but runs fine on the other tank so it leads me to belive it's either the switch on the dash or the valve under the truck. Thoughts?

[wheels67]

Does each tank have a fuel filter? Replace those. Check the rubber lines back at tank for cracks starting. If so a small vacumn leak may inhibit pull of fuel at speed.

[The--Tank]

I had that thought too but the only filter I can find is in the engine bay and the one on the electric fuel pump. I forgot to say the 350 is a center bolt valve cover engine so he had to put an electric fuel pump on it.

[Gregs71]

I believe there is a filter on the frame rail about under the passenger side of the cab.

[The--Tank]

nope no filter the PO must have taken it off. It only does this on one tank the other runs like a champ!

[1LowToy]

Try trading the fuel caps left to right. Dumb but worth a try for free. One may not be venting. The valve may be obstructed on one side. It can be by-passed to one tank or the other to eliminate the tank screen.

[dropd80s]

I would say with your initial description it would be a split in the fuel line on the one side. Now that both sides are screwing up it may be possible that your wiring to the selector valve may be not let it fully switch from one side to the other. Its a relitively simple system but, if you get tired of diagnosing problems you can bypass the valve and one tank untill you get time to mess with it again.

[Prerunner1982]

The Tank... welcome from Edmond. Where in OK are you?

With your initial problem being related to one tank I would suspect it is in the lines for that specific tank to the engine (as mentioned a split) or with the tank itself. If it only does it around 70mph this would also support the leak theory due to high pressure by the fuel pump.

As far as the gauge problem, a bad ground/connection at the senders, or perhaps a bad connection at the gauge can cause it to read incorrectly or bounce.

[The--Tank]

Thanks for the reply. I'm down south by Blanchard but my folks still live in Edmond and that's were I went to High School. I guess I will have to pull the bed off and just check the hoses up there I don't see any cracks on the ones I can see.. I did rub a hole in the fuel line yesterday though!!! Great fun!! Nothing like watching the guage go from full to empty in 20 miles. I really need to just replumb this thing motor to tank. Any reason I should have a fuel pressure reg on this thing. It's a stock motor with a 4 barrel. I have never had one on any motors I have built before but then again this is the first electric fuel pump I've had too.