So I have been hunting and throwing parts at this truck for awhile now with no help.

The truck has a miss with part throttle and will die off (no power) as you get to and try to go over3K RPM's.

Originally I thought ignition and went at the truck with plugs, wires, cap, rotor, PCV valve. It seemed to help a little but then the symptoms came back just like before.

We had one bad fuel pump in the rear tank so I changed that and even running on that tank the problem is the same.

So I went and changed the fuel filter which when disconnected didn't flow out full stream so I thought I had it for sure this time. Once again it seemed better for a little while then back to the same deal.

After all this I finally checked the fuel pressure with a make shift air pressure gauge and fittings. Pulled the shradder valve out and screwed in the gauge. I got 20PSI with barely any change with the vacuum line pulled. So I change the FPR. Check pressure again. 31PSI engine off, 25-28psi engine on and around 34PSI with the vacuum line pulled. When I would pull the vacuum line and the pressure would rise the engine would run better (like it should).

So now here I am, New plugs, wires, cap, rotor, fuel pump, FPR, filter, injectors replaced 20K miles ago and still a miss and low fuel pressure.

The two things I question yet are the tank selector (doesn't do anything it shouldn't but still in question) and the fuel pump relay. I question if there is only one relay if it is just old and not putting full 12V current threw to the pumps?

There are times when the truck will run a bit better than others. Sometimes the truck will die at idle or not even start and then other times it will run like it should (kind of). The dieing at idle and no start is very very rare. Runs the same on both tanks.

Anyone have some ideas? Are both fuel pumps ran off the same relay? Which relay is it? Anything else I should be looking at? Thanks for any help!

 

Just tried moving relays around with no change. Ran a code check and only got back the EGR code that has been in this truck for the last like 10 years. Tried doing the cylinder contribution test without success.

I can feel a pulse in the fuel lines, FPR, fuel rail as the truck is running. I tried unplugging the FPR again and while it does idle smoother when I try to rev up the motor it acts like it is flooding out.

Vacuum gauge reads about 17-18 inches at idle.

 

Anything below 30psi fuel pressure and the motor won't make full power, you should see 40-45psi with vacuum removed engine running and it should not drop at any rpm so you still have a problem. Does your truck have dual tanks? There is no selector valve on gasoline trucks built after 1989 so that's not your problem, but if it's a dual tank truck you could have the fuel transfer problem where fuel is pumped into the other tank as you drive and this will also affect pressure at the motor. There are check valves in the FDM inside the tank that are supposed to prevent this but they get gummed up and fail over time, so in your case you would have to disconnect and plug the lines to the other tank or replace the FDM.