low fuel pressure

If it seems to be running fine otherwise, maybe the restriction is in the line to the gauge giving you a false reading. Some trucks have a manual valve (with a "T" handle) installed in the gauge line where it comes from the filter head used to snub the pressure wave that causes the gauge to bounce. If yours has one, it could have been bumped slightly closed while the conversion work was being done causing a low gauge reading.

 

I use gliserin filled guage it takes most all the fuel pump vibrations. But he should still see increase when pump is shimmed. I put a regulator out of sdp and gained 10 psi.

 

Ok sorry this is very strange situation

 

1st take of the return line from the secondary filter that returns back to the tank and put a cap on the filter side to block it.
WARNING though!! don't go above idle RMP whilst doing this test!!!
Start the engine and watch the gauge and see what PSI it reaches at Idle.
You should see the needle jumping on on the gauge as the Safety valve in the transfer pump cracks off.
This eliminated all other valveing in the system and only shows the Safety Relief Valve in the pump operating pressure.
Once you have recorded this you can gently raise the idle slightly but watch the gauge and make sure the safety Relief valve is managing the pressure and flow. You will be able to determine if its a Pump or a Safety relief Valve problem.

 

That line shouldnt matter if it was plugged u would just get the pump pressure because of safty valve.

 

Let me no what happens