I have a stewart warner electric fuel pressure gauge. I mounted the sending unit to the fuel rail, I had to ground the fuel rail to the valve cover. The gauge works fine when its not running,, but when I start it up the tach shutters then goes down and doesnt work. Just curious what you think could be the reason for this? Thanks'

 

Does anyone know why its not working wile engine is running?

 

Sounds like a ground issue. Try running a temporary ground wire from the sending unit to the negative post on the fenderwell (where the battery ground is located). This should tell you if it is a ground issue.

 

Ok will do thanks for the info. See I had to ground the fuel rail so that the sending unit could be grounded maybe I need to find a better location other than valve cover to ground the fuel rail