Checking fuel pressure.

[wanabebig]

Ok, as it says, checking fuel pressure, and I have searched but havn't seen the answers i'm looking for. I have a 1985 F350 with the 6.9, and it has all the factory set up. i'm having fuel issues as it won't start. i've changed out the filter, it ran fine before just seems like i'm not getting fuel pressure. On other vehicles, that i've tested which were gas engines you just hooked up a fuel gauge to the conector on the fuel rail. Since theres no rail, do i put the fuel psi gauge on the shrader (spelling) valve on the filter head to get the pressure from my lift pump? If that is the right spot, then what psi am i supposed to be seeing there?
Thanks
Jim

 

[dgr]

The new pump you may pick up at Napa is rated for 4 to 6 PSI. You can take the core out of the schrader and "screw" on the hose to your pressure gauge. I believe that will give you pressure after the fuel filter element. But with a new filter, it should be accurate.

However, holding the schrader in while cranking the engine should give you enough of an indicator as to whether or not you are getting enough fuel pressure for the engine to start. Or you can disconnect the bleed line that goes from the fuel filter head to the return cap on the injector and watch for a stream of fuel there.

 

[dgr]

One other thing. Did you fill the filter with fuel or ATF? If you did, pull it and it should still be full. If you didn't, bleed from the schrader to fill it or pull it off and fill it.

If you have fuel flowing through the filter and if you got enough air in the system, you may have air in your injector lines. Loosen them slightly and crank with the throttle open until diesel leaks out of them. If you get lucky, the engine will start on a couple cylinders and that will bleed the other lines for you. tighten the lines as they each start leaking fuel.

By the way, how did you ascertain it is a fuel pressure issue?

 

[TWeatherford]

Thats where you want to tap in for your pressure. I have always read that you should see 4-7 psi out of your lift pump. Once I put a gauge on (mine is in the cab), I have never seen more than 4 psi and usually only 2-3, even after changing out 3 different Carter fuel pumps in an attempt to get the 4-7 psi (and changing to a fresh fuel filter). After the 3rd pump gave me the same result, I said forget it and the truck has been running ever since. Could be a bad gauge, but its an autometer which are supposed to be good. Sometimes running hard down the interstate on a cold morning, it'll drop to zero, still not sure why it does that (really need to figure it out), but the truck never slows down.