Having low fuel pressure on a 1995, Cummins of course. Installed new overflow valve. Helped a little. Was suggested I check vacuum at the lift pump on back to fuel tank. Looking in the shop manual for these trucks, it mentions a special hose adapter tool, a tee. Gives part # as 6837.So far, haven't found this tee. This is on page 14-108. Anyone know where I could get this tee? Or any other way to check for a leak from the lift pump to the tank. Trying to avoid removing tank. Have not tried new lift pump. Want to keep it mechanical. Only 70K on the truck. Wouldn't think the pump would be out. Fuel heater is gone, screen there is clean. 10-15# at idle. Going down the road it drops to zero. Can only get to about 70-75 MPH . Could use some help!! jps

 

you didnt mention a new fuel filter????? this would definatly cause your problems!

 

Yes , it does have a new fuel filter. Sorry, forgot to mention!! jps

 

is the truck bone stock? injectors/dv's ect. i ran my stock lift pump for a long time prolly in the rehlm of 400hp and my fuel pressure would fall way off. if not sounds like the LP is on its way out. how long did this truck sit? wouldnt think at 70k it would be acting up though?

 

Kinda what I thought on the lift pump. 70k isn't a lot of miles. Pretty much stock. We drive in probably once or twice a month. Made 400 mi. trip to twin cities is when we noticed the problem. Did just put in new over flow valve. Seems to help a little. Now approx. 15# at idle. Had 10# before. When I test on road, 70mph is about it. Pressure drops back to zero. Do not want to drop tank if at all possible. Thinking of trying lift pump first. Thanks for the reply, by the way!!! jps

 

i would go lift pump instead of lines UNLESS it is VERY hard starting? if you have a air leak in a line than the LP has to catch up every time you start the truck which will make for long cranking periods. if its just a weak lift pump then it should... fire right up just have no power under a load because the fuel pressure isnt there.

also dont keep running it hard thinking things will change or you will eat an IP and then you are out lots for dollars.

 

I think you are right. Hope it is not fuel tank related!! jps

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Also tried tying up shut off . Made no difference. Starts good!!! jps

 

pressurize the fuel system via the tank and fuel leaks will show. you can remove the fuel line from the tank at the TP and using leak detector bubbles blow through the line. the running test is to pinch the return line. thus the adapter cause the stock line is hard plastic not to be deformed. it can be lots of stuff you can do it. be systematic and determined in your elimination. They are strong motors but like all diesels they will act like the princess that slept on the pea when they get air in them. but your running fuel pressure should build up. and the over flow should be closer to 20 psi.