7.3L fuel pressure with black spring

[gooseman80]

I'm looking for some opinions. Truck is a 2002 F350 and I currently have the three Dieselorings fuel pressure shim springs. As of right now, i have the black spring in because pressures using the silver and gold were less than expected. Fuel pressure with the black spring in should be between 67-70 psi but I am running a constant 59 psi. This is primarily the reason why I have the black spring in. I know one of the reasons that could be causing this is a weak fuel pump. I've never had a problem with this and the truck only has 178K miles, however, this can't be disregarded as a reason. Note that I purchased this spring kit around the same time that I installed a fuel bowl rebuild kit. The last time I researched this issue I believe it was suggested that I should bypass the fuel tank and see what my pressure is when the pump is directly sucking from a portable fuel tank. Do you think this would be a good start for investigating the issue? Right now the tank is amount 1/2 full and I really don't drive the truck much. Are there other reasons you can think of that could be causing this other than a weak fuel pump? Thanks guys

 

[6.0 Tech]

First off, did you monitor pressure prior to changing stuff? If pressure was low before, then there’s a truck issue, if it was good before, there is an issue with what you did.

If it’s a truck issue it could be quite a few things.

The filters in the tank are a definite possibility, those would be ruled out by running a suction hose directly off the suction side of the pump, eliminating the suction line also rules that out, and while uncommon, I’ve pulled my hair out over a couple of suction lines that had pin holes and had air leaks causing low pressure before, so that is another possibility.

Second, (or third if you count the suction line as #2), could be the pump, done plenty of them.

Third, make sure you’re getting a full 12v to the pump. As these trucks get older, wires start going to shit, relays start wearing out, grounds get corroded, etc.

Fourth, injector o rings are a possibility, a cut o ring is gonna lose pressure

Fifth, check the lines from the bowl to the heads. The one running to the rear of the passenger head has a tendency to get cut thru by the clamp that holds it to the plenum. Also, you could have got the o rings for the fuel lines kinda ****ed up and have some rubber blocking the line.

 

[gooseman80]

First off, did you monitor pressure prior to changing stuff? If pressure was low before, then there’s a truck issue, if it was good before, there is an issue with what you did.

Negative on the monitoring because my truck had a bad fuel leak at the bowl which prompted me to by a rebuild kit in the first place. After the repair is when I first started monitoring pressure in that I ended up coming up with some interesting fittings to connect my gauge to the upper pre filter port.

If it’s a truck issue it could be quite a few things.

The filters in the tank are a definite possibility, those would be ruled out by running a suction hose directly off the suction side of the pump, eliminating the suction line also rules that out, and while uncommon, I’ve pulled my hair out over a couple of suction lines that had pin holes and had air leaks causing low pressure before, so that is another possibility.

I never really thought about pin hole size air leaks pre pump. That's a pretty good point. I knew I would eventually have to test thing out by running the suction is a portable tank thereby bypassing everything in the main tank. It's just been on the back burner I guess. I've look at these fuel tank sumps that can be easily installed but haven't been able to afford anything like that yet plus I really need to verify why my pressure isn't higher before making more modifications I guess.

Second, (or third if you count the suction line as #2), could be the pump, done plenty of them.

I wish your was an easy way to test the health of the pump. I guess one would need to hook a pressure gauge directly post of it but figuring out all the fitting connections sounds like it would be a pain plus not sure if pressure along would tell me anything or not.

Third, make sure you’re getting a full 12v to the pump. As these trucks get older, wires start going to shit, relays start wearing out, grounds get corroded, etc.

I have not thought about the current or voltage feeding the pump. That is a really good point. Tomorrow I'll look it over to see if I could even pin the connectors to it or not. If not, then I'm not sure how to go about it. I would hate to have to pin directly through the wire insulation.

Fourth, injector o rings are a possibility, a cut o ring is gonna lose pressure

Got to be a why to test that without physically looking at the orings.

Fifth, check the lines from the bowl to the heads. The one running to the rear of the passenger head has a tendency to get cut thru by the clamp that holds it to the plenum. Also, you could have got the o rings for the fuel lines kinda ****ed up and have some rubber blocking the line.

Yeah, I ran through all lines and replaced the orings. It was a cheaper option then buying new lines. I'm pretty sure they are how they were before.

Thanks for the help.....