Not a truck question, but...

[Bogger Man]

What would cause my buddies boat to have low fuel pressure? He has had the fuel pump tested, it's at 20psi. All new fuel lines, pressure gauges on both sides of the regulator. Screen filters cleaned or replaced, new water separator. He, says he is only getting 4-6psi and should be getting about 14psi. The pick ups are clean in the fuel cells. It doesn't matter if it is at an idle or revved up. He has went up 8 jet sizes and the plugs will not richen up(no change in appearance on plugs). It is a mechanical pump also, so it is mounted where it should be. He doesn't think there are any vacuum leaks, he is at a loss. Any ideas?

 

[K5dreamer]

did he check the lobe on the camshaft that drives the pump? if that lobe went flat, or the rod that connects the pump to that lobe bent, or wore down, it wouldnt be moving the diaphram on the pump as much as its designed to, and youd get low pressure and flow.

with everything else thats been addressed, thats the last thing i could think of.

 

[4X4HIGH]

What would cause my buddies boat to have low fuel pressure? He has had the fuel pump tested, it's at 20psi. All new fuel lines, pressure gauges on both sides of the regulator. Screen filters cleaned or replaced, new water separator. He, says he is only getting 4-6psi and should be getting about 14psi. The pick ups are clean in the fuel cells. It doesn't matter if it is at an idle or revved up. He has went up 8 jet sizes and the plugs will not richen up(no change in appearance on plugs). It is a mechanical pump also, so it is mounted where it should be. He doesn't think there are any vacuum leaks, he is at a loss. Any ideas?

First off, what kind of mechanical fuel pump is it (brand and also diaphram or gerotor type)? I've never seen a factory mechanical pump that would produce more than about 9 psi of fuel pressure. Unless he has some aftermarket high pressure pump he will never see 14psi and assuming the thing is carbed he doesn't want more than about 7psi anyways or you can overcome the needle/seat in the carb and flood the engine.

 

[Bogger Man]

It is a Clay Smith fuel pump,I have no idea what type. I do know that he has the regulator set at 7psi. I was just saying that he should be getting 14psi or so out of the pump. And I asked him about the cam and push rod, he doesn't think that is it since they are fairly new but he will check them. He is also going to check and see if the anti-siphon valves on the tops of the fuel cells might be sticking shut a little. Thanks for the input though, we appreciate it!

 

[4X4HIGH]

It is a Clay Smith fuel pump,I have no idea what type. I do know that he has the regulator set at 7psi. I was just saying that he should be getting 14psi or so out of the pump. And I asked him about the cam and push rod, he doesn't think that is it since they are fairly new but he will check them. He is also going to check and see if the anti-siphon valves on the tops of the fuel cells might be sticking shut a little. Thanks for the input though, we appreciate it!

I'm not seeing where he's having a problem if he has his regulator set for 7psi then that's all the pressure he's going to get regardless of what the pump is "capable" of producing. The regulator determines what the fuel pressure will be.

Having a pressure gauge mounted before the regulator will read what the pressure is with the regulator adjusted (7psi in this case) and a pressure gauge after the regulator shouldn't read any pressure if it's a return system.

 

[Bogger Man]

Now you see why we are stumped, the pressure gauge before the regulator is only reading 4-6psi? He tried a different gauge also.

 

[4X4HIGH]

Now you see why we are stumped, the pressure gauge before the regulator is only reading 4-6psi? He tried a different gauge also.

Ok, i'm going to assume that your questioning why the regulator is set to 7 psi but you're only getting 4-6 on the gauge?

Let me first say that a mechanical pump won't generally give you a precise reading because of the design of a mechanical pump. It is probably that the regulator isn't accurate. Have you/he adjusted the regulator for a higher pressure and not get a higher reading on the gauge? If so then i would suspect a faulty regulator if you've dead headed the pump and know that it is capable of producing 20 psi.