Normal fuel pressure?

[Sharecropper]

As many of you know I am assembling a P400 6.5 engine to replace the OEM 6.2 in my M1028. Details can be followed in my rebuild thread link below.

My question is, I am installing a mechanical fuel pressure gauge immediately upstream from my injection pump, between the pump and filter, and was wondering what a normal fuel pressure should be. I plan to primarily furnish fuel to the engine via the OEM mechanical fuel pump, however I have routed the fuel supply line in such a way that I can swap over to an electric fuel pump if necessary, or if the OEM pump becomes defective while out in the boonies. The P400 engines were designed to be used in the upfit HMMWV's which would have been turbocharged. I do not plan to turbo the P400, however that's an argument for a different thread. The P400 is rated at 250 HP turbo'd, so I had Huckstorf Diesel set the initial fuel delivery of my rebuilt DB2831-4911 for 200 horsepower. John Hucksdorf stated that I would be able to turn the fuel up or down on this IP to match the pump with the power of the engine. My goal is to provide the exact amount of fuel the engine can burn efficiently, no more or no less. Too less fuel would be wasting the potential of the engine, and too much fuel will be sent out the exhaust as un-burnt black smoke and wasted money. So what I am looking for is a starting point for fuel pressure as the fuel is entering the IP. I will monitor the fuel pressure gauge when the engine is under full power to make sure sufficient fuel is being delivered.

Thanks in advance for knowledgeable comments.

 

[chevymike]

I don't think there is an issue with too much fuel pressure before the IP, problems arise if you have too low of fuel pressure getting to the IP. As for adjusting your IP, that will be based on your exhaust. Start with what they set it at and then drive it. If under heavy load you are getting black smoke, then turn the pump down 1/8 turn and test again. You want to find the point where you are getting no or very little black smoke at full load (like uphill with your foot to the floor). At that point you are using the max amount you can.

Having the gauge in the low pressure side of the fuel system is good to know if you have a fuel pump going bad. Personally I would put it after the filter, so you can see if your filter is getting clogged and pressure is dropping. At the point after the filter, that is really what the IP will see and any problems would be at that point. Doesn't matter if your fuel pump is putting out 20 psi (just a random number), if after the filter it is only seeing 5 psi. The IP is only looking at pressure after the filter.

Not sure if that helps or not. So love how that engine is turning out! Good luck.

 

[Sharecropper]

I don't think there is an issue with too much fuel pressure before the IP, problems arise if you have too low of fuel pressure getting to the IP. As for adjusting your IP, that will be based on your exhaust. Start with what they set it at and then drive it. If under heavy load you are getting black smoke, then turn the pump down 1/8 turn and test again. You want to find the point where you are getting no or very little black smoke at full load (like uphill with your foot to the floor). At that point you are using the max amount you can.

Having the gauge in the low pressure side of the fuel system is good to know if you have a fuel pump going bad. Personally I would put it after the filter, so you can see if your filter is getting clogged and pressure is dropping. At the point after the filter, that is really what the IP will see and any problems would be at that point. Doesn't matter if your fuel pump is putting out 20 psi (just a random number), if after the filter it is only seeing 5 psi. The IP is only looking at pressure after the filter.

Not sure if that helps or not. So love how that engine is turning out! Good luck.

Thanks for your reply. - Yeah that's exactly what I am doing. I have mounted a new FFM on a new HMMWV intake and fabricated a -4AN hose from the FFM to the IP. I installed a ported adapter into the out-flow of the FFM so the mechanical fuel pressure gauge will be measuring the precise pressure going into the IP. Here's a photo of the adapter before I installed the intake -

 

[MarcusOReallyus]

Having the gauge in the low pressure side of the fuel system is good to know if you have a fuel pump going bad. Personally I would put it after the filter, so you can see if your filter is getting clogged and pressure is dropping. At the point after the filter, that is really what the IP will see and any problems would be at that point. Doesn't matter if your fuel pump is putting out 20 psi (just a random number), if after the filter it is only seeing 5 psi. The IP is only looking at pressure after the filter.

Agreed.

If you want to get really crazy, you can put one before and after, and that will tell you when it's time to change the filter.

 

[Sharecropper]

Agreed.

If you want to get really crazy, you can put one before and after, and that will tell you when it's time to change the filter.

Ummm.... not that crazy ............yet

 

[Mainsail]

I have one on the filter input. I'll go out after telework and fire it up and let you know what the pressure reads if that's what you're looking for.

 

[frank8003]

We used to put on gauge on each side of everything, but that was US Navy submarines. You gottah be able to fiqure out in a heartbeat what the machine/device is doing right now. Underwater there is few second chance guesses.
It adds complications and it all must be failsafe but valves and gauges are cheap.

 

[Sharecropper]

I have one on the filter input. I'll go out after telework and fire it up and let you know what the pressure reads if that's what you're looking for.

View attachment 796996

Yes that will be good information to have. Thanks.

 

[fitz]

Mainsail,
I have the same spin on filter base as you, where did you get that fuel gauge?
Thanks

 

[Mainsail]

Mainsail,
I have the same spin on filter base as you, where did you get that fuel gauge?
Thanks

Napa

See: https://www.steelsoldiers.com/threads/spin-on-fuel-filter-mod.114158/#post-1434074 and https://www.steelsoldiers.com/threa...ment-system-upgrade.93781/page-2#post-1433286

 

[Mainsail]

Yes that will be good information to have. Thanks.

Found it in the other thread: The gauge indicates between 9 and 10 psi at high idle, then when the idle drops it’s between 6 and 7 psi.

 

[Sharecropper]

Found it in the other thread: The gauge indicates between 9 and 10 psi at high idle, then when the idle drops it’s between 6 and 7 psi.

Thanks!

 

[fitz]

Thanks for that info Mainsail.
Looking forward to see Sharecropper's progress.