Fuel Pressure

[ISX]

I made an article on fuel pressure and am having some issues. I think I know what the problem is but I figured I would keep tabs of the problem on a thread so someone else can learn too. In that article, my fuel pressure tops out at ~22psi. It is supposed to "never fall under 25psi under a load" so the fact that it was just idling and couldn't get to it (even when at 2500RPM) tells me there is something going on. After restricting the return line, pressure rose and I stopped restricting at 30psi and it remained at that pressure throughout the entire RPM range. Ok, bad overflow valve. Got the new one in today and stuck it in. Pressure is now normal. 17-22psi idle, 25-35psi at 2500RPM. After getting onto the road, it was a different story. Pressure was fine until you floored it and it would reach a low of ~22psi. The overflow valve works fine, so the next thing in line is filtering. I haven't touched them in a while and I have a feeling they are not going to be pretty. After changing the main filter and cleaning the fuel heater prefilter, I will test again. If no change, we will move on to the lift pump. Should be interesting. This shows that pressure alone means nothing. We need flow too. All the test procedures say to run all the tests idling and mine is perfect, but driving needs flow. So they need to add it to their procedure. I will get the filter tomorrow and see what happens. If nothing, I will try and dig up some lift pump diagnostics. I ran a flow test at idle a couple weeks ago and got I think it was 36GPH. The lift pump is mechanical so the flow increases as RPM increases. Naturally, idle RPM will have a lower flow.

[Mopar1973Man]

Yeah its very simular to the electric versions... As demand volume increases (WOT) supply volume is restricted (plugged filter or weak lift pump) you'll start to see the pressure fall at heavy demands this is pointing to supply volume being weaker than demand volume. So now if you insure your lift pump is supplying good volume the pressure should keep up under load...

[ISX]

Yeah its very simular to the electric versions... As demand volume increases (WOT) supply volume is restricted (plugged filter or weak lift pump) you'll start to see the pressure fall at heavy demands this is pointing to supply volume being weaker than demand volume. So now if you insure your lift pump is supplying good volume the pressure should keep up under load...

Yeah I'm just thinking the fuel filter isn't letting it flow. It can let it flow down lower but when it needs a lot of flow (floored) it just won't let that kind of volume pass through. Have to see tomorrow. I've gone a long time on this fuel filter lol. Long enough that I don't want to talk about it I might drill and tap the filter housing like it is stock on 24v's so then I have some prefilter test ports.

[Mopar1973Man]

You need a in cab fuel pressure gauge... You'll love to see the pressure as you drive... Trust me...

[ISX]

So I changed out the fuel filter and cleaned out the prefilter. Problem solved. I didn't really see it go over 35PSI before, now it will get to 45. I read that you don't want to ever go over 45 so I am at the limit and don't think I will do anything about it since the spring will wear and then it will be lower. It actually only hits that pressure when you are high in the RPM's and let off, since it isn't burning any fuel and the pump is still pumping really good, the pressure just builds up. I think it might be an overflow valve inlet size issue that causes it not to relieve all the pressure fast enough. On this site http://torkteknology.com/products.php?product=TORK-TEK-CUMMINS--ADJUSTABLE-OVERFLOW-VALVE-OFV040 it says they went to a smaller inlet size to make the overflow valve last longer. The good thing is that when I floor it, it only drops to 35. I am going to have to change up the article I made so it includes all of this, including that site for the fancy valve that supposedly is the cats meow.

[Zacharynels]

Interesting, I have no fuel pressure gauge and no means to test my fuel pressure, without the help of my mechanic but I think I may be having some low pressure issues and think it may be my overflow as well. I made a writeup on cummins forum awhile back about the Tek Tork valve and everyone seems to love it and Don is a great guy from what i have heard and will help people get their perfect overflow parts. I will be ordering the adjustable overflow, as this is what i made the writeup on. I will post up how it works out for me. Still wanna get my gauges and make sure everything is where it needs to be yet.Need more $$$!