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Well, my 2c - the supply line is 10mm ID (very close to 3/8") and the return 8mm.
The "problem" with the in tank module for very high HP applications is known, but if everything is up to par should be OK for up to 500 hp on the wheels.
Air in the fuel is a problem over time- it increases wear because air does not lubricate as good as diesel. (Who'd have thought )
If it was my truck I'd go over the suction side very thoroughly for peace of mind. Pull tank module and check all the lines, connectors etc- if in doubt replace.
The draw straw or the sumps are better for extremely high horsepower, but come with disadvantages.
Mainly less usable fuel for the draw straw, more wear on the lift pump (no screen, stock has screen) and for the sump- water will always settle there and will get into the pumps.
I just wanted to say again guys, thank you for all of the valuable input.
I went through the suction side again and it looked like the hose clamp on the 5/8" tubing connected to the -in tank module- was a little bit loose. I also completely removed the module and inspected the inside for the health of the tubing and parts in there.
If i'm being honest the fuel pump in the tank looks a little worse for the wear, the outside of the metal of the pump actually has a minor amount of rust on it, who knows how old this part is?
There was a small amount of dirt at the bottom of the fuel bowl as well.
After cleaning the fuel sending assembly, I reinstalled everything and made sure to crank the heck out of the hose clamp holding the tubing onto the fitting @ the sender assembly. I went for a drive and while the issue seems reduced, I do feel like it's still present. I primed the FASS pump as well.
When I went for a test drive, I had the genius idea to turn my Edge Juice down to 0. The fueling issue is either so minimized or completely not apparent at this level that i'm convinced that the problem is related to turning up my tuner. I don't know if you could say this is a high horsepower related issue, because I really don't know what setting 5 (the setting i've been running at) actually corresponds to in terms of horsepower, but it has me convinced that a sump or draw straw is the right next move. I'm not interested in going back to factory fueling, this is a truck capable of high power and I am going to take advantage of it.
I found a kit from AirDog that allows piping a larger diameter draw straw right into the OEM-style fuel sender bowl, and this is probably the route I am going with. I will report back in a few days with how this impacts my truck performance.
If you still have the in tank pump your setup is rubbish. You can remove the in tank pump and replace it with a piece of 5/8" or 10mm id hose.
The FASS alone will then give you more than enough fuel to support what you have now.
The in tank pump is a massive restriction of the FASS has to suck through it, this exacerbates any minor pinhole before the FASS pump.
If you still have the in tank pump your setup is rubbish. You can remove the in tank pump and replace it with a piece of 5/8" or 10mm id hose.
The FASS alone will then give you more than enough fuel to support what you have now.
The in tank pump is a massive restriction of the FASS has to suck through it, this exacerbates any minor pinhole before the FASS pump.
**** that hurts
But, that's why i'm here! I didn't build the truck from the ground up, I just intend to fix what problems I acquired.
But, that's why i'm here! I didn't build the truck from the ground up, I just intend to fix what problems I acquired.
Well I know it can hurt, but a lot of people mod these trucks without the slightest inkling about physics.
To put it simple- 2 pumps in a row can only deliver as much fuel as the "smaller" pump passes through.
So, if the in tank pump is working it will deliver fuel to the FASS pump, and if that's working it will be delivered to the IP.
If one of these 2 pumps is not working either the stock in tank pump pushes the fuel through the FASS pump bypass, working against a big restriction compared to the stock system, or the FASS pump needs to suck fuel through the in tank pump bypass, sucking against a restriction.
The funny thing about that is that you can easily press large amounts of fuel through a small hole- just enough pressure differential needed, but for sucking fuel you have a maximum pressure differential of about 14-xx psi, depending on where you live. If you heat the diesel fuel to 50C you lose more than 10% of that pressure differential to vapor pressure.
So, the solution id to have one pump that has a good supply at low resistance and some way of monitoring the system.
Even a fuel pressure gauge will not show you if you get air into the fuel.
Well I know it can hurt, but a lot of people mod these trucks without the slightest inkling about physics.
To put it simple- 2 pumps in a row can only deliver as much fuel as the "smaller" pump passes through.
So, if the in tank pump is working it will deliver fuel to the FASS pump, and if that's working it will be delivered to the IP.
If one of these 2 pumps is not working either the stock in tank pump pushes the fuel through the FASS pump bypass, working against a big restriction compared to the stock system, or the FASS pump needs to suck fuel through the in tank pump bypass, sucking against a restriction.
The funny thing about that is that you can easily press large amounts of fuel through a small hole- just enough pressure differential needed, but for sucking fuel you have a maximum pressure differential of about 14-xx psi, depending on where you live. If you heat the diesel fuel to 50C you lose more than 10% of that pressure differential to vapor pressure.
So, the solution id to have one pump that has a good supply at low resistance and some way of monitoring the system. Even a fuel pressure gauge will not show you if you get air into the fuel.
I disagree with that point I highlighted in your post. Not sure if you put "not" in front of the word show by mistake.
In both of my air leaks, my FP gauge showed it by unstable fuel pressure, coupled with rough/strange running. I was able to eliminate a clogged filter as I had periods of making good power along with good pressure until another slug of air came in. A plugged filter generally causes the engine to fall on it's face as it is starving for fuel all the time.
You can catch clogged fuel filters on the gauge, assuming the gauge is tapped in after the filter. Normally you'll see a steady decline over time with that. In mine, a fresh filter gives me a FP of about 14 PSI at idle, and 12 PSI running down the interstate. As it filters, over time I'll see the FP decline. Once it drops below 10 while going down the road, I'll replace the filter at the next oil change (I do 10k mile oil changes).
As far as the fuel tank module goes, I agree, get rid of the in tank pump. It wasn't a great design, and didn't do any better than the block mounted lift pump it replaced.
Keep in mind, these engines are very efficient. Based on the information on my engine's data plate, the 235 HP Cummins ISB burns 13.2 gallons per hour at full rated power. Anything more than that supplied to the VP44 is returned the tank, but with limits. You can only push up to a certain amount of fuel through it's inlet, you can't force it to flow any more fuel through itself, either to burn or to pass through for cooling. FASS makes a good pump, but it is certainly is not pushing 95 or 150 GPH through a VP44. 3/8" fuel line and the factory tank module will flow plenty of fuel, even if modified for more power.
To keep that in perspective, that 3,100 HP Caterpillar I mentioned before, it was a 3608. Big inline 8 cylinder that weighed about 23 tons. 147.8L total displacement, each cylinder was 18.475L in displacement. It only needed a 1 inch fuel pipe, and burned 155 gallons an hour at full power (900 RPM).
I disagree with that point I highlighted in your post. Not sure if you put "not" in front of the word show by mistake.
Keep in mind, these engines are very efficient. Based on the information on my engine's data plate, the 235 HP Cummins ISB burns 13.2 gallons per hour at full rated power. Anything more than that supplied to the VP44 is returned the tank, but with limits. You can only push up to a certain amount of fuel through it's inlet, you can't force it to flow any more fuel through itself, either to burn or to pass through for cooling. FASS makes a good pump, but it is certainly is not pushing 95 or 150 GPH through a VP44. 3/8" fuel line and the factory tank module will flow plenty of fuel, even if modified for more power.
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I omitted the word "necessarily", I meant to say that the gauge will read the same as long as there isn't enough air to make the lift pump break suction.
I had ISBs that ran like (expletive of choice) due to air in the fuel. Not enough to get it to hiccup, but enough to mess up effective burn timing.
Getting rid of the aeration of the fuel got rid of the problems. Almost the same thing on a 12V last week. No issues except higher than normal EGTs and a rise in fuel consumption.
6 ft of 10mm ID fuel hose and back to normal.
According to a Bosch booklet on the VP44 I read it was (IIRC) about 1/3rd of the diesel gets injected at max torque wide open, and the rest is returned to the tank.
This was for the BMW engines where there is no lift pump, so this may vary for the Cummins.
I think that the pumps are rated at 95 or 150 gph free flowing. Going up to 20 psi or wherever will reduce the output.
A "too big" LP will circulate a lot of the fuel in the internal pressure relief, heating it up... maybe good for winter
The fuel burn rate is a known figure. It is published on every data plate mounted on every engine that Cummins produces. The data plate for our B series engine is on the timing case, drivers side. Rated HP is listed at a specific RPM, and fuel rate is in mm³ (cubic millimeters) at full power for each injection for one cylinder.
Using my data plate (pictured, bottom right of plate) for a 235 HP engine, full power is at 2,700 RPM, and each injection squirts 103 mm³ of fuel each time a cylinder fires. Using those numbers we can determine the fuel burn in gallons per hour:
103 x 2700 = 278,100 This is a 4 stroke engine so we have to divide by 2 (cylinders fire every other revolution)
278,100 / 2 = 139,050 This is the amount of fuel in cubic mm per cylinder burned every minute, now we need to multiply by 6 cylinders
139,050 x 6 = 834,300 That is the amount burned at full power every minute, multiply again by 60 to get fuel burned per hour.
834,300 x 60 = 50,058,000 cubic mm fuel burned per hour
Now to covert to GPH. It takes 1,000 cubic mm to equal 1 milliliter, and 1,000 milliliters equals 1 liter. So you either divide by 1,000 twice or simply divide by one million.
50,058,000 / 1,000,000 = 50.058 liters per hour burned at full power. Now to convert to gallons. 1 gallon equals 3.785412 liters.
50.058 / 3.785412 = 13.223 GPH burned at full power.
To get Brake Specific Fuel Consumption (BSFC) we need to divide fuel weight by rated power. Diesel weighs 7.1 lbs per gallon.
7.1 x 13.223 = 93.8833 lbs per hour
93.8833/235 = 0.3995 BSFC
The lower the BSFC, the more efficient an engine is at converting fuel to useful power. Not to be confused with fuel mileage.
A 1st gen Ram with 160 HP @ 2500 RPM, 78mm³, has a BSFC of 0.411
An early 3rd gen Ram with 305 HP @ 2900, 114mm³ has a BSFC of 0.365
A late 3rd gen Ram with 325 HP @ 2900 RPM, 132mm³, has a BSFC of 0.397
Yep, but to feed the pump correctly you'll need to feed the volumetric flow of the internal vane pump in the VP44. Which is much more than the fuel that can be injected by the same pump.
For sure. Where it gets confusing for most is how much that vane pump (and VP44) needs to be fed. The amount that vane pump can move is tied directly to RPM, and whatever doesn't make it down the injector lines, goes out the overflow valve and the bypass valve into the return line. I believe the maximum possible amount of fuel that can move through a VP44 is around 45 GPH (fuel burned and bypassed) at full power, assuming an unmodified VP44. Even if you tried to force feed it with a higher pressure lift pump, it cannot move any more fuel through itself. This is why the VP44 tends to max out around 500 HP without significant modification, the bypass solenoid is under very high duty cycle/stress and there is not much fuel left over for VP44 cooling going out the bypass.
The point I'd like to make here is that 3/8" lines coupled with a single lift pump capable of supplying 50 GPH @ 10-15 PSI is perfectly adequate for the needs of most VP44's.
The point I'd like to make here is that 3/8" lines coupled with a single lift pump capable of supplying 50 GPH @ 10-15 PSI is perfectly adequate for the needs of most VP44's.
I second that, and I want to add that a too big lift pump will only cycle fuel through it's internal pressure regulator- and that heats the fuel.
Multiple lift pumps in a row are a bad idea, we do not need anywhere near the pressure that would make them necessary, but increase the probability of a fault.
Now you know why I said that the 2 pump system is rubbish
Glad you got that fixed.
I think that the return hose should go into the cup to have the return fuel always enter below the fuel level to prevent foaming. But maybe I just didn't see it on the pictures.
I agree, and that's what I wanted to do but I couldn't easily remove the internal return hose without damaging it. I had actually planned to use the third hose that I removed as a replacement there but for now i'm just going to leave it. Sometimes when I try and finish things -perfectly- is when I cross into breaking **** territory.
03-11-2020, 04:45 PM
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Now you know why I said that the 2 pump system is rubbish 
