Just how much fuel is there being pumped from the tank, into the filter, and back to the tank on these Cummins engines?

Like, is it a half gallon per minute, or just a trickle, or what?

Has anyone run a CDT by itself to see how much fuel is spitting out of the return fuel line destined for the tank?

I need to run some hard figures on this for a project I am doing. I'm not sure if I can do it to my truck or not, but I'd like to know this.

I see that there is a 5/16" line going back to the tank, but I'm not sure how much fuel travels in that line. I know it is less and less as you use more fuel during acceleration and stuff, but I was wondering about idle, when there is not much fuel being burned.

Thanks for any clues. I've seen a much bigger engine before which seemed like it just poured the fuel back into the tank at a pretty high rate. It didn't take long for the fuel tank to heat up.

If anyone has done this, I'd be keenly interested. Or if anyone could test this out, I could cough up some dough for you or the benefit of the forum.

All I need is someone with a stopwatch and a 5 gallon diesel can. And if the forum admin thinks it's okay to donate or to make offers like this, I will be definitely willing to.

 

Well, it really depends on the condition of your LP, as one of the factors. For example, in morning, and my LP is cold, I will have 10-12 PSI @ idle AFTER the filter, but BEFORE the CP3. When the pump warms up after a few miles of driving, I can come up to a red light and will be at 3-4 PSI @ idle.

So, right there, you would have 2 possible different amounts of fuel being returned to the tank. However, in the same breath, I do believe that even at 3-4 PSI or 10-12 PSI, the SAME amount is being returned at IDLE at those pressures since the fuel is being dumped into your fuel filter cannister, then drawn out by your CP3.

Now, as a mathemetical eqaution, you would have look at:

Pump delivery rate. Injector rate (from a prgramming standpoint and a static standpoint). Also need to look at BSHP to determine how efficient your motor is, which probaly isn't very @ idle. Or, you could do this:

Disconnect your return line, put it into a five gallon bucket, start your CTD, and time it with a stopwatch.

 

That's the only method I can come up with that will give the baseline figures I need for the project! As a side note, I figure that this is one way to obtain a bucket full of clean, warm diesel.

 

Urriamme, I think the majority of it goes back into tank, just from what I have read. A VERY interstling article all about 3rd Gen L.Pumps with great pics and flow rates etc. can be found @www.glacierdieselpower.com
Richard has probably done the research you are talking about already. Go to sight and look up 3rd "Gen lift pump exposed" hope this helps

 

Good stuff at Glacier. That's interesting, but I need to know the flow rates in the fuel lines once they leave the tank. I may call and ask Richard about this.

 

I was wondering this too... At full power, how little is being returned to the tank? Hmmm, That may be harder to see without a dyno run. I'm sure there is still something going back to the tank -- but I don't think there is a check valve on the return line.

 

I just tried to do this test. Problem 1: why is fuel spraying everywhere but into the funnel? To make a long story short, there is a little hose clamp on what apparently is the fuel supply line, where the line goes from 5/16" aluminum to a 3/8" rubber fuel hose. I took the clamp off and thought that this was the return line. I had tried to capture the fuel from the engine, but instead, fuel was being pumped from the tank.

I can't figure out why the return fuel line is BIGGER than the supply line. The return line is 3/8" aluminum, and the supply is 5/16". Go figure! And since I don't see anywhere that the return fuel line can be easily broken into, I have to do something else, maybe. I didn't want to cut the line, and I getting to either end of the fuel line is difficult.

Oh well, the truck pretty easily reprimed itself. Took three or four tap cranks to get it back in fuel, once I hooked its SUPPLY line back up. I sure wish the return line changed to hose line somewhere.

 

What kind of project is this?
Joe

 

And where are you located?

 

so there is no back pressure on the LP

and yes, what are you doing?

 

I one decided to drain my fuel tank that way, before I removed it...

I have a first gen, so things are probably a lot different, and I didn't bother to time it, but I would say it was getting out about a gallon every 5-10 minutes or so... Just for estimation purposes. (Sorry I couldn't be of more help.)

 

This is an interesting thread....

Along these lines, here's my question:

How much fuel does the Cummins burn at idle? I was always under the impression that diesels burned next to nothing at idle. However, it seems like at idle I can sit there and watch the MGP guage go down. Except to warm it up, I don't idle too much. I have hand calculated the MPG, and the overhead is usually within .1 - .2...

 

If I have my way, I will be able to tell you exactly in about a month or so. I am planning to ask Cummins these questions here soon, but haven't gotten the chance, yet.

 

Perfect data, if I understand you. You mean that you prevented fuel going into the main tank? And you somehow watched or figured out how much fuel the engine was, uh, rejecting? Just so I understand, I am trying to see if this is the amount of fuel coming back from the engine, in the return fuel line, supposedly destined for the fuel tank, which you had re-routed elsewhere? And you were running the engine at idle or something? Until you ran the tank out of fuel, I guess? Sounds like one way to skin a cat. I guess it worked for you, which counts!

Or perhaps you mean you just drained the tank with gravity or the fuel pump without the engine running? I have to see what you mean.

And you think it was roughly 1 gal per 7.5 minutes? That comes out to 18 gph, which equates to 68 Lph. A popular aftermarket fuel pump will put out a max of 255 Lph to an open discharge. So I would say you are in the ballpark. Not sure what a standard OEM lift pump puts out, but it's way less than 255.

 

Well, it's a special project of course! It is research for a major corporation, for developing a new patented product, and it is ultra top secret and if I told you I'd have to you. Just kidding.

I promise that when I finish the project, that I will have some very interesting data for everyone here. This is just some preliminary info I need to start, but once I get going I will be the one providing the data. I just needed a clue or two so I don't start on the wrong foot. I don't work on trucks everyday like some of you perhaps do.