fuel level=power?????

[Goddard]

sounds stupid but here goes. on the way bac from bristol this weekend pulling the 5ver i thought the truck was running ok. after stopping for fuel the truck seemed to pull better? more power?... ... ... ... i was almost to empty when i stopped and topped it off. sounds stupid but what could make the difference? everything is as signature says. thanks for any help. ?

 

[Whitmore]

Goddard

At one time I thought that the level in the tank could be in direct connection with the amount of head pressure that feeds the pump. I dont know for sure but I think the elevation to the suction of our lift pumps is higher than the bottom leval of our tanks, If that is indeed a fact than if we showed a 1/4 leval in the tank and say we broke the connection between the two and allowed some air to break the seal than theroeticaly we would loose suction at the lift pump, now if that seal is never broken the suction (although negative) should remain in tact.

I hope this makes sense to you, and after looking at the set up and understanding how it works I do know that the system could be alot better,



#1 the draw point from the fuel tank could be alot better feed if its takeoff point were from the bottom, the only problem with this is than there could be a chance of breaking it off as it would be a very low point, but it would enhance the performance of the lift pump.



#2 Several members have already proven the validity of this one, the closer the pump is mounted to the supply the better. That is a simple rule and applies to all pumps and the flow they deliver.



So after all that rambling I will comment that thru my observation between the fuel leval and the discharge pressure from my lift pump I have noticed no difference in performance... ... ... ... ..... JMO... ... ..... some may want to argue though... ... ... ..... Kevin

 

[chuck3]

Kevin, good point. That the same observation I came too upon reading this thread.

Kevin, you say you see no difference with your pump, but what if your pump was dying? I just wonder if it might show up then?

 

[Whitmore]

weak pump

Chuck, I would certanly think that if your lift pump was not at full strength and your tank level were 1/4 or lower that the low pressure or no pressure may show then soley due to the negative suction... ... ... ... ... . I would like to see a pump curve on these POS lift pumps and how they corilate to the tank level . this would tell us a big story.



I still think that one lift pump back by the tank with a possitive head pressure would be the ultimate set up and live as long as you did not run it dry!!!!!!!!!!!!!!! JMO. Kevin

 

[Mac]

I think there is a possibility that as the tank level decreases, the fuel gets warmer due to the recirculated fuel. Warmer fuel is less dense maybe, less power,maybe.

 

[Steve Campbell]

Here is an excert from the Fuel Preparator site...

The easiest is to entrain tiny bubbles in the liquid by shaking or agitating it.

The source of the vapor is the fuel itself. Like water, fuel contains a certain amount of dissolved air depending upon fuel temperature and the amount of aeration. ”



>The second way to develop air/vapor in a liquid is through vaporization

This can be accelerated by heating the liquid or putting it under a vacuum. As fuel enters the fuel line, it is then placed under a vacuum and vaporization occurs. The hot fuel condition of the electronic engines, combined with the increased flow rate, creates higher vacuum and major vaporization. Hot fuel foams at approximately 2 in hg vacuum. As a fuel filter gets dirtier, it causes increased fuel flow restriction, or simply, it increases the vacuum in the fuel line, increasing vaporization. Pump cavitation also creates vaporization. As vacuum increases, so does pump cavitation.

With the lower fuel level in the fuel tanks, the fuel pump had to create more vacuum to pull the fuel to the fuel pump. This increased vacuum creates more air/vapor. Everyone realizes that a dirty fuel filter creates poor performance/fuel mileage. When fuel is under a vacuum, air/vapor is produced. When vacuum is increase due to a dirty fuel filter, lower fuel tank levels, etc, more air/vapor will be produced creating more of a problem. Why tolerate any vacuum/restriction?





Sounds plausable.

 

[LSMITH]

Sounds like you got a tank of good quality diesel. I have had the same thing happen a couple of times. There can be some pretty big differences in the power with #2 diesel, BTU content varies quite a bit.

 

[Goddard]

don't think on the fuel because it was bought in the same area on the way down. also in coal country and these guys don't put up with bad fuel. but it is possible! time for some gauges.

 

[fj40charles]

Might be related to fuel pressure. I've noticed that I generally get better fuel pressure (measured at the filter) when the tank is full.

Near empty, it shows lower pressure. I believe there might be a correlation between lift pump life and amount of fuel you have in the tank.



Charles

 

[chuck3]

Kevin,

I agree with the pump at or around tank area with head pressure being the ultimate setup. I maintain and rebuild pumps at my job, and can tell you they need head press. to work right and to last.

Don't know what D. C. was thinking when they put those pumps there. Or did Cummins do it? I hope not.

 

[rashwor]

Cummins supplied and equipped.

I believe the lift pump is selected and placed on the block by Cummins, not DC. Cummins, give us a pump that lasts please!

 

[Whitmore]

head pressure

I agree with the pump at or around tank area with head pressure being the ultimate setup

Chuck 3, yes head psi is very important for pumps to maintain a positive feed pressure so they wont cavitate.



At work we have some set ups where there is no or little head pressure on a vessel that holds a supply to a pump and what we do is put a few pounds os nitrogen on it as a blanket thus giving a positive or addiquate supply to the pump,



Maybe we need to do that with our trucks, some members have on board compressors its a ****ty fix for a **** poor design but it would work... ..... Kevin

 

[Bigsaint]

Fuel temp.

I've had a sender rigged up for a while now, to monitor fuel temp. Mine is plugged into a pressure port, right after the outlet to the Mallory pump. After it has been sitting all night, start up fuel temp. is very close to the ambient outside air temp (no brainer there). After a 10-20 mile drive, my fuel temp is typically 10-15 degrees higher than the ambient outside temp, doesn't seem to matter whether I have a 1/2 tank of fuel or a full tank. I never go below 1/2 a tank, so I can't report on those readings. Common sense would suggest that the lower fuel level in the tank would give higher temp. readings, due to the return of fuel in a smaller supply source, though I don't believe the temp. difference is enough to lose any seat of pants power felt. Some of the guys that run the 1/4 mile use coolers, perhaps the colder fuel helps them shave 1/10's.



I can tell when we have switched from summer diesel to winter blend, and back again. My MPG's drop with the winter fuel and so does the trucks performance. They must have recently started to return to summer diesel here, my MPG's have gained about1 MPG and the performance increased as well.



Scott W.