Thread: Fuel pressure.
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Old 09-08-2010, 12:48 PM
barry123400 barry123400 is offline
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Join Date: Nov 2004
Location: Nova Scotia, Canada.
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Quote:
Originally Posted by 4x4_Welder View Post
True, but that pulse is not timed to the inlet of another element, and it isn't a very large amount of fuel either. The lift pump, however, does send out a fairly large amount of fuel on each shot, and has the potential to increase the pressure to whichever element it's timed closest to, causing uneven filling and differences in timing/power output between cylinders. It's just a theory, though, I have no direct research to back this up.
The pulses are not timed to any other elements loading period perhaps. Yet at low injection pump base pressure the resultant longer lasting turbulance may have more of an effect.

By it's design I see a good lift pump with fairly tight internal valves having a design of least disturbance pulsewise to the fuel supply. If the internal valves are leaky enough the fuel pressure supply pressure gradient may become less constant through one cycle. More likely the pump will not maintain 30 pounds plus pressure though.

The lift pump repositions it's fuel pressure piston once every injection pump rotation. The simplest test to verify that excess internal leakage is not present is to close the return line on the injection pump off. Your pressure gauge should slam to thirty pounds. This indicates any leakage losses inside the pump are still acceptable. If lower than 30 pounds there is either an obstruction to flow somewhere or the pump needs a rebuild. A ten dollar kit and a little care should do it if it turns out to be the pump.

The actions ocuring inside the pump base are chaotic in my opinion. The pump is set up on a machine that allows for those chaotic events. The saving grace is they are repedative as well as seeming chaotic.

This is where the proper background fuel pressure of 15-19 pounds becomes so important. With all the interactions being present the pump was calibrated at a certain base pressure. Start dropping that base pressure and the chaotic events start to have more influence. Especially when the injection pumps base pressure becomes lower than the relief valves opening pressure.

With the change of the primary elements filling pressure. The effects are going to become abnormal or outside the injection pump manufacturers intent by design.

On a pump being fed the proper higher fuel pressure the relief valve is always open.In my opinion this allows the cigar hose to moderate some of the pulse effects. Or once again get the calibrated injection pump back into the operational parameters it was set up for.

Especially when the return fuel line in the tank is submerged in fuel. A lot of people believe the cigar hose is only a noise reduction device. I believe it has been proven otherwise. Also the cigar hose does reduce the noise component. In doing so it is tending to average the overall effect of the sharp pulses or excess turbulance downward I believe.

Fortunatly we have no real concerns here as long as the base presure in the injection pump is fed properly and the relief valve is calibrated to say 15-19 pounds with the upper side of the range being prefferable.

I also do not hear of cases where the cigar hose has gone hard with age. If you live in the south it may be otherwise. If you suspect your has check pliability or hardness against a new one. It can be the small details in any well designed system upsetting the applecart.

Fortunatly everything in that system of fuel supply is both managable and restorable to good condition at minumin cost and some effort. The vast majority of site members can manage this in my opinion. But you do need a 0-30 pound liquid filled gauge to verify it is where it should be and all is well.

The gauge mounted as a permanent item allows forward monitoring. Warning you in advance of deterioration of fuel filters and other things. This is worth serious consideration in my opinion.

Better fuel milage, smoother idle, and most importantly the survival of the number one rod bearing in the engine may depend on the proper base pressure in the injection pump being present.

Quite some time ago I felt a company that could build sophisticated aeroplane engines at one time. Would not leave an oiling issue unsolved for the length of run of both the 616 and 617 type engines. So until proven otherwise low fuel supply pressure feeds more fuel through the number one element or retards the timing of injectors past number one in comparison. This results in loading the number one cylinder with more work than the others. Over time this wears out the number one rod bearing first besides reducing overall power and fuel economy.

If what I believe to be true it is only good economic sense to pay attention to the fuel supply area. In a good percentage of cars it will be substandard. The added plus is the more you learn about this system the easier it is to keep it in good condition or troubleshoot it if it comes to it.

Who in there right mind wants to take their older cars to the average service garage in todays economy anyways. Brings a total new meaning of you get what you pay for. They got the pay for part of it right..
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