Diaphram Pump Failure Mode

[DonTX]

:--) Just thought I would share what can go wrong with a diaphram lift pump. The washer is peened on the end of the shaft, and just fell off. I temporarily put it back on for a photo shoot to show how it should be. I thought I had found the starting problems when I found this, but it has not made any difference to install a new pump. When this happens, you will find that the priming lever will not spring back, but just stay wherever you put it.

 

[JLEONARD]

Interesting... too bad it wasn't the cause of your problems though.

Jay

 

[DonTX]

I think it had been broken for a very long time, in the photo you can almost see the marks on the shaft where it was wearing from the yoke rubbing up and down from the cam action. It certainly did not have any apparent effect on the speed or power of the engine. (Pre lst gen, turned to 210hp)

 

[ptmoore]

so the prime lever is supposed to be spring loaded? does it pop all the way back up to the lock position by its self? expecting my fsm from genos any day now Oo.

 

[DonTX]

Yes it should come back up when you push it down. It also should feel like it is pumping something. On mine with this broken I could place the lever up or down. I could not find in the book where it should be stowed! That of course is because it stows itself and led me to find the broken pump. It is very easy to diagnose too, just open the bleed screw on the fuel filter banjo and if it is busted, it won't pump out fuel or bleed the system when you pump the prime lever. Since it was running OK, I mistakenly assumed that the manual priming part of the pump was all that was shot, and the rest was ok. .

 

[BushWakr - RIP]

FWIW..... the lift pump lever should be in the "up" position when not being used. You can also have a situation were the pump/lever won't do anything because the pump actuator arm is not on/in the right cam location..... in this case you need to keep kicking the engine over until there is resistance when operating the lever and after a while it will begin to push fuel for you... . just an observation...



pb.....

 

[pepecat]

mine doesn't spring back either, does this mean a new lift pump is in order?

Also my engine lacks power like it's running out of fuel after 4-5 seconds on WOT launches to top speed.

 

[DonTX]

You sure got that right! Easy to replace, cheap too, $40 at http://www.davesdiesel.com/DD88-93Dodge.html

Great people to deal with as well.

I never really laid my foot in mine hard, but in normal driving you would never know it was not operating.

Don't know if running it that way might have done my VE44 in yet or not.

 

[BushWakr - RIP]

The lift pump lever does not 'spring back' on these pumps, even when brand new. In fact the manual on these trucks says to be sure to return the leve to the 'up' position when done in order to prevent damage to the LP. .

The VE has it's own supply pump built in... it will 'fill the gap' without any damage if you LP is failing , but, if for any reason you loose prime the VE will rarely be able to restore the prime and let you keep driving. . so don't loosen or open any bleeder/banjo bolts if you suspect your LP is dead...



pb.....

 

[bgilbert]

Silly diaphram lift pump users:-laf...

 

[Fred Swanson]

Yeah, what Bill said.

 

[DonTX]

I am certainly far from being an expert on these Bushwakr, but my new one does definitely spring back UP, very smartly, I have damned near worn it out trouble shooting already. You must use a lot of pressure down, and in these pumps the spring is what does the work really, I cannot imagine making them so that did not happen. Could you photograph or scan that instruction for me? Do you have to use force in both directions?. My old one (an AC brand, definitely original equipment) of course did not spring anywhere, AND it was broke. I searched 6 older Cummins manuals, and none of them would speak to where the lever should be kept, maybe Dodge in the later years put something different on, do you know what brand they used?. Most interesting. How about it guys, will you be going out and priming yours to see if they come both ways? Of course if the cam is up, nothing happens.

Good advice though, if it is busted, you will about have to have a new pump to prime it.

 

[paccool]

Yea what Bill and Fred said! I chased my tail for a few months trying to get the twins setup and one of the problems was the stock lift pump could not supply the fuel I needed. The pressure at full load was 1-2 psi and the truck just didn't have the "umph" at full throttle.



Put the new piston pump on last weekend and actually picked up another pound or so of boost. Was a pretty easy install except for that silly sound pad! Had to take the die grinder to it with a cutting wheel to clear a path for the new line from the pump to the filter.



I recommend anyone that has increased the power to replace the stock pump with the piston pump *(or electric) to insure adaquate fuel flow and pressure.