Dying Engine Driven Fuel Pump

[scsmith]

I have just this week noticed that the fuel pressure will fluctuate between a fairly normal 25 psi and slowly drop as low as 21 psi for an instant, then back up to 25. The pressure fluctuation is like a sine wave variation over a 6--7 second period.

Based on what Nigel shared from two years ago, I think it is time for a new fuel pump?

[scsmith]

So, I ordered a new Tempest AF-15473 fuel pump. When it arrived, I was kind of surprised that I can not cycle the pump manually by pushing on the lever.

This is a high pressure pump for fuel-injected engines.

Are the springs just so stiff on the high-pressure pump that I should not be able to move the lever?
My recollection on old auto fuel pumps is that it was easy to move the lever and cycle the pump. But those are all low pressure pumps.

So I don't know if I should be worried that this one is so stiff or not.???

[N184DA]

There is very little movement of the arm. Surprised me as well when I replaced my low-pressure pump last year.

Somewhere here on VAF, there is a post describing the limited sweep range of the arm.

[DanH]

Originally Posted by scsmith

So, I ordered a new Tempest AF-15473 fuel pump. When it arrived, I was kind of surprised that I can not cycle the pump manually by pushing on the lever.

Has a big 'ole spring, but...didja remove the plastic plug from the inlet?

Just spittballin'

[Ironflight]

Originally Posted by scsmith

So, I ordered a new Tempest AF-15473 fuel pump. When it arrived, I was kind of surprised that I can not cycle the pump manually by pushing on the lever.

This is a high pressure pump for fuel-injected engines.

Are the springs just so stiff on the high-pressure pump that I should not be able to move the lever?
My recollection on old auto fuel pumps is that it was easy to move the lever and cycle the pump. But those are all low pressure pumps.

So I don't know if I should be worried that this one is so stiff or not.???

When you see how small of an eccentricity you have in the drive cam, you’ll realize just how little motion the pump actually has - maybe 3/8” at the tip (from memory). With a stiff spring, it is hard to hold the pump body still enough to see motion at the tip of the arm.

[scsmith]

Thanks guys.
Yes, I removed the plugs. Mine has a bit over 3/16" of what feels like free play motion, and then it is extremely stiff. Must be that big ole spring. If I push it against a bench, it does indeed cycle. I was just being a little too gentle. I'm not generally a 'use a bigger hammer' kind of guy.

I also note that the mounting holes are tapered (conical) as if the pump body fit over tapered pins. Didn't expect that.

I also decided that while i am at it, I will install a cooling shroud. I have a blast tube aimed at the pump currently, but no shroud. The ACS shroud doesn't fit as shipped. Think of it as a kit to make a shroud from and you will be happy. Think of it as a shroud ready to install out of the box and you will be unhappy.