Low boost pump sounds different

[Donny Hall]

I’ve read all the threads.My issue is slightly different. Need help. Low boost sounds sickly weak, it makes a sound and kind of works, but won’t really prime the engine as it did for the entire time I’ve had the plane.  This is a change and something is obviously wrong. High boost works great!  Strong as ever.  That’s what I’m using to start it now.  I’ve replaced the low boost switch in the panel but have the same results.  I’m reading a lot about the fuel boost pump pressure regulators and have found there’s a replacement regulator kit no. 940150-507 for 28 volt planes with dual alternators.  It’s got to be either that or the pump right?  Anyone have any experience with this issue?

[ArtVandelay]

 Could be electrical, something as simple as a deteriorating circuit breaker, wiring connections,  switch.  Can you use a jumper cable and bypass all of the above to see if it’s an electrical problem?

[carusoam]

Welcome aboard, Donny!

Since Hi and Lo are the same pump...  the difference is the electricity that is being supplied to the pump...

What does the regulator look like? A voltage regulator? A resistor?

The low boost runs the pump slower...

The output difference should be able to be read with the FF gauge.

I start counting Mississippis once the FF starts....

Full throttle, mixture in, boost on....

PP thoughts only,

-a-

[Cardinal767]

 “Low” pump voltage is adjustable with an adjustable resistor on my K, not sure about the R model. 

[Donny Hall]

Thanks it does not.

[carusoam]

Something to check...

as the electric pump may be getting on in years...  the diaphragm doesn’t have infinite life.  When it tears, it sends fuel out the drain...

Not sure if the sound change is related...

I’d be interested knowing more about the resistor that sounds like it is in the circuit... where it is and what Ohms it is measuring lately...?

PP thoughts only, had to change seals in mine a couple of years ago...

Best regards,

-a-