1986 951 Fuel Pump Problem

[kck-drum]

Does anyone have any idea what is wrong with my car?
listen to the fuel pump.
https://www.youtube.com/watch?v=BBSFXkS282I

It doesn't like to accelerate under full throttle.
It happened all of the sudden. One day when I went to take off it stuttered and struggled to accelerate. When I came to a stop I could hear the fuel pump whining.

I did no further diagnosis and just assumed... "I need a new fuel pump"
So, I put in a new pump. The new pump whines too. The car still doesn't accelerate properly.
I put in a new fuel filter. No change.
I checked the fuel strainer. It is clean.

When I start the car from cold the pump sounds normal. I drive around for 10 minutes and it starts to whine.

I checked the voltage at the terminals on the pump while it was making the weird whining noise. It was about 12.3 volts.

Any ideas?

[Fast Freddy 944]

Some fuel pumps make a whirring sound, I did an 84 Jag xj-6's fuel pump, and before and after it made the whirring sound. I just depends on the car and its design. My 87 Fiero had a long triangle under body tank and I knew the pump was working when I heard it whirring while running.

[mytrplseven]

I'm wondering if the pump is cavitating from lack of fuel supply to it. I'm thinking either plugged tank strainer or fuel filter. I'd start with the filter first as it's easily replaced.

[walfreyydo]

My experience a pump whining means there is a restriction causing the pump to have to work harder. You changed the filter and strainer, so my next check would be the fuel dampener and pressure regulator, and also verifying your return line is not restricted.

Getting a reading of your fuel pressure with a gauge off the rail would be first step, making sure its within spec (see clarks below).

Fuel Pressure Regulator - General Information and Replacement
Fuel Pressure - Checking

"The Bosch fuel pumps used in Porsches are generally extremely reliable and not prone to failure. If you have a fuel pump that needs to be replaced, there is likely something else that has caused the fuel pump to fail. So, before you simply replace the fuel, you may want to see if there is another problem that caused the fuel pump to fail. A clogged fuel filter can cause failure of the fuel pump. A failing fuel pressure regulator can also result in pump failure. It's a good idea when installing a new pump to perform a fuel pressure check and pump delivery rate check. This will check the condition of the entire fuel system and may prevent pre-mature failure of the new pump by identifying potential system problems."

FUEL-10, Fuel Pump Information and Replacement