I was using a rental Autozone fuel pressure tester before, and then went out an bought the $19.99 gauge from Harbor Freight to verify the numbers. With the Autozone gauge, I was usually getting 26 psi, but once got 30, and it held steady, no fluttering.

The needle on the Harbor Freight gauge flutters rapidly in a blur between 20 and 30 psi with engine running. When I shut it of it stays up at 30 psi. Is the HF gauge defective since it flutters so much, or is that just what a cheap gauge does? No dampener?

When I rev the engine, the range of fluttering widens to 15 to 35 psi.

Is the real psi an average of the low and high numbers? Or the higher number?

Thanks

 

Is it a liquid filled gauge? If not, the needle will bounce all over the place.

 

In any event, the pressure seems about 7-10 PSI too low.

 

Thanks for the reply.

No, no liquid in the gauge.

I know it's supposed to be at least 39 PSI at idle, so my pump is probably slowly dying. Just wondering what the real numbers are. It bounces consistently, up and down between 20 and 30, in a blur.

I don't think the Autozone gauge had liquid in it either, though, and it was steady.