That’s the thing that is confusing me.
The scenario: Investigating a rough idle issue.
I’d replaced a noisy pump and filter and still had rough idle so moved to investigate pressure.
I had disconnected the supply side at the fuel rail and ran the pump, emptying into a container. Result: plenty of volume of fuel delivered ( though I don’t have an adapter for exact pressure measurement)
The FPR may or may not be working, I have fluctuating vacuum due to zero compression on #3. But I disconnect at the outlet and run the pump again. Result: Again plenty of fuel volume.
The weird part: FPR is disconnected still, the key is off and I’m fiddling about dumping container into a gas can. And I see that the return line is a pretty strong stream. Strong enough that putting my finger over it results in back pressure that is hard push against. Strong enough and that I didn’t really want to just let it keep dumping fuel, so I reconnected the FPR.
This would make sense if the car was facing downhill, but I have a slight grade to my driveway and this stream is pushing UP against gravity. This is a surprise - should it have back pressure like that? Going uphill?
All this is probably moot, as I later realized my filler drain hole was clogged and the cap was sucking in water from a recent rain. Water in the gas maybe the source of all my problems, but still doesn’t explain the backpressure on the return. Thoughts?