I got the truck back after the lift pump conversion was complete, bill payed
by DC, Very expensive job and a lot of work. I now see 8-9 lbs of pressure
at idle and 6-7 under throttle. There was a statement on the conversion
paperwork saying that pressure is irrelevant and no aftermarket pressure
gauge should be believed and that it is all about flow. Sounds like a pretty
stupid comment for them to print. Do you know the story?
Well, yes and no. While it's true that the test procedure in the service
manual for the lift pump is all about measuring fuel flow, and not pressure,
pressure is still a valid way to verify the health of the lift pump. The
CP3 injection pump isn't nearly as sensitive to fuel pressure as the VP44
was, and will still operate safely at near-zero fuel pressure (so long as
there's fuel flow). But, barring any kind of abnormal (and unlikely)
restriction, you can safely assume that the CP3 is being fed a constant
supply of fuel so long as your FP gauge registers some amount of pressure.
So, to me, an FP gauge is still plenty valid, and much cheaper than a flow
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