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Paul Workman · 09-22-2019

Putting a pressure gauge on the fuel rail and turning the key ON (not start) the pressure should come up to ~44± a couple psi.
Then turning the key OFF, pressure should hold to within a pound or two for as much as 30 minutes. Failure coming to or holding pressure could be the pressure regulator, a check valve (my experience with Airtek pumps).

Also, if the diaphragm in the regulator is bad, there will likely be fuel in the hose between the regulator and the plenum. (Do you smell gasoline near the rear of the plenum with the ignition switch in the ON position?)

Also on the checklist, especially since you used the bypass jumper already, is to measure the current draw of the pumps. Normal draw is between 4-5 amperes for each pump (8-10 Amps total, in other words). (With the ignition switch OFF, configure the VOM for AMPERES and put the VOM in series between the positive battery post and the little black diagnostic pump connector with a red wire [found jutting out of the big wire loom next to the windshield wiper motor].

And, of course, being able to scan the ALDL connector could provide significant clues as well.

So...after this, what have you found? Let us know.

09-22-2019	#2
Paul Workman Join Date: Nov 2007 Location: Squires (near Ava MO in the Mark Twain N'tl Forest) - Missouri Posts: 6,466	Re: Fuel pump fail on my 91 ? Putting a pressure gauge on the fuel rail and turning the key ON (not start) the pressure should come up to ~44± a couple psi. Then turning the key OFF, pressure should hold to within a pound or two for as much as 30 minutes. Failure coming to or holding pressure could be the pressure regulator, a check valve (my experience with *Airtek* pumps). Also, if the diaphragm in the regulator is bad, there will likely be fuel in the hose between the regulator and the plenum. (Do you smell gasoline near the rear of the plenum with the ignition switch in the ON position?) Also on the checklist, especially since you used the bypass jumper already, is to measure the current draw of the pumps. Normal draw is between 4-5 amperes for each pump (8-10 Amps total, in other words). (With the ignition switch OFF, configure the VOM for AMPERES and put the VOM in series between the positive battery post and the little black diagnostic pump connector with a red wire [found jutting out of the big wire loom next to the windshield wiper motor]. And, of course, being able to scan the ALDL connector could provide significant clues as well. So...after this, what have you found? Let us know.