Strange fuel pressure behavior
Thread Starter
Drifting
Joined: May 2020
Posts: 1,663
Likes: 702
From: Baton Rouge, Louisiana, metro area
Strange fuel pressure behavior
1991 L98 stock
Just finished pulling intake. New gaskets all around.
New FIC injectors
New fuel pressure regulator
6 month old AC Delco fuel pump (yes, I did put the Pulsator back in the line)
New fuel pump/gauge assembly
Old fuel filter, have not changed yet.
Fuel rail just rebuilt
Car runs great. Idles perfectly smooth. Performs well for street driving.
Been starting slow when engine is at outside temp whether 40 degrees out or 80 degrees out. Takes about 3 seconds to start. After warming up, it starts very quickly.
Checked fuel pressure at the rail.
On key up, fuel pressure builds to 40 for about 1 second then “snaps” down to 35 and holds. Does this every time. On start up, pressure drops to about 30 and holds in that area.
Shut down and while engine is off, pressure immediately builds up to 40 for about 1 second then suddenly snaps back down to 35 and holds.
I pinched off the Return line at the tank and repeated the test. Results are exactly the same.
From my research, the fact the pressure drops when the Return is closed off means the Pressure Regulator is not this problem. The pressure should build to 40 or higher with that line shut off. Since even if the Regulator is faulty, the fuel has no where to go, the pressure will build.
Thinking I should have not re-installed that damn Pulsator like I did OR I read where there is an internal Check Valve in these pumps that can be defective.
Educated opinions from knowledgeable folks?
Just finished pulling intake. New gaskets all around.
New FIC injectors
New fuel pressure regulator
6 month old AC Delco fuel pump (yes, I did put the Pulsator back in the line)
New fuel pump/gauge assembly
Old fuel filter, have not changed yet.
Fuel rail just rebuilt
Car runs great. Idles perfectly smooth. Performs well for street driving.
Been starting slow when engine is at outside temp whether 40 degrees out or 80 degrees out. Takes about 3 seconds to start. After warming up, it starts very quickly.
Checked fuel pressure at the rail.
On key up, fuel pressure builds to 40 for about 1 second then “snaps” down to 35 and holds. Does this every time. On start up, pressure drops to about 30 and holds in that area.
Shut down and while engine is off, pressure immediately builds up to 40 for about 1 second then suddenly snaps back down to 35 and holds.
I pinched off the Return line at the tank and repeated the test. Results are exactly the same.
From my research, the fact the pressure drops when the Return is closed off means the Pressure Regulator is not this problem. The pressure should build to 40 or higher with that line shut off. Since even if the Regulator is faulty, the fuel has no where to go, the pressure will build.
Thinking I should have not re-installed that damn Pulsator like I did OR I read where there is an internal Check Valve in these pumps that can be defective.
Educated opinions from knowledgeable folks?
Thread Starter
Drifting
Joined: May 2020
Posts: 1,663
Likes: 702
From: Baton Rouge, Louisiana, metro area
Update.
I had a Racetronix Walbro pump I was planning to install this winter. (I picked up the pump and a tank from Sleazy Rider a few months ago.) I went ahead and installed the pump and removed the Pulsator. Also changed the filter to a new Wix.
Checked fuel pressure again at the rail. The pressure has increased a few psi over all and comes up quicker on key up, but the pattern is the same. The old filter was definitely full of funk and gunk.
I am thinking my pressure is actually fine now...the el cheap o pressure gauge may be my issue.
On key up, I will get to 41-42 then when the pump relay shuts off, the pressure now drops to 38ish and holds until my patience runs out.
Engine starts good and runs good.
It was likely a combination of issues: dirty fuel filter, crappy Pulsator, cheap fuel pump, and garbage gauge all hooked a rock-solid 91 base coupe.
I will run it for a while as it is now and post if I have any issues.
👍
I had a Racetronix Walbro pump I was planning to install this winter. (I picked up the pump and a tank from Sleazy Rider a few months ago.) I went ahead and installed the pump and removed the Pulsator. Also changed the filter to a new Wix.
Checked fuel pressure again at the rail. The pressure has increased a few psi over all and comes up quicker on key up, but the pattern is the same. The old filter was definitely full of funk and gunk.
I am thinking my pressure is actually fine now...the el cheap o pressure gauge may be my issue.
On key up, I will get to 41-42 then when the pump relay shuts off, the pressure now drops to 38ish and holds until my patience runs out.
Engine starts good and runs good.
It was likely a combination of issues: dirty fuel filter, crappy Pulsator, cheap fuel pump, and garbage gauge all hooked a rock-solid 91 base coupe.
I will run it for a while as it is now and post if I have any issues.
👍
