Fuel Pressure Questions

[Module Unknown]

I recently had a fuel related issue arise, so today I went and installed a B&M fuel pressure gauge (the one the mounts atop the fuel filter) so that I could monitor what's going on.

My question is, how long should fuel pressure remain constant after the car is shut off? Will it eventually bleed off? Mine holds around 42psi for a good while after I shut the car off, but eventually it will begin to bleed down.

Another thing that I thought was odd was the the pressure actually rose a couple psi a couple minutes after I shut the car off. Is that normal? If not, why might that happen?

Here's the reason that I installed the gauge. Recently I installed some FIC 650cc injectors. After the install I began to experience issues that pointed to vapor lock. After running the car (long enough for everything to get nice and hot under the hood), if I shut off the car and come back to it within 30mins to a few hours later it is very difficult to start the car (as if there was no fuel). But after cranking if for a bit, the car will start (sometimes stutter or idle roughly for a few moments), but then operate normally. However, if I were to drive the car, shut if off, let it sit over night and come back the next day it would fire right up without issue.

Info on my fuel system: Walbro 190lph pump (not rewired), stock fuel lines/rail, recently changed fuel filter with oem filter, FIC 650cc injectors, stock fpr, B&M fuel pressure gauge that I installed today which reads at about 42psi.

 

[GalantGst]

its normal for the fuel pressur eto hold for a while and then bleed down.

Try starting it by putting it in the on position and wait for the lights to all go off before u start it.

For me it starts right up when i wait for all the engien lights to go off first which is like 3-4 seconds.

 

[steve]

My question is, how long should fuel pressure remain constant after the car is shut off? Will it eventually bleed off? Mine holds around 42psi for a good while after I shut the car off, but eventually it will begin to bleed down.

Another thing that I thought was odd was the the pressure actually rose a couple psi a couple minutes after I shut the car off. Is that normal? If not, why might that happen?

With the stock FPR the system will hold pressure for quite a while, a lot of aftermarket FPR with their larger return don't seem to hold pressure for more than a few mins after shutting down.

The pressure will rise over idle when you shutdown because you no longer have a vacuum applied to the regulator lowering it.

Steve