Fuel pressure question...real quick

[jspaeth]

I am about 90% sure I know the answer to this question, but....

Does everyone's fuel pressure go down after the motor turns off?

When I prime the fuel pump, the pressure goes to like 33 psi and stays there.....even when I turn the car off, it stays there for a long time, as it should, since the system is sealed well.

However, last night I was watching my car turn off (turbo timer) from the outside and watching the fp gauge.

It was at ~30 psi as the car was idling, and when the engine turned off, it dropped down to like 18 psi or so......it held at 18 after it dropped.....

Please tell me this is normal.

[ROIDMONKEY]

yes it is normal . ur fuel pump goes off after ur turn the ign off , pressure goes down. mine is 45 while running

[jspaeth]

That's kinda what i figured


My fuel pressure demons have me just completely shitting my pants lately....it's like what the fuck, why is the car idling and it is 10 psi too low.

Then i tap the FPR with a small crescent wrench and the pressure goes back to normal......piece of shit Nismo FPR

Did i mention that it is a piece of shit?

[SamuraiSam]

What's wrong with the stock fuel pressure regulator?

[GSXRJJordan]

^^^ Long story, in another long thread.

Yes, your FP readings are "normal". The pressure initially drops, but then stays kind of steady for a while - it takes like a day for the pressure to completely drop.

[g6civcx]

FYI, low pressure mechanical fuel pumps are a different story though. When the pump stops I instantly lose fuel pressure. Now I know why it takes carb'ed engines with mechanical fuel pump longer to start. The first couple seconds of cranking has no fuel pressure.

[jspaeth]

Hmmmm I am hoping the fuel pump is okay....it's a Walbro 255 lph High Pressure fuel pump that I have had for 2 years or so now..

The first 1.5 years were just with a stock setup so I don't think it's been overworked.


Am I the only one that worries about this? It's like you spend 100s of dollars to get a good, accurate tune, where the timing and injector duties are VERY fine-tuned.

But then, if your fp drops by just 1 psi, this corresponds to ~ 2% less pressure driving the fuel through the injectors.....yet a 2% change in injector duty is SIGNIFICANT!

There has GOT to be a better way of keeping fuel pressure consistent and so that it doesn't fluctuate.....otherwise what's the sense in tuning injectors so precisely?

[g6civcx]

Check the fuel level. I know S13s have a problem with the fuel pickup if the fuel is too low.

[jspaeth]

Thx for the input.....fuel is 3/8 tank and it's an S14....

I have heard that sometimes those FPRs don't work well if the pressure is down the low end of their range, bc their isn't ENOUGH pressure on the spring.

Anyway, I don't want to make this thread the same as the other one I have where I am ranting...I just wanted to mainly know about the pressure dropping after turning the engine off

[LeonL]

My fuel pressure drops to 0 once I cut the engine off. I am wondering if that is the reason sometimes it takes a few kick to crank. Will that be FPR issue? Because this is my second one and it is still the same.

[jspaeth]

My fuel pressure drops to 0 once I cut the engine off. I am wondering if that is the reason sometimes it takes a few kick to crank. Will that be FPR issue? Because this is my second one and it is still the same.


Yeah it shouldn't go down to ZERO IMMEDIATELY....I mean after sitting a few hours, okay, but not right away.


I was just asking to see if it's okay for it to go down somewhat right away after pulling the key

[SamuraiSam]

^^^ Long story, in another long thread.

Link? Or search terms to find the thread?

If you don't have any pressure issues besides the drop immediately at shut-off, suspect the fuel pump. Perhaps a failed relief valve or other issue causing pressure to not hold.

[flip3d]

Mine drops too. I don't like the Nismo FPR though. I find myself constantly adjusting it.

Aeromotive FTW

[jspaeth]

Link? Or search terms to find the thread?

If you don't have any pressure issues besides the drop immediately at shut-off, suspect the fuel pump. Perhaps a failed relief valve or other issue causing pressure to not hold.


This interests me.......and I haven't heard anyone else mention this..........

Can anyone else corroborate this as a possible issue?