Fuel pressure at idle

So I’ve had this problem where my idle fuel pressure will drop to around 360 and slowly climb up to what it should be around 420 after pulling up to a stop. I’ve noticed it more severe when I get on it and then come to a stop not shortly after. I have replaced my prv and got corksport hpfp rebuilt kit and rebuilt my hpfp and the problem still protists. Also when I let the car build pressure after a drive it only goes up to about 1500 and vents. I’m kinda of at a dead end to my knowledge. Anything would help.

 

Is the car running rough at all? What are your fuel trims like? Have you checked fuel pressure from the LPFP to the HPFP?

 

Runs perfect. No codes afrs are good aswell. LPFP? I don’t know that that is if it has to do with long term fuel trims mine are never above 5 -/+

 

LPFP means low pressure fuel pump or In Tank Fuel Pump.

Did you check all your connectors for corrosion or moisture? Test the spill valve? Clean the Spill Valve?

 

Yes it goes up to 68 when it turn the key on before I start. And I cleaned and replaced the o rings on my whole hpfp. I think I might have just gotten a faulty part

 

Is the HPFP upgraded Internals or just stock internals?

 

Upgraded. It runs totally fine. Fp at wot is perfect it’s just coming to a stop it drops when returning to idle. Then it climbs back up

 

Does it do it with idle rpm change? Such as loads coming on or going off? It's normal for RPM to drop when things like fans, compressor, headlamps, generator come on and off. You may not even notice anything on the tach when this happens unless it's really loading the system.

The HPFP is going to react the same with RPM change. If the engine slows a little then so does the pump.

Don't worry about it. If it keeps holding proper pressure, no misfires or issues then you're probably being overly cautious.

 

Alright so I'm at a dead end of a fueling issue. So when I drive normally getting the car up to temp and everything my idle fuel pressure will go down to ~400 and slowly build pressure and firmly idle in between 420-435 when I come to a stop and let it idle. But say I give it the beans then come up to a stop light the idle fuel pressure will go down to ~350 and then slowly climb back up to ~420 where it should be. It completely depends on my driving for ex. I will do a 2nd to 3rd WOT then come to a stop and let it idle, it drops to ~380 and climbs up to where it should be. ill do a 3rd to 4th WOT putting more load on the motor and then it will go down to ~350 and it does what I expect. It climbs back up to where it should be. Keep in mind this building of pressure happens within a minute. When I do the KOEO test to check my pressure relief valve the pressure will go up to ~1300 and release the pressure but it is very inconsistent, I could do it 3 times in a row I would get ~1100 then it bleeds, ~1400 it bleeds, ~750 and it bleeds. I have replaced my pressure relief valve twice and completely rebuilt my hpfp with corksports kit. I am at a dead end anything would help

 

Thread's merged, seems like same issue, keep them together one thread makes it much easier to help. You didn't even respond to the last question when L337turboz was trying to help.

So you've replaced PRV with a new OEM one rebuilt hpfp and still having the same issue? Is the car driving normally? You said you're able to go WOT in 3/4th gear

I wonder if there's a connector issue on the spill valve or perhaps the fuel rail pressure sensor is going out the latter if the cars driving fine but that's a reach

 

I have upgraded hpfp in my 2nd gen speed3 and mine drops to 300s and high as 400s on idle or stoping at signs or traffic lights it should be fine