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Help with rail pressure pre-start-up.

ROH ECHT

K04 PLAY
Location
PDX OR
Car(s)
2007 MKV GTI
I planned on looking for them tomorrow. (y) I hope I find some.
 

GTI's

Drag Racing Champion
Location
MD
The problem with checking fuses it that the car does not go to sleep because you have the driver door open


Is that not why you lock the various latches by hand, particularly the driver door and the hood latch so they are closed as far as the car is concerned, but in reality they can be in any position you want them to be in except actually on the striker. Of course you have to make sure you have no issues(dtc) with your latches to begin with.
 

ROH ECHT

K04 PLAY
Location
PDX OR
Car(s)
2007 MKV GTI
The problem with checking fuses it that the car does not go to sleep because you have the driver door open
The latches, hood and driver door, were reset so as far as the car knows...the doors were closed.
A full scan was done to insure there's no issues with the door module. The vid in my post, #24, shows this.
 

ROH ECHT

K04 PLAY
Location
PDX OR
Car(s)
2007 MKV GTI
I want to try something now...tonight, I am going to start the engine when it is cold but shut if off quickly. This should pressurize the rail but not create much heat. Then check the rail pressure and temps in MB 004 and 230 and again in the morning. I would expect the rail pressure would be higher in the morning than when it is shut off hot. The hpfp outlet valve, the FPRV, and the injectors should contain the pressure resulting in a higher residual pressure in the morning...ambient temp will show fluctuations in the morning pressure of course. If you feel like doing the same...much appreciated.
 
Last edited:

ROH ECHT

K04 PLAY
Location
PDX OR
Car(s)
2007 MKV GTI
Can anyone confirm this...is the minimum pressure the G247 reports is 7 bar? when any of our posts show low pressure primed to under 7 bar...the fuel rail reports 7 bar for all.

And so, when the LPFP primes, does the HPFP's regulator valve open so the fuel rail is also primed? I suppose I could simply disconnect the outlet tube on the HPFP to see. But would be messy.
 

BurgerGuy

Drag Race Newbie
Location
Charlotte
Car(s)
'07 K04 GTI
Not sure, but after turning the key to accessory Polar FIS reported 7 bar on the rail and 6.3 bar on the LPFP. Once I start it up, rail pressure immediately jumped to 57 bar and the LPFP dropped to ~4.3 bar, then 4.0 bar. Rail pressure eased out to 50 bar shortly after the spike and stayed in the neighborhood once the cat warm up completed.

My door module is a bit wacky so I rely on turning to accessory to prime the LPFP for a couple seconds before start up. Since the LPFP read lower than the rail I guess it's possible the prime fills the rail as well. It would make sense as more work would be required to take it from 0 to 50 instead of 6.x bar to 50 bar. Maybe the messy test is the only way to find out for sure. 🤭
 

ROH ECHT

K04 PLAY
Location
PDX OR
Car(s)
2007 MKV GTI
Not sure, but after turning the key to accessory Polar FIS reported 7 bar on the rail and 6.3 bar on the LPFP. Once I start it up, rail pressure immediately jumped to 57 bar and the LPFP dropped to ~4.3 bar, then 4.0 bar. Rail pressure eased out to 50 bar shortly after the spike and stayed in the neighborhood once the cat warm up completed.

My door module is a bit wacky so I rely on turning to accessory to prime the LPFP for a couple seconds before start up. Since the LPFP read lower than the rail I guess it's possible the prime fills the rail as well. It would make sense as more work would be required to take it from 0 to 50 instead of 6.x bar to 50 bar. Maybe the messy test is the only way to find out for sure. 🤭
Right, doesn't it seem likely that the G247 minimum, it is able to report, 'is' 7 bar? But we just wouldn't know if the N276 valve is opened to allow the priming to reach the rail without literally checking if it is so. I re-read all of SSP 334, and am left assuming the N276 is open by command for start up. Because all it says is this (in the pic)...which may explain the over 50 bar you saw, as well as it nearly confirms the LPFP initial prime pressure is meant to charge the high pressure 'system' for start up. Notice it said 'system'?
a.png
 

BurgerGuy

Drag Race Newbie
Location
Charlotte
Car(s)
'07 K04 GTI
Based on that snippet I'd say the rail is definitely getting the 6.x bar prime from the LPFP before turning the engine over. Pump age and/or atmospheric differences likely caused mine to only prime to 6.3 bar instead of 6.5 which is just shy of 3 PSI. Not a big deal imo.

Explains the jump to 57 bar on the rail as well, like you said. More pressure for a better start up experience. Once the engine gets going the rail eases out to 50 bar.

Edit...
If the LPFP could prime to something higher than 7 bar that would tell you for sure. Either way, the computer calls for 57 bar on initial start up and the LPFP pressurizes as needed to achieve that.
 
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