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Seeking help for stumbling at start-up

ROH ECHT

K04 PLAY
Location
PDX OR
Car(s)
2007 MKV GTI
Hey!

Had a look today, car sat for about 36 hours (temperature is 10°C) so not sure if it's relevant to you:

230: spec: 49.9bar / actual: 5.8
231: 5 bar / 5.4 bar / load: 5.9%

It starts normally although not as quickly as when hot.
OK...thank you. I really think it is just dependent on temps and pressure limits within the bits to contain it...because fuel should be trapped in the rail by the hpfp oulet valve, the fprv and the injectors. Perhaps after a drive the pressure is reaching fprv limits or even an injector may not be holding as much pressure in that brief moment when the pressure is high due to heat. Then after some pressure and fuel is ejected when hot, and it cools down, the pressure is falling way down. For some reason...for the past few drives...it hasn't stumbled as badly upon start-up.

Usually when cooler here, the data looks exactly like yours...5 bar target and 5.5 bar real in the low side...and 6 or 7 bar in the rail.
 

ROH ECHT

K04 PLAY
Location
PDX OR
Car(s)
2007 MKV GTI
Couple other possibilities

1. Air in fuel line. VCDS is measuring pressure but it sees air or fuel pressure as one. (pin hole leak intank tubing)
2. Could you have some moisture/water in fuel.

pull each plug before starting next day to see if any of the cylinders have a little fuel in them.

Sorry just grasping for ideas. Probably won't help.
If this is the case on mine...the new lpfp will fix this. Oh, and that code I had a while back that I posted on the PM3 thread...My battery volts with this new oem battery since last summer have never been over 14.25v. You mentioned holding 14.3v in the thread...so not sure what to do about that. The code has not returned. Anyway, go and take a look on that thread if you get a chance please.
 

GTI's

Drag Racing Champion
Location
MD
8/10 4 pm



8/10 10pm



9/10 8am



9/10 8:30pm



10/10 am

 
Last edited:

ROH ECHT

K04 PLAY
Location
PDX OR
Car(s)
2007 MKV GTI
Good stuff again and thank you GTI's for continuing to update. I think this is confirmation that mine is leaking given yours remains in the 30 bar range when temps drop. Cannot yet say it is the injectors without looking into each cylinder for signs of raw fuel but I will likely get a look in each tomorrow. If they are all dry...I suppose it could be the fprv. I doubt it is the hpfp outlet valve as the hpfp is less than one year old. I hope to find fuel in one of the cylinders.
 

ROH ECHT

K04 PLAY
Location
PDX OR
Car(s)
2007 MKV GTI
Great...thanks for that. I'll see what I can find out.
 

ROH ECHT

K04 PLAY
Location
PDX OR
Car(s)
2007 MKV GTI
OK...to my understanding...Jack is saying that normal is around the 6 to 7 bar range when cool and if higher, then it is the rail pressure sensor. The OP is seeing his in the mid 20 bar range when cool and Jack is telling him that his is abnormal. Everyone else that is posting their rail pressure when cool is saying they see the same as I...about 6 to 7 bar. Am I understanding that thread's posts correctly?

Anyhow, I started a new thread and maybe Jack will clarify what he was telling that OP.
 

GTI's

Drag Racing Champion
Location
MD
That post at RT is mine and I am not sure what Jack means at times. I am not sure that he had an answer after I suggested that if sensor was bad would it not be showing actually pressures that are out of line with spec.
 

ROH ECHT

K04 PLAY
Location
PDX OR
Car(s)
2007 MKV GTI
I get it as I only got that he is sort of suggesting yours is sort of common with the rail pressure sensor...but not 100% he is spot on with that statement or not.
 

vwengineer

Ready to race!
Location
Switzerland
Did you finally sort this out? I am asking because I am wondering if I do not have a fuel leak, when checking my engine oil, I always smelt a gasoline odor when pulling the dipstick.

I did not really think it was abnormal until I saw a recent post on Facebook about it, then I also remembered that my fuel pressure was not holding (did not do the hot pressure rising test yet). This concerns me since I use fairly light oil 5W-30 or 0W-30 on 7-10k intervals generally.

I guess you could test the injectors by unplugging them and crank the engine? If they were leaking the spark plugs would then be wet, right?
 

ROH ECHT

K04 PLAY
Location
PDX OR
Car(s)
2007 MKV GTI
No, I haven't. I've been "down" for a bit with the wife having surgery in Nov and I in Dec.. I recently changed the plugs...so I put a bit of paper towel in a grabber tool → ( https://encrypted-tbn0.gstatic.com/...o6vZ8JijtDE_pRr9sA-rfO1CacLNBpE1Rt4RAuBpeDgkj ) and ran it down to each piston and found no signs of gas. So ??? It hasn't stumbled at start-up since before this post or the last time mentioned.
 

vwengineer

Ready to race!
Location
Switzerland
Good to hear from you again, I hope all is well. Yeah, still strange that the pressure doesn't hold, so that would be the HPFP? Since then I did this very unscientific oil drop test:



The outer circle developed at the same pace and with the same shape as with fresh engine oil which, as I understand, say that the oil still has more or less the same viscosity after 7k, so I concluded the oil is fine... I will also check when replacing the spark plugs
 
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