New boost issues - when letting OFF the gas...?

[Pabs]

Hey guys and gals...

Just recently my cars been hitting limp mode and only boosting to 10psi, even though with my remap i usually hit around 20psi. On occasions, its gone up as high as 23psi peak, and i thought this was the cause of the limp mode. I backed off the remap settings.

Now, on the way home tonight, I hit limp mode again, and i wasnt pushing the car in the slightest. Just when i accelerated i noticed the 10psi barrier again.

The strangest thing - when i used to let my foot off the gas after accelerating, the boost gauge would snap down to the -20(vac) reading very quickly. (I assume this is normal?)
Now when i use any boost over 5psi and let off the gas, the gauge drops to -10vac really quickly, but seems to get stuck and then drops to -20 much slower. I can almost hear the dv sound like it dumps in 2 stages (noise through my CAI)

VAG-COM shows 0 errors.

I have very limited technical knowledge, and can only guess at either the DV sticking, or either N75 or N249. DV has been serviced quite a lot, so i can't really see it being the issue (although can't write it off completely) and N75 has only been on car 1yr...

Does ANYONE have any clues or links? I'm sure the strange behaviour of boost is the reason for my limp mode, but not getting any clues from vag-com at all

Please help. Thanks in advance!

 

[m0rk]

get a bit of silicon hose & bypass the N249

also take the DV apart & check it's not sticking / full of crap

 

[Pabs]

Doesnt bypassing the n249 increase the possibility of higher boost? I'm already worried about my boost levels seeming a bit high...?

I'll do the DV service next weekend (again) but thats the 3rd if not 4th service it'll have had in the 2yrs i've had the car..

Bypassing the n249 seems tricky on the how-to thread..
Also, the vac reservoir likely to have anything to do with it??

 

[Pabs]

at the advice of m0rk after discussing on msn, I am going to check the DV out and make sure it isnt sticking, and then bypass the n249 and remove the vac reservoir, and see if this helps/solves the issue.

Some of you may remember my fluctuating boost issues - i wonder if this bypass might have solved that too?

 

[traumapat]

hope its an obvious sticking dv... be intresting to hear what the bypass achieves? whats the n249 do? and the vac res?

 

[Pabs]

n249 works with the vac res - the ecu uses these to control the boost.
But the ECU tends to mess with it when it shouldnt, so I'm told. Bypassing it means the boost is controlled purely by the throttle.

I just don't think it can be sticking DV - surely the boost gauge is reading from the vac hose - and so it SHOULD see the -20 straight away, just cos the dv isnt lifting open it shouldnt affect the vacuum??? Does that make sense? does to me...?

 

[traumapat]

just after i asked pabs , i searched and found the main thread on it

it sounds a safe mod from what others have said. be intrested in your results as now im running higher power im getting occasional surges after lifting off the throttle, i think this is due to a slow reaction in the dv? so it might sort that for me...

good luck mate

 

[Pabs]

i need it

I've got some vac hosing, and a t-piece. All i should need now is cable ties..

I'll do photos etc, but m0rk has already provided me with EXCELLENT pics

 

[m.r.davies]

Sorry to hi jack the thread,

traumapat, you said you were getting occasional surges, i've not had my car long, and noticed a surge of power the other day when i lifted off the accelerator, it worried me as someone pulled out on me so i lifted my foot off the gas and it kept going .....nuclear pants for a second!

Has anyone else had this? what would be the cause and the solution to fixing this? new DV ?

 

[Andi]

Im interested in bypassing the n249 but cannot find how to guide. Any info / help appreciated.

Thanks

 

[Pabs]

well i will try and document what i do - but again i must stress that I DON'T know what I'm doing - lol...

m0rk has been very helpful and told me what to do

 

[m0rk]

in short....

you want to operate your DV from manifold vacuum (same as FPR)

so t piece from the FPR to the inlet manifold & run the remaining 'connection' to the top of the DV

 

[Pabs]

yeh - way i understand it is instead of the pipe coming from the n249, you unplug this from the DV (top hose) and block it (screw+tape) - then run new hose down to FPR - remove hose from side of FPR, insert T piece - reconnect 1 t-piece connection to new hose, 1 to the FPR, and the other one on the hose you just disconnected from fpr.

Apparently as the vac reservoir is used only by the n249 it can be removed (and hose plugged again) to remove the clutter from the engine bay. However, I will only do this if the bypass of the n249 works for me

 

[neil_f225]

ive been having a problem with my car hitting limp mode....but it is only when it is really hot and the air con is on... car goes to standard boost. No fault code

 

[Pabs]

how strange - i do NOT have aircon on, as i don't use it that often.

Not particularly hot when it happened end of last week - but admittedly every other time it was hot.

Can anyone else with a boost gauge confirm that when foot is let off gas it drops straight to maximum vac without hesitation or slowing down?

Mine is dropping to about -5/-10 and then it slows down as it drops to -20. It doesnt stop - it just seems to hit "resistance" or similar and slow down.

On idle it doesnt seem to be reading as -ve as it used to : seems to idle about -18/-15 on occasions, when i'm used to seeing -20.

I'll see how the bypass goes and what happens!

 

[Saul]

maybe a bit of a stupid question, but have you checked the boost gauge line and connections for kinks and leaks?

 

[Pabs]

well, i havent. yet. But that would only correct the weird boost reading on the gauge - and I'd still be hitting limp mode for some reason.

Probably me assuming the two are linked to be honest, but i can't see nout else wrong. Will be having a closer look over the weekend when i try the bypass.

EDIT: I'd also have thought a kink in the gauge hose would affect all readings, and not just the let off boost. Other readings, ie when on the gas, are as they have been for a while now.

 

[gazjones]

mine drops to max vac very fast all the time after boosting!

 

[Pabs]

thanks mate - just hoping more people will agree with you so i know i've got an issue somewhere, and its not just my imagination!

Hopefully sort out the limp mode as its making me drive slow, just in case i hit it again no fun! lol

 

[gazjones]

it always hits - 20 when either idling or litfing of the throttle at any speed or boost!but with full throttle it hits - 30 which is as far as the gauge goes!