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View Full Version : cold weather causing increased boost?



EuroA4
02-05-2007, 11:31 AM
Today it was 5 degrees F outside. On the way to work driving on the backroads I started to realize I had a little more boost than usual. With the K04 and FMIC on...I usually peak around 15-16psi during the winter...and all of a sudden it was overboosting to beyond 22psi...

I was a little nervous to go WOT, but as I got close all of a sudden it kicked into limp mode...(7psi).

All last week when the temps were in the 20s-30s it was fine...I could hold it WOT and hold 16psi....so why is the colder temps making the boost go up?

Any ideas?

98a4
02-05-2007, 11:42 AM
Timing gets changed and allows higher boost.
Colder air is more dense, turbo cars love cold weather.

Peaking 15psi with a ko4??? What file?

AudiRacerS4
02-05-2007, 11:56 AM
you should be getting less boost in the cold and more boost in the heat

A4Rob
02-05-2007, 11:57 AM
you think +5 is cold. Try -16 here this morning in Minnesota. My car pulled like a chipped S4 :)

AudiRacerS4
02-05-2007, 11:57 AM
unless your running an MBC or your N75 crapped out 16-18psi sounds normal for cold temps with a K04 and around 20-24psi in the heat

94jedi
02-05-2007, 12:02 PM
yeah, I'm getting the same thing....but I'm only mbc inline w/ n75 at the moment. As soon as the polar caps melt, I'll install my EBC.

AudiRacerS4
02-05-2007, 12:04 PM
too much boost in teh cold will cause bogging

Poopie
02-05-2007, 12:51 PM
could be a crapped out maf or n75. you shouldn't boost that much in the cold

AudiRacerS4
02-05-2007, 01:22 PM
yup my bet is either maf or N75

94jedi
02-05-2007, 01:36 PM
could be a crapped out maf or n75. you shouldn't boost that much in the cold
yea, I know my n75 is toast but once I go w/ my EBC, I'll rule that out. Poopie - this will apply to you: I've always had some questions about the 4" lightning maf I bought on the ford SVT boards. I should've bought direct from CTapp. I'm wondering if mine is dead....I may replace it in the spring time to see if it makes a difference. it's never actually run "perfect", always been a tad bit "off".

Militant-Grunt
02-05-2007, 01:40 PM
you think +5 is cold. Try -16 here this morning in Minnesota. My car pulled like a chipped S4 :)

Yeah seriously, it was 8F here in the morning, boy the A4 got nice and nippy at those temps.

Poopie
02-05-2007, 02:30 PM
yea, I know my n75 is toast but once I go w/ my EBC, I'll rule that out. Poopie - this will apply to you: I've always had some questions about the 4" lightning maf I bought on the ford SVT boards. I should've bought direct from CTapp. I'm wondering if mine is dead....I may replace it in the spring time to see if it makes a difference. it's never actually run "perfect", always been a tad bit "off".

Was yours used? Mine is new off ebay.

mike-2ptzero
02-05-2007, 02:36 PM
Maybe the wastegate actuator froze so that it could not open the wastegate.

94jedi
02-05-2007, 08:28 PM
Was yours used? Mine is new off ebay.
yep used. I bought mine off a forum. I think I'm going to have to get a new one. PM me the link to where on ebay you got yours....please!

EuroA4
02-06-2007, 07:28 AM
Well I keep the car in the garage at night, so I'd doubt (althouth just a guess) that it would be the wg actuator...but I guess you never know? It cleared limp mode on its own overnight...so this morning I noticed it almost felt like a wg line was kinked...it pauses at about 10psi...then rockets to 20+...very hard to keep in the middle...you feel like you are either on or off boost, no in between.

I have the regular GIAC ko4 file (soon to upgrade to the hammer file). In the summer with the FMIC I hold at around 20-22psi. So its normal to see 16-18psi in the winter, from what I know.

...I read on the archives that there was a guy that mad a cut MAF wire...causing overboost...so that's something to check (but I'd think there would be a CEL).

It could be a N75 too...its the original one (5+ years old)?

AudiRacerS4
02-06-2007, 07:40 AM
sounds like your wastegate is getting stuck

Daft
02-06-2007, 08:02 AM
^^^^ I concur. ^^^^^^^^^^^^

If the wastegate doesn't open when expected, boost will keep rising and will go well beyond the specs of the software.

Colder air is denser thus is requires less boost to equal the air flow of hotter air.

I'd wager that this is either vacuum line issue with the wastegate actuator or somehow, the mechanical workings of the actuator or wastegate flapper and effected by the cold weather.

AudiRacerS4
02-06-2007, 08:12 AM
if you wastegate gets stuck that is why you cant go into moderate boost, you need at least 10psi in order to open the wastegate but when you hit 10psi its not openeing, yours is staying shut causing you to overboost make sure the line going to the actuator is not kinked

RAyala2.7T
02-06-2007, 08:20 AM
i have the "race" valve and even though i boost 18-19psi now, mine boosts higher in the cold and lower in the heat when it should be the other way around. i have to watch my throttle in extreme cold. i also had a slit vacuum line at one time that caused more boost and threw me into limp.

EuroA4
02-06-2007, 06:05 PM
^^^^ I concur. ^^^^^^^^^^^^

If the wastegate doesn't open when expected, boost will keep rising and will go well beyond the specs of the software.

Colder air is denser thus is requires less boost to equal the air flow of hotter air.

I'd wager that this is either vacuum line issue with the wastegate actuator or somehow, the mechanical workings of the actuator or wastegate flapper and effected by the cold weather.

Is there any logs I can VAG-com to see if the wg is opening properly?
Or is there a procedure to manually move the actuator to check?

I actually thought I might have a slight leak at the vacuum line to the bpv...because it seemed to be opening too soon tonight on my way home.

Ugg..this sh*t has to happen on the coldest week of the year so far [rolleyes]

Thanks guys.

BTW...anyone know the diamter of the larger vac. hose to the BPV?

mike-2ptzero
02-06-2007, 06:12 PM
Is there any logs I can VAG-com to see if the wg is opening properly?
Or is there a procedure to manually move the actuator to check?

I actually thought I might have a slight leak at the vacuum line to the bpv...because it seemed to be opening too soon tonight on my way home.

Ugg..this sh*t has to happen on the coldest week of the year so far [rolleyes]

Thanks guys.

BTW...anyone know the diamter of the larger vac. hose to the BPV?



If you want to know if the WG is opening you can bypass the N75 valve by connecting the hose from the turbo housing to the one that goes to the wastegate actuator. Doing this should cause the boost to go no higher then 5psi.

EuroA4
02-06-2007, 06:16 PM
Cool, thanks....I've mess around this weekend when the temps get into the 30's.

maxspeed
02-06-2007, 06:28 PM
Maybe the wastegate actuator froze so that it could not open the wastegate.


im pretty sure he would notice the accompanying compressor surge really damn quickly, i know i sure did when i tightened my WG too much.

it sounds really cool, but im sure it wreaks havoc on the turbo