awx limp mode running low on ideas now as iv tried everything

[jonathan bees]

http://www.ukpassats.co.uk/phpbb/images/smilies/14.gif http://www.ukpassats.co.uk/phpbb/images/smilies/14.gif http://www.ukpassats.co.uk/phpbb/images/smilies/14.gif http://www.ukpassats.co.uk/phpbb/images/smilies/14.gif http://www.ukpassats.co.uk/phpbb/images/smilies/14.gif http://www.ukpassats.co.uk/phpbb/images/smilies/14.gif http://www.ukpassats.co.uk/phpbb/images/smilies/14.gif http://www.ukpassats.co.uk/phpbb/images/smilies/14.gif hi all i hav a 2001 passat wax with nearly 200k on and it keeps doing in to limp mode
fault code is boost pressure upper lim reached

thinks iv changes
all vac lines
n75 valve
map sensor
taken turbo off cleaned and refitted (actuated moves ok) but it also did before

And from what i can tell the vacuole pressure seems ok

it will rev to redline in 1st an 2nd but the soon as you hit 4k isn in 3rd it goes in to limp mode and and seems to be worst under load i.e. overtaking in 4th an 5th on motorway ext an on hills

witch off back on its ok

no other fault codes also out of interested what is the ecu's max preset boost limit before it goes in to limp mode


this is driving me mad lol as i can't find the fault (could there be anything see wrong with the turbo ect

any help would be much appreciated
won't rev the engine hard when cold but if i start from cold an go for a drive for about 2 mile then floor it in 3rd it will go past 4k with no probe once hot after say 5-6 mile mile floor it in 3rd it goes in to limp mode pretty much bang on 4k every time so is it likely to be the vnt in the turbo sticking once hot

[passat 130 tdi]

has the ecu been remapped ???

you've covered everything i did to fix mine , only thing I did different was to fit an uprated map sensor with a higher boost limit , I also flushed the turbo with innotec and blanked off the egr .

[Gary03]

I would say boost control valve but I spose that's what the N75 valve is?
Theoretically, theres only 3 things that will cause overboost and that's boost control solenoid, MAP sensor and the VNT operation of the turbo.
One other thing, do these turbo's have a waste gate? Im sure they do.
Is the waste gate actuator OK? is it operating the waste gate when full boost is reached? Is the diaphragm in the actuator OK?

[jonathan bees]

had a good look today with a bosch kts looking at 2 things actual boost pressure and nominal boost which i guess is that the ecu is asking for


ath idle HOT
nominal 1071 mbar
actual 1065 mbar


Hot engine one hard rev
highest recorded readings
nominal 2478 mbar
actual 2457


go for a gentle drive using little acceleration the actual boost is just above the nominal


then go for a drive using bursts of hard acceleration
nominal 2478 mbar
actual 2984 mbar


if you used prolonged hard acceleration in 3rd gear and above for fore that 5-10 seconds it does in to limp mode
but when checking the highest readings achieved are still the same as above
nominal 2478 mbar
actual 2984 mbar


the vnt does seem to move freely so is there any way the adjustment on the vnt is somehow out or am i missing something

[jonathan bees]

yes it has been mapped but i got a different ecu and had that mapped it was doing the same thing with the existing map/ecu

[passat 130 tdi]

yes it has been mapped but i got a different ecu and had that mapped it was doing the same thing with the existing map/ecu


Mine was cured with an uprated map sensor for the 150bhp golf- it copes with the higher levels of boost after a remap

[jonathan bees]

what value should the boost pressure be with the engine turned off mine is reading 950mbar

[passat 130 tdi]

what value should the boost pressure be with the engine turned off mine is reading 950mbar


all depends what the weathers like and where you are globally . up a mountain or down in a ravine etc