Turbo underboost

Stephen Harman · May 16, 2022

Hi, Stephen here from Cape Town, I am new to the group and a recent Cali buyer. 2008 2.5 tdi axe manual. i am suffering with terrible turbo lag, nothing under 2300rpm and all-round poor performance in 5th and 6th gear. I have had the turbo overhauled and the injectors checked. I now suspect a vacuum issue as there are no turbo hose leaks. Is there anyone else who has suffered this problem and managed to resolve it<

WelshGas · May 16, 2022

Stephen Harman said:
Hi, Stephen here from Cape Town, I am new to the group and a recent Cali buyer. 2008 2.5 tdi axe manual. i am suffering with terrible turbo lag, nothing under 2300rpm and all-round poor performance in 5th and 6th gear. I have had the turbo overhauled and the injectors checked. I now suspect a vacuum issue as there are no turbo hose leaks. Is there anyone else who has suffered this problem and managed to resolve it<

Welcome. I’m afraid I cannot help you on this problem, but if you don’t get any joy it might be worthwhile searching or posting on this Forum. They tend to concentrate more on the basic vehicle, T4 & T5, than the camping/ lifestyle side of things.

https://www.vwt4forum.co.uk/whats-new/posts/867670/

Perfectos · May 16, 2022

Stephen Harman said:
Hi, Stephen here from Cape Town, I am new to the group and a recent Cali buyer. 2008 2.5 tdi axe manual. i am suffering with terrible turbo lag, nothing under 2300rpm and all-round poor performance in 5th and 6th gear. I have had the turbo overhauled and the injectors checked. I now suspect a vacuum issue as there are no turbo hose leaks. Is there anyone else who has suffered this problem and managed to resolve it<

https://www.vwt4forum.co.uk/threads/2-5tdi-lacking-low-end-grunt-turbo-lag-under-load-mid-revs-goes-like-stink-top.146322/

Emil Silenhag · May 16, 2022

Check your exhaust and diesels particle filter. Make sure it’s not restricting flow…

Pauli · May 22, 2022

Motor code AXE does not have DPF (unless retrofitted for obtaining the green environment sticker in Germany which I highly doubt since the question came from South-Africa).

Is the situation such that it even goes to de-rate ("limp home") mode due to lack of boost pressure?

Vacuum side is definitely something to check as there's several small hoses that over the time may crack. Problems with boost regulating valve N75 are also nothing exceptional with older Volkswagens. If I don't remember wrong I got a new part with number 1K0906627A for my previous Cali.

Stephen Harman · May 22, 2022

Pauli said:
Motor code AXE does not have DPF (unless retrofitted for obtaining the green environment sticker in Germany which I highly doubt since the question came from South-Africa).

Is the situation such that it even goes to de-rate ("limp home") mode due to lack of boost pressure?

Vacuum side is definitely something to check as there's several small hoses that over the time may crack. Problems with boost regulating valve N75 are also nothing exceptional with older Volkswagens. If I don't remember wrong I got a new part with number 1K0906627A for my previous Cali.

Hi, yes goes into limp all the time if I put my foot down. new valve, hose o-rings and vacuum lines arriving tomorrow. fingers crossed.

Perfectos · May 22, 2022

Stephen Harman said:
Hi, yes goes into limp all the time if I put my foot down. new valve, hose o-rings and vacuum lines arriving tomorrow. fingers crossed.

Good luck keep the updates coming (to help others in future)

Keith Warne01 · Jan 4, 2023

Stephen Harman said:
Hi, Stephen here from Cape Town, I am new to the group and a recent Cali buyer. 2008 2.5 tdi axe manual. i am suffering with terrible turbo lag, nothing under 2300rpm and all-round poor performance in 5th and 6th gear. I have had the turbo overhauled and the injectors checked. I now suspect a vacuum issue as there are no turbo hose leaks. Is there anyone else who has suffered this problem and managed to resolve it<

Howzit Stephen... just bought mine... same issue exactly... VW said turbo settings but another test showed up the only recurring fault is cam position sensor. Autodoc in retreat say it's a timing issue so I'm booked in tomorrow am for the cam gears to be done... quoted R6k... he says it common issue just like a stretched cambelt (only they don't have belts)... I'm trusting it will fix the problem... will post an update when I pick it up

Keith Warne01 · Feb 4, 2023

Keith Warne01 said:
Howzit Stephen... just bought mine... same issue exactly... VW said turbo settings but another test showed up the only recurring fault is cam position sensor. Autodoc in retreat say it's a timing issue so I'm booked in tomorrow am for the cam gears to be done... quoted R6k... he says it common issue just like a stretched cambelt (only they don't have belts)... I'm trusting it will fix the problem... will post an update when I pick it up

So last update for anyone interested... turned out to be a bolt that had come loose in the timing gears... caused havoc... result... new engine! Advised by two different mechanics cheapest and safest option. R80k .. hardly cheap!