2.5TDI Low Inlet Manifold Pressure Cured!!!

[Equinoxstudios]

Oh I haven't laughed so hard in years.

1998 A6 2.6TDI. With fault codes showing low inlet manifold pressure and pressure regulating limit not reached we started replacing parts - MAP sensor and N75 (turbo boost vacuum control valve). Even replaced the hoses into and out of the intercooler as they had started to delaminate and showed pinholes.

Still no boost and car went into limp mode within a few yards of driving.

Checked the boost diaphram for leaks with my vacuum hand pump - no leaks. Then I looked at its travel. I looked at the small 'arm' on the turbo that is moved by the diaphram and noticed that it never lifted anywhere near its end-stop (defined by a lockscrew with some white paint on it).

Released the vacuum and noticed the pushrod/shaft coming out of the diaphram has a thumbscrew and locknut to adjust its effective length. The locknut for this was loose.

I pumped up the vacuum till the diaphram had travelled its full extent and adjusted the thumbscrew on the shaft until the little arm on the turbo lifted up to its end-stop i.e. I matched the limit of the diaphram's travel to the end-stop of the small arm. I then did up the locknut to lock the thumbscrew adjustment.

Voila! My flying machine has returned to being the Alton Towers ride of your life.

Moral of the story - DON'T MISS THE BLEEDIN' OBVIOUS

I hope this post saves someone a bit of money!

[SiliconS]

Hi,
I've got the same engine as you and (among other problems) the power is inconsistent. For various reasons I'm beginning to suspect the turbo vane control actuator and wondered whether you could give me any info about how/where to check it please? Do you have any photos that would help illustrate what you mean by the description above?