APC gauge not working

[george2490]

I wonder if anyone can help? I have a 1990 T16 and my APC gauge has stopped showing any boost.
The car is going like the clappers, never driven anything like it, but I suspect this is bad, even though it is the most fun I've had with a mechanical fault. Fuel consumption is through the roof and idle is uneven when cold.
I hope someone can point me in the right direction, if not I'm certain it will end in tears

[woolf]

Don't panic!

Sounds very much like a simple vacuum leak. Trace the vacuum line from the inlet manifold into the bulkhead, and then inside the car to the over-boost cut-off, and then to the gauge.

Somewhere you should have a fairly obvious hissing and either a split or disconnected pipe.

[Matthew]

You can see behind the instrument cluster to find out if the APC gauge's vac hose has popped off by removing the driver's side dashboard speaker cover. Just three or so small Torx screws. May take a bit of careful wiggling to remove it though.

[george2490]

Thanks for your help, I finally tracked the problem down to a vacuum hose that had come away from a "t" in the intake manifold.

Gauge is working and the car is much smoother but not half as much fun. I don't really understand why the difference?

[Si]

I would take a wild guess that because the APC did not see any boost (the pressure transducer is on the same vac line) it was constatly ordering up more boost! You'd still have the knock protection but it may have always been thinking....boost is below 0.4bar, close the sol valve, more boost!