Boost gauge

[rogerthechorister]

Suddenly the boost gauge on my Sport edition with turbo+ is under-reading. Plenty of boost judging by power but hardly showing on gauge. Suggestions please.

[Forrest]

Leak or blockage in the hose that goes to it? Probably easiest to start at the manifold end and see how the gauge responds to pulling a vacuum or applying pressure to the tube. Stick something suitable in the brass nipple to check it’s not blocked too.

It’s not all that hard on a 940 to pull the cluster and check that end if necessary. You might be able to see what’s going on just by removing the driver’s kick panel.

If it is a faulty gauge it’s fairly easy to swap instruments between clusters if you can find or have got a spare.

[RollingThunder]

IIRC the rigid vacuum line that comes off the manifold goes into a rubber type pipe at the back of the cluster - maybe there is a split in that? Otherwise just check for a vacuum leak in the usual places.

[rogerthechorister]

Surely the oddity is that the gauge shows little boost (works OK off-boost) but the power in the engine (on my butt-dyno) says plenty boost.

[Chris1Roll]

Originally Posted by rogerthechorister

Surely the oddity is that the gauge shows little boost (works OK off-boost) but the power in the engine (on my butt-dyno) says plenty boost.

Its what I would expect if there was a split in the pipe to it TBH.

Under vacuum the split closes up.
Under low boost the split opens a touch but still shows some pressure.
Under more boost the split opens up further and acts a bit like a bleed valve for the gauge.

[rogerthechorister]

But surely that would also reduce boost to or from the turbo+ so also reducing actual boost from the turbo.

[Chris1Roll]

If anything, dependent on how the pipes are routed to the ECU, the opposite could be true and you could even be overboosting but not hitting the ignition/fuel cutout because the ECU isn't seeing it.

Fun, until something melts.


I've just skimmed over the installation manual for the Turbo+ and it looks to me like its just an electronically controlled bleed valve installed between the compressor and the wastegate that is activated at certain times.

That leaks off air deliberately in order to increase boost over stock.
If you put a gauge either side of the Turbo+ valve, the the one after the valve would show a lower pressure when the Turbo+ is engaged but the actual boost is higher than without the 'leak'.


You've got three options:
1) Your gauge is faulty.
2) You have a leak in the line to the guage (and possibly the ECU too).
3) You are really only making a tiny bit of boost.

Since you say the car can still move iout of its own light, my money is on 1 or 2.