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I’ve been having a problem with my NG900 (1994) and wondered if any of you guys had seen this before? When I nail my car in 4th or 5th gear the dash mounted APC/Boost gauge rises towards the end of the red section, but then backs of to the middle of the red section. It then oscillates between these two points while I keep my foot on the gas.

I think I read on this BB once before that the dash mounted APC/Boost gauge is in fact an indication of engine demand – not boost pressure. Is this correct?. Does this mean that the oscillations I’m seeing on my dash gauge are in fact an indication that Trionic5 is detecting knock, and retarding ignition? Will pressure test hoses etc tonight - from Turbo exit pipe to TBTC inlet pipe just to rule out any hose leaks. Anybody got any other thoughts?

Cheers

Neil J

NG 900 fitted with K&N, J.T Superflow cat-back, Maptun Stg 2, X-flow intercooler, standard Bosch re-circ valve, TBTC, Abbott (Koni) Suspension., springs, VRK, poly bushes, etc etc
 

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No no no ... only the T7 cars boost gauges are controlled by the computer. The T5 cars have a direct link. However it is probably the computer tuning the engine to avoid knock through the powerband. Could be a dodgy boost controll solenoid perhaps, but it is normal for a car to need to retard the timing and even boost slightly due to small amounts of knock. Hard to tell what's causing it in your case for sure though.
 
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