[s-cars] 94 S4 hesitated

[FvAMI at aol.com]

In a message dated 6/10/05 10:14:39 PM Pacific Daylight Time, 
sam at edgetoedge.co.nz writes:


>  drove it again today, initially it did the same thing, then the boost 
> readout went flat at 1.0 bar and the hesitation appears gone. The boost 
> reads 1.0 bar no matter what speed/throttle position, whether full boot 
> up hill or full overrun downhill or at idle. Power seems normal, 
> everything drives smoothly.
> 

1) If the reading is 1.0 the hose between the ECU and the intake manifold has 
blown off. Probably the water trap.
2) If this happens the ECU will cut boost control and the maximum absolute 
pressure you would see is 1.3 bar ... so it may seem smooth ... but you also 
have limited power.
3) The other symptoms sound like an overboost cutoff which could mean leaky 
hoses (x-over to intake) and/or a stuck WGFV (Waste gate frequency valve) or 
any hose related to controlling boost.
4) The gross inaccuracies of the internal boost display system (due to 
design) are a myth ... small inaccuracies (+/- 0.1 bar) are do to separate voltage 
regulation circuits (ECU and boost circuit ... differences between Bosch 
production 2.5 bar sensors ... etc.) Gross inaccuracies can occur and are caused 
usually by a corroded or bad ground connection. A good way to check for that is 
... turn the ignition on ... it should read 1.0 to 1.1 bar (sea level). Hit the 
auto check system it should maintain it's previous reading. Low readings due 
to a long averaging period are definitely a negative with this display (i.e. 1 
and 2 gears). But readings in 3rd are typically within +/- 0.1 bar.

Best regards,
Feico van der Laan