Date: Sun, 26 Jun 2005 20:39:14 GMT From: Paul Halliday <pjghnospamyonder.co.uk> Subject: Re: c900 boost gauge at idle
in article 1119816651.229301.166160nospam2000cwa.googlegroups.com, ebarter at cartoonman5nospamo.com wrote on 26/06/2005 21:10: > where should the boost gauge sit at idle, neutral or in the white? The > gauge barely gets into the yellow at full throttle on mine, and in an > effort to figure this out I disconnected the wastegate hose to the > solenoid valve and test drove it. The fuel pump cut out as the gauge > approached the orange but before it entered it. Could the gauge be > reading low? I do get boost and the car doesn't really feel sluggish, > though I suspect that it might be capable of more than it has right now. The dash boost gauge shows a white section, a very short white section, a yellow section and and orange (or red) section. With the engine off, the gauge should show just at the start of the broken white section. That is 0 bar pressure. Okay, yes, 1 full atmosphere at sea level, but not to confuse things; "0" :) When you start the car and sit at idle, the needle should drop into the white section. This is normal. The gauge is showing that your engine is "sucking" ... This is called vacuum pressure. A vacuum is generated at the intake manifold by the combustion powering the crank and following through with an exhaust cycle. Okay ... Boost :) When you drive and use the turbo-charger to "blow" air into the engine, rather than rely on the crank to suck air into the engine, your needle will enter the yellow zone. The exact pressures differ from car to car, but the end of the yellow zone represents anywhere between 0.8 bar and 1.0 bar of pressure. The C900 has a safety cut-out switch to cut the fuel when a pre-set pressure is reached - 0.95 bar on the T8 or 1.1 bar on the T16, IIRC (and "dunno" on the LPT 16V). You are experiencing that fuel shut off. It would appear to be set correctly, since the car should not really enter the red (orange) zone on the gauge. The manual does say that under certain circumstances, it will, but should not be for long. Once the default cycle of the APC system is superceded by the internal tuning cycle, the boost will be lowered to the correct pressure and maintained by the APC system. It would appear, therefore, that you are getting higher boost than standard. This means that the "default (or passive) cycle" for the turbo computer is over-shooting. The most likely reason is that your wastegate has been setup a little too high. There are a couple of remedies ... One is to bypass the fuel shut off system and the other to lower the wastegate setting. The former is preferable :) Since APC will lower boost when it detects knock, inefficient fuelling (which will lead to knock) is not strictly a problem. Paul Var tog v”gen v”gen? SAAB : Nothing on earth comes close
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