Date: 29 Jun 2003 14:23:49 GMT
Subject: Re: Calling all "What's that thingy?" experts ...

Someone who looks an awful lot like Paul Halliday <> wrote: > in article bdllcd$opkst$, at > wrote on 29/06/2003 04:11: >> Has the apprentice become the master? > Oh boy! Far from it. I realised after I sent that that it could have been read as me being arrogant; I hope it wasn't interpreted so. > Mechanics I can understand, but don't have the time, > space and tools to do anything about it - I'd like to though. Electrics and > associated systems are becoming less of a mystery to me and I'm finding I > can do a lot of the ground work myself. I've had 'em all apart and back together from the '60 93f that is awaiting my attention, to the '88 900T that I sold about a year ago. I learned an *awful* lot about the Sonett, as my first car. Nothing like trial by fire - it has been assembled from at least 3 cars before I got it, so it had some, er, strangeness to overcome. > I'm still only half-trained on the 900 8V models which are easy compared to > the later 900s (pre-GM of course, which I wouldn't even look at). I've never owned a 99 (want a turbo though), a NG 900, or a 9000. Or a 9-3, or a 92. I can live without an NG900/9-3, the 9000 doesn't do much for me since I have the 9-5, but I'd kill for a 92. > The first car I ever had to even open the bonnet on, other than for > re-filling the screen wash, was an '88 900 turbo with a whole load of > aftermarket stuff added. Whoa! What a learning curve. I know what to leave > alone with this one, so I don't end up like Disney's apprentice with > everything spinning out of control ... Heh...great visual, thanks. Need to watch that again. > I've got the ignition system, cooling system, egr system, and the vac system > all figured out now and I'm pretty good at finding faults in these areas and > sharing those experiences. I'm still learning with the turbo stuff - the > mechanics and theory all make sense, but the APC system still needs some > understanding. OK, here's Dave's oversimplified, fairly accurate as far as it goes, one-paragraph "how your '88 Turbo's APC works": The key to the system is the knock sensor - basically a microphone, screwed to the engine just below the intake manifold. The APC will increase the boost until there is knock, and back it off slightly. Repeat until you're done driving. The APC has internal controls for knock sensitivity (how loud it gets before it triggers the box), maximum boost, and the rate at which the boost rolls off as you approach maximums. (so you don't get an abrupt decrease when you hit the max). As you stomp the loud pedal, the turbo boosts, wastegate fully closed. APC is watching your boost, listening for knock, and when you get enough knock or close enough to maximum boost, it starts opening up the wastegate, bypassing the turbo - this changes what the APC's sensors are seeing, and it reacts to that. Not sure how many times a second it does this, but it's really an analog computer; lots of integrator circuits, potentiometers for the adjustments. > The in-car systems are starting to fit together now I can actually see it > better (through the speaker apertures, eh? Duh!). Still not comfy to work through, but beats going in through the radio slot or whatever. Yikes. Getting the vent hoses back on can be tricky, though. Dave Hinz

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