Date: Sun, 29 Jun 2003 16:09:35 GMT From: Paul Halliday <pjghnopsamyonder.co.uk> Subject: Re: Calling all "What's that thingy?" experts ...
in article bdmspl$ufou2$4nopsam34476.news.dfncis.de, davehinznopsamcop.net at davehinznopsamcop.net wrote on 29/06/2003 15:23: > Someone who looks an awful lot like Paul Halliday <pjghnopsamyonder.co.uk> > wrote: >> in article bdllcd$opkst$4nopsam34476.news.dfncis.de, davehinznopsamcop.net at >> davehinznopsamcop.net 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. I didn't read it that way. I read the invisible smiley. We Brits are good at wit and inference :) <snip>First cars ... Learning curves and all that</snip> > 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. I'd love a 96. I think they look really nice. The 99s are great, but I much prefer the earlier models. A Sonett? Well yep, I'd like one of those too, but the Triumph Stag is higher on the list :) >> 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. Gottit! So, it's all about the knock sensor really. That's the function that is imperative to keep working right and why people spend silly money fitting aftermarket turbo sensing systems to their old turbo-charged cars. The notion of default wastegate cycle (the P pot) is beginning to sink in - once I understand it, I'll know what I'm actually doing with any APC mods. Previously, I just kind of turned F up a lot and P up a little then backed down to suit my own preference. My previous 900 turbo broke before I had any real fun and I'd like to intimately know the theory first with this one, rather than blindly do what others have done. I still have the APC box from my first 900 turbo and it was setup just nicely. I got a document from somewhere on the internet (I can't find it again), detailing APC information. I'll post it as a new thread for information. >> 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. Getting the heat controller arm back onto the far end (not the dash end) through the DIN slot was one f*cker of a job. I was cursing Saab for a while about that one until I pulled the speaker clusters out :)
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