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Car Forum / Saab Cars / May 20061985 900 Turbo - APC question
Hello, I have a perfectly running 1985 Turbo, except I'm only getting base boost (about 1/3 into the yellow on the gauge). My local indie mechanic who's very heavily used and highly regarded in these parts, says the APC needs to be "rewired," and said it would cost about $65. This was simply jotted onto a work order for a different repair, and I haven't yet asked for specifics. Anyway, I'm thinking this might be one of the DIY things I can tackle, and I try to do anything possible myself (which isn't much...:)). I posted this on Saabnet, but nobody has said much about the APC unit. Can any of you C900 gurus give an indication of what rewiring the APC would entail, and how complicated the procedure might be? With the engine so strong, and the body pretty decent, it's a shame not to get all that the car can offer. Or maybe I should just install another APC? As for the notorious 1985 wiring issues, almost all electronics work, except power central locking, heated seats and power mirrors. btw, I'm at 246K miles...coming up on a quarter million! It's the one in the top two pix: http://the_urchin.home.comcast.net/photos/saab.html Thanks for any assistance. -jw > Hello, Hi! <snip> > Anyway, I'm thinking this might be one of the DIY things I can tackle, > and I try to do anything possible myself (which isn't much...:)). I [quoted text clipped - 4 lines] > engine so strong, and the body pretty decent, it's a shame not to get > all that the car can offer. Or maybe I should just install another APC? This page on 900 Aero shows how to graft the APC system onto an LPT car, so the principle is the same for re-wiring an existing APC system: <http://www.900aero.com/main/diy_main_lpt.htm> How's that? Paul 1989 900 Turbo S http://saab.go.dyndns.org/ > > Can any of you C900 gurus give an indication of what rewiring the APC > > would entail, and how complicated the procedure might be? With the [quoted text clipped - 6 lines] > > How's that? Very nice, thanks! That engine is cleaner than mine though.:) I suppose I should focus primarily on numbers 7 through 12 in the "engine bay" section? -jw >I have a perfectly running 1985 Turbo, except I'm only getting base >boost (about 1/3 into the yellow on the gauge). My local indie mechanic >who's very heavily used and highly regarded in these parts, says the APC >needs to be "rewired," and said it would cost about $65. This was simply >jotted onto a work order for a different repair, and I haven't yet asked >for specifics. I know on my old 1984 T16S, the APC solonoid on top of the radiator would sometimes not work as it should. I traced it to very old wiring and heat from the turbo. The heatshield wrap/tape had failed, and the insulation was something between cottage cheese and candle wax. It would lead to shorts between the crack. Taping then up temporarily solved it, until the turbo heat would melt the tape adhesive and it would unwind again.  SignatureCarl Robson Car PC Build starts again. http://smallr.com/rz Homepage: http://www.bouncing-czechs.com i wouldnt bother.. fit an a/market boost controller, 70$, set is once and no more boost issues. 2 mins to fit and 100% reliability mike > Hello, > [quoted text clipped - 25 lines] > > -jw > i wouldnt bother.. > > fit an a/market boost controller, 70$, set is once and no more boost issues. > 2 mins to fit and 100% reliability I disagree strongly. The APC is engineered and optimized for that car. aftermarket boost controllers will not be. Sounds like turning a simple repair into a hassle and a project by going aftermarket for this. Dave Hinz Dave. I agree that apc works great.. repair procedure.. apc has several sensors of which makes it work correctly. knock sensors, pressure transducers, apc computer., the expensive coax from the apc ecu to the knock sensor which is a common fault, apc solenoid. etc etc. there could be thousands spent to rectify the apc, then u find out that your 250 000 km engine has a slight bottom end rattle which causes the apc to run basic boost. on the other hand it could be as simple as a brake pedal switch. this is why i would go with a/market. much more simple. on that age of car anyway. Michael Saab M.Tech >> i wouldnt bother.. >> [quoted text clipped - 7 lines] > > Dave Hinz > Dave. > > I agree that apc works great.. repair procedure.. > > apc has several sensors of which makes it work correctly. Thanks again, all. I'll probably just start by taking a close look at the APC to determine, based on the input and pix here and elsewhere, whether it's something I can adjust. Will keep in mind the input about the aftermarket swap. I'll try to post with results! -jw Blimey - I've had a 900 Turbo continuously since 1981 (current one 1990 vintage). What's APC ! sb > Blimey - I've had a 900 Turbo continuously since 1981 (current one 1990 > vintage). > > What's APC ! Automatic Performance Control ... There is a Swedish translation, too :) It was designed around 1982 and launched somewhere around 1983. It is essentially a knock sensor with an electronic brain to give maximum performance given any grade of fuel. It was present on all C900 turbo cars from around 1983 with the exception of the LPT model. Look on the LHS wing/fender for a black or red box with the words "Strydon Control Unit". <http://en.wikipedia.org/wiki/Automatic_Performance_Control> Simple, ingenious and keeps the C900 running. People who complain that the C900 is not a good boosted or lacks performance invariably have a non-working APC system. Keep it in good shape and the car will keep lovin' ya :) Paul 1989 900 Turbo S http://saab.go.dyndns.org/ Thanks for that Paul, I remember lots of things about that first one - which I guess from your dates wasn't APC'd: I went to Goteborg to fetch it back to England - it had 1 mile on the clock, (These were times when there was a custom duty advantage in "go fetch"; tho sadly at Newcastle they'd never seen one so was there a day while they decided what I had to pay). Sadly they forgot to (Z something?) it so it rusted away, Was 'sold' it in W. Wittering - nice man said, "I can tell you like it, take it back to London for a few days". Course I liked it! I left my old Austin 1300 with him and drove off! No names, no nothing. (Times present times past, huh!). Repaid his trust - got girlfriend to buy one from him a while later. In London and Paris it beat nearly everyone from the lights; in both places there was a crowd around it every time I came back to it. Re recent thread - the fan got disconnected while in traffic jam. £2000 for a new cylinder head. Current one (1990-1 - well G reg anyway) has 300,000 miles and been turned over in airborne treble somersault; no garage service since 95. I love 'em! Still have both! Keep this one cos don't like the new (GM) ones so much. PS - apologies to all for memory lane trip >> Dave. >> [quoted text clipped - 6 lines] > whether it's something I can adjust. Will keep in mind the input about > the aftermarket swap. I'll try to post with results! Feel free to follow up with questions based on what you find. Really, APC is not difficult to troubleshoot. If it's not the usual handful of things, like stuck brake switch, bad grounds or the APC box shorting due to it being full of rain water by all means fit an aftermarket controller. Personally, I would advise renovating APC. While this may not be complete, this is the order I would check things: 1. Press the brake. Does the solenoid valve on top of the radiator click? Yes? Continue. No? Fix that. Usually, this is just a bad ground. Just double-check that your brake lights are not stuck on, too :) 2. Pull the multi-plug off the APC box, spray over with WD-40 and re-fit a couple of times. Clean again and re-fit. Better? No? Continue. Yes? Great. Feel free to check the ground on the APC box. Pin 5 (or rather the connection on the multi-plug that connects to pin 5) should have continuity to the chassis. See <http://www.900aero.com/phpBB2/viewtopic.php?t=150> for an inventory of the function of all the pins. If you're electronically minded, rig up the knock sensor LED to facilitate troubleshooting the knock sensor. 3. Remove the power to the APC solenoid valve, connect a known good pressure gauge to the intake manifold, find a long road and floor it in 4th. Note the maximum pressure reached. It should be 0.35 bar or thereabouts. Too low a pressure will give a poor max boost, which might feel like a failed APC system. Still bad? 4. Check the power to the knock sensor. You'll find this under the intake runners. No power/not connected and you'll get basic boost. Better? Yes? Fix the knock sensor wiring. No? Continue. 5. If you can reach, are inclined and the power is definitely good, unbolt the knock sensor from the block (and wrap in padded cloths) and go for a drive. Better? Your engine knocks. No? Continue. 6. Is the charger okay? Remove the vac pipe from the APC solenoid to the wastegate. Connect a pressure gauge, find a long road and slowly raise the boost to around 0.75 bar. If it won't make that boost (we already checked the wastegate, remember), then the charger is poor. 6. Beyond that, come back with more questions. Paul 1989 900 Turbo S http://saab.go.dyndns.org/ |
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