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APC system STILL doesn't work HELP!

1318 Views 14 Replies 4 Participants Last post by  synoptik
I still can't figure out what the problem is with my APC system. It just doesn't want to allow anything over basic boost. I recently bought a complete APC system that came off of a working 89' Saab 900 Turbo, just like mine. I have fitted everything I got from the other car and it still didn't want to work. I currently have a MBC connected and I don't like it (boost is all over the place) but I can't figure out what the problem is with the APC. The wastegate works great and holds pressure when the vacuum line was disconnected. The only visible problems I have noticed is that the seat belt light blinks because the fuse was pulled (passive seat belts don't work) and someone removed the housing for the oil filter and replaced it with the N/A housing so I can't connect the oil cooler to the engine. I can't think of anything else to do or what it could be! The APC solenoid will click when turning on the car as well as when I apply the brakes. I get a series of clicks when tapping on the knock sensor. I have two of everything related to the APC system and have replaced everything and still nothing. What else could cause it to run in base boost????? What color are the wires that go to the boost sensor under the dash?
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I've just retrofitted an apc to my lpt. Initially I had problems that couldn't be tracked down (by back-probing the contacts on the apc lead connector) to the
a) pressure sensor (gave correct ohms at 0 and 0.6Bar),
b) brake light (no 12V when brake not applied),
c) knock sensor (continuity thru' leads and thru' shielding),
d) 12V power supply or ground
e) rpm signal in (got a voltage at idle)
f) apv valve - clicked when applied voltage and allowed me to blow down the W connector and get air coming out the R side of the valve.
It turned out it was the connector to the APC valve giving an intermittant connection. Have you checked that you get +12V out of the APC wire going to the apc valve at idle?
Best of luck...
So your APC system is functioning correctly and you’re not getting full boost but you are getting proper base boost? It’s not your wastgate. Does your dumpvalve hold vacuum when you suck on it? I guess just because your APC valve is opening correctly at idle doesn’t mean it’s opening under load (but before knock comes into play). I guess I’d rig a test light from the APC soloniod control (i.e. APC pin 12) into the ****pit and see what happens when you drive. Under normal conditions you should have 12V, under knock conditions you should have zero volts, or pulsing at least. < edit ****pit? I'm not allowed to say co*kpit? What kind of screening software is this?!! />
If you disconnect the APC connector from the unit, undo the screw in the top of the connector, remove the gasket and pull the connector apart, you can see the connector numbers. When probing for signals using a voltmeter probe from the back ("backprobe") in order to prevent damage to the metal contacts.
Best of luck,
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