I am trying to use the Saab APC system on my 89 745T automatic, but the results are confusing. The only way I have been able to get it to work is by disconnecting all the inputs except for the pressure transducer. This is my second transducer which measures about 12ohms at rest, 9ohms at vaccuum and a max of about 100ohms at fuel cutoff,the first transducer measured infinite ohms at any pressure/vaccuum and was obviously bad. With only the transducer connected and the pots readjusted, I am able to run the boost pressure to 12-12.5 lbs at WOT, just below the fuel cutoff, which is where I want it. However if I connect the knock sensor or the neg coil connection ( either or both) then boost pressure drops to the base 7.5 pressure. I can do without the rpm mapping if necessary but I would like the anti-knock protection feature of the APC. The ECM is a Saab #7524135 and I wonder if this is an early black box that cannot handle the electonic ignition. This theory however does not explain the knock sensor problem. If I connect just the knock sensor (not the pressure transducer or the ignition connection) the boost is raised but naturally with no upper limit because of the unconnected pressure transducer, I keep hitting the fuel cutoff limit at WOT. The knock sensor wire had been cut by the salvage yard but I reconnected the two inner wires and the outer ground shield. The inner wites show low impedence to the plug, the shield is impossible to measure as there is no connection at the plug. Could this wiring be the problem? My power is being drawn from the positive side of the coil and the 3way valve seems to be functioning normally. I don't understand what the problem is. Does anyone with APC experience have any ideas how to get both the pressure transducer and the knock sensor to operate correctly?

Junk that POS and install a manual boost control.

http://www.dawesdevices.com

http://home.earthlink.net/~turbogus/index-old.html

Much better and simpler too.
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Warren Bain - '99 V70GLT G-Valve > 70K mi, '96 965 >110Kmi Wifemobile near Manassas Va.. Check the 700/900 FAQ via the 'features' pull down menu.

Here is an archive of the old APC site.

http://web.archive.org/web/20010124085700/http://www.teleport.com/~bertram/volvoapc/

jonnyewell
You almost got a big hurrah from me for this address, unfortunately I can only get one page of the site. Attempting to access the other pages brings up the dreaded "not in archive" page. Am I missing something? From what I can see I gather that Mr Bertram is not completely happy with his APC either. Do you know why?

I wired a risistor accross the pressure sensor to fool the APC that it was operating in a normal range. I don't remember the exact value but 50 ohms sounds about right. The APC is set to like 5-7 PSI for normal operation. The resistor will fool it into thinking this.
I also had problems with the 3 way selonoid not being able to hold at higher boost levels. It would just let the boost keep rising. ANd I did try different Saab selonoids. I ended up using the old 240 selonoid and drilling out the oriface. Now if the engine pings the boost goes all the way back to the base setting. The 240 selonoid is not capable of "vibating" like the saab one. Let us know if you have the same problem with the saab selonoid.

Volvo4dv8
I was able to adjust the boost pressure to the desired range by connecting only the PTrans and using a pressure guage listening for the clicking of the 3 way valve. If I remember it also took some road testing to get it just where I liked it (a hair shy of fuel cutoff). So I have no doubt that this ECU can handle the pressure I want, it just can't handle the knock sensor at the same time. My 3 way valve seems to be operating correctly now but early in this grand experiment it would just flutter off and on even at idle. The way to check for a good 3way valve is to listen for an audible click when the ignition is turned on or the APC is powered up. I sure wish that APC/Volvo website was still in existence. My APC unit is producing the boost I want now, it just does not have the knock protection that made it so attractive in the first place.

I ran in to the same problems when I first installed mine and by hit and miss I got it to work. First is the thermostat in the Air box working? If the door to the preheat tube is open and pulling in heated air you will get detonation thus the system will drop the boost to stock. Two is the bolt that runs through the knock sensor torqued to the correct foot pounds of torque. Third are you running premium or weasle piss gas. If you get a bad tank of gas this system will let you know real quick. With 89 octane I can't get the boost over 9 psi, 10 on a cool morning.
If you can find a pick and pull get a new complete wire for the knock sensor. If it needs to be cut, cut it at the base of the control unit. I wouldn't think that the wire would be the problem but it's better to be safe instead of sorry. As far as the hitting the cut out, it is caused by a slight over boost as the turbo spoils up. The turbo wheel inersia causes the boost to jump 1 to 2 psi over your set boost level. It will settle back to your set level with in a second or two as the waste gate kicks in. So you will need to set the overboost switch a little above your set boost level.

AL - Thanks for the info, the thermostat in the air box is ok but I am not sure what the torque spec on the knock sensor should be. By the way I have the two sensors stacked with the APC closest to the engine. I remind you that the knock sensor connected alone will produce higher boost without reverting to base boost. It is only when I connect the PT also that I get only base boost. This infers to me that the knock sensor circuitry is working but the combination of knock and pressure is not. By the way what part number ECU do you have?

I stacked my Knock sensor on top of the Volvo unit. I don't think it really matters. As far as which unit I have unknown other than I pulled it out of a 1988 900.