upgraded ECU on/off switch? [Archive] - SaabCentral Forums

: upgraded ECU on/off switch?

7th July 2003, 04:07 PM
Bit of an odd one this - most people only want to increase horsepower, not decrease it.

So does anyone know, if I fit an upgraded ECU & APC hardware to my LPT, would it then be possible to 'insert' an extra switched circuit to the APC solenoid to give either:

1.Normal ECU controlled fuctioning.
2.Overidden - ie fully open( or close) the solenoid ,allowing air from turbo straight through to wastegate as per normal LPT function allowing base boost only.

If this would cause problems for the ECU could it be done by having a parallel connection in the hoses between turbo & wastegate fitted with a remotely switchable valve.Then the ECU would be no wiser

I only ask this because there are occasions when LPT power is sufficient ( like most winters & when my better half is driving the car) & it would be handy just to be able to push a button & turn the extra power on or off.

I don't want it to be adjustable, just on or off.

7th July 2003, 05:09 PM
Yes you can have a switch to the magnetic valve.

Just cut the earth wire and put the swich in line.

7th July 2003, 06:37 PM
Wouldn't that just allow the APC solenoid to function either normally or not at all, rather than force it to open?

I don't have a grasp yet of APC solenoid operation - I know exactly what it does ,but not the 'logic' of it's operation.

Is turbo to wastegate connection in APC solenoid normally open or normally closed with zero volts applied? :-??

8th July 2003, 05:48 AM
Wouldn't that just allow the APC solenoid to function either normally or not at all, rather than force it to open?

Thatīs right... If you have the valve in use then you have a full turbo pressure, and if you donīt you have a low turbo pressure.

On my 9000 I have 230hp if the switch is on (closed circuit) and 170hp if the swith is of (open circuit).

12th July 2003, 07:38 AM
Well it all works!

Heat plate out, modded air filter housing, stage 1 Speedparts ECU with 'LPT/aeroish' on/off button

As recommended, I cut into the lead out of the APC fuse ( No 5) and ran a cable to a air conditioning on/off switch that fitted into a spare slot on the dash ( switch very kindly supplied by local Saab dealer free of charge & they even photocopied dealer APC & Ignition system wiring diagrams so I didn't cock it up).

I plugged in my new Speedparts ECU and plumbed in the APC solenoid.

Went & did a few adaption runs & it flies.

It's a long time since I've driven a car that requires both hands on the wheel when you floor the throttle

Around town the car is as quiet as ever but above 2500 rpm it's an abosolute blast. If I try hard enough I can just about make my rear mudflaps drag on the ground.

But for those sensible moments, like winter or when the wife is driving I can just press my little air con switch and revert back to LPT which loses me more than 65 hp and a bucket load of torque. It's a bit like having a traction control system that works!