Classic 900 cruise control
Discussion
I've had my Saab (900 turbo cabrio) over at Bill in BonnyBridge to tidy up the engine and get it all sorted. The thing is he doesn't know much about cruise and we can't get it to work. I renewed the Vacuum unit and Bill done a pressure test and everything seems fine but it just wont work. Is there something we are missing.
Take the front left speaker out of the dash top so you can look down from through the windscreen. Remove the plug connect from the vacuum pump in the left inner wing. With test leads live and ground, place ground to one of the pins on the pump then place live momentarily on one of the other pins. If you have it the correct way around the pump will run and suck, or wrong way blow and do nothing, so swap it. If it does then look down the speaker aperture and see if the diaphragm has pulled the chain linked to the throttle bar, and see if the pedal is down to the floor. If this proves so and you can bridge the live lead at the same time to the remaining pin on the pump, this will hold the pump at any point between non vacuum to full vacuum. If the diaphragm is working but the pedal doesn't move, check that the toggle chain hasn't come off the diaphragm to bar.
Pedal switches can easily be reset by feel and ear providing they are not broken. Lay in the foot well and look at them. They are similar to brake light switches and require that they sit in the closed position with the brake and clutch pedal in rest position. This is easily determined by making sure the switches line up with the tin plates on the pedals, which easily get bent out of place, and that the switches in pedal rest position are not past the point of 'open contact' which can be determined by hearing them click. They should basically click and go open just as the respective pedals are touched. Make sure the vacuum hoses are attached to the switches and the 'T' piece that leads off across the underneath of the dash to the diaphragm. Assuming of course, you do have vacuum from the pump to the diaphragm to start with as many 900 cruise failures are caused by split or perished hoses underneath the fuse box.
There are other things that can prevent cruise such as brake light filaments blown, but these are the basic checks which are fairly easy to do. If all of the above check out ok and you're still not cruising, I'd suspect the cruise control ECU which is located above the drivers side leg area under the dash. It's also worth pointing out that the switches can fail too and a good indication of a working switch is you can usually hear the ECU clicking as you operate the switch. Also worth checking then.
Hope this helps. Apologies it's not in any particular order. I just typed it as I went along thinking about it.
Lady
Pedal switches can easily be reset by feel and ear providing they are not broken. Lay in the foot well and look at them. They are similar to brake light switches and require that they sit in the closed position with the brake and clutch pedal in rest position. This is easily determined by making sure the switches line up with the tin plates on the pedals, which easily get bent out of place, and that the switches in pedal rest position are not past the point of 'open contact' which can be determined by hearing them click. They should basically click and go open just as the respective pedals are touched. Make sure the vacuum hoses are attached to the switches and the 'T' piece that leads off across the underneath of the dash to the diaphragm. Assuming of course, you do have vacuum from the pump to the diaphragm to start with as many 900 cruise failures are caused by split or perished hoses underneath the fuse box.
There are other things that can prevent cruise such as brake light filaments blown, but these are the basic checks which are fairly easy to do. If all of the above check out ok and you're still not cruising, I'd suspect the cruise control ECU which is located above the drivers side leg area under the dash. It's also worth pointing out that the switches can fail too and a good indication of a working switch is you can usually hear the ECU clicking as you operate the switch. Also worth checking then.
Hope this helps. Apologies it's not in any particular order. I just typed it as I went along thinking about it.
Lady
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