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Discussion Starter · #1 ·
Greetings,

I have been trying to get the cruse control to work on my 89 spg. The vacuum system is in good order except for one thing that may need attention. I found that the vacuum control switch with the red cap that is mounted near the pump does not hold a vacuum. The switch part works fine but as soon as I try to pull vacuum through it, the vacuum seeps away. Does this need to be replaced? Will one from a non-turbo work on it just to see if I can get the thing to work?

I had to change the blinker switch today and the one that I got for it was from a 1988 900. The plug was different (old style) so I soldered on the one that the original had. I would have been happy to have been able to take the cruise part off of the blinker arm to switch them, but it seemed to be on there pretty good. The green and yellow wires seemed to be backwards compared to the original one that was on there, so I switched them.

As I was checking the wiring I found that according to the instructions, that pin 3 was supposed to be RED but it was BLACK instead. It did work fine when I hit the brakes and clutch to see if the dump valves would work.

Next the orange wire pin7 was supposed to have continuity with pin 1 of the vacuum pump, but it didn't.

I also checked out other sits that may have more info but could not find any. I thought that townsend imports would have something but he didn't. I could not bring anything up in regards to this. I have checked the threads on this but nothing like this that I could find.

Any help would be much appreseated.

Thanks,

Dennis
 

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I spent many hours with my head stuck between the instrument cluster and winsheild replacing all the vacuum lines and checking switches for the cruise. The problem the whole time was a blue plug that plugs into the back of the speedometer. Without that plugged in the cruise won't work, you might want to check that. Also the vacuum switch that you are talking about controls the APC solenoid, so that when the car is running with cruise, you just get base boost.
 

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Discussion Starter · #4 ·
One of the problems that I have in regards to the vacuum control switch ( one with red cap ) is, when I apply vacuum to the thing it only holds vacuum for about 2 seconds. The vacuum bleeds away slowly. I personaly don't think that it should but I have to ask. I want to get another one if it is not good and can I just bypass the control switch until I get another one?

The rest of the system for wiring is also a little mest up. No red wire in pin 3, although it seems to do what it is supposed to do.

Pin 7 (and orange wire) does not have continuity to pin 1 on the pump. Any Ideas?
I still have to check the blue wire. When I checked there was no voltage, but I learned later that I was to check it with AC not DC.:confused:
 

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Well..........



I'm not an expert turbo-wise, as my profile indicates, my 900 sucks whereas yours blows...

The switch you ellude to I believe is a vacuum switch that is used to reduce the amount of boost by disabling or reducing the APC when under cruise control. It's only fitted to turbos and depending on how you see it, I tend to regard it as a safety feature. This is an attempt to limit the amount of power on tap in case the cruise becomes unstable. It may be a touch to agressive with full boost in cruise active mode.
The switch is a simple closed or open contact arrangement depending on vacuum applied. It should, however, hold vacuum.
If it is connected to the cruise vacuum line in that condition, it will compromise the action of the cruise actuator but to what degree, I don't know.

I guess you could remove the switch from the vacuum line and try the cruise again.....if the cruise still fails to work, well there would still be a more common cruise fault to diagnose.

I have not ever changed a stalk assy so I'm afraid I'm not in a position to help you with that.

Cheers
 

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Discussion Starter · #6 ·
So it is evident that the vacuum control switch is bad. As for the orange wire that is pin 7 on the ECU that is supposed to have continuity to pin 1 on the pump has a brake somewhere. I found a wiring diagram and the only thing that is between the two is a white 29-pole plug. I will check this next.
 

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Discussion Starter · #7 ·
I now have continuity to pin 1 of the vacuum pump and pin 7 of the ECU. I just lift it plugged in to check and it was fine. As for the blue wire one the speed sensor (pin 5) the instructions say that I should have a varying voltage here while driving the car. Well I do, but I get the same varying voltage while sitting still and just revving the engine.

It also says that if I have continuity from pin 5 of the ECU and pin 2 of the speed sensor, that it is bad. Well I have continuity and why not! Isn't this a straight line from the speed sensor to the ECU?

Every thing else checks out but can someone make it a little clearer, Please! This has really turned out to be a time sucker! And if the blue wire situation is fine then I know that there is a problem with the ECU. You are a great bunch of guy's and I appreciate your help, Thanks,

Dennis
 

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Discussion Starter · #9 ·
Thanks Rodentmaster for the link. I don't have a bently manual, all the info that I have is coming from Townsends sit. Right now the blue wire on pin 5 of the ecu that runs to pin 2 of the speed sensor has me stumpt. The instuctions say that continuity here between the two is bad, well I have continuity. This is even with the plug off of the back of the speed sensor. It also has power beteen the blue and black wires off the the speed sensor. Eather way weather driving or just sitting still bringing up the rpm's I get varying voltage up and down according to the rpm not the speed. I have done this with AC. Eather way the two contradict one another. Any Idea?:confused: :cry:
 

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There will

:eek: (***Sub note*** Depending where the sensor trigger's last position is,) :eek:

be voltage on pin 5-ecu/pin 2 speed sensor wire, approx, 9 to 10 volts, or no voltage, engine off, ignition on.

The attached is a rough guide of what one might expect to see if an oscilloscope was connected.

If the device in the speedo is a hall sensor, the output generally will be quite square.

What is the actual reading you are getting?
If the meter is very sensitive, it may be reacting to general ignition noise or alternator noise. The meter in AC mode would need to be in, at least, 12v range minimum. Even then, most meters will average out the reading such that the signal would need to be running at a frequency of 50 to 60hz minimum before the reading is stable and reflective of the signal being measured.

I tend to think that the DC mode is better for this check.
Firstly, confirm the voltage when car is idle with ignition on, engine off.
Secondly, take the car for a small drive while still connected to the speed signal. The meter reading will go up and down slowly at first but as you get faster the reading will average out again. It's the slow up and down reading that confirms the signal presence. As long as that occurs the speedo sensor,
I beleive, will be ok. The signal will always be there regardless of the cruise being on or off.

Confirm the other two wires on the speed sensor are correct, that is, a healthy +12 volts or more and the other, 0.00 volts.
The cruise module and the speed sensor share the same earthing point but strangely have independant sources for +12 volts. Pin 3 on the cruise module needs to 0 volts for the cruise to work. This is the 'pedal break' input. Any voltage there would indicate the pedal switches may not be right.


Keep going

Cheers


***Just went for a drive............

Duty cycle = 50/50, 50% high - 50% low
Ratio Freq/kmh = Approx 7hz/10kph. At 100 kph, I was getting fluctuation from the meter reading of 70-71-72-70 hz. At 120 kph, 84-85 hz. Minimum speed appeared to be approx 32 hz which is close enough to the 50 kph point on the speedo.

Voltage swing of the signal = 0.0v to 12.8v, thus a 12 volt peak to peak signal.


Still thinking........
 

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Discussion Starter · #12 ·
Ok, here are the numbers or values of pin 5 (blue) wire on the ECU or pin 2 of the speed control on the back of the instruments.

RPM DC AC km mph

1000 13.60volts .053 to .057 0 0

1600 13.64volts .04 to.045 50km 30mph

2000 13.66 to 13.68 .034 to .04 60km 40mph

I hope this will help to determine if the speed sensor is working. If you need more let me know.

Thanks,

Dennis
 

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Discussion Starter · #14 ·
Ok, here are the numbers or values of pin 5 (blue) wire on the ECU or pin 2 of the speed control on the back of the instruments.

RPM.............. DC.................. AC .......................km .......................mph

1000 .........13.60volts ........053 to .057................. 0 ..........................0

1600 .........13.64volts .........04 to.045................. 50km .................30mph

2000 .......13.66 to 13.68 ......034 to .04................ 60km ................40mph

I hope this will help to determine if the speed sensor is working. If you need more let me know.

Thanks,

Dennis
 

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Hmmm..........


Something not quite right there........:confused:

All you need to do is put the car into 1st gear and IDLE along the road and you should see the meter dance up and down quite merrily between 12v and 0v in DC mode. That is all you need to establish the speed pulse is working.
Try disconnecting the ECU end of the wire, (Just disconnect the ECU) and measure again.

The ECU may, in fact be the problem......


Getting there!
 

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Discussion Starter · #16 ·
Hmmm! is right!!

Well I disconected the ECU and did the voltage check between the blue and black wires on the back of the speed controle. There is no voltage, but when I shut the car off there is voltage for 25 seconds, then I hear a click from a cilinoid and the voltage is gone. Just turning on the ignision won't bring back the voltage. I have to start it and then shut the car off again to have voltage (12v) again for another 25 seconds. The 3rd wire on the plug of the speed sensor has the proper 12v that it is supposed to have and the black has ground. Do I need both ECU and speed sensor?:confused:
 

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Well,

At this stage it may be necessary to start swapping parts to narrow this down.
Obviously, there's good and bad..................
The ECU would be easy to change but the speed sensor in the cluster is not easy to change. After that, I'm beginning to think there is some cross wiring or otherwise that needs to be sorted.
Does the car look to have had any other work done in the past?

It's getting harder to diagnose from the southern hemisphere!
 

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Discussion Starter · #18 ·
I appreciate every bit of info that you have been giving. You’re a real trooper! Thanks.

I will go and get the parts tomorrow off a car that I know has a cruise control on it. The car is as far as I know is a 1988 and mine is a 1989. Will there be any problems going with a different year for speed sensor and ECM? The blinker and cruise switch that I have on my car is from the 88 and the only thing that was different from the norm was the plug for the cruise. I took the plug that was on mine and cut it off and soldered it on the other one. All the wires were the same except yellow and green. I had to switch them around when soldering them together to make the controls work proper. What I mean is instead of yellow for yellow, I put yellow and green together and the same for the other.

Are all the speed sensors the same? And other than taking out the gauges is there any other thing that I should know or may encounter putting in another speed sensor?

Thanks again for your help!

Dennis
 

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I'm not at home to check..........
I'm not in a position to say with confidence what is inter-changeable.

There are differences in various years, but I'll need to read the book closely to confirm.
They are section years........... I think they are, 86 to 88, 89 to 91, 92 on.

The ECUs appear on paper to be identical in wiring between 86 through to 91,
definately NOT compatable with 92 on. The wiring around the ECUs are subtly different between the '86-'88 to the '89-'91.
Once again, I'm not going to foot in my mouth and make you take a leap of faith on my word as to what to mix and match. I am lucky to be able to fix this kind of stuff but I don't want to be responsible for you to lose more money on my whim or notions.

It may require to go back to the start and try and re-trace any steps along the way and see if there has been anything over looked.

I'm more than happy to advise but I'm running out of ideas.

Hope you don't have an angry 'other half' watching this as I experience from time to time.

Cheers

P.S. Have you tried to suck on the vauum hose from the pump, (with car off) to see if the actuator draws in and holds vacuum? IE: Remove hose from pump and watch throttle body and suck on hose, hold vacuum and throttle should not move. This basically confirms pedal switch alignment.
 

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Discussion Starter · #20 ·
No problem with my wife, she knows how much money I save on doing the work on our own vehicles. As for testing for leeks, I have pulled the line off of the pump and sucked on it to get a vacuum and no problems, The throttle holds
 
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