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More info... Posted by JerseySaab [Email] (#666) [Profile/Gallery] (more from JerseySaab) on Fri, 18 Dec 2015 10:11:28 In Reply to: '86 900S: high HC at idle, JerseySaab [Profile/Gallery] , Thu, 17 Dec 2015 13:05:57 Members do not see ads below this line. - Help Keep This Site Online - Signup |
I checked my service log for this car and the AMM was replaced, but it was nearly 13 years and 120K miles ago, shortly after the vehicle was purchased. I was able to adjust it to the nominal 380 ohms indicated in the Bentley manual. (It wasn't very far off from that to begin with.)
I found the following Saabnet post regarding the 3-wire diagnostic connector which identifies the wiring:
http://saabnet.com/tsn/bb/900/index.html?bID=210522
Using a Simpson analog voltmeter, connecting between the fuel mixture connector identified in the above and ground I got a constant 12V, which according to the same post means a rich mixture (which is the symptom the car is experiencing).
However, turning the AMM adjusting screw has no affect on the voltage on the test connector, at no point does it start pulsing. At 380 ohms the AMM is fairly close to the clockwise limit on rotation, no change in anything going fully in that direction. Rotating several turns counterclockwise causes the idle to drop, like the lean idle drop method we used to use on 1970s carbs. Still no change in the test connector voltage though. (I also don't know for certain that I have the voltmeter hooked up correctly for the test, but I'm using the best info found so far.)
Connecting directly to the O2 sensor in-circuit with a digital voltmeter yields a fluctuating 0-0.15 volts. Testing the O2 sensor out-of-circuit results in 0-0.5 volts. So the O2 sensor appears to be producing a signal. The engine does stumble when the sensor is disconnected.
There are no vacuum leaks to be found. I used the old method of spraying carb cleaner in places air could be leaking in and looking for a change in the engine idle. Idle remained steady no matter where the stuff was sprayed.
So that's where it sits right now. Anyone know if counterclockwise is the "lean" direction for the AMM adjustment? (That would be opposite of most carbs, I have a half-memory in the back of my head that this is the case but have not found any confirmation yet.)
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