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Some updated information on my broken SAAB. I don't believe it's the AIC. I've cleaned it, measured the correct resistance and applied varying voltages to it with a current limiting power supply. Moves nicely and smoothly. So tonight I put a scope on the two outside pins and here's what I've found.
The LH2.2 supplies 14V to the middle terminal and grounds the two outside terminals. It does this with a 100Hz 50% duty cycle PWM signal that holds the motor in place. i.e. For 5ms terminal 1 is pulled to ground, then for the next 5ms the other terminal is pulled to ground... This continues holding the motor at some position. To change the opening size one or the other terminal pulse width is extended (probably by 5mS) for one cycle and then it reverts back to 50%. That way the LH2.2 can shift the motor in either direction. The bounce on the output when the driver transistor is turned off is up to 27V.
Next, I put the scope on an injector. The engine starts and runs reasonably well for about 5 to 8 seconds and then starts to run very rough. I mean smoke out the tailpipe rough.
The injector sits at 2.1mS for the first 5 to 8 seconds and engine vacuum is 18"Hg. It then suddenly goes to 16.6mS and stays there and almost stalls but just barely stays running and of course vacuum drops to about 5"Hg.
Next I disconnected the Mass Air Meter connector and started the engine again. It does run rough but idles just above 1000RPM, vacuum is at 18" and injector PW is 8.2mS which is about what you'd expect for limp home mode with the check engine light on.
Now finally, with the fuel pump fuse out, the PW at cranking was measured and it comes out at about 6.0mS. That's with an engine temperature sensor at 1.97K Ohms. (BTW, it matches the Service Manual values at 10C and warmer so I am assuming it works).
I'll post a followup message once the engine cools again and measure the output from the Mass Airflow Meter as it goes from cranking to running well to not. If it is working properly, I should not see much of an increase in airflow when the engine is barely running. (less if anything). If I do see an increase I can assume a huge leak somewhere but if not....
Somehow, the LH2.2 is being fooled into thinking it needs to create a 16.6mS pulse and this problem started 200Km after a total engine rebuild where the engine ran perfectly for the first 200kM.
Once I have checked the airflow at the sensor, I'll test everything again at the LH2.2. I'm hoping it's just a wiring problem.
Any suggestions are welcome.
Regards,
John
posted by 64.180.68...
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