1991-93 Buick Park Ave 3.8 vin L (trouble code 17)

 There are things that are said about getting older that at a glance seem pretty good. For instance, you have more experience. True. Life experiences are very often helpful but I'm going to say that one thing I've learned from life experience is that some of the things you've learned over time and maybe learned extremely well, no longer apply. It wasn't really helpful in the long term for me to know a lot about DOS or Windows 3.11. Do you see what I mean? I know a lot about automobile systems on cars that no one drives these days. I just hate to dismiss things that were important to know at one time in history and perhaps it would be interesting to someone? I don't know. If you get nothing else from this, get that in diagnosing car problems you need to have an understanding of how the system works to most effectively repair it. 

Let's go back to a 91-93 Buick Park Ave 3.8 vin L engine with a recurring trouble code 17. Here is how it works. The crankshaft sensor is a dual signal sensor. Each full turn of the crankshaft is supposed to produce 18 pulses of signal on 18x circuit and 3 pulses on 3x circuit. A reference voltage and ground is provided by the ignition module to the crankshaft position sensor. That voltage passes through the sensor and back to the module. As each blade of the crankshaft pulley trigger wheel passes the through the sensor the voltage drops to 0 volts and becomes your 18x and 3x signal, repectively. The module passes those signals on to the Engine Control Module which uses the signals to determine spark timing and injector pulse. A code 17 sets if the Engine Control Module sees that the 3x and 18x signals from the module aren't in correct sync or erratic. If the ECM sees 240 fuel control pulses since a last spark reference pulse, you set the code. This code will not turn a light on and if the signal quits while the engine is running, it will continue to run. 

Normal suggested diagnostics will often find the fault but if your 3x signal is only quitting during running you won't find it with that testing. You'll need to clear the code and attach your scope to monitor the 18x and 3x signals from the crank sensor to the module. Start the engine and watch the 3x for any drop out or missing pulse. If you see the problem you have narrowed the cause down to the wiring, sensor connector or sensor. 

Kenny@ggauto.repair