Can you check to see if you are getting an AC component on the B+ voltage?
This evening I had another shot at the Jetronic, I first checked the power quality (Pin 8) and found 13.1 V on it, with 96 mV of 5 kHz ripple. (This is its own internal chop frequency coming out.) This is probably just fine. I then used the 'scope to probe around the connector pins, Pin 17 has what looks like a non-chopped low voltage frequency valve waveform on it, so I rewired the test cable to swap Pin 17 (Duty Cycle) for Power and then hooked up the meters and went for a drive.
I put the Fluke 83 on the Duty Cycle wire (since the 87's analog bargraph is better suited to the O2 sensor voltage) and measured about 3.5 VAC, which varied from 69-72 Hz somewhat irregularly. That's probably fine. The Duty Cycle signal was hovering around 50% at idle before the drive began. I had to invert the meter plugs to get 60% at WOT (rather than 40%), but that was no matter. (The duty cycle is obviously referenced to the other side of the valve, which is at B+, and not ground. Reversing the meter leads takes care of that difference.) While driving with a lot of throttle extremes the duty cycle ranged widely, in the 30-82% range, but under more steady-state conditions it looked like it was going to stick to the 45-55% range where it belongs. Some further test driving is called for. Grounding Pin 7 (WOT switch) results in an instant cut to 60% duty cycle, exactly as specified. When parked and idling, after the run back up the hill to the house, the duty cycle was about 65%, though the O2 sensor voltage was circling the 500 mV point normally. Interesting, but likely insignificant. Still looking good! -- Jim _______________________________________ http://www.okiebenz.com For new and used parts go to www.okiebenz.com To search list archives http://www.okiebenz.com/archive/ To Unsubscribe or change delivery options go to: http://okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
