Thread: Chevette blues

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I appreciate your more detailed explanation, but I've gotta say it still doesn't make a lot of sense to me which is OK. Your pulse width modulation sounds like the control mode for a fuel injector where the solenoid pulses open for a measured time, and the high pressure fuel is then admitted to the nozzle to be injected into the cylinder, or into the throttle body plenum. I believe that you'll find that the OEM carb is a Holley 6510, and the "electronic control" is simply the ECM raising & lowering the metering rods in the main jets, instead of them being linkage controlled. Your "pulse width modulation" feature may have to do with the positioning of the metering rods vertically.

I'm not sure about your dwell concept, as in the old days the dwell angle was the amount of time the points stayed closed before snapping open to initiate spark. I suppose your concept is the time, expressed in the angle of rotation, between spark signals. Regardless, the difference between open loop control and closed loop control is feedback. I believe what you're trying to say is that your ECM assigns a dwell setpoint in order to achieve efficient burn of the fuel air charge, and then uses the O2 sensor signal to confirm - the feedback to close the loop and if the O2 is off the dwell setpoint is adjusted to bring the O2 into range. Open loop would be where the ECM assigns a dwell setpoint based on a predicted performance (a curve that says dwell vs rpm should be this line), and assumes it's good regardless what really happens. All good as long as everything's in good shape and adjusted right.

If it were mine, I'd buy a Holley 5210, the same carburetor without any of the electronics, and let the ECM wonder why nothing is listening to it anymore!! Good luck with the Chevette, and I'll leave you alone now.