You can hear the freq valve standing next to the car with the engine cover closed as long as you don't have a horrible exhaust leak. If it is buzzing like an angry cricket the circuit is probably working but for a further check use a dwell meter at the diagnostic plug. Look up in the workshop manual M:03:01 pin 3 + and pin 2 ground. The value is not as important as that the dwell should vary about 10 degrees indicating that it is hunting about the "stochiometric mixture" or the optimum fuel air ratio. You can also test the micro switch at full throttle it should increase the dwell and be steady. Your exact dwell reading will vary due to the mixture adjustment setting of your car. Refer to D:04:15. You do not need a scope to do ordinary toubleshooting but it does impress the customers! David Teitelbaum vin 10757 --- In dmcnews@xxxxxxxxxxx, "Walter" <Whalt@xxxx> wrote: > I agree with John Hervey on this one. You really need an oscilloscope to > see what is going on. The signal going from the ECU to the frequency valve > is a square wave signal oscillating at 70 Hertz. (Switching on and off 70 > times a second). The first thing to check for is if the signal is present. > A very cheap and effective way to do that is to listen for the frequency > valve buzzing. It sounds like a noisy fluorescent light fixture only > slightly higher pitched (70 Hertz instead of 50 or 60 Hertz depending on > which part of the planet you are on.) If you are in doubt as to whether or > not you hear it while the engine is running, get a very long handle screw > driver and hold the tip against the valve and put the handle against your > ear. The sound is unmistakable. If you don't hear that sound, then you > know you've got problems. If you do hear the sound and you are still > wondering if the Lambda ECU is properly adjusting the duty cycle of the > signal to the frequency valve, then you need a scope or a dwell meter. A > typical Volt-Ohm-Amp meter won't do this trick. > > I've said too much! :) > Walt Tampa, FL