I have scoped the VB921 using the 0.01ohm resistor between the emitter & ground. And I saw an almost perfect triangle waveform - fast rise of the left side and almost vertical drop on the right. The time measured is 2.8ms
These were measured with the car idling & warming up.
The question is: Based upon the calculated dwell, it should be 3.3ms. So I set mine to 3.1ms. Is this too much or should I just trust the scope?
Will I need more dwell if the car is revving close to redline / under boost / under heavy load?
thanks.
Dwell setup question after scoping it
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Measure in the car when running and enter whatever dwell number gives the "ideal" charge. With the MS1/Extra code this may not be the exact same due to rounding issues, prediction and the 0.1ms resolution in dwell at higher speeds.
James
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From your description of the waveform, I think the dwell you set is too low. You should be able to see some 'leveling' of the waveform. At the point where it begins to level off is the dwell.
To actually determine the dwell from the scope, you need to set the dwell higher than expected. Try setting the dwell higher (3.5-4.5ms) and see of the waveform changes shape. Expect to see a rounding near the top (approaching horizontal) before it drops off. Can you post a picture?
To actually determine the dwell from the scope, you need to set the dwell higher than expected. Try setting the dwell higher (3.5-4.5ms) and see of the waveform changes shape. Expect to see a rounding near the top (approaching horizontal) before it drops off. Can you post a picture?
duh - of course! I re-did the test and see that the coil starts to level @ 3.4/3.5ms. Now I set mine to 3.6ms.woh wrote:From your description of the waveform, I think the dwell you set is too low. You should be able to see some 'leveling' of the waveform. At the point where it begins to level off is the dwell.
To actually determine the dwell from the scope, you need to set the dwell higher than expected. Try setting the dwell higher (3.5-4.5ms) and see of the waveform changes shape. Expect to see a rounding near the top (approaching horizontal) before it drops off. Can you post a picture?