How does dwell timing work with logic level spark outputs?

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William_Irani
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Joined: Sun Jan 07, 2018 6:49 pm

How does dwell timing work with logic level spark outputs?

Post by William_Irani »

Hi,

I’m in the process of doing an engine conversion, haven’t yet decided on a ECU but have decided the coils I will be using. They are high current coils with no built in drivers (2 wire).

What i’m finding difficult to understand is how dwell timing is controlled when using an external driver like a Bosch 211 or multiple BIP373s. From what I understand, the logic level signal from the ECU is at 1 (+5v) when the coil is charging and switches to 0 (0v) for the coil to fire, events which spaced by the duration of the ignition timing. Am I correct?

What i’m Struggling to understand is where is the capacity in this logic level signal to include information about the dwell timing aswell as ignition timing? I’m rather confused. If anyone can help that would be greatly appreciated.

Thanks in advance.
Matt Cramer
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Re: How does dwell timing work with logic level spark output

Post by Matt Cramer »

William_Irani wrote:What i’m finding difficult to understand is how dwell timing is controlled when using an external driver like a Bosch 211 or multiple BIP373s. From what I understand, the logic level signal from the ECU is at 1 (+5v) when the coil is charging and switches to 0 (0v) for the coil to fire, events which spaced by the duration of the ignition timing. Am I correct?
Precisely. The dwell time is the difference between the time the signal goes high and the time the signal goes low. It is effectively the pulse width of your ignition signal.
Matt Cramer -1966 Dodge Dart slant six running on MS3X
elutionsdesign
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Re: How does dwell timing work with logic level spark output

Post by elutionsdesign »

And the ignition timing is when the signal goes low. Signal goes low, current stops flowing through the primary, primary collapses into secondary and plug fires.
Graduate of EFI University.

I build, repair, install and tune Megasquirt systems in North Dakota and beyond!
jsmcortina
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Re: How does dwell timing work with logic level spark output

Post by jsmcortina »

Is the OP perhaps thinking of a "dwell meter" where dwell is reported in degrees? That representation doesn't apply to EFI controlled ignition coils.
For inductive coils at a given voltage, the required dwell is measured in milliseconds as the other posters have mentioned.

James
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