Megasquirt Support Forum (MSEXTRA)

I'm using the default setting of 1.0 for high Z injectors (30 lb.) But the notes in TS say it's typically 0.9ms. If I change it to 0.9, what can I expect? It's been suggested to me to get the dead times right before getting to the dyno tuner.

Is the only way through calculations? (barely made it through calculus)

Can I tell via megalog viewer?

Can one tell via seat of the pants?

Is an assumed 0.1 difference worth concern?

thanks,

kj

The maths is far simpler that calculus.

However, for 0.1 I wouldn't be too concerned. Ideally though, measure your injectors physically.

If the deadtime number if longer than actual, the electrical pulsewidth is a bit too long. To compensate you would need to reduce your VE table a little. Barely any at high loads and a little bit at low loads. Check datalogs for actual pulsewidths and see the percentage change.
e.g. with 11ms reported PW, thats 11.0 - 1.0 = 10.0ms fuel. Your "real" deadtime is 0.9ms so you want the PW to be 10.0 + 0.9 = 10.9ms. i.e. about 1% change.
However, at a 2ms PW that would be 5% change.

James

I must have caught you about dinner time (west coast at 8 hrs to GMT?). Thanks for the quick response.

kj

jsmcortina wrote:The maths is far simpler that calculus.

However, for 0.1 I wouldn't be too concerned. Ideally though, measure your injectors physically.

If the deadtime number if longer than actual, the electrical pulsewidth is a bit too long. To compensate you would need to reduce your VE table a little. Barely any at high loads and a little bit at low loads. Check datalogs for actual pulsewidths and see the percentage change.
e.g. with 11ms reported PW, thats 11.0 - 1.0 = 10.0ms fuel. Your "real" deadtime is 0.9ms so you want the PW to be 10.0 + 0.9 = 10.9ms. i.e. about 1% change.
However, at a 2ms PW that would be 5% change.

James

Is it that way round? I assumed that the actual fuelling PW was calculated from VE, enrichments etc and then dead time was added. So if dead time is too long (as it appears mine is also) than VE is actually low because the DT error causes additional fuel above that dictated by VE (PWt = DTa + DTe + PWf - where PWt is total, DTa is dead time actual, DTe is the dead time error and PWf is the PW calculated from VE...).

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It depends a lot on how big your injectors are relative to your engine. If you're running large injectors with very short idle pulses, a small error in DT will make a big difference.

I physically measured my injector flow for different pulse widths to determine the DT and it made tuning much easier and consistent.