MicroSquirt.com read only forum (Jan.15,2018)

What exactly does cold accel mult do? I think I understand everything else in the enrichments dialogue box, but I can't seem to find anywhere that explains the cold accel mult. Thanks.

On Wed, December 1, 2004 12:04 pm, muythaibxr said:
> What exactly does cold accel mult do? I think I understand everything else
> in the enrichments dialogue box, but I can't seem to find anywhere that
> explains the cold accel mult. Thanks.

AE = acceleration enrichment pulsewidth
CM = cold accel multiplier
CA = cold accel additive

PW = reqFuel * MAP * VE + (AE *CM + CA) + ...

It is a linear scalar for the acceleration enrichment based upon
temperature, whereas the other cold accel value is just an additive
constant depending solely on temp).


--
Eric Fahlgren http://www.not2fast.com/

Yeah, the cold accel parameters are something people don't pay enough attention too, I think.

I have mine set at 3.0 and 130%, and these make the car much more driveable right after a cold start - there's no hesitation at all.

Sounds like I need to add a sub-section to the tuning section manual! :D

Lance.

so if I understand this correctly, the cold mult % you have set will be 30% more than whatever your accel enrichment settings are, + 3 ms until you're warmed up. Is that correct?

This would be a good thing to say specifically in the manual, although I think given that equation above, I should've probably figured it out on my own

muythaibxr,

so if I understand this correctly, the cold mult % you have set will be 30% more than whatever your accel enrichment settings are, + 3 ms until you're warmed up. Is that correct?

It would be true if you are at -40°F. However, both are scaled to the current coolant temperture, so that they have:

- no effect at 160°F (100%*AE + 0.0),
- 50% effect at 60°F (115%*AE + 1.5),
- full effect at -40°F (130%*AE + 3.0).

(If I understand Eric's post correctly, I didn't look at the code myself.)

This is now documented here:

http://www.megasquirt.info/manual/mtune.htm#accel

Lance.

lance wrote:

> - no effect at 160°F (100%*AE + 0.0),
> - 50% effect at 60°F (115%*AE + 1.5),
> - full effect at -40°F (130%*AE + 3.0).
>
> (If I understand Eric's post correctly, I didn't look at the code myself.)

Yup, that's correct.

--
Eric Fahlgren http://www.not2fast.com/

I'll have to second that: not nearly enough people spend time on the cold AE. I tended to ignore it myself, but the simple change to 130% made a tremendous cold drivability change. I had been (wrongly) chasing the bogging with more WUE.

Nathan

and what about the cranking pulsewidth at -40°F and 170°F?

Is that an add on to the priming puls or what?

so if the Priming pulse= 2ms
and pulsewidth at 170F=2.2ms

the priming pulse get 4.2ms if you start your enginge with CLT=170°F

Priming pulse is applied only once to all injectors (except for some versions of the dual table code, etc.) when MegaSquirts starts, it is independent of any ignition events.

Cranking pulsewidths are applied only at each ignition event from all injectors, and only when rpm is less than 300 rpm.

So priming pulse and cranking pulse widths don't really add together, they are different events applied under different conditions. However, too much priming pulse might mask (or create!) a problem with your cranking performance.

Generally, keep your prime pulse short (say under 5 milliseconds) and tune your cranking pulse widths for best starting ability.

Lance.