[Diy_efi] Why do some EFI systems use a cold start injector?

[Perry Harrington]

GM uses a cold start injector on the Corvette TPI too.

I would suppose it's mainly due to software design.

On my Corvette it has a Bosch MAF, if the primary injectors are tied algorithmically
to the MAF, then it won't compensate for temperature.

So if they just have another routine that says: "Cycle the cold start injector this
much based on coolant temp".

A lot of manufacturers that had these got rid of them in later revisions of their
ECUs, going straight to a sane way of doing this.

The oldest and simplest EFI cold start app I've seen is the old VW bugs.  The
cold start injector on those was just turned on by a simple temperature controlled
switch.

On a side note, these injectors are usually a small fraction of the flow
rate of the main injectors, they might be useful for small engines.

To answer your last question, yes, there is a substantial difference in fuel
consumption.  If you look at tables for -40f vs 180f, the cold portion flows
almost 50% more fuel -- Ford ecus are like this.

--Perry

On Fri, Apr 26, 2002 at 12:27:46AM +0100, Chris Wilson wrote:
> 
> Wondering why some (noticed Toyotas mainly) EFI systems use an
> electronic cold start injector, rather than just raising duty cycles of
> the 4 or 6 existing ones? Noticed this on MR2 turbos and Supra MKIII
> turbos for example. Does cold start need THAT much fuel the stock ones
> won't flow enough?
> 
> Thanks.
> 
> -- 
> Best regards,
>            Chris Wilson                          mailto:chris at formula3.freeserve.co.uk
>                                      http://www.formula3.freeserve.co.uk
> 
> 
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-- 
Perry Harrington             Linux rules all OSes.               APSoft      ()
perry at apsoft dot com 			                 Think Blue. /\

Those who would give up essential liberty to purchase a little temporary safety
deserve neither liberty or safety. Nor, are they likely to end up with either.
                             -- Benjamin Franklin


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