[Diy_efi] Additional Injectors

[Marcell Gal]

Hello,

> I've been looking at all the posts I can find about running another set of
> injectors parallel to the oem set (for adding a turbo), but haven't had any
> luck finding complete information (I would need a schematic or VERY
> detailed information... I've taken one electronics course, years ago, which
> stopped short of IC's).  It looks like the most common approach is to use a
> 555 timer, but I was thinking there must be a way to snip off the end of
> the injector pulse to the extra set, and vary how much is snipped off based
> on MAP input.
>
> I would like to have the 2nd set open based on the time of the oem set to
> let the ECU take care of factors like IAT, water temp, load, etc.

Tough. You have an intelligent system that measures MAP or MAF.

---- first let's try with MAP or MAF signal to orig ECU unchanged
It might handle a low amount (5..20%) of boost with no problem, without 
any extra injectors. 
However it will plateau: weather because injectors reach 100%,
or because it assumes that VE<SomeValue which is no longer true.
The first can be detected easier than the 2nd.
Anyway, when it's plateaued, you than need to make your 
own calculations (which can be in analog of course * ).
When it's plateaued, nothing useful can be based on the
 time of the oem set, of course.

---- now allow the changing of MAP or MAF signal to orig ECU
If you change the MAP or MAF signal to the original ECU to make 
the ECU think it is in the normal operation range when it is not, 
you loose the benefits of the well-tuned original EFI. 
Theoretically if the factory ECU sees the 1/1.3 of actual airflow, but
 drives 1.3x original effective-injectorsize 
(because of higher fuel pressure or parallel injectors) it should work in a 
reasonable range, but almost certainly
it will be hazardous in many circumstances because of nonlinearities.
This way the time of added injectors completely depends on
the time of the oem set: equal or a constant multiple of.

--------
If you make an intelligent EFI, than any gray-box left in the system
(original ECU) will just make your life harder.
Someone, who can do what you want safely, would NOT WANT TO DO IT.
That's why you find little information on it.

Why not install your own ECU to take total control?
Think of AtmelMega128 like a smart 555, which can 
- handle your other few Analog signals
- can be finely tuned unlike any hacked-on solution
- costs $10 more, but the original ECU can be sold

Marcell

-- 
analog calc may be :
0 if factoryECU's output pulsewidth < SomeConstant 
0 if MAP < 0.98 Bar
AddedInjectorPulseWidth = MAP * constant - offset
This is a simple linear relationship, which might work
for 
Anyway, you can easily  ruin your engine.
In a better case you just have suboptimal performance.
Your mileage may vary (in the true sense ;-).


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