[Diy_efi] Fw: Misc injector stuff, hardly worth reading

[Bruce]

While intented to be Turbobuick specific (again Turbo buick, and in
particular vehicles in street trim), it might shed some light on what
other's are doing.   For those not familiar with the TBs, they run a MAF
system, and the meter pegs are 255gm/sec., which is easy to exceed  even
with a stock engine.   So while you can change the injector constant to
accomodate larger injectors, the whole plan still collapeses, since the
healthier the motor the faster you peg the meter, and the engine winds up
too rich too early.   There are some ways around this, but, to date, IMO
they seem rather crude.   Using the following you wind up with a blend of
Alpha-N and MAF.   While not perfect, it does give complete control of the
fuel curve, as compared to just hammering the calibration with a pegged MAF.
   For those that have taken tuning seriously and have an ecm bench you can
fire it up, and if you scanner looks at the commanded AFRs this whole puzzle
falls into place instantly.  If not then just doing the math, makes it easy
to figure out what's actually going on.   The difference in the two figures
are normally the scanner is looking at a RAM location, and that computation
has the battery voltage correction in it.


> Just to shed some light on this I ran some chips on the bench and added
some
> observations.
>
> Given a set of normal operating conditions for temps, and TPS values.
> Using an injector size of 55PPH, and a MAF of 160 to acheive a commanded
AFR
> of 12.5:1
>
>      At 3K RPM, the DC is 63% and at 5K 62.6%
>
> Now to repeat that with a MAF of 255 we get
>
>      At 3K, 98.4%,  and at 5K 100.1%
>
> So what does that really mean?.
> If you want to peg the meter, fine, but when you peg it you've just about
> totally wiped out getting any resolution, with the 255 entries there is
just
> nothing left.   You can't change a darned thing.
>
> HOWEVER,
> Look at what happens when you limit the MAF reporting to 160.  You still
> have PW to play with.   Lots of time to add PE vs TPS, or RPM.
> If you want to run on a pegged MAF that is a valid option, but your hands
> are tied for what you can do.
>
> to continue........
>
> Since we're at 24 PSI +-, those 55s are more like 70s, since the FP
increase
> as function of boost.
> So we'll run the MAF at 160, and we get
> At 3K 49.7% DC, and at 5K 49.4%
>
> Now the run the 255 value,
> and we get
> At 3k  78.5%, and at 5K, 77.9%
>
>
> So now whatdawedo?.
> Let's see we know what DC give what AFRs, for a Given injector.  We know
> when our boost begins, we know the injector's new flow at max boost, and
the
> DCs we need to get a desired AFR, so we just need to figure out if we want
> to add the fuel via RPM or TPS.   Yes, there are other options,  in how to
> handle this, but my suggestion is this way.
>
> But, it still takes a Translator to get around the oem electronics.
>
> And this was just about Table #5, and there are 4 others to worry about.
>
> Not to be attempted without adult supervision, for off-road use only,
> educational purposes only, feet on the floor and don't hit Billie.
>
> Bruce



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