EFI mapping ideas.

[Craig Pugsley]

> > >From what I can determine, the load is much more important than the RPM.
> > (I did some measurements of an aftermarket computer, and the pulse time
> > the injector was on for did not vary with RPM (Well, when under engine
> > vacuum. When under boost it did)
> 
> Depends a lot on the engine. The volumetric efficiency of the engine
> can vary from a 10% difference between the VE peak and a lower value
> (like at 1500 rpm or a fast idle) to a 60% difference or more... depending
> on the engine. Typically, in OEM computers, the RPM is quite important, as
> they are trying to fuel within a couple of percent (or even closer) as to
> what the engine needs.

As I said, the assumption that load was more important than RPM was
based on:
i/ measurements of a computer (a/market)
ii/Haltech using 32 loadx16 rpm

However, MoTeC uses:
11 load x 20 rpm on their entry level computer
21 load x 40 rpm on their advanced level computer

Perhaps this means that RPM and LOAD are of similar importance. The odd
number for load suggests that maybe only the load is interpolated in a
MoTeC computer. (Hey, I'm speculating)  

Am I correct in assuming that this load setting is just the engine
vacuum? (IE using a MAP sensor). Is this relative to the ambient
pressure or to absolute zero (IE a single ported sensor)?

> If I sound like I'm praising the OEM ECM's, it's because they have a lot
> more research invested into their algorithms than any of us... or
> pretty much any aftermarket company... can afford to put into the
> box.

No question. Now if only they had a nice ECU that would let me program
it with my PC :-). Even detailed algorithms would be nice.

> > If you're using interpolation 32 wouldn't matter, you might even get
> > away with something as low as 4 or 8. I'd say 17x17 w/interpolation
> > should be more than adaquate.
> 
> 17x17 is good for most engine applications. It can even meet emissions
> to 1994 levels, so it'll do for most of our applications.

Really? I'm impressed/surprised that it is that straight forward.

> >>>I'm un-decided if an 8 bit injection time will have enough 'dynamic
> >>>range' from idle to full throttle, though it's probably easier to >deal with
> > > an 8 bit number.
> 
> An 8-bit number is fine for a typical table, however, these values are
> multiplied and rounded, etc. so you want to keep as many bits as possible.
> Normally you have a Base Pulse Width, a Power Enrichment, and an Air
> Density Correction. Since these are multiplied out, I'd suggest the
> following:
> 
> BASE_PW * AIR_DENS
> result: 16 bits

Does BASE_PW come from the Load vs RPM table?
Where does AIR_DENS come from? Would just an air temp sensor be OK?

> * (POWER ENRICHMENT FACTOR + COLD START FACTOR)
> result: 24 bits.

I presume the power enrichment is an 'accelerator pump', and the cold
start is determined from the coolant temp sensor.

> * ADDITIONAL FACTOR
> result: 24 bits.
> round down to 16 bits.
> 
What's this part?

Basically what I would like to see is a (simplified) algorithm that
shows where all of the parts come from (IE what sensors and if you
add/multiply by the number).

Craig.

pugsley at trl.oz.au