[Diy_efi] Re: Minimalist micro based EFI ?

Mike erazmus at iinet.net.au
Wed Mar 12 08:09:40 GMT 2003


At 03:47 PM 3/12/03 +0800, you wrote:
>I don't believe that a MAF's accuracy is that important, except at
>or near idle; isn't that the reason for the log scale? When the
>control loop closes, the errors in measurement will be compensated
>in the same way as variations in conditions (e.g. O2 content,
>humidity).

nop, not according to holden/bosch. The reason for log scale
is imply one of dynamic range.

ie. The workshop manual for my car states somewhere that the MAF
is not used at idle, the input is ignored for any flow calc but
might be used to determine the pertubation point around minimum
flow to provide the base reference at that time its also open
loop. This does actually make sense since when tuned for
operation at idle one knows within a good tolerance just how
much air the engine needs at minimum throttle opening (idle
switch on) and the ECU knows whether air con active (has a f/back
for that) and other loads are negligible. Also at this time it
gives the ECU a chance to find out what the base AFM figure
is as to determine its reference. Fromt he 6 AFMs I've had
on my bench in last 5 years, they all have different quiescent
settings - from 1.3v (one only) to 1.7v, most 1.5 to 1.7, but
all worked reliably without noticeable difference in the car,
until one failed outright and it wasnt the 1.3v one.

>> Well, I'm talking my car and the vast majority of aftermarket MAFs
>> ostensibly for people who want larger throat sizes for more flow
>> and have ECU's which accomodate these with retuning of course.
>
>That makes the objective a little clearer. The amount of air is
>directly proportional to the gross engine power; which could vary
>from 10kW to 300kW in your case. Sure, the 10kW to 40kW is the
>most-interesting in terms of emissions control, because that's the
>typical cruising power requirement - given our low speed limits.

Sure, highest resolution is at lowest 15% or so of scale, another
reason why we want a log output !

>Anyway, is there a religious issue with programming log-airflow
>tables?

Er no, its just a complication in that I dont have cal graphs
for any AFMs <sigh>

Any .gifs or .jpegs of cal graphs showing V out versus Cubic
feet per minute etc ?

rgds

Mike





>> Eg. In the performance market for turbos for RB0 type engines,
>> GTRs etc All of these are log output MAFs with a pretty similar
>> DC offset and the same 5v max output - variety of fow rates
>> and throat sizes...
>
>> rgds
>> 
>> mike
>> ps: put the supp cap in yet ? ;)
>
>No... too hot and too busy.
>> pps: Next time you are over I'd like to take a pic of your engine bay.
>
>No big deal.
>
>> ppps: Variety of beers cemented to back inside shelf of fridge ;)
>
>-- 
>/"\ Bernd Felsche - Innovative Reckoning, Perth, Western Australia
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