[MR2] MK1 ECU quesiton
briank at glmotorsports.net
Fri Sep 28 21:13:04 EDT 2007
We'll leave everything except fuel out of it for now, and make this the
quickest possible tour de ecu that I can muster... :-)
Open loop reads directly from open loop MAP(s) (depends on ECU, some
might just have a WOT MAP, others may have some other such thing).
Closed loop reads the closed loop map for a given air flow range (revs
and or throttle position may also be part of the calculation for which map),
applies the learned LTFT value, then applies the current calculated STFT
(from the narrowband O2 averaging) value to determine what to do. STFT
values are gradually migrated into LTFT.
Short version is I make "x" mod that makes the fuel require 5% more
fuel. We'll assume LTFT was 0 (never true, but makes the point easier).
We'll assume cruising at say 2000rpms. O2 (once warmed up) is used to
determine that hmmm, need 5% more (so, STFT goes to +5%, or whatever
numerical equiv. this particular ECU uses (1g DSM would be "105")). Over
time, the ECU bumps the LTFT up from 0 gradually, watching/adjusting the
STFT, until the STFT hovers around 0 at that given situation. Hence, LTFT
is learned to be 5% (and stored until power removed from ECU) AND STFT is
available for instantaneous corrections (that are ONLY migrated to LTFT if
consistently not zero). LTFT and STFT can be different for various rpms/air
flow maps, depends on the manufacturer.
----- Original Message -----
From: "Scott Lelievre" <scottl at cape.com>
To: "waynearndt" <waynearndt at waynearndt.com>
Cc: <mr2 at mr2.com>
Sent: Friday, September 28, 2007 9:25
Subject: Re: [MR2] MK1 ECU quesiton
> Open loop goes off stored values in the ECU. Closed loop the ECU uses
> the oxygen sensor to adjust the fuel mixture.
> waynearndt wrote:
>> Can you tell us dummies the difference between open & closed loop? You
>> have to bury me with too much detail, just a couple lines. ;)
>> ---------- Original Message -----------
>> From: "Brian Knoblauch" <briank at glmotorsports.net>
>> To: <mr2 at mr2.com>
>> Sent: Fri, 28 Sep 2007 07:58:04 -0400
>> Subject: Re: [MR2] MK1 ECU quesiton
>>> Long Term and Short Term Fuel Trims (LTFT/STFT) are adjusted (on
>>> modern computer controlled) cars when parts/weather/whatever changes
>>> require the car to do so. Only operates under closed loop, no
>>> effect on open loop. Takes, at most, about 5 minutes and it's fully
>>> adjusted. That's the only thing I count as learning. I don't even
>>> count timing retard due to knock, since it'll try the same advance
>>> next time you do the same thing, detect the knock all over again and
>>> have to bring it back... (The DSM algorithm is to drop 1/3 degree
>>> of timing for each count of knock (and I suspect others are the same)
>>> , so you usually end up with just a flatter than normal timing curve
>>> unless you have something that goes seriously wrong!).
>>>> There is NO learning capabilty. They measure sensor inputs and then
>>>> compare those inputs to preloaded maps. 99% of ecu's have zero learning
>>>> capability and will not magically adjust for new parts by resetting.
>>>> is all urban myth. I have no idea where these rumors started and why so
>>>> many people belive it. The only learning I have ever seen on an ecu is
>>>> timing. For example a WRX will advance timing until it sees knock then
>>>> back a few degrees.
>>> MR2 Mailing List
>>> MR2 at mr2.com
>> ------- End of Original Message -------
>> MR2 Mailing List
>> MR2 at mr2.com
> Scott Lelievre
> My extension is 114
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