ECU Tuning as per "Down Under".... (LONG Part 1)

[Chris Pronios]

List members that frequent SR20DEFORUMS may have seen lately postings from a
person named "badbiki" who is selling daugtherboards for ECU modification
(practically a version of the hardware that any modification house like JWT,
GRID, TECHTOM etc.) is using. Similar boards are WIDELY available down-under
from several (at least 3 persons excluding the aforementioned) and certainly
commodity items in Japan.

Discounting the "attitude" of the person offering this board, we all realize
that the mod is legitimate if we know what to put in there. In this spirit I
include below a "Sort-list" of important pages for anyone that may be
interested. Keep in mind that most of the following originated in the
NISSANS13@yahoogroups.com group/list so I am not doing any original work
here.

=========
Best freeware rom editing tool available (there are 2 more -GTROMeditor and
ROMediter- but definitely less capable than this one):

ROMEDITOR from http://www.925style.com/editor_direct.html
You will need to register to download it or simply use:

ID: romeditor
PASS: giveme

to get it.

You can also get from there ROM-address files that describe where in each
ECU/ROM the valuable data is. This files are ascii files editable so you can
add additional information about ROM data that is not described in there as
of now.

You can also get sample ROM binary images to play with and alternative MAF
calibration files in case you plan to use an alternative Nissan MAF.

==========
Most comprehensive 2nd hand site pointing to available information and
"Altavista"-translated Japanese pages (this is a brand new one):

http://www.boostcruising.com/members/chado/ and follow link ECU TUNING on
the left.

==========
Most helpful write-up: from Diarmuid Tyson whose simple pages are located
in:

http://members.optushome.com.au/silent8ob/
and
http://members.optushome.com.au/silent8ob/ecu.htm

Those pages are incomplete but the ROM Analyser program he has in there is a
VERY NICE little utility to help anyone figure out what goes on in a Nissan
ECU. granted, it is for the CA18DET ECU but the principles are the same.
 Now, since those pages are incomplete I am posting below a LENGTHY message
he sent today. This is the realy detailed info and it is reproduced here
after asking for his permission.

===================================================
POST FROM Diarmuid Tyson  STARTS  HERE
===================================================

I currently modify my ROMs with a hex editor and a custom ROM  Analyser I
wrote in Delphi. I've also used ROM Editor, which is excellent to get
started. I'll try and make these articles application neutral so you can use
whatever tools you're comfortable with

--

Firstly - Background

(If you object to me using Horse Power (hp) as a measurement of airflow,
simply substitute in CFM or whatever you're happier with...)

Air Flow Meters (AFM), a.k.a Mass Airflow Meters (MAF):

The basic function of any ECU is simple. Calculate the correct amount of
fuel and ignition advance required by the engine at any time. To make these
calculations it needs to sense how much "load' the engine is under.

The primary load sensor on the Nissan ECCS ECUs is the Air Flow Meter. It is
the ECUs biggest asset and also it's achilles heel (from a performance
viewpoint).

The AFM measures the true mass of air entering the engine. Since mass of air
entering the engine is known, determining the mass of fuel required for an
appropriate Air Fuel Ratio is a straight forward calculation. This also
means the majority of modifications will not require a retune, unlike MAP
based systems.

Unfortunately the standard AFM can be a considerable restriction in the
intake. A 50mm diameter is not a large area for a turbo to draw through.
AFMs also have a set operating range from 0-5V, representing a flow of air
from 0 to their max rating. 5V on a CA18DET AFM is equivalent to enough air
to make around 200hp. 5V on a 300ZX TT AFM is enough for over 500hp.
Fortunately, retuning for a larger, less restrictive AFM is possible.

Once the CA18 ECU senses the AFM is at its limit (ie at or close to 5V), it
will cut fuel to protect the engine. The dreaded boost cut. Or more
accurately, Air Flow Cut.

Once the Airflow meter is at 5v, any increase in flow will still result in a
reading of 5v, as the sensor is at its limit. The ECU can no longer
calculate the correct amount of fuel, so it shuts down the engine to prevent
a lean out. Once the AFM reads below 5v, the ECU will inject fuel once
again.

--

ECU Injection Calculation - Overview

Ok, we need to know about a few of the ECU's basic variables first.

K Required Number:
This constant is the basic injector pulsewidth time. All calculations of
injector pulsewidth start here. If you make it larger, all injector
pulsewidths will get longer. If you make it smaller, all injector
pulsewidths will get shorter. This is a very powerful tool when it comes to
changing injectors, AFMs etc.

VQ Map:
The VQ Map is used to translate the AFMs non-linear voltage response, into a
linear load reading. Confused? Don't worry too much. For the moment just
think of the VQ Map as a "filter" that the AFM voltage goes through, and
gives a load percentage as a result.

Eg, 5v = 100%,
4v = 75% etc...

Fuel Maps:
The ECU has two fuel maps, High Octane and Low Octane. It will always run on
the High Octane Map unless it senses a problem.

The Fuel Maps have 3 components, the RPM scale, the Flow scale and the AFR
correction Map itself. All Maps are 16x16, giving 256 load points. The
scales must match the sides of the map so are 16 entries each.

Flow Scale a.k.a TP Scale: (labelled 'Boost' in Rom Edit)
The Flow scale (as I call it) gives a basic injector pulsewidth(K constant)
multiplyer, depending on the load sensed by the AFM.

RPM Scale:
This scale determines what RPM each axis of the AFR correction map is
plotted against. Stock is from 500 rpm to 6800 rpm, in (mostly) 400 rpm
increments.

AFR Correction Map:
This is the business end of tuning. Full mapping of your AFRs across load
and RPM.

Putting it all together:
Ok, go through a quick example to see how all the above works
together in determining an injectors pulsewidth for a given load and RPM.
For the example lets suppose:

K constant = 0.125 Milliseconds
AFM reading = 5 Volts
RPM = 6800.

1) ECU reads AFM - 5v.
2) 5v is "filtered" by the VQ Map - 100% load.
3) Flow scale at 100% load is consulted (column 16) = 83.
4) Basic Pulsewidth = K constant x Flow scale
   Basic Pulsewidth = 0.125 x 83
   Basic Pulsewidth = 10.375ms
5) ECU consults RPM Scale,
   6800 rpm corresponds with row 16 of the RPM scale.
   (We have already calculated column 16 for the Flow scale.)
6) Entry in the AFR correction Map: row 16, col 16 = 1.6.
7) Injection Calculation = Basic Pulsewidth x AFR Correction
   Injection Calculation = 10.375 x 1.6
   Injection Calculation = 16.6ms

(CONTINUED IN NEXT MESSAGE)