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Summary -
Motronic Ignition Advance Values and Offsets |
| Type |
Offset (Decimal)
|
Offset (hex) |
Offset Angle
(in Degrees)
|
Resolution
|
| ML1.1,
ML1.2 & ML2.1 |
0 |
00h |
0º |
90º / Tooth#
|
| ML3.1 |
20 |
14h |
1800º
/ Tooth# |
90º
/ Tooth# |
| 60-2 timing wheel |
30 |
1Eh |
22.5° |
0.75º |
| 60-2 timing wheel
[MP9.0] |
60 |
3Ch |
45.0° |
0.75º |
| 60-2 timing wheel |
90 |
5Ah |
67.5° |
0.75º |
| |
| Ignition
Advance Formulas - ML1.1, ML1.2
and ML2.1 |
| Ignition
Advance Angle = 360º x Hex# / (4 x Tooth#)
Ignition
Advance Angle = (90º x Hex#) / Tooth#
|
Tooth#
Hex# = Map value to be converted to
ignition angle
Offset = 0 |
ML1.1 - The first of the
BOSCH Motronic family ECUs first appears in 1982. This
"first generation" of Motronic ECUs had no
capability of ignition advance below Top Dead Center. No negative numbers.
The angular rotation of the engine is determined by counting the teeth on the
flywheel's ring gear.
"Quarter Tooth" Technology
- Each ring gear tooth is counted as 4, hence a "Quarter Tooth" is the
minimum resolution. A130 tooth ring gear has a
resolution of 4 x 130teeth or 520teeth. Resolution of 360º/520teeth
= 0.6923°/tooth. This changes with different ring gears.
|
Starter Ring Gear -
Porsche 944 Flywheel |
|
Car Type
|
Flywheel Teeth |
Map values |
Motronic Types |
|
|
944
|
130 teeth
|
0.6923°
|
ML1.1, ML1.2,
ML3.1
|
|
944Turbo
|
132 teeth
|
0.6818°
|
ML3.1 |
| 911 |
129 teeth
|
0.6977°
|
ML3.1 |
| BMW |
116 teeth
|
0.7759°
|
Various |
| Volvo |
116 teeth |
0.6338 |
ML1.2 |
| Ignition
Advance Formulas - ML3.1 |
|
Ignition Advance Angle =
(360º / ( 4 x Tooth# )) x ( Hex# - 20 )
Ignition Advance
Angle = ( 90º / Tooth# ) x ( Hex# - 20
) |
Tooth#
Hex# = Map value to be converted to
ignition angle
Offset = 20 |
ML3.1 - Next generation of Motronic ECUs
first appears on the 1984 Porsche
911. Negative numbers appear for the first time. An offset
of decimal 20 [14h] is defined as 0º ignition angle.
Ignition
Advance Formulas - Motronic
with 60-2 timing wheel |
|
Ignition Advance Angle Formula
= (360º / (4 x Tooth# )) x (Hex# -
30)
Short Version 1 = 0.75º x
(Hex# - 30)
Short Version
2 = (0.75º x Hex#) - 22.5º
|
Tooth# =
120 [for all 60-2 timing wheel]
Hex# = Map value to be converted to
ignition angle
Offset = 30 [In this example] |
|
"Quarter Tooth" Technology
60-2 timing wheel
- Each 60-2 timing wheel "Tooth" has a rising edge and a falling
edge. The math is similar to the starter ring gear describe
above. 60-2 timing wheel gives a count of 120 edges. 120 edges per 360º.
In the "Quarter Tooth" scheme, each 360º
revolution has 4 teeth/edge times 120edges = 480 Quarter-teeth.
One revolution 360º.
Resolution is 360º
/ Quarter-teeth = 0.750°/tooth. |
M1, ML4.1, M2.1 etc. The starter
ring gear was abandoned. A standardized "60-2 timing wheel" was
introduced.
 |
Changes...
 |
Microcontroller from 8051 based to 8052 [or equivalent] |
|
standardized "60-2 timing wheel" |
|
offset of 30 [1Eh] is now defined as
0.0º ignition angle. |
|
Minimum ignition advance 22.5° |
|
1h = .75º |
|
| |
The 60-2 timing wheel |
 |
In the mid 1980's Bosch standardized on
this dedicated timing wheel with 60 equally spaced teeth. A single
sensor is used. Since the teeth are equally spaced, both the leading
edge and falling edge are now counted. This gives a total of a 120 count
[triggered events] per 360º revolution. Two teeth are
missing and this indicates the location of top dead center. |
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