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The BOSCH ML3.1 series Motronic Fuel Injection systems, used in the late model
Porsche 944, 944 Turbo & 911, is
actually 4 DMEs in a single package. Two coded connector plugs are used to switch between
the four maps sets. The first a 2-pin connector "Impedance Adapter" is a 1.8K ohm
resistor. The second
connector "Coding Plug" is a wire across a 2-pin shorting plug. The US DME is selected with both connectors
not used. The "Impedance Adapter" disables the DME's Lambda
Sensor (This changed in 1988).
The
Porsche 944 ML3.1 coding has 4 options. Only due to the small size of the 2732 EPROM,
it was limited to three map sets, not four.
Options DME #0
(US/Canada) and DME #2 (California/Japan) share the same map set.
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Porsche 944, 924S, &
951 - 1985.5 to 1987 |
| Where Used |
Impedance Adapter
(1.8k ohm) |
Coding Plug
(Shorting) |
DME# |
Description |
US, Canada,
Australia, M298, M299 |
|
|
0 |
Cat (Catalytic Converter)
with Lambda (O2 Sensor) |
| Rest of World (ROW) |
X |
|
1 |
No Cat
No Lambda |
California,
Japan |
|
X |
2 |
Cat with Lambda |
Switzerland, Sweden,
ROW "Stage A" |
X |
X |
3 |
No Cat
No Lambda |
Options
M298 - Prepared For Unleaded Fuel - Manual Transmission
M299 - Prepared For Unleaded Fuel - Automatic Transmission |
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Porsche 944, 924S, &
951 - 1988 |
| Where Used |
Impedance Adapter
(1.8k ohm) |
Coding Plug
(Shorting) |
DME# |
Description |
USA
ROW with Cat |
|
|
0 |
Cat with Lambda |
| ROW without Cat |
X |
|
1 |
No Cat
No Lambda |
California,
Japan |
|
X |
2 |
Cat with Lambda |
| Australia |
X |
X |
3 |
Cat with Lambda
Changed funtion in 1988 |
| Description |
Schematic Diagram |
944 DME Connector |
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| Coding Plug |
 |
Pin 10 |
Porsche Part No.
944.612.525.00 |
| Impedance Adapter |
 |
Pin 30 |
Porsche Part No.
944.612.421.00 |
| 944.612.525.01 obsolete, use
944.612.525.00 |
See
Connector & Pin Specifications
| In 1987, the Porsche 911 ML3.1 changed to the larger 2732 EPROM
and used multiple maps. Options are similar to the 944 tables above. The following special adapter allows the use of the
altitude box and multiple maps. The DME responds to the altitude signal by
leaning the fuel to 94%. The altitude box output signal is "open" when
below 1000m and "shorted" when above 1000m and The
"shorted" output of the altitude box negates the 1.8k ohm of the
Impedance Adapter. The 911 allows the altitude box to be plugged into the second
connector. The 911 adapter allows the use of multiple DME maps (ROW maps)
with the altitude box installed. The DME sees 1.8k ohms without the altitude box
signal and the DME sees 525 ohms with the altitude box "shorted". 1.8k
ohm in parallel with 750 ohms is 525 ohms. Previously, the altitude
box was only used on US 944 that do not use the1.8k ohm Impedance Adapter.
Porsche part no. 911.612.421.00. |
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Porsche Part 911.612.421.00 |
Prior to 1987, the Porsche 911 used a smaller 2716 EPROM that
had room for just one map set.
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