Octane Coding Plugs

[Robsey]

I have seen a fair few posts discussing coding plugs, but what is this Voodoo all about.?

Using info from EPC3 (Vauxhall's Electronic Parts catalogue) and also the Top Buzz website,
I thought that I would bring all the info together into one thread.

The Discussion thread is here:-
viewtopic.php?f=83&t=16785

Here is my set-up - Yellow Coding Plug set to 95 RON in a C20NE equipped Car.



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The non-technical blurb is that the coding plug is a little plug with three pins.

The centre pin is a common pin.

The outer pins are both linked to the centre pin via a specified resistor value.

Well almost -
one pin could be a direct connection (zero ohms or short circuit),
or not connected at all (Infinity ohms / open circuit).

The plug has three pins, but the socket on the loom only has two wires coming from it. See the picture above.

The resistance across the pins of the coding plug is used to set the working values within the engine ECU.

This is mainly utilised on the 2.0 litre 8 valve engines. (20NE, 20SEH and C20NE)

The settings are: -

1 - Basic Settings

2 - The ignition timing is retarded by 5 degrees from basic values. (Used to reduce pinking / pre-ignition).

3 - Increase in idle revs of 100 rpm above basic values.

4 - 5% increase in fuel enrichment when accelerating.

5 - 5% increase in fuel enrichment at all times.
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Here are the Coding Plugs listed in EPC3 for the Cavalier mk3 / Vectra-A

BLACK = Coding "A"
For Engine codes :- E16NZ, C16NZ, C16LZ2, C16NZ2, X16SZ, C18NZ, C20NE
Part No = 90276397
Opel Kat Code = 12 86 521

BLACK (USED WITH AUTOMATIC TRANSMISSION) (EXCEPT TAIWAN) = Coding "A"
For Engine code :- 20NE
Part No = 90276397
Opel Kat Code = 12 86 521
Note: FOR GULF COUNTRIES

BROWN = 98/95 RON
For Engine codes :- 16SV, 20XE
Part No = 90276401
Opel Kat Code = 12 86 522

BROWN = 98/95 RON
For Engine codes :- 20NE, 20SEH
Part No = 90276401
Opel Kat Code = 12 86 522
EXCEPT GULF COUNTRIES

BROWN = Coding "A/B"
For Engine code :- C25XE
Part No = (90307657)
Opel Kat Code = (12 86 535)

BROWN = Coding "A/B"
For Engine codes :- 20XE, C20XE
Part No = (90307657)
Opel Kat Code = (12 86 535)
Note: EXC.SWITZERLAND

GREY = Coding "A"
For Engine code :- C16LZ2, E18NV
Part No = 90 506 206 / 90 243 355
Opel Kat Code = 12 86 541

BLUE = 95/91 RON
For Engine code :- E18NVR
Part No = 90 241 961
Opel Kat Code = 12 86 525

BLUE (No Longer Sold.- USE 90307657) = Coding "A/B"
For Engine codes :- 20XE, C20XE
Part No = (90307658)
Opel Kat Code = (12 86 534)
Note: FOR SWITZERLAND

WHITE = 98/95 RON
Part No = 90241962
Opel Kat Code = 12 86 526

YELLOW = 91/95 RON
Part No = 90241963
Opel Kat Code = 12 86 527

[Robsey]

Looking at the TopBuzz website, the following resistances are listed for each of the plug colours.
Noting that some colours are not relevant to the Cavalier / Vectra-A
Also Note that if your plug says "A" then it refers to 95 RON, and
if it says "B" then it refers to 98 RON

And for completeness.
(91 RON refers to the old 2 Star fuel - very hard to get hold of these days)
(95 RON - now called E5 is standard unleaded fuel)
(98 RON - is Super Unleaded or Lead Replacement / 4 star fuel).

Black = 91 Ron (0 ohms)
Black = 95 Ron (220 ohms) - or "A"
--------------------------------------------------
Brown = 95 Ron (220 ohms) - or "A"
Brown = 98 Ron (470 ohms) - or "B"
---------------------------------------------
Grey = 95 Ron (Infinity) - 90 243 355
Grey = 95 Ron (Infinity) - 90 243 355
Vectra-A
---------------------------------------------
Grey = 91 Ron (0 ohms) - 90 506 206
Grey = 87 Ron (220 ohms) - 90 506 206
Vectra-B
---------------------------------------------
Red = 95 Ron (Infinity) = n/a
Red = 98 Ron (4700 ohms) = n/a
---------------------------------------------
Orange = 91 Ron (750 ohms) = (n/a)
Orange = 95 Ron (Infinity) = n/a
----------------------------------------------
Yellow = 95 Ron (2200 ohms)
Yellow = 91 Ron (Infinity)
----------------------------------------------
White = 95 Ron (2200 ohms)
White = 98 Ron (750 ohms)
---------------------------------------------
Blue = 91 Ron (Infinity)
Blue = 95 Ron (0 ohms)
--------------------------------------------
Violet = 95 Ron (Infinity) = n/a
Violet = 98 Ron (2200 ohms) = n/a
----------------------------------------------
Green = 95 (1200 ohms) = n/a
Green = 98 (750 ohms) = n/a

For the Grey Plug, check octane numbers printed on it, as there are two different part numbers. Although the Grey plug for the Cavalier should only be 95/95.

[Robsey]

Referring back to the first post, it would appear that Vauxhall / Opel did the most faffing with the 2.0 litre 8 valve engines.
(Motronic Multi-Point Injection systems).

From memory, the Rochester Multec (C18NZ) had a black octane plug set to "A". (95).

It is known that the C20NE had a lot of customer complaints due to a low idle speed.
Often as low as 650 rpm, compared to the book value of 800 +/- 80 rpm.
The result being the car shaking at idle, rather than a smooth idle.
This probably explains the use of the Yellow Octane plug to lift the revs by 100 rpm over standard idle values.

So raiding the Top Buzz website - we see the following correlation between coding plug resistances and the effect on the Motronic injection systems.

The web page is here - a very useful website.

http://www.topbuzz.co.uk/info/ron_plugs/ron_plugs.htm
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20SEH
91 RON - not applicable.

95 RON -
220 ohms = Basic Settings
1200 ohms = Fuel Enrichment 5% higher than basic setting
2200 ohms = Idle is 100 rpm above basic setting
4700 ohms = Fuel Enrichment 5% higher and Idle is 100 rpm above basic setting
Infinity / Open Circuit / Disconnected = Ignition timing retarded by 5 degrees plus Fuel Enrichment 5% higher and idle is 100 rpm above basic setting

98 RON -
470 ohms = Basic Settings
750 ohms = 100 rpm above basic setting
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20NE
91 RON -
Zero Ohms / short circuit = Basic Settings
Infinity / Open Circuit / Disconnected = 100 rpm above basic setting

95 RON -
220 ohms = Basic Settings
1200 ohms = Fuel Enrichment 5% higher than basic setting
2200 ohms = 100 rpm above basic setting
4700 ohms = Fuel Enrichment 5% higher and Idle is 100 rpm above basic setting
750 ohms = Ignition timing retarded by 5 degrees plus Fuel Enrichment 5% higher and idle is 100 rpm above basic setting

98 RON
470 ohms = Basic Settings
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C20NE
01 RON
Zero Ohms / short circuit = Basic Settings
Infinity / Open Circuit / Disconnected = 100 rpm above basic setting
750 ohms = Ignition timing retarded by 5 degrees plus Fuel Enrichment 5% higher and idle is 100 rpm above basic setting

95 RON
220 ohms = Basic Settings
1200 ohms = Fuel Enrichment 5% higher than basic setting when accelerating.
2200 ohms = Idle is 100 rpm above basic setting
4700 ohms = Fuel Enrichment 5% higher when accelerating and Idle is 100 rpm above basic setting.

98 RON
Not Applicable.

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No listings for any of the smaller engines, and
it is presumed that 'X' prefix engines have knock sensors,
therefore negating any need for an octane plug.

[Robsey]

Full Listing According to TIS2000

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16SV = Brown Plug upto 1993.

C16NZ = Black Plug
C16NZ2 = Black Plug as of mid 1993

E16NZ = Black Plug upto 1993

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18SV = Brown Plug

C18NZ = Black Plug

E18NV = Blue Plug
E18NV = Grey Plug

E18NVR = Blue Plug

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20NE manual = Yellow Plug upto 1991
20NE manual = Brown Plug from 1992
20NE Auto and 4x4 = Brown Plug from 1992

20NEF Auto = Black Plug
20NEF Manual = Yellow Plug

20SEH = White Plug upto 1989
20SEH 4X4 = Brown Plug
20SEH Auto = Brown Plug upto 1990
20SEH Manual = Brown Plug as of 1990

C20NE 4X4 = Black Plug
C20NE Auto = Black Plug
C20NE Manual = Yellow Plug