Mk3 Cavalier Owners Club | Vauxhall Cavalier Dot Com

An absolute Encyclopedia Britannica of data! Fantastic thanks.
I've often wondered if the plug could be replaced with a pot to adjust as required!

Alan

Thanks Alan,

We try our best.
I have moved the main text into the How 2 section. (Workshop Guides).

It is located here.
viewtopic.php?f=83&t=16784&p=169911#p169911

Great write up Rob. Very useful for future reference

I'd really like to know a bit more about the plugs for the C18NZ and C16NZ2 engines and also the A/B plug in the C25XE.

I've heard that the A/B plug is for curtain countries that had strict rules on engine noise. Whether that's true or not I don't know.
Nevertheless, I'd like to know what it actually changes. i.e. ignition timing, injector pulse etc.



EDIT: Just found this on the club Calibra website:

"V6 Regional Coding Plug - Often mistaken for a Fuel Octane Plug but it isn't. Located in the upper right corner of the engine bay (near the diagnostic socket). A small brown plastic plug. Changing this plug round from A to B will increase the target idle rpm by 100 (from 700 to 800); other effects of changing this from A to B have been debated on the clubcalibra forums. If there are any gains to be made swapping this plug around then they are subtle.
All V6 calibra's have twin knock sensors to accurately tune the engine for different fuel octane ratings. This is why an octane plug is not required on this model."

Source: https://www.clubcalibra.net/v6calibra/V ... _Guide.htm

I have looked on TIS2000 for all model years 1987 to 1996.

There is no listing at all for an Octane Coding Plug for 20XE, C20XE, C25XE and X20XEV.

I have updated the thread to include all listed engine codes.

Grey Plug info also added.

C18NZ and C16NZ2 are both listed as the Black plug. No other options.

It is assumed that the coding plug function on the Multec units is purely for timing.

The higher the number, the more advanced the timing.

I remember retarding the timing on my Mk2 Cavalier (13S) by 5 degrees when converting from 4 star leaded (97 Ron) to unleaded fuel. (95 Ron).

So I suspect that it would require retarding even further for 2 star 91 Ron.