Mk3 Cavalier Owners Club | Vauxhall Cavalier Dot Com

It seems to be a question that pops up fairly often, so I thought I'd write up my knowledge on the subject.

Here are some comparisons between my 20NE CD auto and my C20NE Diplomat.

The problem is that the 20NE has something that looks like a catalytic converter, but is actually hollow.
This shot also emphasises the extra underseal they put on the facelift Cavs.
20NE:


C20NE:



The best way of telling the difference is to look at the exhaust behind the engine and looking for a lambda sensor:
20NE (auto):


C20NE (Manual):



Other ways of telling the difference are the metal oil filler cap and the rounded cam belt cover.
However, this is an unreliable way of telling the difference as a catalytic converter (C20NE) was available as an optional extra so older Cavaliers which had this extra also have the metal oil filler cap and rounded cam cover. To my knowledge however, no 20NE was fitted with the square cam belt cover:
20NE:


C20NE:

Wheres the tank canister purge valve on the 20ne. I can see it on the c20ne pic

I have just had the exhaust off my 20NE CDi and can confirm the front box is just a box, you can actually look straight through it.
I have exchanged the middle box (original - nothing wrong with it) for a boxless pipe section - which has given the old girl a 'proper' exhaust note!

btcctroy wrote:Wheres the tank canister purge valve on the 20ne. I can see it on the c20ne pic

The what?

Tank vent valve is the quickest way to tell, the non cat model doesn't have one. It's the little black box with pipes on it between the cam box and the manifold James

planetc wrote:Tank vent valve is the quickest way to tell, the non cat model doesn't have one. It's the little black box with pipes on it between the cam box and the manifold James

Interesting, You should add that to the list and post it in the How To section.

What does a Tank vent valve do exactly? And what is the tank canister purge valve?

I only posted this as I didn't want to take over Mikebmth's WIP with loads of photos.

The tank vent purge valve must be mechanical on the earlier engine whereas electrical on the c20ne
Basically feeds the fuel tank with air as fuel is taken. Without a system the tank would implode

I think the tank breaths to atmosphere on the early stuff. The electronic control valve came in with the cat models

if the tank vent valve isn't working properly what would the symptoms be?

So if I was to replace my C20NE with a 20NE (No Cat) version of the engine would I need to change the ECU due to no lambda sensor etc, thought this may cause faults to flag up as it will be looking for the signal from the lambda sensor..

The engine is exactly the same. It's the management that differs along with an added catalytic converter. More control was needed to reduce emissions

What about an early Sri? 20 SEH I believe? would an ECU off that work? gives more possibilities if so...

Cavalier342 wrote:What about an early Sri? 20 SEH I believe? would an ECU off that work? gives more possibilities if so...

The seh is a different engine. It's a tuned up 20ne with some changes to the ignition Map.
Seh ecu on a ne will work but not much In the way of a power increase. The seh on ne management will not run to full potential

Mike loves his tuned up stuff so he may consider it