Euro 3.2 Air/Fuel Mixture ?

[Siena911]

Hello everyone,

Our cars here in Britain get tested annually for roadworthiness (MOT) and this year the tester said that my car emissions were just within limits and that he couldnt adjust them because he didn't have the right tool.

Now I know my car does'nt have a cat and that it does'nt have an oxygen sensor (I've been told that twice now, not gone and looked at the car yet).

Is this adjustable (air/fuel mixture), or is this under control of the DME as with the timing etc. Can anyone give me a brief overview of how this works then.

TIA
Jakes

[stlrj]

The mixture is dictated by the air flow meter which has a CO or idle mixture adjustment screw that can be accessed from below after removing a factory sealed plug.


Cheers,

Joe

[Siena911]

Thanks Joe,

Is this true for all models regardless of whether they have o2 sensors or not?

Cheers Jakes

[stlrj]

True

Joe

[Wayne 962]

Your 3.2 doesn't have an o2 sensor? I find that hard to believe, as it is an integral part of all Bosch Motronic fuel injection systems...

-Wayne

[Siena911]

Thats what I thought, and the guy who did the testing said it did not have one, I didn't believe it, however yesterday while searching on this board for an answer to this I came across the following thread

3.2 Idle Question

where it was mentioned again. I am doing a service and valve adjustment this weekend and am going to look for myself.

Will post results.

[teardrop]

I have just checked (just in case I was misleading anyone) and have had it confirmed by an Official Porsche Centre in the UK (both the parts guy and a wrench). UK 3.2 Carrera's do not have an O2 sensor.

If anyone else has evidence to the contrary then I would love to see it as I 'know' my 89 3.2 doesnt have one.

Cheers

Andy

[Siena911]

Thanks Andy

I will have a look anyway, I wonder how the DME's are different between the UK based cars and the ROW, i.e. are the chips programmed differently to ignore the fact that there is no O2 sensor etc. etc.

Well one learns something new everyday.

Thanks
Jakes

[Wil Ferch]

Guys:
This is a fairly easy one.....
Yes....US cars with DME have the O2 sensor, as do some specific country models ( Japan comes to mind...and some others). If you look at the pocket "Tech Spec" books ( we all have them...right?)..then you'll see that there is even a "tax break" option for German cars. Normal German market cars of the 80's had no cat and no O2 sensor....the special "tax break" cars were unleaded only...with cat...and O2 sensor, much like a US car but probably with higher CR.
If you look at the factory manual..you will note different DME part numbers for different market cars..as well as certain features added /missing ( O2 sensor)...and also that some wire pigtails are either used or jumpered and not used.
......many combos and not at all "standard" just because it's DME.....
---Wil Ferch

[Wil Ferch]

Guys:
Ohh ....one more thing....
on the backside of the DME, there is a small rubber plug with a cross-hatch cut in it..it allows insertion of a *small* screwdriver, and it has ( from memory here...don't hold me to this) something like seven different click-stop positions. Furthest one way is "Stock" enrichment and timing, under the pre-programmed map of the DME...and the other positions alter either ( or both) the advance and the enrichment. The plug can be seen from the rear passenger footwell...peering toward the front of the car..on the backside vertical face of the DME.
--- Wil Ferch

[Siena911]

Thanks Wil

Yep I had a quick peek underneath last night, and it was'nt there. I then looked at the Haynes manual wiring diagrams and I noticed the differences between the USA/Japan and ROW diagrams.

Well I just leared something new, thanks for your input

Cheers Jakes

[dickster]

wil,

is that definitely the case ?

i would have sworn that all had 02 sensor.

[Wil Ferch]

Dickster and others:
That's right...not all had O2 sensors.
If you think about this for a moment...the function of the O2 sensor is to get to a specific air-fuel ratio...necessary for proper cat operation. I am *quite* sure that not all had the O2 sensor. Another data point ( besides the posts made by some other people here who are not running USA or Japan spec cars).... when I bought the Porsche "euro" pre-muffler to replace the cat on my car...what did I have to do? Well, of course...I had to have a O2 sensor bung added...because there wasn't one on the premuffler used for the Euro cars sans cat !
-- Wil Ferch

[David Ceruti]

could someone give me more information on the setting screw on the DME that Will referred to.
I have got a problem with hesitation between 2000 and 3000 rpm. Changed the CHT, no oxygen sensor or cat (one of the euro spec cars). I have been playing around with the throttle body spring and CO settings in an attempt to improve it. Maybe the DME screw would help???

Thanks in advance

David

[ChrisBennet]

Originally posted by David Ceruti
could someone give me more information on the setting screw on the DME that Will referred to.
I have got a problem with hesitation between 2000 and 3000 rpm. Changed the CHT, no oxygen sensor or cat (one of the euro spec cars). I have been playing around with the throttle body spring and CO settings in an attempt to improve it. Maybe the DME screw would help???

Thanks in advance

David

David,
Here are the setting for the DME screw ("Fuel Quality Switch") that Wil is talking about. Position 0 is at full counter clockwise if I remember:

Fuel mix Timing
0 Std Std
1 3% rich Std
2 6% rich Std
3 3% lean Std
4 Std 2.7 retard
5 3% rich 2.7 retard
6 6% rich 2.7 retard
7 3% lean 2.7 retard

The switch takes a triangular shaped tool but a screwdriver will work.
-Chris

[Mike Feinstein]

So, if I understand correctly, there is still no way to advance timing without altering the chip? Just wondering why the only option is to retard the timing...unless it's to compensate for really bad gas.