Peter F

After removing my intake and finding a couple of vacum leaks and replacing the ISV and flappy valve I thought that the surging and stalling would be gone.
But to my big disappointment it still behave the same
I hooked up my spanner tool bought from John Speake, it showed :
O2 SENSOR OVER_RICH MIXTURE 1223
Sent a mail to John on how to proceed, who replied very quickly to disconnect O2 sensor cable in the car, and disconnect battery cable for 30s and then try starting again.
Did that and now the idle kept steady even after the warmup.
(which was when it started to hunt and surge before.)
John thought the O2 sensor was bad due to this, and here's how it looked when removed.

The green wire is completely broke.
Luckily enough I have a new O2 sensor on its way, did not arrive today so it will have to wait until Monday.
Can't wait to see how this improves things

Thanks John for your excellent support

Here's to you

/Peter

1981 Shark

Still somewhat new. Does anybody have a picture or detailed description of the "flappy valve" so that I can understand what the heck it is? Is it even applicable on my '81? Thanks.

David

AO

You don't have a flappy on the 81.

Vilhuer

Flappy is S4 and later 32V engine thing. It changes engine torque and hp characteristics by opening and closing channel between two sides of intake. Shaft is under black **** on top of intake casting. Throttle is at base low down in engine V and after it air is divided to two sides.



Plate is opened or closed depending on revs and engine load.



Difference in power is somewhat noticeable and end result better than without flappy by having two torque peaks instead of just one:

Adam C

Wow Erkka as always you are a wealth of info with many pictures at hand!

1981 Shark

Now I know. Chalk that up to "what I learned today." Thanks.

David

aaron3

John,

Please enlighten me. I thought the O2 sensor is only a 'fine tuning' control for the fuel injection. After all, some cars don't even have O2 sensors, right? How does a bad sensor make the car surge and stall like this?

Can Cat equipped cars run with the O2 sensor disconnected? What's the impact?

Thanks,

Mark

Rich9928p

The O2 sensor provides closed loop feedback to the LH. During closed loop operation the fuel injection algorithm either moves the mixture towards more rich or more lean in small steps based upon input from the O2 sensor.

928s that do not have O2 sensors have an external adjustable resistor in place of the sensor. The base CO-running level is adjusted via a variable resistor.

ColinB

Hi Rich
Since i fixed a few manifold leaks my car runs a little rich as diagnosed by the tailpipe colour. ( I run it on leaded 97 oct as nature intended though sadly that will be phased out next year). It has no cats. Where's the CO adjustment pot?
Colin. 89GT

John Speake

Hi Mark N.
The O2 loop has a range of around +/-20% so if it slams up to one end of the range the car will run very rich or lean.

If you do the 02 disconnect/battery disconnect that Peter did, then the LH adopts a default setting in the middle of its adjustment range.

Non cat cars do have a mixture pot, this is above the fuse board on MY88 onwards. (pot on the MAF itself is used for LH cars prior to this)

But this pot only has a significant effect at idle, not over the rest of the range.

The LH ECU uses a completely different map for cat and non-cat. The idle mixture pot is NOT an alternative control device that can adjust the O2 loop circuits.

Colin, do you mean the mixture is rich at idle, or when you have been running WOT, and then shut down the engine, so as not to run idle ?

ColinB

Hi John
Nice to hear from you.
At high throttle settings the car runs rich and shows a black tailpipe. Around-town motoring is better but still not the perfect pale grey it used to be before I did the intake work. Haven't checked it after a long idle.

Colin 89GT

Drmark

Colin - I thought perfect gret tailpipes were only seen on cars running on leaded fuel. Black's the new grey ....isn't it?
Mark

John Speake

Hi Colin,
Although your car has no cats, is the O2 sensor also deleted and the LH coding plug suitably coded correctly ? Or are you still using an O2 sensor (X pipe) etc ?

Regards

Rich9928p

This diagram shows the location of the CO adjustment for non-cat equipped 928s. The LH has the fuel maps for all geographic variations of the 928, and a coding plug is used to "tell" the 928 which map to use. I've included the information on the coding plugs so you can verify if you have the correct plug for your 928 type.

The "Australia" coding is used for low octane fuel (91 RON) vs. 95 RON. For S4s, all the compression is the same at 10:1.