gchristofi

Hi All

I was just looking back throught the paperwork for my 964 when I happened across the following description of work carried out by an OPC

'CARRY OUT ENGINE ANALYSIS AND LOCATE FAULT CODES 23 AND 24. CHECK AND LOCATE FAULTS WITH KING LEAD AND IGNITION COIL. REMOVE AND REPLACE THESE ITEMS AND RETEST.. DISCONNECT OXYGEN SENSOR AND SET UP VEHICLE FOR NON OXYGEN SENSOR'

My Questions are:
1- why would the oxygen sensor be disconnected? Surely this would result in poor performance?
2- Is there anywhere on the net that I can find a list of fault code descriptions?
3- Ditto for Porsche Part numbers?

Thanks
Greg
1990 C2

gchristofi

Just thinking about the disconnected Oxygen sensor...... would this possibly prevent me installing an aftermarket performance chip?

Cheers
Greg

gchristofi

well I must be because I'm talking to myself again. Asside from that though I have now purchased an aftermarket chip but don't want to install it before I understand what running with no oxygen sensor means. Where are the experts?

DarrylH

Well, I'm no expert, but I think no O2 sensor means you'll usually run too rich, as I understand the system. Do you have a cat bypass? Often the bypass won't contain a port for the sensor so the shops just jumper the wires. It's generally considered to be a bad idea without having the engine control unit properly remapped for the change in conditions. Maybe that was done, maybe not. You may need to see what the heck you've got - chipped already, for example? I wouldn't start replacing bits, especially engine management bits, piecemeal, without knowing where you're starting from - that could get really ugly, and really expen$ive, really quickly...

Try doing a quick search on oxygen sensor - there are many threads, unfortunately, but some of them seem germane...

JasonAndreas

Fault code 1_23 is "Oxygen Regulation stop" -- The oxygen regulator cannot operate in its control range owing to problems with mixture preparation, e.g. too lean because of additional air (there is a leak in the intake system) or too rich because of a sticking injection valve."

Fault code 1_24 "Oxygen Sensor signal" -- The voltage levels for the O2 sensor are out of whack.

One reason to not bother replacing the O2 sensor is cost, another reason might be the OPC could not find the problem (1_23) with the old or with a new O2 sensor plugged in so they just disconnected the sensor altogether. It does not necessarily degrade performance (that will depend on how far away your engine is from the original "out of the factory" condition) but it will kill your fuel mileage. The DME control unit can be jumpered for one of three country specific fuel schedules; ROW, ROW without an O2 sensor and USA/CANADA/JAPAN. If your OPC removed the O2 sensor the right way you should find a white jumper plug under the drivers seat next to the DME control unit. It will look just like the one in the image below except the wires are connected to the two outer pins (USA based cars jumper the center and outer pin), the part number on the red tag will be 964.607.422.00. Regular ROW cars will not have this plug.

Bill Wagner's rennlist site has them listed, Adrian's book on the 964 also contains them (along with procedure for diagnosing the specific fault codes.)

Its unlikely the aftermarket chip modifies the fueling and ignition advance scheduling for a non-O2 sensored DME control unit. You really need to call and ask the original supplier. I have absolutely no faith in the Porsche aftermarket so if I was betting money I'd say your car will run exactly the same irregardless of the EPROM.


DME control unit Country code 3-pin plug

Red rooster

It is no more difficult to remap a non cat 964 than a cat model and in the UK it is far more likely that the aftermarket has this covered.Unleaded fuel was pretty late arriving !
It seems a pretty poor set up to run a 964 non-cat because it has a problem with lamda.Why not take it to someone that knows the cars and get that fixed ?
It is deep joy adusting the bypass screw on a flap unit to set idle mixture . Porsche didnt care about that because non cat ( no lamda ) is for usually for less developed countries !!

Geoff

gchristofi

Thanks for all the input guys and Jason, thanks for the detailed answers and the photo.

One thing is for sure, I'm not going to change the EPROM chip until I fully understand how the car is set up at the moment. I know it has still runs with the cat. My guess is that the O2 sensor malfunctioned and was not replaced due to cost. How much are they anyway?