Christer

I am staying waaaaaay out of this one...

Greg_L

Mark - sounds like the exact same problem. My specialist said it was the storage oil burning off the new pipe too.
Now that thats gone, i just smell unburnt fuel.

Madrid - pre '93 cars don't require cats in the uk I'll get the specialist to check all connections tomorrow though, thanks.

Loren & Adrian - thanks for the replies, i'm going to the specialist tomorrow morning, i'll do my best to remember everything they say and i'll update this thread soon after. Plus i'll make sure the plug leads are all on properly.

Greg_L

I went to the specialist today and explained the problem. They stuck a probe up its backside and plugged it into the emissions computer. It was reading 2.1% CO . They said thats ok, the limit is 3% . Also that with O2 sensor installed it would be close to 0%. They reset the DME with the hammer and the CO instantly dropped to 0.6% . He showed me the hammer stating "No cat installed" too.

Anyway after a good drive this afternoon the problem is still there and i'd guess the CO is back up. They said its better to use a non O2 bypass as the O2 sensor gets very different reading from a bypass pipe than a cat which sounds fair enough, also that pre 93 RS's had no cats and no O2 sensors ?

After a drive i went to see an old friend who looks after my cars (apart from a stamp in the book yearly service). He thinks there's a chance that the airflow sensor has worn out and thats why i get the waft of smoke when off the throttle. He thinks as there's no O2 sensor to fine tune the mixture then its all upto the airflow sensor to sort it all, and if thats worn that maybe the problem. Other than that he suggested drilling a hole in the bypass and bolting the old O2 sensor in again (wish i'd kept it now ).

Any thoughts?

PCar SBA

The 964 DME has a coding plug that can be jumpered to run without O2 sensor. Adrain is right that cars that came without O2 sensor from the factory (and not cat) had the altitude box installed to assist in mixture control.

I don't understand your "specialist". The O2 sensor on a 964 is upstream from the cat. Its readings do not get influenced by the cat. ONLY the 993 engine has sensors both upstream and downstream to monitor cat performance.

I am puzzled why he thinks running without an O2 sensor is better. IMHO that's BS. The motronic has all these nice features of keeping the mixture ideal under part throttle conditions without any performance penalties. Without the sensor or with a broken sensor the DME switches to another program and does not adapt itself to your engine. I would install the sensor into the byoass pipe and remove the coding plug. Here in the U.S. you simply drive up to a muffler shop that welds the fitting in. 32$ later you are back on the road with a better running engine.

Ingo

PCar SBA

BTW: Spec CO levels are 0.4 - 1.2% (with oxygen sensor connected, measured before cat) and 0.5 -1.5% CO for M150 optioned cars at the tail pipe. 2.1% is out of spec. Without O2 sensor the air flow meter needs to be adjusted. I don't think it's worn out. There is a tiny air bypass allen set screw that needs to be adjusted acording to the factory workshop manual.

Ingo

Greg_L

Hi there,

I still havent solved my rich running problem, and i still get some smoke from the exhaust when i come to a stop, and on occasion an erratic idle. I've spoken to a couple other specialists and one immediatly asked if i had the altitude sensor fitted. I said i didnt think so. He seemed to think this was the reason, and if you had no o2 sensor, then you definitly needed an altitude sensor. I called back the garage who fitted my bypass pipe and they said they'd never fitted one to a 964.

[For those who don't know, the altitude sensor (around £50) is installed under the passenger seat into a black 2-pin socket which is sitting there waiting - ie. a simple DIY fit for me as my DME already has the coding plug to tell it i have no cat installed.]

It sounds like the way forward to me, anyone have any more info/ideas on this ?


Also, i re-read this thread, and Adrian mentioned this sensor in one of the first replies. My humble apologies for overlooking this.

Christer

I don't run an O2 sensor, but have an altitude sensor installed. Although I am sure I do run a bit rich, I didn't get any smoke or erratic idle problems. Maybe this could be at least a partial fix?

In fact, I think you can have my altitude sensor soon-ish!

Greg_L

Thanks for the offer Christer you're car must be nearly done by now ?

I've just spoken to Porsche Chiswick and they think it sounds like the Air flow sensor is either dirty, broken, or most likely you just need to lean it with the alan key adjuster on the back.

Now i'm getting confused as to what to do next.

Christer

At the moment it looks like I might be picking it up on Saturday week if all goes well....but then again.....DOH!

And Saturday was such a perfect day for driving...I did go out in the 320TD Compact anyway and although it has good torque it is hardly the same....

DaveK

I wonder what they mean by this? I'm fairly certain (i.e. 100%) that you can't manually ajdust the mixture.

Adrian

Dear Dave,
The adjstment being spoken of adjusts the CO2 output. Very bad thing to mess about with unless an exhaust gas analyser is fitted to the exhaust pipe. Do not use this adjustment without one because the entire mixture setting will be messed up and the end result can be engine damage if the mixture is leaned out too far.
This adjustment is purely for emissions tweaking to pass tests.
Ciao,
Adrian
964C4

Greg_L

Could this help me out though ? When i went back to the specialist my CO was reading 2.6% which is way too high.

The first thing i plan to do is try the altitude sensor.
If the offer still stands Christer, i'd gladly take yours off your hands

Adrian

Dear Greg,
The prime use of this adjustment is to tweak the system with the O2 sensor installed. It will not help you if you do not have it installed because nothing is adjusting the mixture for you,
Ciao,
Adrian
964C4

eddychan

Dear Greg,

I concur with Adrian, I have been working in the area of fuelling control ( both gas and deisel engine control systems in close and open loop forms for some time). Basically you can only have two major types of control schemes:
1.Open loop using MAPs and compensating with other sensor inputs including driving patterns and climates etc
2.Close loop control using a Feedback sensing device to derive a corrective signal for the changing of control parameter such as the fuel injuection pluse width and frequency/timing.

There are some more advance control schemes such as intelligent (adaptive, fussy logic, ANN) control, predictive/corerective control etc but I do not think we are talking about them here at this moment.

Since you have no feedback sensing and while using the gas analyser as feedback, once that has been taken off , you will be back to open loop and run the control based on your MAP and compensating inputs, the system will be back to where you were before.

The other sensor worth exploring ( if you have not yet been checking ...I am not sure whther you have done it or not ) is the Air Flow Sensor, I had mine contaminated with the overfill of oil ( like you stated in the begining). Like you, I drained the oil and then I found I was running rich and I took the AFS out and clean it and put it back, I got back to normal.

It is worth a try if you have not yet done it.

Happy Motoring!

Eddie
91 C-2

Christer

I'll speak to 9M about it, I assume I won't be needing it. Perhaps you would like to use it for free indefinitely, but that I have an option to take it back sometime in the future if I really need it? (just hedging bets here....)

If you can wait a couple of weeks....?