Advice on O2 Sensors and Cat Bypass - 1985 Ruf 3.2 Carrera

[Pezza]

Hiya Folks,

I am relatively new to the forum - I have tried searching keywords but have not found any direct advice in regard to the subject that I am raising. If any of the more experienced forum members could point me in the correct direction to other topics similar to this, I would be most grateful.

Recently I received a fantastic original 1985 Ruf Carrera 3.2 which has 123,000 original km (76,000 miles). Alois Ruf installed a blue printed stock 3.2 motor in it and it runs and sounds great. The engine has never been out for anything except the rebuild of the tranny nearly 20 years ago.

It was sold to me from an interim owner in the USA and was shipped to me in the Middle East. Whilst in the USA, a Catalytic Converter was installed for the vehicle to pass emmissions legislation in the Mid West.

This weekend, I took it into our local Porsche Dealer Workshop who were incredibly helpful. They allowed me to work with the crew on the vehicle. We re-installed the original Cat Bypass but found that there were no orifices in the bypass to accommodate the O2 sensor.

Due to the vehicle being fully researched and having all history since original order, I was able to trace that it did not originally have an O2 sensor connected to the O2 sensor inputs. This was quite puzzling and appeared to be odd. In my research I also found that the vehicle suffered stalling at idle during cold conditions - something I have experienced without the sensor installed. My Porsche Mechanic who was overseeing the installation advised that it was perfectly OK to run without the sensor except that the engine may run a little richer with higher fuel consumption.

This appears to make sense and we proceeded to disconnect the O2 sensor. The vehicle seems to run OK except that you can smell it is far more distinct with the sweet smell of additional fuel. All temps and pressures appear OK and I have not driven it long enough to notice any remarkable increase in fuel consumption.

Could those who have a great affinity for these wonderful motors advise me on whether it is OK to run without the O2 sensor - is there any likelihood of the mixture being leaned off at all to the point of damaging the engine from excessive barrel heating?

Is it worth having a hole tapped into the bypass, welding a lug nut onto it and installing the O2 sensor again?

Will the lack of the O2 sensor adversely impact the DME and upset normal operation?

All advice would be most welcome.

Regards

Pezza

[911pcars]

W/o engine history or specs, it's difficult to know what was done by the builder to the control and fuel systems.

The DME system could have been designed to run w/o an O2 sensor.

Stock factory system with sensor disconnected operates in an open loop mode (rich).

Testing on a chassis dyno or equiv. with an A/F analyzer, tachometer and timing light should reveal your baseline situation.

Sherwood

[Pezza]

Hiya Sherwood,

Thank you for the sound advice - that was my next mission. I have an engineer who works with me that owns a very large engine tuning business up the road. We also wish to determine the exact output of the motor. I am also in contact with Ruf this week in an attempt to see what the best advice on DME is for the motor as they have the original build sheet.

I have also noticed with both the Cat and the bypass in that after spirited driving that the rear fenders and bumper get a thin layer of black soot - my finger has a black residue when I wipe it across the panel. This is indicative of a rich mixture which may need backing off a bit. Oil consumption is not noticeable and white smoke is not evident, even on cold startup.

It may take a week or two to get through this.

With it burning rich, I presume the worst outcome is gumming up of plugs etc?

Cheers

Pezza

[911pcars]

Originally Posted by Pezza

Hiya Sherwood,

........ With it burning rich, I presume the worst outcome is gumming up of plugs etc?

Cheers

Pezza

Excess (unburned) fuel may result in these various symptoms:
Oil dilution (fuel in oil)
Excessive fuel consumption
Excess carbon buildup of spark plugs, combustion chambers, piston crowns and exhaust system (valve > port > exhaust system)

I would minimize engine operation until this is resolved. Inspect oil level and condition periodically for excess fuel.

Sherwood

[Pezza]

Hiya Sherwood,

Thanks for the advice. I have only run the vehicle for 500miles since shipping here so it is too early to tell. There is no oil dilution at present, fuel consumption does not seem to be an issue (fuel here is really cheap so no issue). I will pull some plugs and conduct routine inspection of these as well as throw the boroscope into the cylinder to check carbon build up.

Our local Porsche Service Manager who is very familiar with these vehicles has advised to go through a simple regime of cleaning the fuel system. All, including Porsche have recommended Forte Fuel System Cleaner which is added to a full tank of fuel. Their specialist advised two cycles with skipping a tank and then a third. The vehicle has no record of any fuel system cleaning for all 28 years of its life so I am quite keen to see how well we can clean the system.

I have also asked Ruf to provide some more background on their setup of the DME for this vintage.

I will keep you posted.

Cheers

Pezza

[911pcars]

Okay. Best wishes. Let us know how it turns out.

Sherwood

[Pezza]

Hiya Sherwood,

I added the Forte this afternoon prior to delivering the vehicle to Zano for a full detail.

Within 8km and 5 minutes, the engine was singing like you cannot believe. When I arrived at Zano, I found that the smell of rich fuel was all but gone. I will let you know over the next few weeks but it seems that this stuff really works.

I also recently purchased a full set of secondhand Up Fixin Books and received them today. I found an incredible write up of the new 1984 Porsche Carrera Engine by Bruce Anderson - Vol 7 page 7. Interestingly, it was only the USA and Japan versions of the 3.2 engine that had a 3-way Catalytic Converter. All others were manufactured without a Cat Converter and without an O2 sensor. There was a distinct difference between the setup of the Motronic or DME between the different versions. In fact the USA version had a noticeably lower compression ratio that was deliberate to incorporate the workings of the Cat Converter.

Mr Ruf really built an interesting beast in my '85 Carrera. Having traced the engine numbers and gearbox numbers, it was definitely an European Version with external oil cooler for the 915 Tranny and a tall 5th gear. The engine is a European 73/ number. This was done even though it was destined for Canada which makes it all the more interesting considering it was a one-off test vehicle for the North American Market to fill the gap left by the discontinued 930 at the end of 1984.

So, in conclusion, this vehicle was designed not to have a Catalytic Converter as well as it was never intended to have an O2 sensor (which primarily is there to assure better fuel efficiency - as I have read).

I will still continue to monitor the outputs and let you know the outcome. The more I dig, the more interesting this tale becomes.

Regards

Pezza