O2 sensor on SSIs??? Where do I drill!

[82SC]

well after SO many complaints from friends and family about the smell of my car I have decided to attach the O2 sensor back on my car...I think it is running rich

well my pre-1974 heat exchangers obviously have no O2 port. I am wondering where I will have to drill the hole?

I have heard some things about it being too upstream or downstream can ruin things...any idea?

anyone have the contact info for SSI? Maybe they will have the answer as to where they put there port on their SSIs

Thanks

MJ

[89911]

Hope this picture gives you an idea. This is a 3.2, but I would think it is in the same postion for all SSI's. If you need an exact measurement, let me know. Just use a high quality steel, preferable stainless for the nut. On my former cheap bypass pipe, the O2 sensor galled to the pipe, destoying it, despite using plenty of antisieze.

[Formerly Steve Wilkinson]

You want the sensor as far upstream as possible--i.e. as close as possible to where the three pipes come into one--and you want them--assuming you're putting a sensor on each side, which I did to run a switchable air-fuel-ratio gauge--at identical locations.

stephan

[89911]

This is how they came from the manufacturer. I would assume they are in the best position.

[island911]

Originally posted by Stephan Wilkinson
. . .assuming you're putting a sensor on each side, which I did to run a switchable air-fuel-ratio gauge--at identical locations.

This brings up a good question: How well does the 02 sensor perform when sniffing only 1/2 the exhaust?

[Formerly Steve Wilkinson]

Whatever it's sniffing is "complete." i.e. if you put a single sensor in a single exhaust pipe, it will tell you what's happening in that cylinder. If you put a single sensor in the exhaust pipe for one entire bank, it will tell you what's happening in the combination of those three cylinders. And if you put one where the total exhaust system, six into one, comes together, it'll tell you what's happening in the combination of every cylinder's exhaust. So for the purpose of running an air/fuel gauge as a (relatively coarse) tuning aid, six sensors and a six-position switch would be the ultimate; a sensor per bank with a two-position switch is next best; and a single sensor would be lest effective. For the purpose of running an ECU, however, a single sensor reading the entire engine is best.

sTephan

[82SC]

a guesstimate of the location in inches would be great...

ho about from the muffler/heat exchanger junction...

the angled picture I think will skew my estimation

thanks

MJ

[Wayne 962]

As long as your engine is running fine, then having it on one bank should work fine. It measures percentage, not total O2, so it's not going to care that only 1/2 of the exhaust is there.

I would place it on the muffler side, as close to the engine as possible.

Newer cars run 2 or more O2 sensors, especially if they are separated into two exhaust paths like the 911. This gives you an indication of whether or not a bank of cylinders is performing well or not.

You should not run your car without the O2 sensor, as it will be running at an improper mixture. Any HP gain you would have gotten from the SSIs will be lost because the mixture will be way off.

-Wayne

[82SC]

yeah I have heard alot of conflicting remarks...

my engine does seem really wacky when cold without the O2 sensor...

and it runs really rich...and smelly...

T Callas told me it was fine off...but I am gonna just weld a nut to put it back...the smell is driving me nuts...

MJ

PS did you ever get the pic os the 917 engine block at his shop?
I have been meaning to swing by...but haven't had a chance...

[Wayne 962]

Really? Tony said it was ok to remove it? Hmmm, I'll have to ask him about that one, as I can't really understand how that could be true...

The 917 case (and 908 motor he has hidden in the back) are indeed very, very cool...

-Wayne

[82SC]

yeah..I've read REALLY long discussions on the board about this...

some say it will make the engine run better with it off...which I highly doubt...

TC said it was fine...He said leave it off is fine for now, tell him if the car starts acting wierd...he was a little bitter that I did the work myself...and didn't throw the work his way...not a very DIY friendly type of guy...haha...but a great resource...

But the car runs fine...definately a power increase from pre-backdate...the smell is my main issue...and gas cunsumption is about 16-ish...before it was 18-ish...

so I guess I will place it right after the 3 to 1 junction...

thanks

MJ

[dickster]

"my engine does seem really wacky when cold without the O2 sensor..."


this doesn't affect cold running does it? i thought it started working once the engine was warm?

sounds like it should be kept though

richard

[82SC]

by wacky I mean running at 3K for a bit (I know it is suppossed to run high...but that high??)

then it drops to 200K...and the stall lights come on cuz it is running so low

it stalls witht he oil cap off...didn't do that before...

anyways...we'll see if the o2 cures these symptoms

MJ

[speeder]

Well, I have an '82 SC and when I disconnect the oxy sensor none of those symptoms happens. Something else must be goofy. FWIW, they will run w/o it, but mine runs better connected, as it logically should. Also, disconnecting the sensor will not send car into super-rich mode. You need to check whole system, (CIS).

[911pcars]

I'd recommend installing at least a 3-wire O2 sensor considering the install distance from the exhaust port. The sensor needs to be hot in order to send valid info. The 3rd or 4th wires bring the sensor up to operating temp.

BTW, when manufacturers install two O2 sensors (before and after the converter), the second sensor is merely a feedback to the ECM letting them know all is well with the primary sensor.

Sherwood Lee
http://members.rennlist.org/911pcars

[Hellgate]

On my '87 with SSI we put the 22 sensor on the left collector just down stream from the where the header pipes converge. Worked great.

BTW...with the O2 sensor disconnected the engine make 4 less hp accross the entire power band. I had two dyno runs this spring. 220 at the wheels with the sensor, 216 without. The power curve was almost the same, just 4 less.

Pete

[Doug Zielke]

Originally posted by speeder
Well, I have an '82 SC and when I disconnect the oxy sensor none of those symptoms happens. Something else must be goofy. FWIW, they will run w/o it, but mine runs better connected, as it logically should. Also, disconnecting the sensor will not send car into super-rich mode. You need to check whole system, (CIS).

Hold the phone a minute, and listen to Denis.

Mark...you have a SC 3.0, right?
Then the 02 sensor does little more than swing the frequency valve in a small mixture variation. The 02 sensor on my SC is not connected, and the mixture is spot on without it. I would suggest you have other issues with the CIS. Make an appointment with a garage that has a gas tester.

[PeteBrown]

My mechanic, Eric Steinel, said the O2 sensor is not needed for cars (SC's and 3.2 Carrera's) running without a cat. He said the O2 sensor is only there to richen the mixture slightly then lean it out to "ignite" the cat. However on later cars (964 & newer) he said the sensor plays a role in determining the mixture.

My concern is that if I run without the O2 sensor, the car will run rich and therefore increase the likelihood of premature valve guide wear. Any thoughts?


Pete Brown
'87 Coupe

[dickster]

82SC

the sensor only works when hot so will not cause your symptoms.

the fact that the engine stalls with the oil cap off suggests an intake leak. this could cause the other symptoms.

check you've got no leaks

have you messed around with any new hoses?

if running without the sensor causes rich running this will be easily detectable by removing the plugs (or one of them). they will be sooty black in colour.

richard