O2 Sensor's and Porsche 912

jashropshire · 11-12-2003, 07:51 PM

Has anyone added one or more 0xygen sensors to their 912 exhaust system to aid in adjusting the carbs? Just curious. Am thinking about doing this.

Thanks

Jeff Shropshire

ron69912t · 11-13-2003, 10:25 AM

Jeff:
Think you have to weld in the O2 sensor and get all the related things.

Why not get a Gunson Gas Tester to adjust the mixture? I have one and it helped me pass the state emissions test with flying colors. I think I paid around $100 for mine.

Thanks,
Ron D

jashropshire · 11-14-2003, 07:12 PM

Thanks Ron, I'll check it out!

craign · craign's Garage

Just came across this.......might give it a shot to see how it works and test my electronic assembly ability.

http://www.markvanderkwaak.com/dbbp/tech-tips/mm.html

Craig

bemumford · 11-20-2003, 04:28 PM

Ron D,

Could you write a short paragraph on how one uses the Gunson Gas Tester -- how does it connect to the car, what form does the reading take, how do you use these results, etc? I've seen these things advertised over the years, but I've never talked with anyone who has used one. Alternatively, are directions you could scan and email me? Email is bemumford3@mchsi.com.

Thanks,

Ed Mumford

ron69912t · 11-21-2003, 05:46 AM

Ed:
If you gop to the Gunson web site you can read & download the instructions.

Very simple, connect digital meter to a 12 volt source, calabrate the CO level in air, warm up the engine, insert metal tube up the exhaust pipe, adjust the mix screws to desired CO level.

The key is the graph of the relationship of the exhaust gasses that comes with the meter. I'll post a copy.

Thanks,
Ron D

bemumford · 11-21-2003, 08:52 AM

RonD,

Thanks for your post on the Gunson Gastester. Looks like I gotta have one.

Ed Mumford

ron69912t · 11-21-2003, 09:20 AM

Ed:
I bought my new Gunson Digital off e-bay without any problems. I recall it cost me $139.00.

Good luck,
Ron D

bemumford · 11-21-2003, 01:09 PM

Ron,

I've seen a similar ebay auction -- perhaps from the same guy. That appears to be the best deal around.

Thanks again,

Ed

jashropshire · 11-24-2003, 01:58 PM

Hi All,

I've been following this thread since I posted the original question.

I hate to sound dumb, but I am wondering how one would make 4 separate mixture adjustments using the Gastester? My initial idea was to install one O2 sensor per exhaust outlet (total of 4) so that I could take a reading (using volt/ohm meter) and adjust each barrel. Can anyone explain the use of the Gastester and how I would go about ensuring each barrel is correctly adjusted? Or, am I making this harder than it needs to be? Thanks

Thanks

Jeff

ron69912t · 11-25-2003, 01:20 PM

Jeff:
If you go to the Gunson website you can read and download the instructions.

As I recall I had to start with all the mixture screws in the same position and work from there. Not sure how many turns open from a closed position I started with on the screws but I would guess 1 or 1-1/2 turns. It has been a while since I used it.

Good Luck
Ron D

Morrie · 11-25-2003, 06:02 PM

WWhat does this do that a 25 dollar mixture guage from pep boys and an O2 sensor won't? I am curious and a bit clueless so bear with me...

Morrie

ron69912t · 11-26-2003, 04:42 AM

Morrie:
The Gunson Gas Meter is a portable digital CO meter and it can be used on any car.

I don't know much about O2 sensors other than it has to be welded into the exhaust stream from what I have read.

Both measure one of the exhaust gases.

I think the O2 sensors are expensive and don't last forever.

Thanks,
Ron D

jashropshire · 11-26-2003, 05:00 AM

Thanks Ron, that's about what I thought I would need to do with a Gastester. It would certainly be more accurate that me trying to do as I have been doing, and that is adjusting each barrel by the number of turns, checking the plugs and exhaust pipe (for a rich condition) or listening for the "pops" and "spits" to go away!

I think I could make the gastester work. Not sure what I'll do yet (going to have to wait until after the holidays now .. too busy) You are correct about some welding needing to be done.

I thought that I would locate 4 O2 "bungs", one per exhaust port on the exhaust system, weld in 1 bung each, and install one O2 Sensor per cylinder. (I got 5 brand new ones on eBay; 4-wire heated, for average of $12 each) These would then be removable when they go bad.

Then, run the wiring from each sensor to a junction box that would be located in the engine compartment, with a 4-way switch so that I can take an individual reading for each exhaust port with my volt/ohm meter while making the necessary adjustments.

Admittedly, this method will likely cost as much as a gastester by the time I get the welding done (can't do that myself) and a good deal more effort. It might be an advantage for those with less patience in that each barrel can be adjusted accurately and individually as opposed to working each cylinder until you get them all to balance.

I think either method is fine really. Now I have something new to think about! Thanks for all the information and advice .....

Jeff Shropshire
68 912

HarryD · 12-04-2003, 02:49 PM

An issue to consider:
If you look at the O2 curve, it does no have a particularly sharp "knee" at the place where you want the mixture to be when compared to the very sharp knee for the CO values. This sharp knee means that it is very easy to see that you overshot. Also, once you go too lean, the CO becomes a flat line and it is very easy to tell that you are there.

Add to this, the very real risk of O2 infiltration from the outside that can booger up your readings.