Aftermarket O2 sensor placement?

[JP Noonan]

Well it's about time I figure out my A/F mixture better than by reading the plugs. I was wondering if anyone had some ideas on where the best place is to weld the bung for an O2 sensor? I have a 73-74 SS 2.0L system and have access to a good SS welder. Should I keep it near the head for higher temps? Or should I weld it in the 2 to 4 collector of a Bursch muffler for better sampling of all the cylinders? Thanks.

BTW I haven't bought the sensor yet, but instead of building (a.k.a. Pelican Tech Article) it myself I plan on buying a comercially manufactured one.

[John Rogers]

Getting pretty hi-tech aren't we John? The O2 sensor is supposed to be as close to the engine as possible, which means on a single outlet line, not the collector. This is supposed to help with the heating and give a more accurate reading of what is in the engine. If you use a heated sensor, like the one on our 87 turbo, you could put it on the collector of one side. EFI makes a dual model so you can read both sides of the engine with two O2 sensors, but I use ours as an emergency indicator, should be green at full throttle so if it goes red during an autocross I'll stop. (Oh yea, the parts to make one are only $25 or so, not counting the O2 sensor)

[This message has been edited by john rogers (edited 02-26-99).]

[JP Noonan]

HI Tech? Like that Star Wars Movie????

Seriously, refering to my EEC-IV Ford EFI...
My Lightning ( a mustang 302/351 in a F-150 4500 lbs truck, GT-40 intake, heads, and all, but I digress) the Lamda sensor is in the "crossover" tube as Ford calls it ( a 1" pipe between the 2 1/4" duel exhaust about 3' after where the headers leave the head). I know a little about heated O2 sensors, I'm under the impression that they are used so that the O2 sensor gets up to temp quicker, not to keep the O2 sensor at temp. It made sense to me that only one primary had to be sampled, but when I looked at my truck and Mustangs (Mustakes) the O2 was in the collector. Soooo what you are saying (and I believe you) is that it is more important to test the exhaust gases close to the head (at a high temp) vs. a sample of all the tubes at the collector.

This means I must find a SS "bung" ( 18mm x .75?) and have a local mig/tig shop weld it into the primary off the head?

The dual sensor seems cool. I guess they are isolated by a diode? Do you also run duel cylinder head temp sensors?

BTW is an O2 sensor thrown off by ring blow by, i.e. does the oil in the exhaust read as a rich condition?

[John Rogers]

Closer is better, faster response, more accurate, etc. I think most companies sell a stainless bung if you check. Oil/oil vapor has no affect on the O2 reading. Sounds strange, but our old clunker used about a quart of oil every two weeks and could pass smog easily as the fuel mixture was right on. The dual systems use two signal lines and two complete circuits.

[JP Noonan]

Thank you very much for the help. I'll let you know how it goes.

[rich]

Is the reading that the O2 senor giving require a cat to do the final exhaust gas correction? With out a cat or any real back pressure are you getting a true reading? Does back pressure even enter into the equation? Is there a senor(volvo,ford, gm,ect.) that will work better for the air cooled motor? Are exhaust gas tempetures hotter on air cooled motors? I never took any engineering classes. Oh one more thing, are you doing this to an injected or carbed motor or does it matter.

[John Rogers]

To answer your questions: The O2 sensor in independent of cat or backpressor. O2 sensors are made as a generic unit with 1, 2 or 3 wires and air/water cooled engine makes no difference. I think the O2 sensor has to be over 300 degrees F to give accurate readings so I think air-cooled engines tend to heat up faster. The intake system doesn't matter as the air/fuel ratio in the exhaust is what is measured. As an example, on our 1987 Turbo it gies accurate readings in about 5 minutes and it uses a heated sensor to speed things up and the lights react about 4 to 8 times a second so the reading is accurate. Also you see nearly instant reaction to blipping the throttle.

[This message has been edited by john rogers (edited 02-28-99).]