Oxygen Sensor Placement

blykins · #1 (**permalink**) 10-15-2004, 01:35 PM

Guys, where's the best place to position an O2 sensor? I want to buy a sensor and gauge just to check my air/fuel ratio on my Cobra....I'm not gonna place the gauge in the car, and if I could get away with it, I'd rather not have to cut my sidepipe and weld in a bung. Can these things be used at any point in the exhaust? Can I just stick it in the end of the sidepipe like a sniffer?

xlr8or · #2 (**permalink**) 10-15-2004, 04:23 PM

It will be more accurate the closer it is to the exhaust port.

Mohuska · #3 (**permalink**) 10-15-2004, 07:07 PM

It is important that the O2 sensor be placed in the collector down from where the individual header exhaust pipes join. You also need to make sure that no extraneous oxygen is introduced to the sensor, or it will not be accurate

Mike

Dwight · #4 (**permalink**) 10-15-2004, 08:10 PM

I GOT MY COBRA DYNO AT THE FLING LAST JUNE. THEY HAD A TUBE ( 3/4" + - ) THAT WAS 3 TO 4 FEET LONG WITH A BUNG AND A O2 SENSOR IN IT, NEAR ONE END. THEY INSERTED THE TUBE INTO THE SIDEPIPE. THEY COULD NOT GET IT INTO MY SIDEPIPE BECAUSE OF THE CURVE OF THE TIP. HE EXPLAINED THAT THE TUBE HAD TO GO A COUPLE OF FEET INTO THE SIDEPIPE TO GET A CLEAN READING. NO OUTSIDE AIR CONTAMINATION. I THINK YOU CAN MAKE ONE.

strictlypersonl · #5 (**permalink**) 10-16-2004, 05:17 AM

Most O2 sensor won't work unless they're quite hot. That's why they're placed close to the head.

RICK LAKE · #6 (**permalink**) 10-16-2004, 06:29 AM

blykins Are you using a heated O2 sensor? The best location is 6-9" after where the collector pipe meets the muffler. I hope you have an HP coating on the pipe to keep the heat in. A wide band )2 is also what you want for those WOT runs. I have mine on the inside of the side pipe 6" after the collector. The hotter the O2 is kept the better the readings are. WATCH your GAS. Unleaded ONLY stay away from additives for octane boost even though they say O2 sensor safe. The tube idea may work but if the tube is not in the middle of the flow for all the cylinders you are not going to get the correct readings. It could be off as much as 8-10%. I would have the EGT's checked on all cylinders before you go for the A/F readings. FE motors have 2 leaner cylinders than the rest. If you are looking for a in the neighborhood the tube would be OK, I guess. I hope this helps. Rick Lake

Bruce Edwards · #7 (**permalink**) 10-16-2004, 03:05 PM

O2 sensors work by heat. They make their own electricity by way of the heat exciting the material inside the sensor. The gauge reads this as rich or lean by using a standard voltage for the correct mix. The placement of the sensor is important in order to get the correct reading. To close to the head and it will always show lean. To far and it will always show rich. If you look at most new cars the sensor is placed just before the pipe hook up or shortly after. A secondary is used after the converter to be sure it is working. The secondary will always show a lean mix due to the heat of the converter. If you pull the converter it throws off the sensor and kicks you check light.
So if you are installing a sensor to check your mix you will want it placed were all 4 pipes come together in the collector.
I see no way to install one with out welding a bung to the pipe. You could weld it to te bottom so it can not be seen and plug it when you are not using it.
You could also check your instruction sheet to see what it says.

Dominik · #8 (**permalink**) 10-16-2004, 09:12 PM

good morning,

in the late 80s Rochester developed a sensor for leaded fuel, which was used in the south-american market.
it had a lifespan of appr. 55.000 miles in a 1.6l OPEL.

so if you are using leaded fuel it may pay totalk to someone at Rochester (now DELPHI Engine Mnagement Systems?) to find out where this sensor is available.

the current sensors (for unleaded) are heated to make the sytem work in closed loop even earlier.
I wonder if the heated sensor would deliver accurate readings sitting farther back?

Dom

cobrashoch · #9 (**permalink**) 10-16-2004, 09:14 PM

Bruce Edwards has got it right. In addition to the type and design of the sensor you are using, you have to remember what the placement means. For example a header collector sensor will only tell you what the overall running condition is of all the slugs running on that side (bank) of the engine. A sensor on each header exaust tube will let you tune each piston independently too. So you see, it could get quite complex, dependant on what you are trying to do. Most of the guys that I know that tune using a sensor(s) use the early Mustang sensors. Bosch seems to be the make mentioned most often. Time to break out the welding torch.
cobrashock

blykins · #10 (**permalink**) 10-17-2004, 04:52 PM

Thanks for all the help guys. The primary purpose of this experiment is to fine tune my idle air bleeds. The engine was idling way too rich....I opened up the idle bleeds and now it's idling much cleaner.....but I was just wanting an electronic confirmation of how well I was doing. :-)

If I need a bung, eventually I'll cut a hole and weld one in, but I was just mainly wondering how reliable they are by just shoving up the sidepipe's butt......