O2 Sensor Location

[Dez]

I am installing a Mass Air system on my truck and was wondering if the location of the O2 sensors mattered. Do they have to be a certain distance from the exhaust manifold or anything like that or can I just weld them in anywhere they can fit (headers, exhaust pipes, etc.)?

 

[Waverous]

Well......
I just completed my EFI install and I have my HEGO sensors at the end of my long tube headers where all four tubes collect into one area, so as to register all the cylinders. I am not sure if this is the best location yet, we will see. I hae talked with Lars about this and his concern was rather the location I chose would be able to heat the sensor enough to register the O2 content. I have also wrapped the headers to keep the heat in the header as well - I hope this will help.

Lars or Joe - any input?

 

[edge4]

Waverous is correct. The O2 sensors need to be as close to the collector as possible for proper O2 measurement and temperature.

 

[Dez]

Thanks for the help guys. I didn't know if welding the sensors to the collector itself would screw up the headers somehow. ;D

 

[Waverous]

I hope when you say weld to the headers, you are talking about welding the HEGO sensor "bung" to the header and then screwing in the sensor.

 

[iwlbcnu]

Mastangs have them in the collector of there long tube headers.
They make a collecter to bolt on the header that has the bung already in it if you have coated headers.
Some people weld a small flap behind the sensor in order to slow down the flow around the sensor and keep it hotter.

 

[Dez]

I was just talking about the bung and not the actual sensor. I just had a custom exhaust put in my truck. I'm not sure if my headers are coated or not but I had the guy put small (3-4") pipes right after the header before the two flex pipes. If my headers are coated, would it be alright to weld the bungs to the regualr pipe? It would only put them back about 6" from where they would go into the headers.

Also, is it easy to tell whether your headers are coated or not? Mine look coated but I'm not sure if they are just old with a bit of rust around them or not.

 

[iwlbcnu]

Jet Hot and other coatings are the aluminum looking coatings, I myself wouldn't want to weld to them and ruin the coating. Any of the painted headers i would just weld the bung in the collector.
The further down the line you go the cooler the gas temp is so yes it causes a problem. The 02's have to be a certain temp to run right, that's why some weld in a plate just behind the sensor.

 

[edge4]

Dez,
When I bought my JBA Shorty's from WH, they came with a 4" long adapter that had O2 bungs mounted in them. That adapter had a header flange on one end and straight weldable pipe on the other. Sounds just like what you already have. Just mount your O2 bungs in that piece and you'll be fine.

 

[Broncobowsher]

If the headers are coated, you will know it in the wallet. The coated headers are about $100 more then the regular.

O2 should be in the collector to sample all the cylinders in the bank and as close to the engine as possible to keep it in the hot exhaust.

 

[Dez]

Thanks a lot for all of your help guys. When I finally become smart enough I'll post some pics of my Bronco up here. It looks exactly like the one in that awful Charlie's Angels movie. ;D

 

[KST1]

What symptoms will your engine have if the sensors are running to cold? Rich, lean, ????.

Just curious,

-D

 

[KST1]

Anyone???

-D

 

[77bronko]

If you have a single wire sensor, the ECU will wait a certain amount of time before checking the sensor to make sure it is functioning properly. If its too cold, it won't work right, and the ECU will turn on the engine light and go into a slightly rich operating mode. It is possible that if the O2 sensor is on the cusp of not working that the engine would run richer then normal. Most likely the ECU will just thinks its broke though.

If there are problems, you may be able to substitute a 3 wire O2 sensor with a heater. I believe they are self regulating and only require 12v to the heater circuit when the ignition turns on.

 

[Dez]

Hey 77Bronko, where in Boston are you? And is that your maroon halfcab I've seen recently right around the corner from my house in Allston?