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Proper Placement of O2 Sensor
When installing an O2 sensor in a car that never had one or when replacing the exhaust system there's a couple things you have to remember.
First is you want it as close to the exhaust manifold as possible so it reaches operating tempreture. within about a foot is fine.
Second is you want it facing up, not down. This is so any liquid in exhaust like condensation or flooding does not have the ability to "Wick" down into the sensor. Always point so it drains would be a good way to remeber.
[attachment=1:tnyadk3x]o2-correct.gif[/attachment:tnyadk3x]
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Re: Proper Placement of O2 Sensor
I understand that if you are running headers, you should run a heated oxygen sensor in the collector. Should the heater on this sensor be run through a relay?
Re: Proper Placement of O2 Sensor
I'm not sure if a relay is needed but that's how I wire them in. Needs to be wired from Key On Power. Just like your pink wire needs powered when key is on, all the way to start and back to crank. Lots of electric circuts get cut from powere during crank.
As for NEEDING it on headers? Not true. I proved it with a 1990 Chevy Blazer that came with a 7747 ECM. I installed headers with the O2 sensor in the exhaust pipe right behind the collector. Not in the top of header collector. Did not touch the stock chip. Never had an idle issue. All summer it would idle closed loop. All winter it would idle open loop and jump into closed loop after accelerating several seconds.
On performance built engines it is easier to idle open loop all the time. Even if the O2 is hot enough set it to not come on till after throttle position shown in data, this lets it idle nicely where it wants even if not 14.7 to 1 AFR.
For conversion systems on stock motors like the 7747 on an IH (like yours right?) you can play with idle VE tables and spark and get it to idle hotter and keep O2 hot enough all summer, but winter with headers while stopped it's going to go open loop. You can tune open loop to be just as fine as closed loop like a newer chevy engine the system came off of. Or put in a heated O2? Problems with adding more drain on older conversion vehicles is the origanal charging system does not charge well at idle like newer cars. I have seen many conversion vehicles idle for 5 to 10 minutes then start having issues and glitching. Seen it less time same type older vehicle with A/C on! 2 minutes. Diagnostics showed voltage continuenly dropping down to below 12 volts. Not Goood with EFI!!!
O2 sensor is not even needed in EFI. It is a pollution control device to keep your engine at Stoich, 14.7 to 1 AFR.
Detroit started adding heated O2 sensors because cars idleing in long lines at inspection stations would be in open loop and not pass emmissions at idle. Although if they revved the car for ten seconds it would pass at idle...