Proper Placement of O2 Sensor

[EagleMark]

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...

[1leg]

Good info here.

Does a heated O2 act like a non heated O2 if it doesn't have power running to it? Lets say you wire in a relay and the relay goes bad while your driving, Will the O2 continue to send info to the ECU.

[EagleMark]

I think so, when it get's hot enough, although I have never tried?

[RobertISaar]

yes, a heated O2 will act like a non-heated one if it's heater circuit is disabled.

also: the heater circuit will draw ~4 amps at most when completely cold and as it warms, the current draw will shrink to basically self-regulate the temp of the sensor.

[JeepsAndGuns]

So how does the ecm know if the 02 has gotten too cold? Does the 02 just stop outputting a signal when it cools down?

[EagleMark]

You can watch it in your ADX file while running or watching data. One says O2 Sensor Flag, Ready is hot, Not Ready is cold. Then there's also a closed loop flag, Open, Closed.

You can change the wording on an item in adx file. I like O2 Ready, then check the alarm button for not ready and it will show RED Not Ready

[PJG1173]

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.

were these shorty's or long tube? the long tubes threw my o2 way off.

[EagleMark]

were these shorty's or long tube? the long tubes threw my o2 way off.

Right in the middle! Shorties are usually like block huggers to bolt to factory pipe, long tube are really long tube for high RPM race engines, these were full headers but not long tube as the race headers.

The trick is to get the O2 sensor in collector that bolts onto header so getting heat from all cylinders on that side. Most headers have them in header collector and get heat from only one closest cylinder tube. It works much better there but still not as good as a heated O2! In winter on very cold days I would see it go O2 not ready and drop out of closed loop at 40 to 50 MPH do to wind cooling headers, but seemed to stay hot enough at 60 MPH I guess from more RPM. These were also ceramic coated headers which hold heat in! Reduces underhood temps as they say because of the coating heat stays in header.