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View Full Version : Proper Placement of O2 Sensor



EagleMark
02-24-2011, 11:31 AM
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]

[attachment=0:tnyadk3x]o2-wrong.gif[/attachment:tnyadk3x]

jhnyct
09-06-2011, 04:41 PM
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?

EagleMark
09-06-2011, 10:18 PM
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
02-26-2012, 02:29 PM
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
02-26-2012, 04:50 PM
I think so, when it get's hot enough, although I have never tried?

RobertISaar
02-26-2012, 06:43 PM
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
02-27-2012, 05:20 AM
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
02-27-2012, 05:29 AM
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

JeepsAndGuns
02-27-2012, 05:36 AM
How does the ecm know when its ready and/or not ready? Is it a timer or something, based on engine tempature, so it knows after its been running X ammount of time, the 02 should be warm?

PJG1173
02-27-2012, 07:00 AM
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.

RobertISaar
02-27-2012, 08:10 AM
How does the ecm know when its ready and/or not ready? Is it a timer or something, based on engine tempature, so it knows after its been running X ammount of time, the 02 should be warm?

when the O2 is warmed up, it's signal will start swinging, instead of staying near 450mV. when that happens the ECM starts to go into closed loop mode(if you have it enabled). if the O2 cools off to much at any time, the swinging pattern will slowly disasspear and the O2 will start to settle around 450mV.

EagleMark
02-27-2012, 08:29 AM
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.

JeepsAndGuns
02-27-2012, 04:40 PM
when the O2 is warmed up, it's signal will start swinging, instead of staying near 450mV. when that happens the ECM starts to go into closed loop mode(if you have it enabled). if the O2 cools off to much at any time, the swinging pattern will slowly disasspear and the O2 will start to settle around 450mV.

Ok, that makes sense.

FSJ Guy
02-27-2012, 10:44 PM
Somewhere someone also said this is why you don't want to tighten up your O2 "swing points" too much. The computer wants to see the O2 sensor reading oscillating so it know that the O2 is actually working.

EagleMark
02-27-2012, 11:10 PM
That may be the only thing I have never touched in a tune?

RobertISaar
02-28-2012, 09:36 AM
i tend to tighten them up as much as possible, since it will keep the INT closer to a single point, rather than having to swing everywhere to make the O2 do what the PCM wants.

no idea on what it does to emissions, but it does keep me at a single AFR better.

PJG1173
02-28-2012, 09:56 AM
i tend to tighten them up as much as possible, since it will keep the INT closer to a single point, rather than having to swing everywhere to make the O2 do what the PCM wants.

no idea on what it does to emissions, but it does keep me at a single AFR better.

are you talking about the O2 windows?

RobertISaar
02-28-2012, 09:58 AM
both, actually. i tighten the windows to within 1 or 2 A/D counts of each other at all times, but i also have the fueling prop settings set pretty mild.

PJG1173
02-28-2012, 10:01 AM
while we are on the subject of o2 sensor placement... Lets say someone installed long tube hedders and installed the factory heated O2 sensor in one of the collectors. now the sensor shows the engine is lean and tries to add fuel in closed loop causing it to run real rich. How would someone correct that?

PJG1173
02-28-2012, 10:02 AM
both, actually. i tighten the windows to within 1 or 2 A/D counts of each other at all times, but i also have the fueling prop settings set pretty mild.

hmm you lost me at A/D counts. what are A/D counts?

RobertISaar
02-28-2012, 10:08 AM
O2 sensor A/D counts. 1 count is ~4.42mV.

so my rich and lean tables are 4.4-8.8 mV away from the mean table in all locations.

PJG1173
02-28-2012, 10:13 AM
O2 sensor A/D counts. 1 count is ~4.42mV.

so my rich and lean tables are 4.4-8.8 mV away from the mean table in all locations.

Ok I think I'm following. still not getting what A/D stands for. when you say prop gain are you talking of the setting like this "Proportional Gain if Rich (Stable)"? if so how does this work?

RobertISaar
02-28-2012, 10:26 AM
A/D: analog to digital. it's how the PCM interprets sensors. since it has an 8-bit A/D system, there are 256 possible counts. 0 counts for a 5V sensor is 0volts, while 255 counts is 5 volts, with steps of .0196 volts in between each count. with an O2 sensor, the range is significantly smaller, on the range of 0-1127mV.

"Proportional Gain if Rich (Stable)" sounds like the A1 equivalent of "Gain Factor for Positive O2 Error (KPERMOD)", which isn't what i'm reffering to.

i'm reffering to:

Prop Counts when in Prop Duration 1 (KPCNT1)
Prop Counts when in Prop Duration 2 (KPCNT2)
Prop Duration 1 When Idling (KIDLPD1)
Prop Duration 2 When Idling (KIDLPD2)
Prop Counts Gain When Idling (KIDLGF)
Prop Error Gain Factor vs Airflow (F6CLTBLB)
Prop Counts vs Error (PCCNT) (F9CLTBL)
Prop Duration 1 vs Airflow, When not Idling (F12CLTBL)
Prop Duration 2 vs Airflow, When not Idling (F13CLTBL)

not all masks will have the same scalers/tables, and even more likely that their naming will be quite different, but those are the major O2 prop settings for A1/DF and any other MPFI 60V6 mask.

PJG1173
02-28-2012, 11:03 AM
Ah I see thanks for the clarification.

EagleMark
02-28-2012, 11:07 AM
while we are on the subject of o2 sensor placement... Lets say someone installed long tube hedders and installed the factory heated O2 sensor in one of the collectors. now the sensor shows the engine is lean and tries to add fuel in closed loop causing it to run real rich. How would someone correct that?Tune the chip! :thumbsup:

Make sure you have no exhaust leaks. Somtimes you can hear them when reved up causing pressure others you can't. Exhaust causes pulsations and a vacuum in areas sucking in air. Is it really rich? How do you know? Your nose is a terrible indicater especially without a cat. Looking at spark plug color is way better. WideBand O2 sensor on other side would be a good way!

wow Robert that was some great info!

PJG1173
02-28-2012, 01:17 PM
Tune the chip! :thumbsup:

Ok figured that...


Make sure you have no exhaust leaks. Somtimes you can hear them when reved up causing pressure others you can't. Exhaust causes pulsations and a vacuum in areas sucking in air. Is it really rich? How do you know? Your nose is a terrible indicater especially without a cat. Looking at spark plug color is way better. WideBand O2 sensor on other side would be a good way!

no exhaust leaks, Sniffing exhaust gasses is bad for your health, soot on plugs, WBo2 on other collector says rich, and the NB band is new.

EagleMark
02-28-2012, 01:35 PM
Well you got er figured out! Headers alone made that much difference? Must be maxing out rich BLM... sometimes lowering that point gets you more BLM numbers to work with. I us an AutoProm so I get em in the ballpark live before I start data looging BLM numbers and making finer adjustments.

RobertISaar
02-28-2012, 01:39 PM
narrowband shows lean, wideband shows rich, plugs are covered in soot.

sounds like the narrowband isn't working properly, even with it being new.

JeepsAndGuns
02-28-2012, 04:33 PM
Would the long tube headers placing the 02 further away from where it was stock, and since the headers shed more heat than cast iron manifolds be causing this problem?
What about wrapping the headers in that insulation, to keep heat out of the engine compartment and in the exhaust?

EagleMark
02-28-2012, 04:51 PM
Could be but he would see that in O2 not ready or closed loop. Wrapping headers does keep heat in, also keeps moisture in and rots them...

PJG1173
02-28-2012, 05:28 PM
closed loop is disabled because of this issue. every time I enable closed loop things go down hill fast. WB says 14.7 and the NB shows blm of 145 and starts dumping fuel. I've replaced the stock sensor twice with the same results. from what I read this should not be affecting a heated O2 enough to cause this. I just pulled the truck off the lift after searching for evidence of an exhaust leak and nothing. just for grins I am readjusting the valves once the engine cools. I just don't understand.

EagleMark
02-28-2012, 05:43 PM
Odd? Can you swap sides with the O2 sensors and see if one side has and issue?

one92rs
02-28-2012, 05:58 PM
i have shorty headers where the 02 sensor is mounted in the collector of the header. every once in a while i would get an 02 sensor code. put in a heated 02 and that went away. maybe since they are ceramic coated. maybe just the way it is in there. seems to me it idled smoother ever since.

FSJ Guy
02-28-2012, 07:12 PM
i have shorty headers where the 02 sensor is mounted in the collector of the header. every once in a while i would get an 02 sensor code. put in a heated 02 and that went away. maybe since they are ceramic coated. maybe just the way it is in there. seems to me it idled smoother ever since.

You probably solved one of two problems or both at the same time! Adding a heated sensor eliminated any problems of the sensor getting too cold. And if it was a 4 wire sensor, that added a dedicated ground which the old sensor may not have had. The ceramic coating may have prevented the sensor from grounding through the rest of the exhaust.

EagleMark
02-28-2012, 07:32 PM
I wonder if that's PJG1173 issue? O2 ground? Wonder if you could just run a ground from O2 sensor to block?

one92rs
02-29-2012, 03:38 PM
wow never thought about it like that. it is a 4 wire sensor. but 2 wires are tied togther which are ground, one signal, one power. but i do know it works great. since i will be going with headman ceramic long tubes in my engine swap it might be a good thing to have the heated.

EagleMark
02-29-2012, 03:46 PM
IIRC four wire should have ground for power, ground to ECM or block, but not tied together... then power and sensor = 4.

one92rs
02-29-2012, 05:48 PM
http://www.installationinstructions.com/103025.pdf

EagleMark
02-29-2012, 08:09 PM
I was reading the LC1 heated wide band and it made such a big stink over grounds, but when I looked again today they do end up in same spot as you showed. So I stand corrected.


5. TheBLUE and WHITE wires should all be grounded to the same ground source
Optimally, these (and any other MTS device ground) will be soldered to the same lug, and
connected to a single point. When this isn’t possible, connect each one to a separate lug,
and attach in close proximity. Multiple lugs on the same bolt is not optimal, and can result in
unwanted signal “noise.” When possible, soldering is always better than crimping. Please
see chapter 2.3 for more information on Electrical Grounding Concerns.

PJG1173
02-29-2012, 09:12 PM
hmm I might have to look into a 4wire setup

FSJ Guy
02-29-2012, 10:11 PM
I bought a Bosch sensor P/N 15510. Less than $25 and I snipped off the attached connector and used a Weather Pack connector.

JeepsAndGuns
03-01-2012, 05:38 AM
On the 4 wire sensor I installed, I tied the sensor and heating element wire together right after the connector and ran one wire to ground. Doesnt seem to have effected anything.