Oxygen sensor

DOG ON

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I am finishing my prerunner, I have put the original ECU on the engine, nevertheless sometimes I feel the exhaust fumes are too rich and my eyes can get irritated fast in a fairly enclosed garage....

I think this is because I didn't use the oxygen sensor in the exhaust manifold as you can see in the picture.....

The car works fine , except for that little problem....can this lead to ECU going crazy and command an injector to flood a chamber , then having a bent connecting rod?

Can I do without the oxygen sensor safely?
 

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B Page

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I am new to this game; but I am not new to engine tuning.

Is there some valid reason not to use an O2 sensor? Are they known to cause problems during a race?

The computer only needs a couple inputs to operate properly, and the O2 is one of them. It will run better as the air temps changes, elevation changes, fuel quality changes, etc. It will allow the engine to live longer, as the cylinders won't get washed with fuel, etc.

Without the O2 sensor signal coming in, the ECU usually goes into some type of "limp" mode, or defaults to a specific fuel curve, based on RPM or mass-air-flow.
 

steveG

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You definitely need an Oxygen sensor. You should run every sensor the system originally came with. If you're not, you're not going to get maximum performance or fuel economy out of it. Also make sure you have a functioning check engine lamp. Otherwise you won't know when there's problem.
 

DOG ON

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Is there a specific practice or precautions installing an oxygen sensor in an offroad application? Dos, donts?
 

steveG

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Is there a specific practice or precautions installing an oxygen sensor in an offroad application? Dos, donts?
Do: Install it.

Don't: Not install it.

HA!

Seriously, though, I would put it on the header at the collector. If you don't want to ruin the finish on the headers you could put it in the pipe that attaches it.
 

B Page

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I would mount the O2 sensor near your collector flange; so it will stay hot during operation and you can use a more simple O2 sensor.

If you mount it closer to the exhaust tip (cooler exhaust), you will need a heated O2 sensor. The heated ones are more complex and need more wireing.
 

steveG

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I would mount the O2 sensor near your collector flange; so it will stay hot during operation and you can use a more simple O2 sensor.

If you mount it closer to the exhaust tip (cooler exhaust), you will need a heated O2 sensor. The heated ones are more complex and need more wireing.
I would use whatever the ECM was designed to use.
 

cancinoj

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have heard of people test-tunning an engine just by connecting a digital voltmeter to the o2's to see if the mix is the way they want, not to lean, not even normal, they want it a little bit above normal to prevent head or piston melting,, something like that you know,. on our case the ecu detected a lean mixture on one side of the engine,. end up to have clogged fuel injectors, they not just tell the ecu if something is wrong but also they ar used during normal operation to get the best performance out of your engine,. i dont know if i made my self clear, im not an expert, but thats what i know , haha,. good luck,.keep us updated to see if you fix that, thks,.
 

clogking

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Do use O2 sensor
Don't run Race fuel with lead in it!
 

DOG ON

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I had an awesome test run yesterday, I will follow all the advice here......
Meanwhile, let me post a pic of how the car is looking , I just finished and I am a proud Papa!
 

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FABRICATOR

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It's hard to say if an OEM sensor would stay hot enough.
There is something called an "O2 simulator" that eliminates the one in the exhaust and lets you dial in a false A/F input to the ECM.
 

DOG ON

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Do you the header being so much cooler?
 

steveG

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I'm not sure where Chuck was going with that, but it was the only thing I could think of. I really don't see any reason not to use the OE sensor. I don't think the header will have any problem staying hot enough and I don't see why you would want to "fool" the ECM about anything. I'm a fan of just letting things work as intended.

I would like to hear more about what Chuck meant, though.
 

movindirt

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From Advanced Engine Performance Diagnosis, third edition:

An O2S does not send a voltage signal until its tip reaches a temperature of about 572 deg. F (300 C). Also, O2 sensors provide their fastest response to mixture changes @ about 1472 deg. F (800 C)


You will see above 600 F @ the header so the O2S should work fine but may be a bit slow. My 2 cents is that a slow reacting O2S is better then a fixed A/F for overall performance.
 

steveG

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I just consulted one of my techs and he agrees that it would be fine at the collector. There is a chance that the sensor will stop functioning when idling and cruising around at very slow speeds but as soon as you start using the skinny pedal it'll heat up and start working again.

He sited the old GM 4.3L TBI engines that were actually programmed to go into open loop at idle because the Oxygen senor would drop in temperature. He also said that it took very little for them to start functioning again.
 

FABRICATOR

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The key word was 'OEM'. If it doesn't keep up he can always upgrade to a heated 02.
Headers get hot, cast iron gets hot, but what really matters is the EGT. Just changing to a high flow muffler(s) often lowers EGT out of range.

I'm not suggesting he not use an O2 sensor, he already made that choice. A simulator is closer to using one than what he has now.

Personally, I would run the O2 and go from there, but people often get upset when I tell them what I would do. :)
 

B Page

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I must agree. Use the O2 sensor. The reason for placing it in the collector, is to have the exhaust gas from all 4 cylinders blasting across the tip of the sensor. This keeps the heat up in the working range.

Many of the OE O2 sensors are the heated (4 wire) models. They are functional at all RPM, and only take a minute to heat up, from a cold start. They only heat up to the lower functional temp range, so they do have a sluggish response for the ECU, until the RPM brings the EGT up to proper levels.

No O2 = BAD.
Fake O2 signal = Limp Home mode
2 Wire O2 = functioal
4 wire O2 = more functional
 

cancinoj

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we recently swap our 4.o ohv to 4.0 sohc for our class 3 ford explorer,. juanco did the ecu tunning and we were having missfiring problems from iddle to 3000, well, after replacing almost everything on the engine,. juanco did a scan to the ecu and it showed some problems with the o2 sensors,. i did the wiring so have to recheck again,. well, it end up to have the left sensor connected to the right sensor and viceversa,. and one sensor was not receiving voltage, we just fix that, and did some test today, and the engine is smoth and strong from idlle to red line,. awsome,. now we are ready for some action this weekend in ojos negros, http://www.essoroffroad.com/ rumors said that roger norman will be driving a class 7s, so, our score class 3 is a class 7s here, ha, so, will see what happens,. see yahh then.
 

clogking

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Almost all systems go open loop at idle anyways.
 
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