I was told that our trucks (I have supercharged '02 HD, but I assume they are same as Ls) have two O2 sensors. I know one is on driver side of exhaust close to engine, but where is other one?

Also, how computer uses values from them? Are they averaged? Or they are read and processed independently? If one of them is malfunctioning what would happen? Would computer know that or it would get incorrect values and then make incorrect decisions based on incorrect values?

Thanks in advance!

ZoranC

 

Actually there are 4. 2 on each side, and then on each side one is in front of the cat and one is after the cat.

 

Which ones are the ones that truck uses to determine A/F ratio and adjust it accordingly? Just one of them, all of them, or just front ones?

Also, when we hook up aftermarket A/F gauge, like Autometer, we usually tap into wire that goes from O2 sensor to computer. How many wires go from O2 sensors to computer? One, two, or four?

Also, do you happen to know can I find out what computer is seeing through OBD II / diagnostic port in real time?

Thanks again!

ZoranC

 

look closely at this picture and you'll find all four of them.

the two at the front nearest the exhaust manifolds are the HEGO's that monitor oxygen. They vary voltage to the PCM from 0.0v (lean air fuel) to 1.0volt (rich air fuel). HEGO stands for "Heated Exhaust Gas Oxygen", I think our hegos use 4 wires, two for the heater and two for the O2 sensor, but some hego's only have 3 wires.

The two at the rear near the tailshaft of the transmission are actually called Catalyst Monitors, all they do is monitor the air there and make sure that the catalytic converters are working properly.

later,
chris

 

What most of us do on Cobras when we want to run off road pipes is simple take out the two CM's and replace the wiring hardness with a MIL Eliminator which basically contains a diode and resistor wired up to fool the computer into the corrected voltage without throwing a MIL/SES light on your dash. This can easily be adapted on a Lightning as well if you choose to run offroad pipes.

 

When checking A/F #s some people weld in bung within 6" from factory sensor that is prior to cats. They usually just one. However, what is that based on? Are they assuming value from sensor on driver side is going to be same as from one on passenger side? If yes, can they do that assumption safely? Is engine exhaust coming from all cylinders through same "tube" and then gets divided into two exhaust lines OR exhaust from 4 cylinders is not mixed with exhaust from other 4 and they can have different A/F ratio? If yes, wouldn't one want to monitor both (through two separate taps feeding potentially two separate A/F gauges) at same time when they are on dyno or wherever?

What I am also interested in is can one sensor send a signal "too lean, make it richer" while other one is at the same time sending signal "too rich, make it leaner" or any of other possible contradicting "statements" while both are operating properly? Or that can happen only when at least one of the sensors is malfunctioning? Also, what would computer do in such scenario? This is brainstroming on an idea that both sensors should be sending approximately same voltage at approximately same point in time and that if there is a significant lag or difference between two than something is wrong. I am trying to find out does this logic work or not.

Can you, please, explain to me meaning of this?

If I am trying to check is exhaust system partially clogged somewhere between engine and exhaust tips would this help me in figuring that out? Would difference in drops between sides point that out? If yes, that would work for stretch between sensors, but what if congestion is after sensors and before exhaust tips?

Thanks again!

ZoranC

 

hego is an acronym for your 1st pair of oxygen sensors. (forgot what it stands for) our L hegos use 4 wires, 2 to sense with and the other 2 are the heater wires, there are also o2 sensors with single wires, and 2 wires. i dont think o2 sensors have anything to do with testing for blockage, the most acurate way to do that is to weld in some sort of pressure tester. most likely any blockage would be the cats, if those arent it then it would be the muffler. most of the time a pipe just cant be blocked unless its been kinked. someone correct me if im wrong

 

Can you please elaborate? I know nothing about this area. What you mean with "sense with"? Does that mean one wire is ground, other wire is voltage? What is the heater?

I was thinking they could be if purpose of rear ones is to indicate potential issue based on voltage drop. But because I don't know anything about this area thats why I posed that question.

Thanks!

ZoranC

 

ZoranC, you have alot of questions and I don't have alot of time. As I said before, HEGO stands for Heated Exhaust Gas Oxygen. The sensor itself is heated, thus two wires power and ground for the heater circuit portion of the part, the other two wires are used to send the signal to the pcm. O2 sensors measure oxygen content, nothing else. Yes, it's possible that you could be rich on one bank and lean on the other and the O2s could be sending two different messages. so you are correct in you question about needing two guages. It really doesn't matter though, because the guages you are talking about aren't accurate anyway, you'd need a wideband o2 sensor on each side of the motor. an EGT in each header tube would be more accurate, but more complicated. The guage that I think you are talking about is mostly just for looks. Neither the upstream hegos nor the catalyst monitors will tell you if your cats are clogged. The cat monitor sensors also measure air, again, thats all O2 sensors can do, they then calculate lean or rich based on how much air they see. the upstream sensors switch from rich to lean to rich to lean, etc, if they do this the engine is running correctly, the cats change the Oxygen levels in the exhaust and the cat monitors should just read a steady voltage, IF they are switching like the upstream sensors, they you know that the Catalytic converters didn't do there job or aren't there. The only way I know to check for exhaust blockage aside from removing the exhaust is to use a vacuum guage to check manifold vacuum (intake), at idle you should have ( depending on type of engine) approximately 15-21inches of vacuum, if the vacuum signal is low this is an indication of a blockage, if you rev the engine or raise the RPMs this would increase the exhaust flow to the blockage and accentuate the readings if there is a blockage, but won't always show it if it is partial. BTW, why do you think your exhaust is blocked? it probably isn't.

good luck.

later,
chris

 

Iam dizzy from reading all this, and I still don't understand nothing. But that might be a good thing

 

Chris,

I completely understand. I am sorry about this avalanche of questions. Main reason for it is need to learn a lot fast without making mistakes. I've been having issues with my truck for a while and I have progressed some but not much. I go somewhere, they make one step just for me to find out what was done was incomplete so I have to go back in line, which costs me more time and more money, and sometimes thing have to be undone, and some parts are unneccessary or wrong, etc, and I don't have neither money nor time nor knowledge nor resources to do it myself, all while my truck is still having issues. So I have to stop that insanity and I have found out best way to do it is by asking lots of question around here. Just in last few days my knowledge has grown in leaps and bounds thanks to you and others that are helping me out so your patience and willingness to help and explain is already extremely appreciated.

Thanks to your explanations there are very few questions left and I promise they are short so if you could hang with me just a lil more I will be thankfull...

Is being rich in one bank and lean in other normal behavior or it could happen only when there is an issue with fuel or air delivery or when sensor is malfunctioning? Is there a way at all to say is sensor malfunctioning?

How one can know what is going on with air/fuel ratios (is one reach, lean, or just right) based on temperature of exhaust fumes from cylinder(s)? And should one monitor just two temperature values (one per each bank) or 8 of them (one per cylinder)?

What part about is complicated -- is it installation (tapping into wire vs modding the header tube) that you had in mind when you said that?

If you mean that I mean regular A/F gauge, then yes, we are talking same gauge. I am still undecided about these gauges. From all I read they are showing values only during regular drive and when I go into WOT computer is not reading out from them but is using embedded tables. My truck doesn't have issues during regular drive, it has issues only when I step on it hard. Therefore, I am suspecting those gauges wouldn't be of much help in my scenario (like already said). If that's the case I am tempted to ditch them and save that money for later installation of wideband O2 and EGT. In the meantime I could maybe, if I really want to see values from O2 sensors, get OBD II software, hook it up to laptop, log the data in real time and analyze it to my heart's content later, plus OBD II software would give me much more besides those 4 values. Any input/opinion on this?

Where on manifold intake you would hookup that gauge?

Because some people in forums told me I should check it out because it could cause symptoms I am experiencing. I know it is not completely blocked because I can see exhaust flowing from both tips and because none of the piping underneath is red hot after drive. I just want to check it out and get it off my back as "checked that, next".

Thank you again! As always, I am looking forward to your reply.

ZoranC

 

No, that would not be normal behavior by any stretch, but it is not impossible. Normally a vehicle would be lean or rich on both banks if there was an Airflow measurement or fuel delivery (too much or too little) problem. But you could be rich or lean on 1 bank due to a vacuum leak (would have to be at an intake gasket to affect only 1 bank), a clogged, stuck or leaking injector, spark/ignition problem. it is theoretically possible to have one bank be rich due to one problem, and the other bank be lean due to another different problem. however, this is pretty unlikely. if the hego is malfunctioning, you would likely get a code for "circuit malfunction" or "hego lack of switches", NOT a simply a lean or rich code.

High or Hot EGT means more air and less fuel or LEAN.

Cooler EGT readings mean a richer mixture.

it would be adviseable to monitor each individual exhaust port. otherwise you'd just be averaging and this could mask a problem that you might be having on one cylinder.

You are correct, under WOT, the fuel and spark are based on preset tables or maps, the HEGOs are effectively just along for the ride during WOT. they are "out of the loop" during full throttle.

anywhere that there is a vacuum hose going into the intake plenum. You could unplug a vacuum line anywhere, it will be the same reading wherever you check it. there are numerous places to check. try pulling the vacuum supply line off of your fuel pressure regulator and checking there.

hope this helps.

later,
chris

 

That's what I thought. Seems to me current design of A/F gauges would not show this and that only logging of data for later analysis would catch something like this.

Do you happen to know how many times a second computer readds out voltage from O2 sensor and adjusts A/F ratio based on that?

Also, do you happen to know how many times a second we can read out values from OBD II port?

Thank you for confirming this. I see now why you said it would be more precise but more complicated. In any case I would not want to see 8 gauges in my truck just for this. Are you aware of any product that would gather data from 8 probes and display all values on LCD panel at the same time?

Now I see why A/F gauges of usual design will not help me much. However, DakotaDigital gauge that shows voltage value with precision of .001V, or Gadgetseller's modified Autometer gauge that indicates only .78V to .98V range in 0.01V, might at least serve as a safety indicator of leaning out during WOT. If I am at WOT and I see voltage starting to drop off then I am leaning out and I should back off because I am having a problem. What you think of this?

Also, wide open throttle is defined as throttle opening greater than 80% as indicated by the throttle position sensor. How do I know am I in WOT or not? How do I know what is value on throttle position sensor?

Hmmm, seems like a list of questions is getting shorter and shorter and easier and easier. Thank you for the opportunity to learn from you! I have much clearer picture now how things work.

Thanks again!

ZoranC

 

Chris,

1st: Happy Birthday!

2nd: Any comments on few remaining questions above?

Thanks!

ZoranC