I am 75% done with my 3800sc swap in to my 85 notchie with a Getrag 5 spd. First off, I bought a set of OBX headers off of Ebay for $300 which is actually a pretty good deal since they are all polished 304 SS mandrel bent headers with downpipe and collectors.

Well, it would have been a good deal if they would have fit.....First of all, I knew the crossover wouldnt clear the slave cylinder so I was prepared for that, but, I found out the crossover didnt even have the right bends to meet up with the collector. Sooo, I did a little working on the headers and I think I have it mostly figured out. My plan is to keep the exhaust true duals the whole way, they wont merge.

My question is, I have only one pre-cat O2 sensor. I will not be installing a cat so it will be my only one. Do you think it would be okay to just install it on one of the banks and call it a day, or will that be too far off from the other bank? My PCM is a 99 GTP stock bin for now that I plan to tune myself with my tuner.
My only other thought is to put an "H" pipe or something like it between the two and just put the O2 in there, but I really wanted to keep it true duals to see if that would improve on the sound at all.

Let me know your thoughts.

-Joe

I dont really like running any narrowband O2 sensors anymore, I find them to be way more of a pain than they are worth.

You only "need" to run 1 if you want to have a functioning stock O2 system, the post cat sensor is for cat diagnostics, and not needed if you dont have a cat.

[This message has been edited by darkhorizon (edited 11-30-2009).]

Yeah, I understand the post cat O2 is not needed,as that is why Im not running one. Are you suggesting just running without an O2 sensor all together? I would love to have a wideband, but funds are low right now and I want to get the car on the road asap, so I dont think I will be getting one until maybe next summer. If I run without the O2 sensor, how will that affect tuning the PCM?

-Joe

Derrek of the East Tennessee Fiero Club has programmed the after-cat O2 sensor out of his ECM. Seems he's developed some programming that others haven't been able to accomplish. Contact him at:

http://home.comcast.net/~robsfieros/site/

Scroll down about midway and you'll see the Forum button.

quote Originally posted by fierofool: Derrek of the East Tennessee Fiero Club has programmed the after-cat O2 sensor out of his ECM. Seems he's developed some programming that others haven't been able to accomplish. Contact him at: http://home.comcast.net/~robsfieros/site/ Scroll down about midway and you'll see the Forum button.

There are some "advanced" techniques to eliminate the cat test procedure, and a few people have discovered the switch to turn it off, but that function is only found in 2001+ PCM's. Using a previous year PCM will eliminate the test procedure (which is run rich for a while and see how the post cat sensor reacts).

quote If I run without the O2 sensor, how will that affect tuning the PCM?

It will just default to "open loop", which means you will not get fueling adjustments from the o2 sensor. On my bone stock gtp, i rarely see fueling adjustments more than 2%, so I could safely run it without a o2 sensor, and I then gain the advantage of being able to run it leaner than 14.7 at cruise.

You would be surprised to know that you really need very few sensors to run your car at maximum potential. You really dont even need a map sensor, iat sensor, or a cam sensor either. A TPS, MAF and a crank trigger are all anyone needs to run a motor effectively (you may have to at least spoof the coolant temp sensor, but running one would be a really nice feature).

[This message has been edited by darkhorizon (edited 12-01-2009).]

Okay, well then now I am leaning to just putting it on one bank, since I already have it wired up and have all the pieces necessary. If it makes that little effect on the fueling, then it should be okay on the one bank. At least then it will still go into closed loop.

Thanks
-Joe

Yes, the single bank will work, but I have a feeling it may be a bit inaccurate. With cams that have funny exhaust pulses, it can severely screw up a narrowband, and I fear it may do the same in this situation to some degree, such to the point where I would just leave it out completely.

quote Originally posted by joesfiero: Okay, well then now I am leaning to just putting it on one bank, since I already have it wired up and have all the pieces necessary. If it makes that little effect on the fueling, then it should be okay on the one bank. At least then it will still go into closed loop. Thanks -Joe

Just run the pre-cat O2 sensor in one bank. It will work fine. GM did this for many years on many cars. The only drawback to running the sensor in only one bank is it will only get to sample the exhaust gases from 3 cylinders, not all 6. But assuming the engine is properly maintained and in good working condition, this shouldn't cause any problems. Try to mount it as close to where the 3 exhaust primary tubes come together (such as in the header collector), if possible. This will eliminate the number of gasket/exhaust leak points that could occur before the O2 sensor which can throw off its accuracy.

And I certainly don't agree with NOT running a narrow band O2 sensor altogether. Every bone stock car I have scanned has always shown more than a 2% variance in fuel trims, depending on weather conditions. The O2 is in there for a reason, and removing it cripples the PCM's ability to correct for variances in atmospheric conditions as well as fuel composition or other issues. Let me give you some examples...

Lets say you regularly fill up at a gas station that uses 100% gasoline. And you have the PCM tuned for this. But then you go on a trip and all you can find is E10 fuel (10% ethanol / 90% gas), which many areas of the country have switched to. Ethanol does not contain as much energy per unit as gasoline, so using the E10 fuel vs. 100% gasoline will result in the engine running LEANER if the PCM is not tuned (or cannot self-correct) for this. If you have a narrow-band O2 sensor installed, the PCM can detect this slight change in fuel composition via exhaust oxygen content and adjust fuel trims as necessary. And depending on the programming in your particular PCM, these "learned" fuel changes can be applied to full throttle operation as well.

The narrow-band O2 sensor is the check/balance to the entire engine control system, and it is a sensor I deem vital for proper street EFI system operation. If you have another sensor fail or start failing on your engine without the PCM setting a code for it, the O2 sensor can compensate for this failure and adjust the fuel back to where it is supposed to be. A great example of this is if the MAF sensor becomes dirty. Usually when this happens the sensor will start reporting less than actual airflow numbers to the computer. Without an O2 sensor to see that the engine is running lean, it will continue to do so until either a MAF code sets or the problem is corrected (hopefully before engine damage occurs). But, the O2 sensor (if present) will tell the PCM the engine is running too lean and then the PCM will self-compensate by richening up the fuel trims to correct the condition. At the very least, having the O2 sensor present and working can tell you or the PCM if something is not right.

-ryan

------------------
6+ years on this same swap -- NO engine or transmission failures...

Custom GM OBD1 & OBD2 Tuning | Engine Conversions & more | www.gmtuners.com

In areas of faulty hardware, the o2 sensor can fix issues... but i would say it is fairly uncommon for things to fail in terms of a few percent.

I run E10 gas, and after a few fillups, my cruising trims are always 0 or near zero on a completely untuned pcm. It is not completely stock as of now, but the only thing I have changed were a few trans settings and significantly increased timing, and trims have stayed the same. I have not scanned "thousands" of stock cars.. but all of the ones i have scanned, have shown similar fuel trims to what I see.

I dont see the problem with running in the 2-5% lean during cruise anyway... my fiero cruises at 16-17:1 as it is.

quote Originally posted by darkhorizon: In areas of faulty hardware, the o2 sensor can fix issues... but i would say it is fairly uncommon for things to fail in terms of a few percent.

You've never had a MAF sensor start to get dirty? You've never seen corrosion build-up in a broken coolant temp sensor electrical connector that caused a false coolant temp reading to the engine? These things happen more often than you think. Especially on older cars.

quote I run E10 gas, and after a few fillups, my cruising trims are always 0 or near zero on a completely untuned pcm. It is not completely stock as of now, but the only thing I have changed were a few trans settings and significantly increased timing, and trims have stayed the same. I have not scanned "thousands" of stock cars.. but all of the ones i have scanned, have shown similar fuel trims to what I see. I dont see the problem with running in the 2-5% lean during cruise anyway... my fiero cruises at 16-17:1 as it is.

I don't have a problem with lean cruise. But going lean under a moderate to high load is not good on the engine. I'm not discounting what you say YOU'VE seen on the vehicles you have scanned. But that's like saying because I've never seen something happen on a car I personally work on around here where I live, can't ever happen regardless of where the vehicle is being operated. I can tell you a car that operates at 5,000 ft altitudes or in the deserts of Nevada has much different fuel requrements then what it would need if it was driven here in the midwest.

I haven't scanned thousands of cars but I have scanned and tuned hundreds. And I've seen enough in the field that tells me it would be a BAD IDEA to remove the O2 sensor; unless of course it was a strict Race-only application or an application where the vehicle or engine was only going to be operated in very specific conditions. But for a street car, it is just a plain bad idea to remove the O2 sensor, in my opinion.

I have, but in every situation the o2 sensor merely bandaided a problem and typically makes it worse...

On my turbo car, I had 1 charge pipe blow off a few times, and when it did the car wouldnt run due to the fact that the tube was right in front of the maf. The o2 sensor would have not saved me there... I ended up just unplugging the maf.

If you drive around with a wideband staring you in your face for 2 years, and open loop only tune... I imagine you would have a small change of heart to see just how damn good the maf is at reading temperature change, air pressure change (due to elevation, etc), moisture content, etc.... It is a MASS air sensor, not a volume air sensor that would be found in a map sensor based PCM.

Will a o2 sensor make a car run perfectly with a bad maf? maybe, but every situation I have ran across, a dirty maf caused a fueling issue that would cause the car to not run at all the way it is suppose to run. Improper airflow calculations wreak havoc on other parts, including timing, and transmission shifting. Will you get home? yes, but your trans would have been shifting "soft" and your timing would have been much higher than it should, basically defeating the 10% fuel the PCM added.

Here for the discussion, not the argument, Scott

quote Originally posted by darkhorizon: I have, but in every situation the o2 sensor merely bandaided a problem and typically makes it worse... On my turbo car, I had 1 charge pipe blow off a few times, and when it did the car wouldnt run due to the fact that the tube was right in front of the maf. The o2 sensor would have not saved me there... I ended up just unplugging the maf. If you drive around with a wideband staring you in your face for 2 years, and open loop only tune... I imagine you would have a small change of heart to see just how damn good the maf is at reading temperature change, air pressure change (due to elevation, etc), moisture content, etc.... It is a MASS air sensor, not a volume air sensor that would be found in a map sensor based PCM. Will a o2 sensor make a car run perfectly with a bad maf? maybe, but every situation I have ran across, a dirty maf caused a fueling issue that would cause the car to not run at all the way it is suppose to run. Improper airflow calculations wreak havoc on other parts, including timing, and transmission shifting. Will you get home? yes, but your trans would have been shifting "soft" and your timing would have been much higher than it should, basically defeating the 10% fuel the PCM added. Here for the discussion, not the argument, Scott

Can the O2 Band-Aid a problem? Sure. It can get you home without blowing up your engine (depending on what the problem is). If you have no O2, you have no backup system that can Band-Aid anything. And with no O2; if the driver is not paying attention to what is going on with the car, they can seriously damage their engine if something is wrong.

I think it's great that you drive around with a wideband staring you in the face. But what if your wideband reading is incorrect? You know the wideband O2 reads the same exhaust stream the narrow band does right? ANYTHING that you have going on that can throw off the narrow band signal will do the same to your coveted wideband. Exhaust leaks, mechanical issues, electrical issues, you name it. The only difference is the wideband won't be there to tell the computer something is up unless you have the computer using the wideband's signal. And I don't know about you, but when I drive I can't just stare at a particular gauge or display 100% of the time while I'm trying to concentrate on the road. I can occasionally glance at it, but I haven't got the whole keeping one eyeball on the gauge and the other on the road thing down yet.

Car companies put O2's on there for a reason. And it is not just for emissions. Because if they could do as you say YOU can do and tune a car to run perfectly all of the time no matter what the conditions are, they wouldn't need O2's either. But they keep putting them on cars. WHY? Simple: because it is the ONLY sensor that can tell the computer what is going on in the combustion chamber (at least as it relates to air and fuel). No other sensor on the engine can do that.

Oh and MAF's aren't perfect either. They cannot accurately measure humidity. This has been proven time and time again on my own Turbo 3800.

quote And with no O2; if the driver is not paying attention to what is going on with the car, they can seriously damage their engine if something is wrong.

The story I have been thinking of during this thread, was a friend of mine with a 4.3 v6 S10, which had a bad/dirty maf. The car ran, but crappy, it shifted poorly, and most likely made his timing go crazy at times, and he drove it like this for months. If the maf sensor failed, and the o2 was not around to make his truck run, but run crappy... He could have unplugged the maf, and drove home, then got a new one in the morning... heck, he would have been better running open loop via the map sensor at that point.

While its speculation, I would imagine he took some life off the trans... some of the things it was doing was not very nice.

Lets say in our turbo cars.. our maf fails and it accurately reads 30% less air than it should. The pcm is going to correct to a maximum of roughly 15%, causing our actual afr to be 15% lean, instead of 30% lean. On my setup, seeing how I am already in the 12:1 zone... It would be quite apparent that I was running lean with or without a wideband in the situation where I lost all 30%, compared to running 15% lean. I would imagine I would be blowing out spark, and just all around making stranage noises, forcing me to get out of the pedal, compared to running like 13:1, which would run fine, when the o2 would give me 15%. Another downfall is my trans would fall into the non maximum pressure shifts if I lost 30% of my airflow readings, and timing would be about 3-10 degrees higher as well.

quote Originally posted by darkhorizon: The story I have been thinking of during this thread, was a friend of mine with a 4.3 v6 S10, which had a bad/dirty maf. The car ran, but crappy, it shifted poorly, and most likely made his timing go crazy at times, and he drove it like this for months. If the maf sensor failed, and the o2 was not around to make his truck run, but run crappy... He could have unplugged the maf, and drove home, then got a new one in the morning... heck, he would have been better running open loop via the map sensor at that point. While its speculation, I would imagine he took some life off the trans... some of the things it was doing was not very nice.

Here's the problem tho. MAF's can get dirty without totally failing. I've seen this happen many times when people clean their K&N filters and then don't properly let the new oil dry on them before reinstalling. The oil ends up on the MAF sensing element and then finite particles of dirt attach to them, adding a degree of insulation which reduces the amount of airflow the MAF sensor reads coming thru it. On 95% of the cases I have seen this happen on in just 3800 applications alone, a MAF code was never set. Yes, the car did run poorly in almost every instance, but how many people are going to think to get out of the car and unplug the MAF to put the system into speed density mode (by letting the computer just use the MAP)? And what if they don't have a MAP sensor present (like you said earlier they don't need either)? Then all they're going to have is an Alpha-N fuel system effectively, which doesn't work too well in a street application. Besides all of that, what if they aren't driving their car? What if their girlfriend or wife is driving it? Are they going to know what to do if the engine starts running poorly? Or are they going to do like the rest of the general public does -- just try to limp it home...???

See, that's why I'm not an advocate that people should just start unplugging and/or removing things that I think they "don't need", just because I don't need them on my car. You never know what is going to happen in the field, especially when it isn't your car. It is easy to sit in your driveway in your car and think about everything that might happen only to you. But you never know what is going to happen out in the real world with other people's cars. The bulk of my customer base is made up of people who what to plug in the computer or chip and forget it. They don't all have scanners, laptops, etc; nor do they want them. Not everybody wants to do their own tuning nor do they want the hassle of driving something that has to be constantly monitored. Just like I have no desire to learn how to knit or sew. I'll let someone else worry about that and I'll just buy the clothes to wear.

quote Lets say in our turbo cars.. our maf fails and it accurately reads 30% less air than it should. The pcm is going to correct to a maximum of roughly 15%, causing our actual afr to be 15% lean, instead of 30% lean. On my setup, seeing how I am already in the 12:1 zone... It would be quite apparent that I was running lean with or without a wideband in the situation where I lost all 30%, compared to running 15% lean. I would imagine I would be blowing out spark, and just all around making stranage noises, forcing me to get out of the pedal, compared to running like 13:1, which would run fine, when the o2 would give me 15%. Another downfall is my trans would fall into the non maximum pressure shifts if I lost 30% of my airflow readings, and timing would be about 3-10 degrees higher as well.

I don't know what system you are using but most OBD2 GM systems allow for a maximum of about +/- 25% adjustment to fuel trims (combined short and long term). In some cases, this can be more in stock programming or can be adjusted so it is more thru custom tuning. But for sake of discussion, let's go with your numbers. Let's say your MAF suffers a failure resulting in a 30% loss of flow reading, but the PCM does not set a code for it. We know the O2 will pick up on this and drive fuel trims up to compensate. Well, they will reach their limit (you say at 15%); the computer will reach this limit and then will set a lean O2 code and illuminate the check engine light to tell you there is a problem. Unless of course you have already removed the O2 and disabled the code for it. Then the only indication you will have something is up is the engine is running poorly. And hopefully you notice this and take appropriate action before stabbing the gas and popping a piston ring land because of a lean AFR under boost.

Again, the computer is in there for a reason. It can watch many more things than you can (as the driver) and can take corrective action much faster than you can vs. pulling off to the side of the road to either unplug something or reflash the PCM. If it were up to me and in the relm of my capabilities, I would design a computer system that used more sensors and not less. I am in favor of giving the PCM as many tools as possible so it can do its job as accurately and quickly as possible. I just don't think neutering the PCM by removing the primary O2 sensor is a good idea.

-ryan

Without a narrowband giving feedback to the PCM you will be in open loop anyway.
The whole fuel trims arguement is moot at that point.
If you don't run an 02 sensor,then why not just throw a carb on?

It gives feedback to the PCM,and it's the only sensor you have that does so.

Hope you don't drive from low elevation to high elevation very often,or drive it in more than one season.

The computer can run without it,hell it can run without alot of sensors.
That's called open loop,and fueling runs off a base map-if you want it to run worth a crap then hopefully that base map is good.
I can guarentee you it isn't good enough for extreme differences in elevation and air mass.

I would try to put the 02 in the crossover personally,but I always lean towards diagnostics.
If the 02 sensor is on bank 1 and you have a bad injector on bank 2 then you might not notice till your compression test is 0.

I can't understand why they didn't put an 02 on both banks,it makes diagnosis so much simpler when you can narrow down an issue from bank to bank,cylinder to cylinder and watch 02 trims/voltages while diagnosing by symptom or code.
Get's hard to narrow down a pinpoint leak on a single bank without 02's providing feedback.

As for the aftercat sensor,just delete it in the pcm it's easy to do if you have the equipment.
Just make sure to turn all of them off.
p0036,p0136,p0137,p0138,p0140,p0141,p0420
p1139 and p1140 shouldn't be active on a 3800 but doublecheck it,I think that's all of them regarding HEGOS2.

GM's do use the aftercat 02 for a tiny percentage of long term fueling I understand (like 1% over time) and deleting them supposedly is responsible for some transient fueling.
I've not personally confirmed this though Darth has read the same info I have regarding it and maybe knows more than I.

If the air pressure changes wont the maf read x amount of air anyway?

quote I can guarentee you it isn't good enough for extreme differences in elevation and air mass.

The cars I tune in open loop are proof that it is able to compensate. Just drove to get pizza in 20 degree weather, and I tuned it in 80 degree weather... same AFR that I was running earlier this year on the same tune.

Comparing running fuel injection without trimming to a carb is quite a conjecture.

OKay, thanks for the responses guys(/gals?)
Im getting what both Darkhorizon and Ryan are saying, I really am. I am/was a GM tech of almost 6 years with PLENTY of GM based training before and during my time as a tech. I went through two years of automotive technology at a vocational school where my instructor was a former GM engineer. The last two years of being a tech I was the shop foreman and in charge of all new cases of driveability/electrical diagnosis at the shop which meant I spent lots and lots of time on the phone with TAC.

Anywho, I trust my own opinion on these motors as I have plenty of experience with them, but its real nice to hear the opinions of other professionals and GM engine experts. I was just torn between putting the O2 on one bank or in a crossover, but it seems I should be fine just putting it on one bank. As Ryan said, the closer to the heads the better, less chance of leaks causing inaccuracy.

Darkhorizon and Ryan, I appreciate both of your inputs on the matter and I want to address then both. I am not discounting either of your opinions nor do I think either of them are "wrong". In my situation, I have seen the problems a dirty MAF has created. We had hundreds of vehicles with this problem, When I worked at Pontiac/Kia, it seems like every single Sportage had a dirty MAF that wreaked havoc on driveability/emmisions. The O2 is there to adjust fueling under not only normal circumstances, but when other sensors go faulty. I would rather have the O2 there as a sort of a "safety net", I know it wont perform miracles if I were to lose an injector or something drastic like that, but at least if its there the PCM can still go into closed loop and do what it was designed by the engineers to do.

-Joe

[This message has been edited by joesfiero (edited 12-04-2009).]

quote Originally posted by Justinbart: If the air pressure changes wont the maf read x amount of air anyway?

Not since the PCM disregards everything when it is in open loop,so it doesn't really matter what the MAF reads as the pcm isn't using it anyway. No 02 sensor means open loop all the time.


Dark,I can't argue with your personal observation-but I stand by the science.
Does your car run in open loop or speed density? There is a difference between the two.
I believe your talking about running speed density,which has the 02's as feedback for correction.

[This message has been edited by DefEddie (edited 12-05-2009).]

quote Not since the PCM disregards everything when it is in open loop,so it doesn't really matter what the MAF reads as the pcm isn't using it anyway.

The map sensor is used sparingly in the PCM , and if anything it is used only for load calculations to control timing and shifting, so I am not using any type of speed density fueling, and it is 100% not supported in 3800 pcm's. In maf sensor LSx pcm's the map is used in fueling during large throttle changes, and idle. All of the above is true only if the maf is there and working correctly, if the maf is put into failure mode, it will revert to a speed density type system.

Trust me on the fact that the PCM uses the maf during open loop. The only thing open loop means, is that the O2 sensor is disabled. MANY if not all of the tuning nerds in the w-body world are running open loop now for lean cruise and consistent wot fueling on modded cars, and many (if not all) of the 3800 files can have openloop enabled full time, which means no fuel trims, and you can still leave the narrowband sensor in place, which means your ses light will continue to operate correctly.

[This message has been edited by darkhorizon (edited 12-05-2009).]