tbi o2 sensor, header discussion PLEASE READ

[89k5350]

so i know there have been many discussions about weather you need an 02 sensor or not or if you need a heated o2 sensor for headers. so a old school guy i know told me that with the tbi engines you dont need an o2 sensor unless you have catylitic converters BECAUSE the converter restricts exhaust for the o2 sensor to read and send to the computer or pcm. meaning no converter then no need for o2 sensor. he said he did that with all his tbi trucks and they ran completely fine a every once and a wile the engine light would come on but go back out. so put long tube headers and dual exhaust on my 87 350 tbi with NO o2 sensor and it runs way better and havent had the check engine light come on yet. so i hope this will save you guys who are devating this to save some money.if youve had different expiriances than speak your mind.

 

[ChrisPerry]

I have a 91 tbi 454, no cat, and truck gets almost 1 mpg better after a new o2 sensor. I'll keep running one.
I'm putting the cat back on in the next few weeks to smog it. Maybe with the cat on it'll work even better and I can get 9 mpg......oh if only...

 

[bp71k5]

Without the O2 sensor it probably runs seemingly better because its running rich using the open loop parameters instead of the closed loop. That would explain the mpg change.

 

[sweetk30]

do your self a big favor .

get that guy to sell you some magical beans and then plant them in your garden and wait for the bean stalk to grow.

he is full of

as stated its not going to run correctly as the computer cant read the sensor and adjust as needed and also go open/closed loop so it will defalt .

this will also drop your fuel mileage and then wait till you cry about that .

 

[89k5350]

well then my engine is trying to trick me too because it runs way better and now has more power so maybe it does have magical beans, sorry.

 

[bp71k5]

well then my engine is trying to trick me too because it runs way better and now has more power so maybe it does have magical beans, sorry.

It's probably because its running rich on the pre-programmed fuel ratios. You'de get better overall performance/mpg with a properly working o2 sensor.

 

[71Bowties]

How long does it take to close the loop now and idle down when warming up?

so i know there have been many discussions about weather you need an 02 sensor or not or if you need a heated o2 sensor for headers. so a old school guy i know told me that with the tbi engines you dont need an o2 sensor unless you have catylitic converters BECAUSE the converter restricts exhaust for the o2 sensor to read and send to the computer or pcm. meaning no converter then no need for o2 sensor. he said he did that with all his tbi trucks and they ran completely fine a every once and a wile the engine light would come on but go back out. so put long tube headers and dual exhaust on my 87 350 tbi with NO o2 sensor and it runs way better and havent had the check engine light come on yet. so i hope this will save you guys who are devating this to save some money.if youve had different expiriances than speak your mind.

 

[89k5350]

it is at normal idle in about 3-4min, after its warmed up once yo can let it sit for a wile and when u go to start it back up it is still at normal idle

 

[chulisohombre]

You have more power because of the headers and lack of a cat. It is Abe to breath freer now with those two things in the system. Did you check mpg before and after. You may get better mileage with a o2 in the system.

 

[sweetk30]

and did this guy also tell you flip your air lid upside down for more power ?

this works by sucking in all that fresh HOT air and also on tbi engines disrupting the spray pattern on the injectors possibly to a non smoth cone effect and making it run diffrently.

 

[dyeager535]

well then my engine is trying to trick me too because it runs way better and now has more power so maybe it does have magical beans, sorry.

It runs better because the stock *open loop* fueling is rich to provide a margin of safety, and you are running on pre-programmed values. Your ECM isn't compensating for it running rich or lean. With your modifications you eliminated the margin of safety, and might be right in the realm of "ok" with the stock parameters, at least in some conditions. The reason it ran worse with the stock tune and O2 is because TBI can only add or subtract so much fuel, and only under stock conditions.

Don't get me wrong, some people intentionally run their vehicles in open loop, but they spend time tuning them with wide band O2 sensors so that they know fueling is correct.

Can't say it runs better or right until you put a wideband on it. Seat of the pants is meaningless, that doesn't tell you rich or lean.

That old school guy doesn't know what he is talking about, at all, but that kind of thought process is normal for people who don't understand anything about fuel injection. Not saying I know everything, but I know enough to say he is dead wrong. I don't have converters on my truck (it is dual, so O2 is only reading one side of the motor) and the o2 sensor very clearly works properly and adjusts fueling as it should.

 

[Keitha]

Just what everyone else here said: The O2 sensor is the only part of the TBI system to give the computer feedback on what the motor is doing (thus Closed Loop). The computer uses the feedback to make constant adjustments to the air/fuel mixture. If it is running poorly before, then you have another problem that is being masked by a rich condition now.

 

[89k5350]

well luckily before i installed the headers i did weld in a o2 sensor bung but, i have a bolt in it because when i found out the stock o2 was rotted and falling aprt i didnt have the money for a new o2. so ill try a one wire sensor and see how it works, i was told by two auto technicians(my auto class teachers) that i dont absolutely need a 3 wire heated o2, but still for a off road toy or slap together truck u dont absolutely need a o2 sensor which was my whole point of this thread. i didnt say it will have more power without a o2 sensor i was stating that you can run a truck with out them and will be very driveable

 

[dyeager535]

Oh you won't have more power with an O2 sensor, that's a given...the O2 sensor doesn't "work" under heavy throttle, so the truck won't run any different with or without O2 in those conditions. Essentially cruise and idle are the only two spots where an O2 comes into play.

I know from experience, on *my* setup (every combination is going to act differently) I did NOT need a heated O2 sensor. I swapped to a heated, and I don't really see any difference. The only time the engine went "open loop" (outside of heavy throttle, cold starts, etc) with the single wire was at idle, and a split second after touching the pedal, the O2 was hot enough to work properly, and it went closed loop. Some of the truck big block setups were programmed by GM to go open loop at idle.

More of a concern than not using the O2 sensor IMO, is that you've made engine modifications and you don't know if the engine is now running right. As a "for instance" my Dad's 454 got a "computer friendly" camshaft (which is a lie, there is no such thing) and headers. Everything else stock. The stock programming on that motor was 20% *lean* just from those two modifications. Under normal use that sort of difference may not cause any issues (although it is huge IMO), but when you start getting into heavy throttle, towing, climbing grades, that lean condition translates into heat, which can translate into melted aluminum that used to be pistons. At the very least, in that situation, you would be leaving power on the table...the engine could make that much more power, but is handicapped by the stock fueling.

Pretty much everyone understands that engine modifications that are effective increase the amount of air and fuel the engine ingests. What some people don't seem to understand is that on injection (actually even on carbs, which is where the necessity of backpressure myth came from), there is no compensation for air/fuel under heavy throttle. The setup fuels the engine just like it was still stock. When you add even just headers, cylinder evacuation and filling is more efficient...that alone increases the need for fuel. But TBI isn't going to add that fuel, it has no way of knowing the engine is lean or rich under heavy throttle. This is why tuning is so critical.

 

[eagle mark]

so i know there have been many discussions about weather you need an 02 sensor or not or if you need a heated o2 sensor for headers. so a old school guy i know told me that with the tbi engines you dont need an o2 sensor unless you have catylitic converters BECAUSE the converter restricts exhaust for the o2 sensor to read and send to the computer or pcm. meaning no converter then no need for o2 sensor. he said he did that with all his tbi trucks and they ran completely fine a every once and a wile the engine light would come on but go back out. so put long tube headers and dual exhaust on my 87 350 tbi with NO o2 sensor and it runs way better and havent had the check engine light come on yet. so i hope this will save you guys who are devating this to save some money.if youve had different expiriances than speak your mind.

As the guys have said there's no truth in anything he told you...

If you don't have a CEL without an O2 hooked up? Something else is wrong because you should set a DTC 13 for O2 sensor.

O2 sensor is not needed for EFI! It's an emissions device that adjusts fueling to Stoich. They run fine without, but do run cleaner and depending condition of motor, pressure of fuel, modifications to engine? Run better as in more power! Why? Because the Open Loop AFR table is richer then the O2 sensor adjusting to Stoich.

The biggest reason people have issues with long tube headers and vehicle not running correctly is you moved the O2 sensor about 3 feet back in exhaust from stock. There is a setting/Parameter for this, "INT Vs Airflow" INT is Integrator which is the Short Term Fuel Trim. STFT moves to adjust fuel and depending on how much it moves sets the BLM (Block Learn Mode) also known as Long Term Fuel Trim. So the O2 sensor is reading exhaust at wrong time since it has last made an adjustment. This ends up as a constant fluctuating fuel trims! It's totally confused as to why it goes up and down and up and down.... this setting is in milla seconds/ms.

EFI is like a miracle tune that constantly keeps you dialed in. But it can only provide miracles within a certain range, it's not infinite! The tune in chip was built for that motor as is! Change exhaust, change intake, change cam etc... well the tune/chip or proper term "Calibration" needs to be set for those changes or you don't see all the benefits. You could actually see a loss in power and MPG!!!

There's also tune up issues, if your cap and rotor are worn? Spark plugs worn? etc... well... the bigger issue is fuel pressure! Most important factor that the ECM has no idea what it is. GM says between 9-13 PSI!!! Yes it will run between those pressures and the ECM is almost capable of keeping it running right through that range. But if you don't have 12-13 PSI you will not have all the power at WOT, no way! Also have issues at cold start when engine is running Open Loop... then WHAM! Goes Closed Loop and O2 sensor feedback says... add fuel, add fuel!!!

The biggest benefit from running an O2 sensor is... say you have dialed in your tune perfectly from data recorded from ECM? You did this on a dry day at 70f... well as temps and humidity change your perfect tune is no longer perfect! But the O2 sensor and calibration in the ECM is capable of keeping it perfect!

 

[Evanjw84]

so i know there have been many discussions about weather you need an 02 sensor or not or if you need a heated o2 sensor for headers. so a old school guy i know told me that with the tbi engines you dont need an o2 sensor unless you have catylitic converters BECAUSE the converter restricts exhaust for the o2 sensor to read and send to the computer or pcm. meaning no converter then no need for o2 sensor. he said he did that with all his tbi trucks and they ran completely fine a every once and a wile the engine light would come on but go back out. so put long tube headers and dual exhaust on my 87 350 tbi with NO o2 sensor and it runs way better and havent had the check engine light come on yet. so i hope this will save you guys who are devating this to save some money.if youve had different expiriances than speak your mind.

I have the same truck. Working on sourcing the EGR delete prom. But am considering also deleting the o2 sensor and removing the cats. Think you can point me in the right direction of an o2 sensor simulator?

 

[rampage]

I have the same truck. Working on sourcing the EGR delete prom. But am considering also deleting the o2 sensor and removing the cats. Think you can point me in the right direction of an o2 sensor simulator?

You might be waiting a while for an answer from him since the last time he logged on here was 2 years ago.

 

[1-ton]

You cannot run an OBDI/ECM without an O2 sensor if you expect your engine to run at all correctly. Removing the CAT will not effect the running of your truck in any meaningful way. There is a thing previuosly mentioned in this 17-year old post, about wide band O2 sensors, but FWIR those do not work with an OBDI/ECM. In order to turn off the EGR in an OBDI/ECM you have to burn a new chip for the ECM that turns the EGR flag off.

 

[dyeager535]

I have the same truck. Working on sourcing the EGR delete prom. But am considering also deleting the o2 sensor and removing the cats. Think you can point me in the right direction of an o2 sensor simulator?

O2 simulator is retarded. Not picking on you, just the concept. Let it do it's job. Even GM pulled their head out on the Ramjet and installed one at some point. It hurts nothing, and helps mileage and driveability. Don't mess with it. I'm sure someone sells a narrowband O2 simulator, but if you are running injection that used one, run it.

There was only one converter from the factory, if it's the old pancake style I can see removing it, but for $80 or whatever new I'd throw a high flow one from flowtech or whoever on there, so that the exhaust isn't so noxious. A modern cat is another of those "doesn't hurt anything, but helps" deals IMO. Especially if we are talking a K5 where you might be driving around with the rear window down.

 

[ToddMcF2002]

I realize this is old but this is a GREAT topic. I've been fighting my truck since I bought it a few weeks back. Its not a CK5 but a 94 K1500 and it has hooker headers and no Cats.
Partial throttle = nightmare of hesitation particularly once its warmed up in Closed loop.
Idle - sometimes good but erratic in Closed loop and will throw an IAC position error if I'm in traffic.
Full throttle - fantastic, once it clears the bogging and hesitation or the transmission finally downshifts.

So today I disconnected the O2 to confirm it wasn't a fuel delivery problem and took a test drive knowing it would stay in Open loop. BAM perfect behavior. So I saw this line earlier in the thread:

...the O2 sensor doesn't "work" under heavy throttle, so the truck won't run any different with or without O2 in those conditions. Essentially cruise and idle are the only two spots where an O2 comes into play.

And also this:

The biggest reason people have issues with long tube headers and vehicle not running correctly is you moved the O2 sensor about 3 feet back in exhaust from stock. There is a setting/Parameter for this, "INT Vs Airflow" INT is Integrator which is the Short Term Fuel Trim. STFT moves to adjust fuel and depending on how much it moves sets the BLM (Block Learn Mode) also known as Long Term Fuel Trim. So the O2 sensor is reading exhaust at wrong time since it has last made an adjustment. This ends up as a constant fluctuating fuel trims! It's totally confused as to why it goes up and down and up and down.... this setting is in milla seconds/ms.

I think I may be a poster child for these issues. My bung was MOVED to the drivers side header on the collector, So I can either have a chip programmed or revert to OEM headers and Y pipe.

I'd love to hear opinions. This has been a fairly nasty and complicated first introduction to early fuel injection for me coming from carbs.