Is an 02 sensor necessary?

[mca]

Originally Posted by psalt

Constant acceleration ?

My bad. What I meant was constant speed - such as maintaining one's speed at 30mph (constant velocity).

Originally Posted by psalt

asked the same question 20 times on this list and continue to ignore the answers, but that is just my opinion

What question is that? We can take this offline if you like.

[psalt]

Try to answer this: do the Euro SC cars have an O2 sensors? my guess would be they do not - and if not how does the Euro CIS system vary from the US setup? This may help answer your question.

Sal,

The ROW cars do not have a cat or O2 sensor. They use K Basic.

The biggest misunderstanding about the CIS lambda system is that the way they made the mixture trim system work was to make the K Basic parameters all way too lean and use the FV to drive the mixture toward rich. This is why you need the ECU and FV to get anywhere near the correct fuel curve, even with a disabled O2 sensor. This is somewhat counterintuitive, the "default" mode should be too rich, it is if only the O2 sensor fails, but if the ECU fails, the engine still runs, but much too lean.

[javadog]

Originally Posted by psalt

the "default" mode should be too rich

On a car equipped with a cat, this could lead to a significant problem. Run raw fuel through a cat and the temperature can go way up. Melting the cat internals is a possibility and setting things on fire might happen, in an extreme case. Ferrari used to use 2 separate ignition systems on their V8 engines, each responsible for 4 cylinders. Every once in a while, one of these would fail and all the unburned fuel from that half of the engine did really bad things when it got to the cat...

JR

[psalt]

It would be interesting to know if this was a conscious decision. It became a moot point once they went to EFI, the engine won't run without an ECU.

[psalt]

Sal,

Do you know, on a Motronic system, what happens to AFR when you unplug the sensor ?

[T77911S]

Originally Posted by psalt

The biggest misunderstanding about the CIS lambda system is that the way they made the mixture trim system work was to make the K Basic parameters all way too lean and use the FV to drive the mixture toward rich. This is why you need the ECU and FV to get anywhere near the correct fuel curve, even with a disabled O2 sensor. This is somewhat counterintuitive, the "default" mode should be too rich, it is if only the O2 sensor fails, but if the ECU fails, the engine still runs, but much too lean.

maybe i have been under this same misunderstanding. i always thought the open loop mode was rich, to provide richer mixtures in the upper RPM's and the O2 sensor was there to bring the mixture back to a leaner condition for emmissions, drivability and gas mileage. if it works backwords from this, the way you say, how does it not go too lean at WOT?

i think what MCA was saying is that if he changes the idle mixture from say 14.7 to 14.2, that the mixture across the whole RPM range and WOT should go richer by .5 points.
i had done a test of this with an LM@ in the past, but i had a fuel line issue back then, but i think the mixture did follow this, dont hold me to it though. so craig, there is another test you can do when you get the LM2. when i get it i will do this again too.

[mca]

Originally Posted by T77911S

i think what MCA was saying is that if he changes the idle mixture from say 14.7 to 14.2, that the mixture across the whole RPM range and WOT should go richer by .5 points.
i had done a test of this with an LM@ in the past, but i had a fuel line issue back then, but i think the mixture did follow this, dont hold me to it though. so craig, there is another test you can do when you get the LM2. when i get it i will do this again too.

That is exactly what I plan on doing - hooking up LM2 and then recording AFRs at WOT. I've done this in the past in order to make the mixture richer at WOT - earlier dyno runs revealed that I was a bit leaner than I wanted to be.

I'd like to get the WOT mixture set the way I want and then let the idle mixture fall where it may. And then plug the sensor back in so that I'm getting better gas mileage and I'm not washing my cylinders with too much fuel.

[psalt]

maybe i have been under this same misunderstanding. i always thought the open loop mode was rich, to provide richer mixtures in the upper RPM's and the O2 sensor was there to bring the mixture back to a leaner condition for emmissions, drivability and gas mileage. if it works backwords from this, the way you say, how does it not go too lean at WOT?


Open loop mixture with the ECU pulsing the FV at the default(s) is rich. When the ECU, fuse or relay fails, the default mixture is lean because of the blocked FV, allowing no lower chamber pressure bleed off. The engine still runs, evidenced by the countless poor driveability questions. On the EFI car, the engine dies with the ECU.



i think what MCA was saying is that if he changes the idle mixture from say 14.7 to 14.2, that the mixture across the whole RPM range and WOT should go richer by .5 points.

This is incorrect, it is in no way linear.

[mca]

Originally Posted by psalt

This is incorrect, it is in no way linear.

I don't think it was linear as Ty stated. But a richer idle mixture gave me richer WOT mixtures.

On that point ... isn't that how I would ultimately get a richer mixture at WOT?

[T77911S]

Originally Posted by psalt

This is incorrect, it is in no way linear.

here is why i have thought is was linear.

if you are idling at 1000 rpm, the plate is near the bottom of the funnel, at 3k rpm it is somewhere in the middle, point X, and at 6k it as the top, point Y, for this purpose. now when you make it richer, the plate position does not change, only the plunger moves up, allowing for more fuel. so the plate is still at the same position for each of those 3 RPM's, but now wouldnt the plunger be higher in relation to what is was before the mixture was richened? the amount of air has not changed for each RPM above, but the plunger has been raised, no? IE, the plate is still at point X for 3k RPM because the air demand never changes for 3K RPM, but since the mixture screw was turned, the plunger is now higher in the cylinder, making it richer at 3K RPM.

it is a linear relationship between the plate and the plunger, mid RPM leaning and WOT richening is determined by the shape of the funnel. so for each MM the plate goes up, the plunger goes up some fraction of that, but it is constant.

this is one of those i just have to see to believe. i will run another test when i get the LM2, i just wish i had the RPM sensor, but i hope to see the change across the RPM range.

[scarceller]

Originally Posted by psalt

Sal,

Do you know, on a Motronic system, what happens to AFR when you unplug the sensor ?

In a properly running 84-89 car if you unplug the sensor you won't even know it for the most part! The sensor was put in to simply fine tune AFR if it moves off it's target of 14.7AFR

The real reason I don't run with the O2 connected is because the fuel in my area has 10% ethanol and this effects the target of 14.7AFR. Fuels blended with 10% ethanol have a AFR target of about 14.2 to be stoch not 14.7! So if you run these fuels with the O2 connected you are running slightly lean, the system was designed for 100% gasoline not a blended fuel.

Ethanol is not like gasoline, it contains an O2 molecule within the chemical structure which means it sort of has it's own oxygen within the fuel and for this reason we do not need to ingest as much air into the engine. Pure Ethanol has a target AFR in the 9.0AFR range to be stoch.. many folks think WOW that's very rich but the reason it's not is because a portion of the O2 needed during combustion is already in the fuel and for this reason we don't need as much air brought in via the intake. This means that ratio of air to fuel is much lower. Or you can think of it the other way: you need more ethanol than gas for the same air unit. If you think about this for a minute you quickly realize that this also means you can jam much more energy into the same cyl with Ethanol than with gasoline. This is why race engines use it.

So if you are trying to set your base CO or base AFR with a blended fuel you really can't use the stock specs.

[mca]

Originally Posted by scarceller

The real reason I don't run with the O2 connected is because the fuel in my area has 10% ethanol and this effects the target of 14.7AFR. Fuels blended with 10% ethanol have a AFR target of about 14.2 to be stoch not 14.7! So if you run these fuels with the O2 connected you are running slightly lean, the system was designed for 100% gasoline not a blended fuel.

I was reading about this last week while I was getting my sensor hooked up again. Fortunately I have access to E0 and use it 99% of the time. But that is a different story if I travel outside of my area.

So how is your mixture currently set?

[javadog]

Sal,

If you unplug the O2 sensor and the fuel quantity injected is the default amount set in the map, are you not lean anyway, when running the ethanol blend? Wouldn't you need a greater quantity of fuel injected than what is stored in the basic map, because of the lesser energy in the ethanol blend?

JR

[T77911S]

Originally Posted by psalt

Open loop mixture with the ECU pulsing the FV at the default(s) is rich. When the ECU, fuse or relay fails, the default mixture is lean because of the blocked FV, allowing no lower chamber pressure bleed off. The engine still runs, evidenced by the countless poor driveability questions. On the EFI car, the engine dies with the ECU.

.

that makes sense. it would pulse greater than 50% to make it rich once it goes open loop?
can you look at it 2 ways, either the O2 leans out the open loop mode, or the open loop mode richens it for high RPM or higher load demands.(?)
so for those that dont use the O2, the only thing making it run richer for hi load demands is the shape of the funnel, which may not be enough unless it is overly rich at idle. (?)

[scarceller]

Originally Posted by mca

so how is your mixture currently set?

14.2

[scarceller]

Originally Posted by javadog

Sal,

If you unplug the O2 sensor and the fuel quantity injected is the default amount set in the map, are you not lean anyway, when running the ethanol blend? Wouldn't you need a greater quantity of fuel injected than what is stored in the basic map, because of the lesser energy in the ethanol blend?

JR

You can sort of compensate for the ethanol, you can adjust the AFR via the adjustment screw on the AFM at idle. Simply set base mixture at idle to 14.2 and this should help.

But my DME has a chip emulator and the maps are all far from stock. I have re-tuned all my maps to 14.2AFR.

But don't mis-understand me, ethanol has some draw backs like it corrodes and you need to burn more of it. But on the good side is it has a very hi octane 130 RON and when mixed with gasoline it helps further raise the overall octane of the gasoline. This is a good thing as it helps reduce detonation. It also packs slightly more energy into the same cyl volume. I have often thought about how these motors would run on E85? my bet is they would kick ass if properly tuned but you'd need to change all the fuel delivery system because of corrosive nature of ethanol. You also need a much higher flow fuel pump to pump 30-40% more fuel needed into the engine. If I had the money to make these changes it would certainly be a fun project. The tuning part is easy for me but not the $$$$.

[scarceller]

Originally Posted by T77911S

here is why i have thought is was linear.

if you are idling at 1000 rpm, the plate is near the bottom of the funnel, at 3k rpm it is somewhere in the middle, point X, and at 6k it as the top, point Y, for this purpose. now when you make it richer, the plate position does not change, only the plunger moves up, allowing for more fuel. so the plate is still at the same position for each of those 3 RPM's, but now wouldnt the plunger be higher in relation to what is was before the mixture was richened? the amount of air has not changed for each RPM above, but the plunger has been raised, no? IE, the plate is still at point X for 3k RPM because the air demand never changes for 3K RPM, but since the mixture screw was turned, the plunger is now higher in the cylinder, making it richer at 3K RPM.

it is a linear relationship between the plate and the plunger, mid RPM leaning and WOT richening is determined by the shape of the funnel. so for each MM the plate goes up, the plunger goes up some fraction of that, but it is constant.

this is one of those i just have to see to believe. i will run another test when i get the LM2, i just wish i had the RPM sensor, but i hope to see the change across the RPM range.

I tend to agree, if you move the plunger 2mm up at 1000RPMs it will also be 2mm up at 5000RPMs. My bet is it will have a large effect on AFR not only at idle but also at WOT. Easy enough to prove with a WBO2. I had this same exact debate on the motronic AirFlowMeter. In the the AFM you can adjust move the wiper arm slight up further on the track (not the spring tension). If you move it up 1mm you just enriched mixture across all RPMs. I proved this by testing the theory on my car with my WBO2.

[psalt]

-that makes sense. it would pulse greater than 50% to make it rich once it goes open loop?

Yes, the default setting is above 50% in open loop.

-can you look at it 2 ways, either the O2 leans out the open loop mode, or the open loop mode richens it for high RPM or higher load demands.(?)

No, the O2 sensor is ignored and does nothing in open loop mode.
Open loop mixture is determined by the FV duty cycle and the basic mixture setting. When you set the idle duty cycle in closed loop, you are only really effecting the open loop mixture. Idle and cruise are corrected in closed loop. In closed loop, higher duty cycle mean a lean basic mixture.

-so for those that dont use the O2, the only thing making it run richer for hi load demands is the shape of the funnel, which may not be enough unless it is overly rich at idle. (?)

This is only true when the ECU and FV are not working properly.

[psalt]

-I have often thought about how these motors would run on E85? my bet is they would kick ass if properly tuned but you'd need to change all the fuel delivery system because of corrosive nature of ethanol. You also need a much higher flow fuel pump to pump 30-40% more fuel needed into the engine. If I had the money to make these changes it would certainly be a fun project. The tuning part is easy for me but not the $$$$.

There are several high output 911 turbos running E85. They are EFI, not CIS, and you need to upsize the injectors and pump around 40% . Alcohol has many advantages for a knock prone hemi head with poor cooling. The highest specific output racing hemis all ran on alcohol, some with benezine, nitro, castor oil and water thrown in. Supplemental direct injection ethanol in a gasoline fueled turbo engine allows a much higher compression ratio and boost then thought possible.

All very interesting, as aftermarket devices that can detect the percentage of alcohol in the fuel on the fly and tell the ECU to adjust pulsewidth accordingly are now on the market. My next project.....

[Sunriseinla]

Sal,

A switching O2 sensor in closed loop control will always give you stoich conditions. For 100% gas that would be a AFR of 14.7 and for E10 that would be AFR of 14.2.

If I take a 3.2 with factory chip meant for 100% gas it will run 3% lean in open loop with E10. The closed loop control will richen the mixture by 3%. If you have changed the calibration to compensate for E10. You can connect the O2 sensor and it will fine tune for the correct AFR of 14.2.

Cheers
Mark