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Closed loop O2 sensor considerations.
https://slantsix.org/forum/viewtopic.php?t=46607		 Page 1 of 2
Author:  Sam Powell [ Mon Oct 10, 2011 7:50 am ]
Post subject:  Closed loop O2 sensor considerations.
In all the advice from the manual, they say to limit the range of the feed back to above idle, and below 90 KPA, but all the logic they state seems to apply to narrow band sensors. It seems as if a wide band sensor would work at idle, and in the higher KPA ranges (and below idle for that matter). Is there experience out there with using the wide band at idle? It seems like this would solve the hot start/heat soak lean condition. I have not employed feed back at all yet, but think I am close enough with fuel tuning to at least drive with the feedback now employed.

Sam
Author:  Matt Cramer [ Mon Oct 10, 2011 8:09 am ]
Post subject:  Re: Closed looop O2 sensor considerations.
Quote:
In all the advice from the manual, they say to limit the range of the feed back to above idle, and below 90 KPA, but all the logic they state seems to apply to narrow band sensors. It seems as if a wide band sensor would work at idle, and in the higher KPA ranges (and below idle for that matter). Is there experience out there with using the wide band at idle? It seems like this would solve the hot start/heat soak lean condition. I have not employed feed back at all yet, but think I am close enough with fuel tuning to at least drive with the feedback now employed.

Sam
On bank fire setups, you're best off tuning the idle by feel and not to a specific AFR.

The only problem with the wideband at full throttle is that having the sensor fail and pull things lean is a much more dangerous problem up there.
Author:  Sam Powell [ Mon Oct 10, 2011 8:47 am ]
Post subject: 
But once you have the "feel" for the AFR your engine likes, why can you not use that as the target for the wide band? I know it hates 17:1, which is where it wants to go for the first minute after a hot start up.

Thanks for the tip on the high KPA considerations.

Sam
Author:  Matt Cramer [ Mon Oct 10, 2011 12:49 pm ]
Post subject: 
You could use that AFR if you wanted; I wouldn't bother, myself.
Author:  Sam Powell [ Mon Oct 10, 2011 3:43 pm ]
Post subject: 
I'll try it and see if it works. If not, I know how to go back to where it was. And, I will let the group know my experience.

Sam
Author:  Sam Powell [ Sun Oct 16, 2011 4:18 pm ]
Post subject: 
Here is an observation I have made of the engine's behavior at idle. After the engine gets out of warm up enrichment, there are still changes that take place in the AF ratio as you drive. When it first gets out of warm up enrichment, it will idle at 14:1. The longer you drive it, the richer the AF ratio at idle gets, even though the the injector opening time remains the same,(1.6 ms) and the ECT temp remains the same, (205). So something is effecting AF ratio besides coolant temp, and fueling amount. After 20 minutes or so, the idle AF ratio gets to 12.5, even though the injector opening is still 1.6. By now I am believing the O2 sensor feedback because at cruise AF ratios stayed right at 14.5:1-15:1 , regardless of how long I drove it in open loop. This was after my sessions of auto tune, and the map had time to be tweaked. I am sorry, I did not think to check the IAT temp. I can do that next time I take it out to cruise.


So, I drove the car about 60 miles yesterday, 30 with autotune on, and than back with auto tune turned off and closed loop enabled by 15%. I was impressed by how closely it followed the specified AF ratio. After I got home, the idle AF ratio had climbed to 12.5:1 so I made the feedback active above 800 RPM. As I expected the AF ratio went back to the 13.8 to 14:1 at idle it exhibited when first out of warm up enrichment. It seemed to idle fine that way.

I did not drive it at all after that, but it seems as if it is going to work OK to be in closed loop at idle. Unless the warm-up drivability gets wanky, or the idle gets really unstable for some reason with the idle controlled in closed loop, I will leave it that way for now. The goal is to have the idle AF ratio be more consistent across the temperature ranges of the engine after it is officially "warm".

I suspect that this change in AF ratio as you drive it has something to do with the temp of the intake manifold, or the difference between the temp of the intercooler, and the temp of the intake manifold.

Any thoughts on this? Are there any thoughts about what settings to use in the parameters for O2 activity? I used the default except I changed the ignition cycles per step to 14 from 16. I was thinking maybe I could make it respond just a bit faster. I know if you make it respond too fast, it gets unstable, and can get into a hunt cycle up and down. However, wide band is supposed to be less susceptible to that.

Sam
Author:  Matt Cramer [ Mon Oct 17, 2011 8:15 am ]
Post subject: 
It would help me if you could get a data log of the behavior and a copy of your current tune - that way I could compare what's changed between the rich and lean idle.
Author:  Joshie225 [ Mon Oct 17, 2011 8:49 am ]
Post subject: 
If the fuel stays the same and the mixture ratio goes richer then there is less air density in the cylinder. It's almost certainly the hot intake manifold and/or intake plumbing. When I ran an unheated Clifford manifold with a carburetor it took a very long time for the manifold to get hot. I would expect that having the inlet air temperature sensor in the manifold would help the situation so long as the temperature correction factor is correct. If it really does try to idle at 17:1 after a hot restart I think the sensor is too hot or the correction factor is off causing it to pull out too much fuel.

Increasing the number of ignition cycles will slow the response as the engine has to complete those extra cycles before the next step.
Author:  Sam Powell [ Mon Oct 17, 2011 2:10 pm ]
Post subject: 
Quote:
It would help me if you could get a data log of the behavior and a copy of your current tune - that way I could compare what's changed between the rich and lean idle.
I'll try to get those to you.
Sam
Author:  Sam Powell [ Tue Oct 18, 2011 4:41 am ]
Post subject: 
Joshua, Thanks for your insights there. I believe you are right about that. I read your post while at work, and could not really think about it, or reply right then. So if the variations in AF ratio, ( if they are real and not an aberration of the O2 sensor), are caused by differences in the temp of the intake manifold over time, then the question is how can this best be minimized?

And I now think that the lean mix at hot start up is because the ECT is at the hottest location in the head, right behind the thermostat, and the intake manifold, and TB have cooled down, thus creating the denser air charge at intake.

Here is the irony. The TB and the intake manifold both have provisions for heating them with cooling system liquid. The TB has an inlet and outlet of about 1/4" diameter, and the manifold is an Offenhauser unit with 2 ports at both ends, one each on the outboard edge, and from below. Unfortunately, I did not realize the import of these when assembling things, and left them all just open to air, and unplugged. This means the front one is sitting over the Dutra Duals flange, and I could not get a plug in it without removing the manifold and the turbo. If you think this is a good idea, I can plan on doing it one of these days.

Would getting these plumbed in help keep the intake air a steady temp? There would still be a warm up process, but maybe the water would help maintain the temp for the five minutes between shut down and hot start up.

And, what is the best way to plum both of these? Could I put a branch in one of the heating hoses? And if so, which side is the hot side, the top or bottom? I think that is answered in my FSM. In any event, it seems as if this would not have much flow unless the heater were being used. True or not? I wonder how the GM TB was plumbed. I wondered at the time what those ports were for. Now I want to get them plumbed up.

Drivability is the most important issue as far as I am concerned. This is not a race car. I want to take it places, and be relaxed while driving it.

Sam
Author:  Joshie225 [ Tue Oct 18, 2011 9:51 am ]
Post subject: 
Sam,

You don't need to heat your intake manifold or throttle body. The throttle body only has heat provisions to prevent icing in extreme conditions. The manifold heat is for a carburetor or throttle body injection where liquid fuel hits the manifold floor, but you have port injection. I would not add more heat.

I don't think the intake manifold is cooling off enough to cause such an increase in air density that your idle mixture goes to 17:1. I think chances are good that the coolant temperature mixture correction is off. It's also possible that the inlet air temperature sensor is either in the wrong place making the sensor too hot or that the air temp correction is off.
Author:  Sam Powell [ Tue Oct 18, 2011 10:37 am ]
Post subject: 
The IAT sensor used to be right before the TB, and it behaved, if possible, worse. It was recommended I move it to right after the IC, which I did. I think maybe it got better, but it has been a few months since I made this change. The goal was to keep the sensor from getting heat soaked.

How to I change the air temp correction? I am not aware of where this is in the tuning software, or how changing it would effect things. I am happy to try different settings and testing things out.

I currently have a rheostat wired into the IAT temp sensor circuit so I can fool the ECU into thinking the engine is cooler when needed. The problem with this band aid is that it easy to forget to turn it back after things get warmed up. This takes only a few minutes. Since the AF ratio gauge is right there on the dash, it gets my attention.

Sam
Author:  Joshie225 [ Tue Oct 18, 2011 11:25 am ]
Post subject: 
Sam,

It looks like plenty of people have problems with the high temperature manifold air temperature (MAT) corrections. Check out this post in particular, but read through the thread too. http://www.msextra.com/forums/viewtopic ... 60#p269863
Author:  Sam Powell [ Tue Oct 18, 2011 3:51 pm ]
Post subject: 
Thanks for the links Joshua. I need a little clarification, in part because I used to have the Accel ECU, which had a separate IAT sensor and MAT sensor. Right now my MSII has only an IAT temp sensor. Do some MS setups have an MAT sensor as well? Or are they using the term MAT interchangeably with IAT?

That thread raised more questions, but I will keep the questions simple, and linear for now. Thanks again.

Sam
Author:  Joshie225 [ Tue Oct 18, 2011 9:00 pm ]
Post subject: 
The terms IAT and MAT I believe are used interchangeably. The air in the inlet/manifold is what the engine is ingesting. The air density is being derived from manifold air pressure and air temperature.
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