Even though the computer and the O2 sensor are supposed to compensate for the cooler air, the AF ratio is leaner today than when it was warmer outside. The air box does draw air from the outside. So there are several questions:

1. Why does the fueling formula not compensate adequately for the denser air?
2. Is there a feature I need to tune to get this working better in this regard? I would say it ran from .5 to 1 full point leaner. There was preignition at 3K under light throttle for the first time tonight. Thanks for the thoughts on this.


I am wondering if I should engineer a cross over tube to get air from closer to the engine when the outside air is cool. Maybe something just as simple as a cap to put over the outside pick up, and adding an inside pickup with a cap to remove in the winter. Of course it would be neat to make it automatic as the OEM set ups are, but maybe a manual deal would be a good beta test.
Sam

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Don't you have an inlet air temperature (IAT) sensor?

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Joshua

Yes, all sensors are in place. I will monitor the feed back and see if it looks right. I did not have my laptop with me.

Thanks, Sam

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Where is the sensor located? Is it being warmed by radiant heat by any chance?

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Joshua

I have found that the IAT on my MSI has never been adequate to enrich/lean the mixture with varying outside temperature for my engines. I think rescaling the enrichment curve is needed, but I've never bothered to do it. On MSI, you need to find the IAT transfer ("easytherm"??) table and rewrite it. On later MS, I seem to recall it is easier, but I don't know.

Also, the smaller (8X8) table in MSI means there are some "non smooth" parts of the table (big jumps between MAP cells), which becomes a problem when air density changes a lot. This should be fixed by later MS versions as well, just by having a smoother table.

I have just built some extra fuel into my table to avoid pinging and have fiddled with the table some when changing seasons or altitudes. I hope I can get rid of this when I got to MSIII. WB fuel feedback should compensate for this. In your case, and in colder temps, I'm not sure why this does not do it for you.

Lou

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Home of Slant6-powered fun machines

I have the wide band feed beck set at two steps. Maybe making this number bigger would help. I know if it is too big you can get into a lean/rich cycle.
O
I wonder if increasing the reqfuel by a tenth or two would correct the ratio.

Is the table you mention code that is not visible from the tuning screen, or should I be able to find it in the tuning program?

Sam

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No, the therm table is not visible from any MSI tuning screen. That is why I have never changed it (lazy).

I bet the reqfuel change would help. Yes, you could also do faster feedback on the WB. I would try the latter first.

Lou

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Home of Slant6-powered fun machines

Why don't you just heat up the air?

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Guess what guys? I discovered that after the last auto tune I forgot to turn the O2 sensor back on. Silly Me. I suspected that was the case when I drove to the most recent cruise on Sunday and the AF ratio was really unstable. I turned it back on tonight, and increased the controller step from 2 to 3. We will see what that does.If increasing it generates some kind of instability by over shooting, I will turn it back down. The default was 2 steps, whatever that means, and 15% correction limit.

I am driving it on my tuning jobs tomorrow. It is supposed to be a nice day, and the last one with no rain for awhile. I have not taken it to work since I went to work on a schedule that has me in rush hour traffic. Things get really crazy around here. Two weeks ago I was going out the door of the Steinway store and watched as a kid in a Honda just ran right into the rear of a minivan at a light. I am pretty sure he was texting at the time. I do not take the Dart into that kind of traffic any longer.

Thanks for the replies.

Sam

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