What kind of intake temp changes are we talking about?

- Bryan

 

Not understanding how the air temps are affecting afrs I thought the ecu made changes for outside temps? What temps are we talking about? Right now I am doing my tunes at night here in north texas with temps around 85-90F. I have yet to log during daylight so Im not sure.

 

I don't think it is so much AFR changes more so than boost profile changing from day to night... I know I loose about 2 PSI in the beat down daytime heat vs night... and I know that everything gets heat soaked way quicker... duh...

 

I've had this same issue, but since no one ever brought it up, I had been wondering whether it was something funny about my setup. My AFRs will go north of 13:1 in the winter. I suspect its due to the relatively high heat of vaporization of ethanol causing progressively more poor fuel atomization as the air temps get lower and lower. Unfortunately, there is no good table to deal with it. The global air temperature compensation table affects both load and IPW, so its no good, and the Airflow/Hz table keys off of air density which is affected by both air temperature and baro, so its no good either. We need an additional table to compensate for it.

 

87 vs 93 in airtemps logged. 87 during the day and 93 at night.
could it be the humidity causing it? i had a coupler come loose
tonight doing a pull also if that gives any insight possibly to the
problem. this was at the jpipe tho of turbo

 

it will be significantly richer during the day for sure. I dont think the stock ecu is very smart when it comes to this type of control.

 

ya we need a table. all the standalone ecu's have compensation for this type of thing.

 

Is this only on E85 or does it do this as well on pump? I just might tune at night closer to 12.5 then if it goes rich in the daytime it wont be too rich. Either that or run a different map for summer and another for the cooler months.

 

Sorry guys, i have been out of town, in the studio recording our new album. I just haven't had the time to get on here.

This is a E85 issue for sure. There just isn't the compensation tables needed to deal with this issue. MrFred's theory seems to be the most logical. E85's poor fuel atomization at lower temps.

To the people that say 12.5:1(gas AFR) on E85 is too lean, i don't believe this to be correct. It's on the upper range of safe lean and going leaner won't necessarily make more power, but i don't think it's too lean at all.

Anything richer than 11.5:1(Gas AFR) on my car and i get misfires and sometimes lots of knock. With everything i've seen, 12.1:1 seems perfect, but with the swing in AFRs with IAT temps changes, it will be hard to hold 12.1:1 all day.

Everybody has to understand, that E85's EGTs will typically be 200c cooler than gasoline. This allows the engine to run much leaner without sustaining damage that would normally be seen with gasoline from running too lean. E85 will simply start breaking up when run too lean. I could be wrong, but has anybody seen melted pistons from running too lean on E85? I can't get my engine to detonate at all on E85, no matter how lean i run it. I've gone as high as 13.5:1 just to see.

My theory is this: E85 runs much cooler, while still producing a high exhaust gas volume and velocity. You have to run E85 super lean to even match gasoline EGTs. These EGTs are known to be very safe. Therefore, we know these EGTs have a very low risk of melting anything. If you go too lean, E85 just starts to break-up, yet still not allowing detonation or melting of parts(once the break-ups start, EGTs start going lower). I think it's as simple as E85 not having the ability to reach EGTs high enough to cause significant damage. This would help explain why E85 has such a high detonation threshold.

I'm not saying to run super lean, but these are my thoughts on the matter. My testing seems to prove my theory, at least a little bit. I would need to do some more testing with good instruments to be sure. So, this is just my theory, take it with a grain of salt.

 

I can second mrfred's findings as well. I was doing most of my E85 tuning during the winter and had my AFRs around 12-12.5, where I like them, but as the season's changed, the AFRs are now at least 1 full point, even sometimes near 2 points richer.

I have always believed it to be atomization issues with E85 at colder temps, as is evident in a lot of the cold starting and running issues as well.

 

i suspect the winter blend of E70 has something to do with it as well. i would like to hear from someone say in socal near the beach where the temps vary maybe 30 degrees all year. i can understand how the cold would affrect afr but not how say 70-90 would given same boost levels.

 

Winter blend to summer blend would have the opposite effect. More ethanol content in the summer would have a leaning out effect on the same tune.

 

I can expand on this a bit further. My filling station using the same E85 blend year-round (verified with my ECA), and if I don't retune in the winter, I'll see 13:1 or leaner and lots of breakup. Typical winter weather is 30-40F. Typical fall day when I might tune would be around 70-80F.

 

I just made 2 maps for now. one for daytime and one for night. Not really a big deal. I keep both maps around 11.8-12.1. I dont misfire or knock at 10.8-11.3 but i wont be running it that rich anymore, since it does lose power.

 

in some recent nights messing around with different afr i have noticed that my car too feels much better during spoolup at 13.5 than it does at 12.8 anf its feels terrible at less than 12.5. during wot it likes 12.1 better than high 11s as well.