MAF questions. Hot vs Cold weather

[Jarren_b]

The past few days have been pretty hot here in utah. My IAT's at night have been around 85 degrees or so. Ive been doing tuning during this time to get the most accurate representation of summer heat. Today has been much colder though, it rained the night before and I now have IAT's around 65 degrees.

My car was originally dyno tuned in early spring at a 12.5 AFR and 24ish degrees of timing.

Due to the much hotter weather I have had to add fuel to around a 12.2 AFR and take out 1 degree basically everywhere.

Today while tuning in the colder temperatures, I noticed that my AFR was .3-.5 richer than what it normally is when ambient temperature is say 80-90 degrees.

Is there a way to dial in my MAF so that it can better account for temperature changes? I dont want to be rich in the spring and fall and lean in the summer. I understand the MAF should make changes based on temperature but i was surprised to see that the AFR was still affected as much as it was..

Attached is a log from today and also my current tune.

Im a novice tuner and have yet to make any changes to the MAF. All those adjustments were done by a professional on the dyno so luckily I have a decent place to start.

[schpenxel]

You can use the injector flow rate vs. IAT multiplier to help offset changes from temp changes. There's an EFI Live document (can't find it at the moment) on how to do this but basically you do a cold start and let it just sit there and idle until IAT gets as high as it will go. Use the change in fuel trims as IAT's increase (or WB reading if open loop) to figure out how much to change the flow rate IAT multi. table

By default the table is usually all 1's

Less than 1 makes the ECM think the injectors are smaller, thus higher PW needed --> richer

Greater than 1 makes the ECM think the injectors are larger, thus less PW needed --> leaner

Some of the ZR1, CTS-V and maybe ZL1 files come from the factory with some data in this table that you could probably use as a starting point

[BigMike42]

Sweet, never knew about that table.

I just did some datalogging now and my fueling was about 5% lean at part throttle. So I guess we can either mess with that table, or just go for a little richer target in cold weather.

[JBZ]

You can use the injector flow rate vs. IAT multiplier to help offset changes from temp changes. There's an EFI Live document (can't find it at the moment) on how to do this but basically you do a cold start and let it just sit there and idle until IAT gets as high as it will go. Use the change in fuel trims as IAT's increase (or WB reading if open loop) to figure out how much to change the flow rate IAT multi. table

By default the table is usually all 1's

Less than 1 makes the ECM think the injectors are smaller, thus higher PW needed --> richer

Greater than 1 makes the ECM think the injectors are larger, thus less PW needed --> leaner

Some of the ZR1, CTS-V and maybe ZL1 files come from the factory with some data in this table that you could probably use as a starting point

would you advise changing this table if there are other than stock injectors in there? I have ID850's and I notice the same thing. in the morning im always a hair rich in the afternoon (warmer temps) im a hair lean. plus not that this has anything to do with this...I probably need to add this to my post I started regarding rich after filling up with gas. but if I stop the car and its up to temp then do a restart it always runs richer for a bit, lets say in the -10 LTFT/STFT range.

[schpenxel]

Yeah try to see if you can find a stock ZR1 or CTS-V tune--I'm pretty sure they had some data in this table that you could copy to start with.

I use this table on mine w/ID1000's for the same reason. I kept being OK or a little rich in the morning then lean in the afternoon once it was hotter outside

[JBZ]

Yeah try to see if you can find a stock ZR1 or CTS-V tune--I'm pretty sure they had some data in this table that you could copy to start with.

I use this table on mine w/ID1000's for the same reason. I kept being OK or a little rich in the morning then lean in the afternoon once it was hotter outside

I have a CTS-V wondering of these need to be modified with the bigger then stock injectors

this is my table here

[schpenxel]

Haha, oops. Well, there ya go... here's what mine looks like. Shouldn't be too bad to adjust it a little further as needed on yours

IAT Corr.JPG

[BigMike42]

Haha, oops. Well, there ya go... here's what mine looks like. Shouldn't be too bad to adjust it a little further as needed on yours

IAT Corr.JPG

I gotta check mine to see if they aren't all 1s. This could be the reason my car goes so lean when my IAT is a bit heat soaked. I may just need to set them less than 1 and I should be good.

[Jarren_b]

I love this forum! thanks for all the help schpenxel

[Jarren_b]

Does changing the IAT vs Fuel flow table only make changes at WOT?

My cruising AFR is consistent at 14.7 regardless of temperature. The only time temp seems to affect is at WOT.

If I change that table, will it affect everything? Part throttle, Idle, and WOT?

[schpenxel]

While in closed loop fuel trims are going to keep fueling right around 14.7:1 pretty much no matter what unless something crazy happens.


Open loop / WOT / PE mode is when fuel trims are no longer active so things like this matter more

[Jarren_b]

Awesome. That makes sense!

Ive messed with the table and will be trying it out tomorrow morning once It cools off a bit.

[JBZ]

You can use the injector flow rate vs. IAT multiplier to help offset changes from temp changes. There's an EFI Live document (can't find it at the moment) on how to do this but basically you do a cold start and let it just sit there and idle until IAT gets as high as it will go. Use the change in fuel trims as IAT's increase (or WB reading if open loop) to figure out how much to change the flow rate IAT multi. table

By default the table is usually all 1's

Less than 1 makes the ECM think the injectors are smaller, thus higher PW needed --> richer

Greater than 1 makes the ECM think the injectors are larger, thus less PW needed --> leaner

Some of the ZR1, CTS-V and maybe ZL1 files come from the factory with some data in this table that you could probably use as a starting point

would you mind providing that info? im really curious because I notice that when I restart the car when its hot or as I watch real time logs even though I started logging when it was up to temp it starts to get pretty rich. I have the factory V settings in there but with the ID850s I think im adding to much fuel when IATs get high. wondering too if its using the IAT's in the maf (IAT1 in my case) or the IAT sensor after the supercharger brick (IAT2 in my case).

[schpenxel]

I think this is the IAT compensation stuff I was thinking about. Page 7

http://download.efilive.com/Tutorial...20Tutorial.pdf

[JBZ]

I think this is the IAT compensation stuff I was thinking about. Page 7

http://download.efilive.com/Tutorial...20Tutorial.pdf

awesome thank you. it seems that it may be the case that my heat soaked IATs are putting to much fuel in. that may also explain why I was seeing such a higher number after filling up my tank. is that a normal thing for larger then stock injectors?

these screenshots are from yesterdays drive home. one with normal IATs and one with heat soaked IATs. any thoughts???

[schpenxel]

It's so weird.. I get the opposite on mine. It goes lean when IAT's get high.

If you're trying to counteract it going rich when your IAT goes high then the IAT flow rate multi. table is actually backwards. Or maybe I'm misunderstanding

[JBZ]

It's so weird.. I get the opposite on mine. It goes lean when IAT's get high.

If you're trying to counteract it going rich when your IAT goes high then the IAT flow rate multi. table is actually backwards. Or maybe I'm misunderstanding

yes im trying to counteract it going rich. what I think may be the case (and this is just a guess) is that the injector flow rate modifier vs IAT is dropping to too low of a number and modifying the flow rate to much? I wonder if at factory flow rates and injectors size it works correctly but with the ID850s its too low and putting to much fuel in?

I really don't know what going on all I know is that when I turn the car off and let it sit for even a minute, stop and get gas...even just stop logging and start re-logging when my IATs are getting higher its starts running rich. but I can drive it for an hour without any of the above and my LTFT/STFT's are all good and with in 2%.

this is driving me crazy

[schpenxel]

You're actually doing it backwards.... I think that's the problem, or at least part of it

If you decrease the multiplier value it thinks the injectors are smaller. If they are (theoretically) smaller then they need to be open longer in order get the same amount of fuel out of them... so the computer opens them longer because it thinks they are smaller, which equals in more fuel coming out.

If you increase the multiplier value it thinks the injectors are larger. If they are (theoretically) larger than they need to be open LESS time in order to get the right amount of fuel out of them...

So, I think that's part of the problem.. you very well may be going the wrong direction on this table and are making it richer by going < 1 in the higher IAT areas

My personal car has the opposite problem and goes lean at higher IAT's, so that's why mine is < 1 as IAT goes up

[JBZ]

You're actually doing it backwards.... I think that's the problem, or at least part of it

If you decrease the multiplier value it thinks the injectors are smaller. If they are (theoretically) smaller then they need to be open longer in order get the same amount of fuel out of them... so the computer opens them longer because it thinks they are smaller, which equals in more fuel coming out.

If you increase the multiplier value it thinks the injectors are larger. If they are (theoretically) larger than they need to be open LESS time in order to get the right amount of fuel out of them...

So, I think that's part of the problem.. you very well may be going the wrong direction on this table and are making it richer by going < 1 in the higher IAT areas

My personal car has the opposite problem and goes lean at higher IAT's, so that's why mine is < 1 as IAT goes up

I actually haven't changed anything from stock values yet and I totally agree with what your saying. im guessing that we are both saying the same thing. so for instance in the 140 degree cell instead of it being the factory value of .962 I could change it to .982 (what ever the correct number is I don't know but closer to 1.00) and see what that does. in theory that should inject less fuel in...right? so I can slowly work those values (anything less then 1.00) up closer to 1 until it stops getting rich with heat soaked IAT's. good thing is I have about 6 months of "swamp ass" to get this figured out.

[schpenxel]

I'd just make it 1.00 straight across and see what happens