Lawone

Good afternoon,

I'm wondering if someone can shed some light or help me understand how IAT correction works and how much fuel it add or removes.

My target AFR for WOT boost is 11.2. It has been tuned to 10.9 / 11.0 which it has been hitting pretty much spot on. But last night the temperature dropped and I was seeing 11.6 11.8 in WOT boost. I added 8 points of fuel to the VE table to bring it back down.

This gets very annoying when you have the season changes.

Am I right in saying that the next step is to adjust the IAT correction values to counter the colder dense air when you hit the winter periods without a re-tune.

Here are my current values.



Reverant has advise to change the values over 25c to 100 - correction. Which I will try. But It be great to also know what other people have done.

Thanks for your help in advance.

Braineack

iTrader: (62)

that should be one of the last tables you tune.

I dont see that table affecting your tune like youre suggesting; look at your logs and look at the gair and total corrections.

Lawone

As you mentioned It not effect my tune if at all.

But what I'm asking or need help with is..

I'm leaning out to around 11.8 in WOT boost due to temperature change (got colder so need more fuel). So rather than me keep doing a re-tune depending on the seasons.

Would I add a higher correction value for lets say 15c to take into account the colder weather and more dense air hence the requirement for more fuel.

elior77

Set it to add 2.5% for every 10C change, hot air will get negative correction and cold air will see positive correction.

Lawone

So currently it's
-40 = 125.7
-20 = 115.8
0 = 107.3
15 = 101.7
30 = 99.8
45 = 98.0
60 = 98.0
90 = 97.0
120 = 97.0



Re-scale to the below.

0 = 105.0
15 = 102.5
25 = 100
35 = 97.5
45 = 95.0
55 = 92.5
65 = 90.0
85 = 87.5
120 = 85.0


I'm guessing from a tuning point of view. You would set it all to 100, get your dyno/tune done.

Then change the IAT corrections. Which would need slight adjustment during cold / hot period to get it correct.

elior77

100% is the temp the fuel map was tuned at, you can set the corr before tuning and just forget about it.

Braineack

iTrader: (62)

Why in the world would you want a map like that? If you were worried about being lean now...


Make it 100% across.

Lawone

Conflicting info here. ��

Im new to this side of things.

Braineack, I'm a little confused. Are you saying make all correction values 100% then tune, and then adjust IAT correction table to suit weather conditions. Using 10c jumps? And a little bit of trial and error throughout winter and summer to get fueling spot on come whatever the tempertures.

elior77

Set it and then tune the ve table

deezums

iTrader: (3)

I had to return to true "ideal gas law" after I fixed my signal ground issue. I was running straight 100%, but that's clearly wrong now. Makes me feel better, since the density half of speed density is working like it should again.

You have a 1.6 car right? Unplug your megasquirt and measure to see if either wire of the IAT sensor is connected to the engine ground. If it is, look for the black/green wire on a ring terminal with a black wire back by the CAS and cut it. When you measure again, there should be no connection.

Lawone

I'm a little confused to why I would have to cut a wire? my IAT is working correctly and as it should. What impact does it have having the IAT wired to a engine ground?

My IAT sensor is wired using the OEM loam that was originally used for the MAF. But I cut the block off and ran the correct wire to the IAT sensor.

deezums

iTrader: (3)

Because it mucks up the entire megasquirt, it's a voltage offset issue except it's not a linear or consistent offset. It apparently interferes with the rest of the inputs, that's my only explanation for it.

Your megasquirt needs clean ground signals for all the input sensors, MAP, IAT, TPS, etc.. If these sensor grounds get tied to the engine block it will cause inconsistent readings, if your traces aren't noise free in megasquirt this would be why. All the sensors need to share a common ground as a reference point. If you ground any of them to the engine it will cause interference, basically.

For some reason Mazda decided to create a signal ground circuit for the ECU sensors, but they tied it to the head compromising the signal ground inside your megasquirt now. The wire I told you to cut is where they grounded it on the block. If you ever wanted to go back to stock, just crimp a new ring terminal on it and reattach.

DNMakinson

iTrader: (3)

MT.net: is there any consensus on this? Since the MS people themselves have pulled the IGL out of the background, I'm thinking running MAT corrections nearer to flat than IGL is not a Miata specific occurance.

deezums: how close to IGL are your MAT corrections? Post an image?

deezums

iTrader: (3)

I run the last version of MS2e that allows you to directly modify the IAT correction table. AFAIK 3.3.3 or whatever it is moves the entire table behind a single percentage modifier. The table is still there, you just can't edit it fully any longer.

Here's my table, should be stock AFAIK.

18psi

iTrader: (76)

My experience is nothing like deezums and I would completely disagree with running that table. I've tried it, it sucked really bad. mine is almost flat, with like 10% variation between the two extremes. (105-95ish)

but if it works for deezums, well. I dunno. I doesn't work for me

(for what it's worth, I usually tune NB's and ms3+. But the last car I tuned was a 93 running mspnp2 and I still had to run the corrections like I said or it would just flood the car when cold and starve it when hot)

18psi

iTrader: (76)

yep

DNMakinson

iTrader: (3)

That is my thought. I'm not sure I'm even 10% total. Deezums, if that is working for you, I think you have found the holy grail of MAT sensor position.

The 1.6 ground thing, I know nothing about.

18psi

iTrader: (76)

or he's running car with some weird issue that most of us never saw before

deezums

iTrader: (3)

I have forever been chasing correct IAT correction, if I had it right for cruise it would be lean at idle. If I had it right for idle, which was the 100% everyone wants to run, it would be rich going down the highway till ego brought it back. Think being stuck in stop and go highway traffic. I even bought a MAF sensor planning to circumvent the mass thing entirely, I was that fed up with it.

It's much more linear now, and while it might need fudged at the extremes still as I've only seen so much variance in temp so far all I know is I don't start surging or going lean when the radiator fans kick on while I'm sitting idling, I like that. I also have much less ego correction on hills and stuff slowly passing through different load cells. My only problem now is that flow force injectors squirt dust at 1.6ms, I need that to run 15.5 at low load like 30 kpa. Riiight on the overrun, just enough to hold 75mph smoothly rolling down a hill. Works alright on cold days, works for **** on hot days. I just need to turn the base pressure down and retune....

Anyway, as easy as it is to check the signal ground circuit everyone should be doing it. It will cause RPM or load dependent noise into the megasquirt, and I know all 1.6 cars have this little wire as it's on all the wiring diagrams. I wouldn't be surprised to find it on newer cars too.

DNMakinson

iTrader: (3)

Deezums, I have been thinking about both those subjects for a while: the fact that having the temp sensor before the throttle give an untrue reading of the charge temp, as the throttling reduces temperature of the charge. I think the VE table inherently includes some accommodation for that. I am using a lot of EGO at idle which may be hiding temp. However, I tune for temp compensation at cruise, and still look flat. Car is not running ATM so I can't play.

I am also rebuilding parts of the harness right now and was wondering if there might be redundant sensor grounds. I can say that, when the car was running, I didn't notice any weird stuff like you reference, except Innovate LC-2 offset, but that is a known, separate issue.