IAT affecting AFR more than CLT?
 

Hey guys, me again :noob:

So i've been trying to tune my car lately, and i'm moving along fairly well, however i've noticed that when it's cold, everything is significantly leaner.

I'm somewhat familiar with the warmup enrichments, but those are based on the CLT not IAT.

I may be wrong here, but to me it feels like even if the car is warm but the temp is still cold outside, then my AFRs are like half or 1 point higher..

Also, i see the car's in "WARMUP" until it hits 160, but then if i'm driving around and the CLT drops back down to 150 or 145, then the warmup enrichment doesn't come back.

Is this normal? Should i be looking for IAT enrichment somewhere??

-Tomaj

clt-based air density corrections table.

IAT - You temperature sensor calibrations are off.

CLT - Your CLT should never drop down below 160 while the car is running once you are over 160. Seriously the thing should run 195+ since the factory thermostat is 195.

A. your thermostat is stuck open
B. your temp sensor calibrations are off


Where did you get your firmware from? I suggest searching for EasyTherm.

We gotta get mine fixed first .... one of these nice spring days.

i got my firmware from scott pre-installed, he said it's hires 10g.

Hey Scott -- did you load a firmware on there that's expecting the GM IAT signal already?

-Tomaj

I read this thread:
MX-5 Miata Forum - 160 degree thermostat?

It looks like a fairly popular mod a while back was to add 160degree thermostats to the miata... Are they marked as such? How could i tell what i have?

-Tomaj

At the point where you could tell if there are markings you might as well just change it anyway.

yeah.. i checked the the m.net garage article, looks pretty easy.. not too expensive too online but i'll stop in at a local parts store 1st to see if they have it.

So assuming i change out to a 195* thermostat, that won't really change my other issue, which is that the car seems (to me at least) to run leaner when air is colder vs when it's warmer..

IOW the car could be hanging out at a toasty 195 CLT, but if it's 90 degrees out, then my tune made at 50 degrees will be worthless no?

Feel free to tell me i'm wrong and i'm imagining things. I mean is htis something everyone sees and knows about, or am i just wrong??

Not worthless, but you may have to adjust your engine start-up settings (cranking pulse widths, ASE, etc.) .... life gets more interesting when you have to tune the settings for cold winter weather.

You also need to understand that MS will never be a "set it and forget it" system. You'll continuously be driving along, minding your own business, when you happen to hit a cell in the VE table that you hadn't hit before. So do not over-react when you see a minor decrease or increase in AFR. It's not a big deal as long as your tune is in the ballpark. You'll need to re-tune (or at least tweak) with every changing season and every performance modification. In theory, once your car's mods are complete (if there is such a thing) for a full 12-month cycle, then your tuning will be done too. Unless the next summer is hotter than the previous one, or the next winter is colder ....

I find it very unlikely that your actual CLT is under 160F while driving unless its down in the teens and you have an oversized radiator. Drive the thing down here and we can go over it, comparing it to how my MS reads your temps.

If your calibrations are correct you shouldn't have this issue. As air temp changes the MS adjusts fuel because air density changes, ie amount of oxygen. If your calibrations are correct you should maintain the same AFR regardless of IAT. If they are off you will experience exactly what you are seeing.

Here is what MS (or any ecu) does:

MS applies X fuel according to your RPM and MAP from your VE table and varies it according to IAT. As IAT increases fuel decreases because the engine is getting less dense air(less O2). As IAT decreases fuel increases because the engine is getting more O2. When functioning properly this maintains AFR.

Are you running standalone or parallel? Send me your car folder.

Even then you won't likely see it. I have a 52mm Koyo and started tuning my car when it was 0*F last month. Even then it would run at thermostat (192*F) temps. Never lower. Surprisingly, it gets up to full temp in one mile of driving 40 mph even at 0*F with that rad. I was worried about that initally.

I should have been clearer, I meant EVEN IF he has a 160 t-stat like he posted previously.

do you clt and ait temps looks correct and match in the morning?

I just checked outside, car wasn't driven all day.

Megatune says 36/37 for both CLT and AIT, various weather sites say 44 degrees.

Paul, i think i have your e-mail address i'll send the car folder & msq.

-Tomaj

I had a few minutes today so i took off the cross over tube (not the right name, i'm sure). I decided to install the IAT sensor on the RIGHT side of the car, if you're looking at the engine bay from the front back.

In this position, it's nearer the turbo than the intake manifold, BUT i did it this way because my coolant hose is actually touching the crossover tube on the other side, maybe one or two inches away from where i'd have to put the bung, so i figured this may reduce heatsoak issues.

I drilled the hole with ever-increasing sized drill bits until i got to my largest :) At first i was thinking that maybe i could thread the sensor directly into the pipe but decided against that for two reasons.. 1 the metal is thin, probably wouldn't be wise :) Also, my largest drill bit wasn't near large enough.

I went to autozone, bought some "jb stick".. i mixed up bit and mounted the bung supplied in the kit and pushed the JB all around, made it look all nice like. It seems to be hardening up, i'll probably shoot the whole ting with some hi-temp black to make it match the rest of the pipe.

So now the next question.. Are there any tricks to wiring this up? As per Paul it seems that my Megasquirt is already waiting for the GM IAT signal which is causing my screwy temp readings, so do i just wire it in? do i have to somehow disable the stock temp sensor? Once this is done - can i just remove the flapper?

-Tomaj

Just cut the wire in the parallel harness(between the db37 connector and the big yellow one) and connect the sensor to the correct side. Other lead from sensor goes to ground.

I think you have to jump something so the fuel pump runs if you remove the AFM. Sorry, not a one six guy.

Hey Paul,

I've already jumped the FP. For the non "MSPNP" (not sure if this is the only criteria) you need to do that as a part of the install..

I will give it a shot on the next nice day..

FWIW my JB-WELD didn't hold... i waited around 3 hours before trying to screw in the iat so i could drive the car even w/o it wired up... the whole weld / bung just came off in my hands once i applied some decent pressure.

I tried again using less material, scored up the metal a little more, and made a little jb-weld circle and pressed the bung directly onto that , maybe that will help..

-Tomaj

FWIW I have installed 7 IAT sensors by just tapping the aluminum/steel IC piping and have had no problems with one leaking or coming loose. Of course I used the correct tap, 3/8 NPT.

Hey, i followed your advice and tapped it (thanks for the tool SamL01). I threaded the sucker in, ran the wire thru the firewall.. I'm about to do the wiring into the MS harness... i'm still not sure how to do it, and i left my netbook at work so i can't see whether i did it right.

OK update... I was trying to find a FAQ on wiring the IAT and i remembered Scott (braineack) sent me a word document with some instructions.

I ended up doing it hte way he indicated, which was to simply remove the harnessfrom the MAF and stick the two wires into the 1st and 6th holes on the female side.

Is that OK?? I drove the car, it started right up and everything seemed to work ok..

-Tomaj

OK if you burn the correct easytherm values in your firmware

Paul, you had looked at my files, I thought you said that it seemed I was already running the GM IAT easytherm values.. Or am i running some crazy numbers that don't correspond to anything? :giggle:

While they may be the correct curve for a GM sensor you still have to have the correct bias resistor value. I'll have to look at it again and at the email from Scott concerning your build. Or he could just post it here.....

Hey paul, sorry to keep harassing you but I'd really be grateful if u could take a look at my setup. The iat's installed and hte car runs OK, but based on all your comments earlier, i am not sure it's configured corrrectly.

My CLT still hovers at around 160, often below.. U guys had said that the stock thermostat is set for 190.. i read around and saw that hte '160 thermostat' was a popular tweak 10 years back, so maybe the prev. owner had done this?

1. i'm drunk
2. did scott built your ms?(answer = potentially worse than me being drunk)[please dont ban me scott[]
3. paralllel or standalone?
4. is iat hooked up directly to ms or through afm harness

I'm working :facepalm:

Yes.

parallel

Through AFM harness.

Thanks for the reply!

ctxspy, did you copy these (see below) three .inc files into your project folder's mtcfg folder?

Index of /MS/msq/Therm Files/16L_piggy

I just put them into the mtcfg folder now. I didnt have the files in there until i just put them in, thuogh it looks like i had them in the 'src' folder.

Do i have to do something with this? burn it to the MS? OK so i did some reading.. i'm still not sure if i have to burn a new firmware or what :(.. From what i read, you need to send these values to the MS, but the actual .inc files are for megatune itself.

If the MS was OK but MT was misconfigured, then i would still be seeing correct AFRs regardless of temp right?, only the temps that show up on megatune would be off... In short, i think maybe i need to burn htese sensor settings to the MS.

Scott, do you have a copy of the firmware i need to load to the MS? Also, i keep readnig about the 'bias resistor value'. You use the DIY default? (2490 ohms?)

-Tomaj

that's it. now your laptop should be seeing what the MS is actually seeing.

unless you happened to reflash it with different values.

OK i'll give it a shot on the way home today, but i'm still confused because of my car's symptoms..

I may be crazy but i would swear that the car runs leaner when it's hot, significantly so... Wouldn't that be aan effect of the air / temp factors being set for a different sensor? Is there any way to verify what is currently on the MS, or i just would have to re-flalsh to be certain?

-Tomaj

the .s19 file in here should match:

Index of /MS/msq/Therm Files/16L_piggy/hr_10g


if you never reflashed it, I'm positive that's what's loaded.


take a log of what's happening, then we can see if enrichment are doing it, if the temps are correct and all that jazz.

hey, thanks for all the help... I never re-flashed it so i'll take ur word for it that it's the rigght firmware.

i ran megatune and logged on the way home, saw temps way higher than previously reported... I was now at 192 to 202 or so for CLT temps, and my IAT was up too, starting from 90 going up to 120 degrees F by the end of my 15 minute drive.

Please see attached datalog, let me know if u see anything right or wrong.

-Tomaj

depending on where your AIT is, that sounds about right, mine is outside of the engine bay and i was logging 97*F on the way home today. If N/A then sounds spot on, it's always above 100*F.

192-202*F coolant is perfect. if i built your MS with fan control (which i believe i did) i have the fan come on at 200 and off at 192, so...

hey,

I'm turbo with a begi-s. The IAT is in the engine bay, past the turbo but on the driver's side of the radiator.. I don't have an intercooler, but if i did,t it would be "pre" intercooler in its present position.

I did it this way because i read that the radiator can heatsoak the IAT so this was the best middle spot away from the turbo and the rad.

so does it look like the IATs are correct given my setup? Also, can you let me know if my temp based corrections seem correct?

-tomaj