MAT vs Air Fuel Ratio - Miata Turbo Forum - Boost cars, acquire cats.

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Old 11-22-2010, 11:59 PM   #1
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Default MAT vs Air Fuel Ratio

OK, I hope this is a dumb question but I can not find an obvious answer on here or at Megasquirt.

Running a 96 miata with an MSPNP at 10psi (BEGi).

The colder it gets this fall the worse my car runs and the leaner it gets. I had it running about 16.5 or 17:1 while on the freeway. Now it is bouncing up to 19. I added some fuel to the VE table and it brought it back to 17. Then it got colder out...and back to 19:1...added fuel again and back to 17:1. My MAT is about 60F right now and when I tuned the car the first time it was about 80F. Obviously I don't want to tune the car everytime the temp changes. What am I missing.

MegaTune 2.25

While I am at it will toss in one more question. My Wide Band O2 sensor bounces up and down about 1 count (16:1 to 17:1) so fast that it makes it hard to read --- is this normal?
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Old 11-23-2010, 12:00 AM   #2
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mat correction table?
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Old 11-23-2010, 01:40 AM   #3
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I'm having the same issue. I've decided to try retuning with mat correction table set to 0's.

Correction % at 100%
Just going to have to use the wideband and tune the correction table in from nothing.
any % you put in is additional to 100%.

I was under the impression this % was subtracted from 100% but in the logs you'll see it adds pw.

So I guess from the temp you tune in at you'd want to add 0% and from there up in temp. From below that temp you would start adding fuel.

For me this is a problem because I don't run an intercooler and the wi doesn't spray out of boost - I read some pretty warm temps in the upper rpms out of boost. 176* @ 77* ambient.

So that said even in cooler climates, the ait is reading warm air.

I'm wondering if I shouldn't relocate the sensor to a pre-turbo location

Not sure about this yet, but I'll do some messing with the car tomorrow during the day.

I plan on picking up a thermal gun and checking the intake mani/piping/turbo against ambient and using that to tune from for now.
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Old 11-23-2010, 03:18 AM   #4
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Pre turbo would be a bad idea IMO because then its not reading what is actually entering your engine which makes it 100% useless.

I would relocate mine to the intercooler end tank (probably best location) but Just don't want to plug up current bung and re-cut and re-weld again. Just too much PITA. I'm going to make a little heat shield for it and then mess with MAT correction to see if I can at least make the problem small enough to not be noticeable. Its only for those 30 seconds to 1 minute after hot restarting. as soon as you get air moving through there it is fine.

Since you have no IC I'm kinda clueless as to what you can do. lol
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Old 11-23-2010, 11:16 AM   #5
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I've been thinking on this... Perhaps a U curve MAT table? :/

I'm thinking like

40* 15%
60* 8%
80* 0%
100* 0%
120* 2%
200* 5%

I'm sure this would require further adjustment but this is my solution for now. - I believe.

Really need more time to play with this.

Fact is, once the car is warmed up, cruising sits no lower than like 112~ and idling stopped around 120

I really need a heat shield at my air filter :/

Also when boosting the temp slowly rises and falls. No sharp spikes or anything that follows the boost/load - so I don't see how mat correction can accurately provide fuel changes in my setup unless I mount it pre-turbo :(

Yes I understand you want the ecu to see actual intake temps - but I also believe this train of thought leads thousands of innocent tuners into bad weather compensation problems.

Perhaps pre-turbo was meant for us all - and we just didn't heed the call...

What matters is how accurate the mat table is vs. actual ambient temp.

If you can't accurately adjust fuel to actual ambient, how can you compensate for cold weather?

And does 120* intake temps mean that the car has heated the air sufficiently to provide fuel for 120* air? no... still running lean because the ambient air being drawn into the turbo to begin with is still cool and dense.

The only fall back here which I don't care for with my setup is I would no longer be able to retard timing via the MAT correction... which especially in my setup is nice, because if temps are getting high for whatever reason, WI failed, day is really hot, whatever, I need to be able to back out the timing.

Right now I have it set for 220*+ starts losing timing. 2* then 8* then 15*

Unfortunately I have to get to work - so perhaps later I'll get to tinker with this.
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Old 11-23-2010, 01:16 PM   #6
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Or not? Gair changes evidently whether there is a table or not.

So what now?

I'm thinking of getting the droid tablet so I can search/read the forums without having to carry around a laptop.

Yep - sounds like a good idea.
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Old 11-23-2010, 01:51 PM   #7
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Default Where is it....MAT Table

I can not find the pull down menu to adjust the Gair or MAT table. There is a table to change your % Fuel VS COOLENT Temp and that has the MAT gauge on it when you open it but the temps are for water (120deg to 200deg). I need to adjust the MAT where the MAT = 40 to 100. I have the middle sized BEGi intercooler (which is a large cooler for a Miata). BEGi Intercooler # 2 [60042]

Also the temp sensor is just before the intake body and after the intercooler (one sensor in case I was not clear) -if the outside temp is 60deg the intake temp is about 70, is that believable?


MSPNP w/out MAF (running speed density but isnt working)
Garrett GT2554 Turbo
WB O2 Sensor (DB Blue Wideband Gauge Kit [3795])
195rwhp

Last edited by PreMixYZ; 11-24-2010 at 05:48 PM.
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Old 11-23-2010, 03:24 PM   #8
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so you're using CLT correction. There is a way to change to MAT correction but you'll have to search a little bit to find what you need to do that.

Maybe thats what I need to do is go by the coolant temp?

60 - 70* isn't that big of a change, if you can swap over to MAT correction you should be able to easily adjust that to suit your needs.

I'm thinking I would actually like 2 AIT sensors 1 pre and 1 post turbo for fuel and timing correction.

Maybe MS4? :P
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Old 11-24-2010, 05:10 PM   #9
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Search! Braineack has posted about this problem with pnp basemaps. Change IAT corrected air density to normal correction and then tune with VEAL. The fuel table should get richer below 3000rpm.

You only need 1 air temp sensor post intercooler pre throttle body.
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Old 11-24-2010, 05:33 PM   #10
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FWIW. I too have struggled with this issue on MS1 and for a few weeks on MS2.

I'm nearly there with it now though. I used VEAL for a few hours in one single session and then hand smoothed the odd lump in the map. This was all done with the MAT correction factor set to 75% and my MAT correction curve zeroed out (AE of GEGO off).

That tune was done on a day where IAT's were ~10-14*C. Today I saw IAT's of 0*C and my tune was still spot on. I haven't had to touch my MAT correction curve yet and GEGO is only set to 5% authority. I don't want to use any more than that.
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Old 11-24-2010, 05:45 PM   #11
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Default Searched!

Yes, I spent a few hours searching. When I could not find what I was looking for I thought that I must be looking for something too easy so it has just never been posted.
My problem is actually at 3000 to 5000 RPM at 66Kpa to 100Kpa (from 10 to 0 vacuum). Due to the lack of simple straight answer I am being lead to believe that the reason I can not find a "MAT Table" is that there is no such thing on the MSPNP for 96/97 Miata - that or it is just hardcoded into the firmware.

Anyway my car is running GREAT right now, but I assume that it will be a bit rich when it starts to warm up in the spring and I will have to bump down the VE table a little bit. The other thing I might try this weekend is to just lie about the injector size. That will richen up the whole VE Table. I think there is also a tool that MS had to do a global adjustment on the VE.
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Old 11-24-2010, 06:08 PM   #12
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Sounds like a similar problem I was having. Read this thread and see if it helps. https://www.miataturbo.net/mspnp-55/cold-weather-warmup-troubles-53340/
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Old 11-24-2010, 07:24 PM   #13
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The setting is coolant corrected air density but the pnp default is iat corrected. Set this to normal correction.
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Old 10-02-2011, 12:39 PM   #14
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Sorry to start beating this dead horse again, but I would like some clarification if anyone can provide it for me.

I have a 97 Miata (stock engine) running MS1 in parallel. IAT sensor is mounted down inside intake snorkel (back near the firewall) before the airbox and that seems to have fixed the worst of the heat soak. I have been noticing that the car seems to run a bit lean when IAT is higher (around 120F) than where I tuned it (around 105F). Clt-related air density was set to "normal correction."

From what I'm reading, this corresponds to what others have been seeing with the normal correction being too aggressive in practical application. So to fix this, I would need to set it to Corrected > IAT Correction > start RPM 7500 end RPM 8000 and then establish a curve that keeps everything running at the correct AFRs regardless of IAT, right?
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Old 10-02-2011, 12:42 PM   #15
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no. that's a horrible idea. there's built in ideal gas law code, that's whats pulling the fuel. this table helps correct that.

use the default curve on the MSPNP basemap.
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Old 10-02-2011, 01:02 PM   #16
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I think that's where the original settings had come from. In the MSPNP9697 base map, the clt-related correction is set to "normal correction" and all of the plotted temperatures are on a flat curve of 100% offset.
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Old 10-02-2011, 01:11 PM   #17
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look at the 9093 map. try those out for size.
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Old 10-02-2011, 01:23 PM   #18
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That seems more in line with what I was thinking. Apparently the 9495 and 9697 base maps don't include the same correction curve by default.

Thanks for the assistance!
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