Can you map the fuelling against IAT on MS1?
Turbo Mini Forums

Just a thought. I think that some of the inconsistancy in my fuelling is owing to differing air temperatures. When I come to work in the moring (7am) fuelling is great, when on the way home (15:30) it's always rich.

I wonder if this could be caused by warmer air in the afternoon? Can this be compensated for by using the IAT? I have looked in the manual, and pressed all the buttons on Tuner Studio, but not found anything.

cheers

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

IAT is a fundamental part of the fuelling equation.

A quick look at the MS1 manual shows it is a bit more crude than an MS2 but it's still fundamental for the ECU to calculate the density, hence mass of air, going into the engine.

As such it's not "adjustable" but if, for example, you had the wrong calibration curve for the sensor you have installed, it would screw things up at different temperatures.

Also, where is the sensor installed ?

Also, considering your other post, is your low coolant temperature keeping some of the warmup enrichment active (have a look at your warmup curve).

Schrödinger's cat - so which one am I ???

Should be under MAT Correction on the Extended menu Wil.

Edit - I do use MS2 however, MS1 sounds like it may be different according to Rod.

Edited by Carl S on 23rd Nov, 2011.

Schrödinger's cat - so which one am I ???

The warmup curve is set so that there is no correction from 60 degrees. So no enrichemnent in normal running.

I calibrated the air temp sensor myself, as I had no data. It might be worth looking at what the MS thinks it's seeing, I'll wack it on the dashboard.

IAT is between the IC and TB, as close to the TB as I could get.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

I just set up a dummy project in TunerStudio for an MS1/Extra and the "Extended" menu doesn't exist.

There is more than one version of an MS1 so I may have picked the wrong one but the menu choices are a lot more limited than MS2/Extra.

Still worth checking to see if you have the "Extended" menu but I doubt it.

Definately worth looking at what MS is actually seeing, also check TS didn't default back to Farenheight when you were calibrating your sensor.

If MS1 doesn't have the MAT trim table (which I never knew existed.....) you could cheat by entering a skewed calibration curve for the sensor.

Schrödinger's cat - so which one am I ???

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

I agree for a normally aspirated engine (the correct units for temperature in the fundamental gas equation are actually degrees Kelvin so the percentage swing isn't much) but on a charged engine where there may be some fairly significant temperature changes (esp. if not intercooled) it is quite important.

(edit - typo)

Edit 2

Also Stevie, for heat soak, a proper IAT sensor will have an open bulb which will be isolated from the metal body to avoid just this and hence only measure the air temperature, not the surroundings.

But as you say, I'm an MS user so I believe in it :)

Edited by Rod S on 23rd Nov, 2011.

Schrödinger's cat - so which one am I ???

It's not just an MS thing but a physics thing. If you want to compute the air mass in a speed density setup, you need the temperature. If the measurement is unreliable then it's another issue and you need to correct it either by getting a better physical setup (which may not always be possible) or using a correction for it.

And to come back to the original issue, not having the correct dead time (opening time) will also create a similar issue since any correction is only applied to the effective pulse width (full pulse width minus the opening time). So if your dead time is longer or shorter than what you have in your settings, you'll get an inconsistent fueling as conditions change from the ones you had when you tuned the fueling.

Jean

http://www.jbperf.com/

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

gotta agree with stevie, im pretty sure i disabled IAT correction on my megasquirt install as i found i could get more consistant fueling without it, i have an open bulb type in the inlet, and the lag on it is incredible, and simply not good enough to be trusted to alter fueling. again, was a post of my datalogs that stevie comented on that prompted this. the IAT would actually go DOWN on boost, this should never happen, and showed that the rubber insulated open bulb sensor was indeed suffering heat soak in low airflow situations. and again i can think of countless turbocharged cars where the IAT sensor is in the pre-turbo ducting.

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

Stevie,

I have never seen an OEM measure ambient air temperature.

My Cosworth (as a typical OEM example) has the IAT in the plenum after the compressor, intercooler and throttle bodies.

My Mini setup is a pretty much a direct copy.

I even use the Cossie sensors because the calibration curves are readily available.

The Cossie IAT sensor is fully insulated against surrounding metal and any form of heat soak.

That's why it works.

If the heat soak you think affects low loads also affects the sensor, then it affects the air temperature going in at low loads. So the measured temperature is correct.

So the laws of physics (as Jean says) still apply.

If there is enough surrounding heat to heat the sensor, then it heats the air too.....

We will have to agree to disagree but I'll stick with PV=mRT (I'll also stick with E=mC^2 too) :)

Schrödinger's cat - so which one am I ???

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

about 2.5 secsreponse on my MPI IAT sensor.

To add, the factory MPi has the IAT sensor mounted in the inlet manifold and isolated by a plastic bush. The Rover T series with multipoint injection also has the IAT mounted in one of the inlet runners, again in a plastic bush. The latter also has a fuel temperature sensor in the fuel rail to compensate for fuel density also.

I'm not sure how Megasquirt handles heat soak if at all, but VEMS has a correction table based on MAT/ TPS

http://www.jbperf.com/

Yes, I too was refering to the speed density programme (which is what MS is usually setup for) rather than MAF as found on some modern cars.

It may be 20 years old technology (even older actually) but speed/density programmes are still widely used, and density is a function of pressure and temperature.

As I said earlier, temperature is not the dominant term as its calculated in degrees Kelvin, not centigrade, so maybe not too much of an issue where you measure it on a N/A engine (where the inlet temperature will be little different to ambient) but on a charged engine, quite significant.

At the temperatures we work (around 300Kelvin) a 10 degree error in measurement is ~3.5% error in density (hence fuelling).

So if you choose to measure ambient air temperature and your intercooler outlet is 20 degrees above ambient, your fuelling is out by 7%.

Not somewhere I would want to be.

If a sensor is slow to respond, use a better one.

If it suffers from heat soak at low flow rates, so does the air going past it.

If it suffers from heat soak at high flow rates, it's a bad installation.

And if you're not concerned about the odd 7% difference in fuel required, use an SU :)

Schrödinger's cat - so which one am I ???

boost ,temperature ,density fairly constant per design .. , so the engine would be mapped for that design ,so taking all that into account .then the variable is the external air temp.

eg ,take an engine putting out 20 psi boost @70%eff,3500 rpm ,intercooler eff =70% so the density of the charge is decided by these numbers .

the cooling eff of the ic is fixed ,so is boost and rpm . ,the variable is the outside temp ,which will affect the charge temp ,nut not as much as requires a new map ,just some compensation ..and as steve stays , id rather run richer and offset detonation in a hotter air sit anyway .

so i'd map for a correct mix ,and then have the iat out near the filter ,then data log and adjust if i think its getting too rich .

but i may be drivelling :)


actually ,thinking a tiny bit more ,heat soak into the system ,particularly the ic ,would create a bit more fragility into the situation ... , personally i d think a bit of ignition timing adjustment ref iat would be more germaine .

Edited by robert on 24th Nov, 2011.

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

So this morning I put MAT on the dashboard. It started at 16 and maxed at 20. Not sure what it's reading though on the dial, it said %?

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

The MAT gauge should read Deg C. but that may be due to your dashboard .ini.

It should read ambient at start, as should the coolant gauge. I would expect it to max out in the 30s under boost.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

That's what I thought. I'll have another poke around for a dial. I remember before I updated tuner studio it was on there and read what I would expect.

Hummm

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

I've had dials come up as % too.....

As Paul says, usually the ini file.

Things often seem to screw up when I update TS, so I avoid it until I absolutely have to.....

Schrödinger's cat - so which one am I ???