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Well, improved anyways.

Check this <1min video explaining how IAT sensors can get heat soaked if theyre installed inside your engine bay.



Dann

Even with a fairly flat MAT air density correction table the hot start problem persists. However the flatter than default curve does seem to help, a couple of throttle blips and it behaves itself.

Nb8b has a returnless fuel system which means the fuel itself gets super hot.

Dann

Hmmm, yes that would be worse than NA8 which I have, I hadn't thought of fuel temp itself as being the cause of this issue. But I reckon you might be onto something there. Might well explain why the problem goes away with a couple of blips, nice cooler fuel gets up there. I've researched the sh*t out of this issue on the big forums, all to no avail.

Actually I also have a stock NB8B and it doesn't do it. It starts just fine hot. I only see the problem on my MS3pro equipped NA8.

Forget the big forum
Buckle up and get ready to get told over at miataturbo.

The stock ecu probably uses the iat in a different way. I cant be sure though.

Dann

On your na8 its probably an untuned hot post start table or one of the others involved.

Dann

The MT guys suggest relocating the IAT sensor to the cold side FMIC end tank. This puts the sensor outside of the engine bay.

Not sure how the stock ECU seemingly gets it right almost all the time.

It probably has a table specifically for heat soak of the sensor, taking into account running time and stationery time not just- the air temperature itself and then plus or minus a few percent due to density changes.

Dann

Curious, since on a non-turbo application there's not much you can do to get the IAT outside the engine bay, would there be any use in trying to insulate the sensor?

ie: making up a thermally non-conductive cover (ABS plastic or something) that can slide over the exposed back end of the sensor.




Granted I havent noticed any starting issues with mine, and my sensor just threads into the intake elbow.

The sensor is being soaked by the material it is screwed into mostly.

Dann

Well essentially.....even outside the engine bay....there is heat soak. Especially if the car sits in the sun and its like 37 deg in tbe shade. And you go & start it
Mine is fitted outside the firewall just underneath the bonnet on the CAI....it gets heat soak...
I guess lesson is.....adjust the fuel mixture....

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NitroDann wrote:The sensor is being soaked by the material it is screwed into mostly.

Dann

Makes sense.

Mines screwed into pvc, so presumably not much heat soak.

Fine for my n/a setup, but yeah, I doubt it would cope with any positive pressure like in a turbo setup.

My AIT is glued into (yes glued, the bung is glued in with JB Weld) a 90 degree elbow on the outlet of the intercooler. This is low down below the motor, hot air rises. It runs lean after hot restart and logs reveal it is not heat soak of the AIT sensor, the AIT sensor is not reading hot in an area of my Mass air density table that pulls out any substantial amount of fuel.

Must be something else that I've overlooked.

Red_Bullet, that sounds like it's injector heat soak. Try cranking up your ASE and extending the time for >90* starts. Also, having EGO on helps add fuel to get your AFRs in the ball park.

ManiacLachy wrote:Red_Bullet, that sounds like it's injector heat soak. Try cranking up your ASE and extending the time for >90* starts. Also, having EGO on helps add fuel to get your AFRs in the ball park.

Thanks, Ill have a look at what you suggested.