Heat soak

[DaveEFI]

My SD1 fitted with a MegaSquirt suffers from what I think is heat soak when stopped hot on a hot day then restarted fairly soon. The ATS shows a high temperature as I suppose you'd expect. And the AFR goes very weak for a short time making a hot restart a bit of a fiddle. Once it does restart and run for a short time things return to normal.

I've played with the ATS compensation, but you don't get long before it sorts itself out anyway. Which makes arriving at a setting rather hit or miss.

My thoughts were the ATS isn't reacting to the true air temp quick enough - it is an enclosed type - and was intending trying an open one. But can't find one to fit the existing thread.

So if I have to fit a new boss, I might as well experiment with the ATS position.

At the moment, it is in an ally tube which replaces the original AFM, and the original ATS was in the AFM. I'm wondering if it might be better in the air cleaner? Further away from the sources of heat - like the exhaust manifold?

I've seen some fitted to the actual plenum - so there doesn't seem to be a universally accepted best place.

[cammmy]

I would think that you'd want it as close to the valves as practicable, so on an RV8 that would probably be in the plenum.

I think ideally it should be mounted in plastic rather than metal, to stop heat soaking into the sensor from it's boss. Might be hard to do though

[DaveEFI]

My SD1 had Lucas injection originally, and the ATS was in the flapper AFM - not plenum. Since the inlet manifold and plenum was specially made it would have been easy to design it with the ATS close to the valves - if that was the best place?

Anywhere is probably ok when running as the airflow past it will keep it 'cool' and I doubt the air temperature varies much along the tract anyway.

[SimpleSimon]

Dave FFS don't stick it in the plenum when you switch off hot it will heat soak like a bastard and you will have even bigger problems (seen it done on the RV8) just move it away from the area of soak in the nose etc its job is to make adjustments on extreme outside temps rather than make allowances for your brief intake temps when switching off (heat soak) lets face it once the motor is fired up from hot the rate the engine consumes air temps drop off rapidly anyway in the intake and normal service is resumed most OE EFI dont stick ATS in the plenum or near the engine heat, its usually mounted in the plastic air cleaner trunking so wouldn't have a clue how hot the inside of the inlet manifold/plenum is and don't need to either its job is ........ "outside air temperature sensor" IMO

[DaveEFI]

I was wondering about trying the new one in the air filter housing? Should be about the coolest place under the bonnet - it's at the front and low down.

[SimpleSimon]

I was wondering about trying the new one in the air filter housing? Should be about the coolest place under the bonnet - it's at the front and low down.

I reckon Dave

[stevieturbo]

If you're n/a just mount it away from the engine itself more as an ambient temp sensor.

Anywhere on the engine it will suffer heat soak, and will cause skewed readings.

And theoretical air temp compensations are rarely workable ones if the sensor is anywhere near the engine.

Mounting the sensor close to the intake valves is a nice notion, but rarely a practical one, especially on a V8 with a huge hot alloy intake manifold right in the middle of the hot engine.
It will get wrong readings due to heat soak.

[DaveEFI]

Mounted a new one in the air filter housing - and initial results are promising. Tuner Studio doesn't show under bonnet temperatures anything like as high as in the old position, on a hot engine left stopped for a few minutes.

However, despite it saying it's a standard Bosch (type) sensor, the calibration is out - it was reading some 8 degrees high on a cold engine, compared to the coolant. So I'll have to measure the resistance and do the calibration manually.

[stevieturbo]

Mounted a new one in the air filter housing - and initial results are promising. Tuner Studio doesn't show under bonnet temperatures anything like as high as in the old position, on a hot engine left stopped for a few minutes.

However, despite it saying it's a standard Bosch (type) sensor, the calibration is out - it was reading some 8 degrees high on a cold engine, compared to the coolant. So I'll have to measure the resistance and do the calibration manually.

Doing a manual calibration is awkward unless you've some way of maintaining a steady temperature for a few seconds for the test

But coolant and air temp on an engine sitting say overnight, should probably be within a few degrees, 8degC sounds a bit too much.

[SimpleSimon]

If you're n/a just mount it away from the engine itself more as an ambient temp sensor.

Anywhere on the engine it will suffer heat soak, and will cause skewed readings.

And theoretical air temp compensations are rarely workable ones if the sensor is anywhere near the engine.

Mounting the sensor close to the intake valves is a nice notion, but rarely a practical one, especially on a V8 with a huge hot alloy intake manifold right in the middle of the hot engine.
It will get wrong readings due to heat soak.

Put better than I

[DaveEFI]

The software allows a three point calibration - enter three temperature points - say 0, 50 and 100C (or whatever) and the resistance at each one and it will interpolate the rest.

With the old sensor, coolant and air read as near as dammit the same after an overnight stop, before starting up.