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The mass airflow sensor in 1999 LS400 senses airflow and temperature of airflow.
I understand 1995 and later LS400's employ dual precision resistive elements by which the ECU determines airflow and airflow temperatures based on measured resistances.
The external flanged mounting base of the Airflow Sensor is exposed both to radiant engine heat and heated air from radiator fan wash...
Airflow/Airflow Temperature sensor in 1999 LS400. Heatsoak from Radiant heat and downstream radiator heat wash?? (The plastic connector shell was as brittle as ignition coil connector shells and literally crumbled when replacing)
As with other underhood engine components, plausibly it too is heat soaking...
Heat transfer can occur thru conduction, radiation, convection, or combinations of those....
Anyone know whether underhood heat affects readings of airflow sensor a few percentage points?
No, the ECU is programmed to adjust to the reading from a MAF based on ambient temp and engine temp and intake air temp to allow for accurate readings and fuel amounts regardless of how much heat there may be under hood.
The sensor itself simply tells the ECU the air density that comes through and the ECU is responsible for making changes based on temperature from the other points it's monitoring. If you try and isolate it from heat it will simply delay how long it takes it to saturate, same as anything else under the hood. Leave the car running for an hour or two or in extreme ambient heat with the AC on and everything will become saturated due to radiant heat to around 200* and is why underhood plastics become brittle even on cold climate cars since the end operating temp is always way hotter than ambient no matter where in the world you are.
You can easily test this by placing various size meta ingots into the engine bay and even insulating them or chilling them beforehand and then simply having your car idle with the AC on for a hour or two. No matter how large, cold it starts, or how insulated it will saturate to the same temperature. Only way to avoid this is active cooling of some sort, and the MAF receives this via air charge movement and even then it's limited to the external air temp.
Carbureted cars actually have big issues with this because in winter the intake air charge is freezing and can ice the carb and is why there is usually a heat pipe leading from the top of the exhaust manifold to the intake tube to keep it warm and let it warm up very early vs relying on radiant. It's also why the TB on the LS is heated via the coolant to prevent the throttle blade from having ice buildup from a very cold intake air charge since they felt there was a risk there would not be enough heat transfer as is from the upper intake to the TB to prevent icing in certain temperatures/humidity combos. Other engines don't have an issue with this and don't have the heated TBs
It's also why the TB on the LS is heated via the coolant to prevent the throttle blade from having ice buildup from a very cold intake air charge since they felt there was a risk there would not be enough heat transfer as is from the upper intake to the TB to prevent icing in certain temperatures/humidity combos. Other engines don't have an issue with this and don't have the heated TBs
i'm not saying you're wrong but is this verified info? i know the throttle body has a thermostat to a coolant passage but i've only ever known that to be there for purposes of cooling the intake not heating it up... and considering there's a thermostat that only opens when intake temperatures reach a certain point, wouldn't coolant initially not even be flowing through there in the first place?
No, the ECU is programmed to adjust to the reading from a MAF based on ambient temp and engine temp and intake air temp to allow for accurate readings and fuel amounts regardless of how much heat there may be under hood.
The sensor itself simply tells the ECU the air density that comes through and the ECU is responsible for making changes based on temperature from the other points it's monitoring. If you try and isolate it from heat it will simply delay how long it takes it to saturate, same as anything else under the hood. Leave the car running for an hour or two or in extreme ambient heat with the AC on and everything will become saturated due to radiant heat to around 200* and is why underhood plastics become brittle even on cold climate cars since the end operating temp is always way hotter than ambient no matter where in the world you are.
You can easily test this by placing various size meta ingots into the engine bay and even insulating them or chilling them beforehand and then simply having your car idle with the AC on for a hour or two. No matter how large, cold it starts, or how insulated it will saturate to the same temperature. Only way to avoid this is active cooling of some sort, and the MAF receives this via air charge movement and even then it's limited to the external air temp.
Carbureted cars actually have big issues with this because in winter the intake air charge is freezing and can ice the carb and is why there is usually a heat pipe leading from the top of the exhaust manifold to the intake tube to keep it warm and let it warm up very early vs relying on radiant. It's also why the TB on the LS is heated via the coolant to prevent the throttle blade from having ice buildup from a very cold intake air charge since they felt there was a risk there would not be enough heat transfer as is from the upper intake to the TB to prevent icing in certain temperatures/humidity combos. Other engines don't have an issue with this and don't have the heated TBs
I can count cards...
The air temperature sensor is inside the MAF.
A resistive element is employed which varies resistance by temperature so heatsoak is a zero percentage factor?
Several posts online Google search for Mass Airflow Sensor heatsoak...BMW especially.
All contend heatsoak at idle the most problematic.
A resistive element is employed which varies resistance by temperature so heatsoak is a zero percentage factor?
Several posts online Google search for Mass Airflow Sensor heatsoak...BMW especially.
All contend heatsoak at idle the most problematic.
Anyone else?
Yeah at idle since there is near zero air movement like I said in my post, if you don't have much air movement the radiant heat will soak everything to engine temp. The fact is that in the case of those BMWs at idle the air inside the intake/airbox tube IS hot due to radiant heat until you get moving/off idle again and the increased airflow cools the tract down again.
i'm not saying you're wrong but is this verified info? i know the throttle body has a thermostat to a coolant passage but i've only ever known that to be there for purposes of cooling the intake not heating it up... and considering there's a thermostat that only opens when intake temperatures reach a certain point, wouldn't coolant initially not even be flowing through there in the first place?
You will note it says more than needed, it's for cold temperatures and as said above it will not allow flow when external conditions are hot. The only reason to allow flow there is for cold weather reasons since you can't use engine coolant to cool down an air charge that is cooler than said coolant.
They want it to remain at least at a certain level in extreme cold situations since the LS leaves nothing to chance.
Plus having had a carbed car give me this exact issue in winter it's extremely annoying if it does happen since the blazes also don't want to to close as easy
You will note it says more than needed, it's for cold temperatures and as said above it will not allow flow when external conditions are hot. The only reason to allow flow there is for cold weather reasons since you can't use engine coolant to cool down an air charge that is cooler than said coolant.
my mistake i was misinterpreting that... so the thermostat stops the coolant flow when it warms up, i was a bit thrown off since i'm used to a thermostat allowing extra coolant to flow once it warms up lol
my mistake i was misinterpreting that... so the thermostat stops the coolant flow when it warms up, i was a bit thrown off since i'm used to a thermostat allowing extra coolant to flow once it warms up lol
this car just continues to impress
Correct! It's a "just in case" feature that the LS has so many of that are very well thought out in a similar vein to the LX/land cruiser having extreme amounts of attention paid to make them nearly totally environmentally insensitive.
It's scary if it does happen since the blade will be stuck open and you have to shut the engine off to stop accelerating. Extremely rare but I had it happen to me on a C3 corvette that had the stock type heater crossover removed
Correct! It's a "just in case" feature that the LS has so many of that are very well thought out in a similar vein to the LX/land cruiser having extreme amounts of attention paid to make them nearly totally environmentally insensitive.
It's scary if it does happen since the blade will be stuck open and you have to shut the engine off to stop accelerating. Extremely rare but I had it happen to me on a C3 corvette that had the stock type heater crossover removed
i've always admired and appreciated the way electronic throttle control was executed on this car and it just speaks volumes about the total apocalypse-proof nature of 90s toyota products
there's not another system i'm familiar with that has a mechanical backup for its electronic throttle control... and the combination of fantastic response and physical cable attached to the gas pedal makes you feel like you're genuinely moving the throttle plate yourself
you can tell toyota had brilliant programmers really put in the extra time and effort to get all the software in this car as absolutely optimized as can be
It's quite impressive, mostly since at the time it was cutting edge to the max and they wanted to ensure it never failed and time has shown that unlike same era 7/S class cars they succeeded.
Back on topic though if you want to try insulating/reducing the MAF temp you would need to actively cool a heat sink of some sort that bleeds heats away from it. Otherwise at idle it will soak if there is low amounts of air movement and the IAT will read hot since the air IS hot. To stop it from reading accurately is not a good idea even though it's a common "tuning" truck used on 80-90s era cars to get more spark advance but that's playing with fire since now you are using hotter IATs but fooling the computer into thinking air density is higher and having it advance spark more. If you are not using higher octane fuel/have really good knock sensors it will have issues, some engines are smart enough to know based on the knock sensors that the IAT sensor has been messed with and will throw a code if you try this type of tweak.
Physically moving the MAF somewhere else can register lower temps but the car was designed with the sensor to be located in a particular area and the maps have been designed around this factor. If you move it you will need to have a way to remap and inform the engine that at idle the part of the air charge that is in the intake tube/airbox is hotter than its sensor is seeing at first when you get moving after sitting a while. That or have a system that allows the intake tube to draw directly from outside and have the sensor relocated 1/3 the way into said tube after confirming by letting the car sit that the air doesn't increase more than 20-30 degrees from the sensor position in the back section.
Otherwise the car ECU will be using too much fuel since it thinks there is more air than actually present unless again you remap it and tune it with a wideband to make sure it's not rich or lean at any point.
The issue is you would have to improve on the fact that stock the LS has a semi ram air setup that once you are moving has colder air quite quickly. First step would be to measure how hot the air gets when fully soaked vs moving 5mph and see how to get those figures to match up
06-28-20, 01:28 PM
Mass airflow sensor heat soak?
