Tree DR

From what I understand there are 3 temp sensors on our trucks. Outside ambient located driver side front of motor, IAT in the intake at motor. The other one is in the airfilter/intake box.

What does the airfilter box sensor do for the ecm? I know you have to have it hooked up or you go into limp mode.

I hooked a OBDII scan tool to my truck and it showed ambient temp to be higher than the IAT temp. The ambient on my overhead didn't move so it would have to be the one at the airfilter box.

Now when I say the abient is higher than the IAT, its during WOT runs to see if we could isolate a problem. The temp of the ambient went up faster and was allways hotter thant the IAT. Also the ambient would spike if I had the jake brake on to slow down from the WOT runs.

53 willys

From the book......The combination, dual function Inlet Air Temperature/Pressure Sensor is located on the air cleaner (filter) cover.
The Inlet Air Temperature/Pressure Sensor is a combination dual-function sensor. The sensor element extends into the intake air stream at the top of the air filter housing. Ambient air temperature as well as barometric pressure is monitored by this sensor. The Engine Control Module (ECM) monitors signals from this sensor. indicating turbocharger boost pressure.

ratlratl

From MY best understanding, after a whole lotta algorithims and other kinds of math I couldn't read and figure out if I tried to. It uses the three different temps to be able to calculate the differences in the temps along the path of air to help the ECM determine density. Unlike a vehicle that uses a Mass Air Flow sensor that can measure temp, density and flow all in one. I want to say that the display on the overhead has a buffer programmed into it so the needles or readings don't fluctuate too much. Some people don't read their gauges anyway, so best that the readings appear stable for when they do. Example mid eighties firebirds or camaros, hit the gas, needle goes one way. Hit the brakes the needle reads the opposite.


Chris

53 willys

intake manifold sensor (MAP)......The combination, dual function Intake Manifold Air Temperature Sensor/MAP Sensor is installed into the top of the intake manifold.The combination, dual function Intake Manifold Air Temperature Sensor/MAP Sensor is installed into the top of the intake manifold with the sensor element extending into the air stream.The IAT portion of the sensor provides an input voltage to the Engine Control Module (ECM) indicating intake manifold air temperature. The MAP portion of the sensor provides an input voltage to the ECM indicating turbocharger boost pressure.

53 willys

overhead temp/ambient....The ambient temperature sensor is a variable resistor mounted to a bracket that is secured with a screw to the left side of the radiator yoke, behind the radiator grille and in front of the engine compartment.The ambient temperature sensor cannot be adjusted or repaired and, if inoperative or damaged, it must be replaced.The ambient temperature sensor is a variable resistor that operates on a five-volt reference signal sent by the Front Control Module (FCM). The resistance in the sensor changes as temperature changes, changing the temperature sensor signal circuit voltage to the FCM. Based upon the resistance in the sensor, the FCM senses a specific voltage on the temperature sensor signal circuit. The FCM then translates the voltage into a temperature reading that it sent over the Programmable Communications Interface (PCI) data bus circuit to other modules utilizing temperature information.

Tree DR

Maybe I don't understand but how does the pressure sensor on the air cleaner indicate boost pressure?

Also back to the original statement of how could the ambient temp be greater than the IAT temp?

53 willys

it does NOT read boost it reads barometric pressure. the MAP sensor reads boost......

53 willys

the 3rd sensor by the headlight is just for the over head from what I can tell....I think the ECM does all it's figuring from the IAT and MAP sensors.......the one that rises in temp would have to be the MAP sensor since it is reading the air after the compressor compresses it???????yes, no??????

Tree DR

Ok the intake or filter sensor would have to be ambient air temp. The intake or after the compressor MAP/IAT sensor is what is tipically called intake air temp sensor.
Why would the ambient air temp be rising faster than the IAT in WOT runs? Both sensors show increases but the ambient goes up faster than the IAT and the ambient temp. spikes when the jake comes on.
I have a scan gauge (I didn't use it to get the readings I'm talking about.) I does tell me what the IAT temp is. During normal driveing the IAT stays about 10-20deg. higher than the overhead computers tells me outside temp. is. Yes the IAT temp goes up during WOT runs. It doesn't spike when the jake comes on though.

jrussell

I think it reads the barometric pressure, and then uses that figure to calculate boost using the MAP pressure/temp sensor.

jrussell

It definitely sounds like the scan tool has the terminology mixed up. Maybe try unplugging one sensor and see if the scan tool will indicate which one is unplugged?

Tree DR

I've disconnected the Map/intake sensor on the manifold before and no info on the scangauge shows anymore. When I start the truck on a cold morning the IAT temp is higher than the outside air because the heater grid warming the air in the intake manifold. After the truck has been running just a (little) while the intake and outside air are often the same temp.

MAP is Manifold Absolute or is it Atmospheric Pressure? My MAP sensor shows around 14.6 at idle and goes up to about 37.4 which would be the normal boost for the 05. 22.8psi of boost.
Why would one sensor one the filter box use barametric and the other MAP/IAT atmospheric? I know the two are related but why not use barametric for both?

jrussell

Probably stands for absolute, but that's just a guess.

It sounds like you know the IAT reading is the one mounted on the intake manifold. I guess that means the ambient reading you have is actually the sensor located at the air filter.

Here's one way to tell for sure. Remove the sensor located near the air filter (leave it plugged in though) and hold a lighter underneath it. Your scan tool should still show the temp sensor readings with the engine off and key turned to run. The reading that increases would tell you which sensor that is.

Tree DR

I know the temp reading I'm getting on the scan gauge is from the intake manifold after the intercooler. How could the other air temp reading at the air filter box be hotter than after the intercooler. Maybe the sensor is bad? It doesn't apear to be dirty. I did have the ECM flashed before I did the testing to see if maybe the problem was the ECM. Is there another air temp sensor reading after the turbo befor the intercooler? That would make more sence than a reading comeing from the air filter box.

Spooler

Well, with that big ol CAC we have I could see it cooling the air down quite a bit escpecially in cold or cooler weather. So I could see the intake air temp being hotter than the map sensor reading to a point.