01-21-2021, 03:39 PM
I touched on this topic in some other threads. But will consolidate that info, and new info here.
My 1989 Dodge B250 has throttle body fuel injection.
At the base of the throttle body, there are several vaccuum ports.
One of these vaccuum ports goes to the air cleaner temperature sensor port on the underside of the air cleaner.
Another vaccuum line goes from this sensor to a vaccuum modulator, which lifts a door, and diverts incoming air to either come from a heat collector stove pipe on teh passenger side exhaust manifold, OR from the cold air snorkel which reaches infront of the radiator.
I had Always assumed this device was ONLY to help the engine run better during warm up, and was useless after full temperature was reached. I was wrong.
The Engine computer is Expecting this system, to quickly get the the incoming aircharge to 100f, and then Keep it at 100F.
The engine computer is programmed for this temperature. There is a throttle body temp sensor, and the O2 sensor, and a coolant temp sensor, and all of these affect the air/fuel ratio and spark timing, but all of these are calculated on a predetermined 100F air charge, and that is dependent on the air temp sensor modulating the vaccuum to the blend door which lifts a certain amount to mix in air from manifold or front and from in front of engine.
When max power is needed there is not a lot of vaccuum available and therefor the blend door drops and allows in the coolest possible air for making max power, but steady eddie 65mph there is plenty of vaccuum and max MPG is achieved by best possible air fuel ratio and this is achieved by firing the injectors precisely.
So Before driving from California to Florida a month ago, I found this blend door, whenever the engine was running, was sucking only hot manifold air, even when the engine coolant and oil was at full temperature, in 70F ambient temps. I disabled it and started driving east, and my MPGS were crap, even considering the elevation changes and headwinds.
The first stop I wedged a fuel hose, lifting the blend door about 5/8", and the next tank I got over 17mpg, with good tailwinds, but it ran like crap when overnight cold. I watch the fuel gauge like a hawk and know how many highway miles to expect, and it was easily noticed that the colder it got outside, the faster my fuel gauge needle dropped even with the blend door lifted 5/8" of its ~2.25 inches of travel.
So it was extremely obvious cutting off vacuum to the temp sensor in the air cleaner was detrimental to my fuel economy and the 5/8" I wedged it open was better, in 65f, but not for 45f.
I bought a Carter TC13 air cleaner temp sensor, even though it ONLY looked to be the same, it was not listed as compatible with my engine.
It appeared identical and took a minute to swap.
So I took my flap sander on angle grinder and sanded the perimeter of the old sensor and took it apart.
There is a Bimetal leaf spring inside, that pushes a pintle and closes off airflow from a snout inside the aircleaner
When the sensor heats up, the bimetal leaf spring bends and allows filtered air from inside the aircleaner to enter the sensor and this reduces vacuum to the modulator and allows the door to drop, allowing in more cool air from infront of the radiator.
My pintle was stuck. Even once I freed it up, and let the bimetal spring push it back home, it got stuck there again.
The snout, in which this pintle resides, can be screwed in and out, to modify the temperature where it starts reducing the amount of vacuum reaching the modulator which lifts and lowers the blend door.
So the New Carter TC13 might not be dialed for 100F, but perhaps for 90F or 110F.
I will Put a K type thermocouple on it.
But I likely could just clean and return the original to function.
Knowing what i know now, from having opened it, I'll assume I could have simply heated up the sensor with a hairdrier and sprayed some silicone lubricant in there and freed up the pintle. I am not sure if there is/was an Oring at teh base of the pintle, yet.
Silicone however can do damage to the oxygen sensor, So One would not want to do this with the engine running, as an Inoperable 02 sensor reduces fuel economy by 50%, in my experience.
If there is no Oring, I think one could stick the tube of a can of brake kleen into the single snout on a sensor warmed to above 120f and free up the pintle.
I think it highly likely at 30 years old that this sensor has failed on every vehicle into which it or similar is placed and is negatively affecting highway fuel economy.
I do not know if a carb'd vehicle could be tuned so precisely as to make much of a difference in highway mpg, but these air cleaner temp sensors are on carb'd vehicles back into the 60's, and seemed to not disappear until the late 90's
My 1989 Dodge B250 has throttle body fuel injection.
At the base of the throttle body, there are several vaccuum ports.
One of these vaccuum ports goes to the air cleaner temperature sensor port on the underside of the air cleaner.
Another vaccuum line goes from this sensor to a vaccuum modulator, which lifts a door, and diverts incoming air to either come from a heat collector stove pipe on teh passenger side exhaust manifold, OR from the cold air snorkel which reaches infront of the radiator.
I had Always assumed this device was ONLY to help the engine run better during warm up, and was useless after full temperature was reached. I was wrong.
The Engine computer is Expecting this system, to quickly get the the incoming aircharge to 100f, and then Keep it at 100F.
The engine computer is programmed for this temperature. There is a throttle body temp sensor, and the O2 sensor, and a coolant temp sensor, and all of these affect the air/fuel ratio and spark timing, but all of these are calculated on a predetermined 100F air charge, and that is dependent on the air temp sensor modulating the vaccuum to the blend door which lifts a certain amount to mix in air from manifold or front and from in front of engine.
When max power is needed there is not a lot of vaccuum available and therefor the blend door drops and allows in the coolest possible air for making max power, but steady eddie 65mph there is plenty of vaccuum and max MPG is achieved by best possible air fuel ratio and this is achieved by firing the injectors precisely.
So Before driving from California to Florida a month ago, I found this blend door, whenever the engine was running, was sucking only hot manifold air, even when the engine coolant and oil was at full temperature, in 70F ambient temps. I disabled it and started driving east, and my MPGS were crap, even considering the elevation changes and headwinds.
The first stop I wedged a fuel hose, lifting the blend door about 5/8", and the next tank I got over 17mpg, with good tailwinds, but it ran like crap when overnight cold. I watch the fuel gauge like a hawk and know how many highway miles to expect, and it was easily noticed that the colder it got outside, the faster my fuel gauge needle dropped even with the blend door lifted 5/8" of its ~2.25 inches of travel.
So it was extremely obvious cutting off vacuum to the temp sensor in the air cleaner was detrimental to my fuel economy and the 5/8" I wedged it open was better, in 65f, but not for 45f.
I bought a Carter TC13 air cleaner temp sensor, even though it ONLY looked to be the same, it was not listed as compatible with my engine.
It appeared identical and took a minute to swap.
So I took my flap sander on angle grinder and sanded the perimeter of the old sensor and took it apart.
There is a Bimetal leaf spring inside, that pushes a pintle and closes off airflow from a snout inside the aircleaner
When the sensor heats up, the bimetal leaf spring bends and allows filtered air from inside the aircleaner to enter the sensor and this reduces vacuum to the modulator and allows the door to drop, allowing in more cool air from infront of the radiator.
My pintle was stuck. Even once I freed it up, and let the bimetal spring push it back home, it got stuck there again.
The snout, in which this pintle resides, can be screwed in and out, to modify the temperature where it starts reducing the amount of vacuum reaching the modulator which lifts and lowers the blend door.
So the New Carter TC13 might not be dialed for 100F, but perhaps for 90F or 110F.
I will Put a K type thermocouple on it.
But I likely could just clean and return the original to function.
Knowing what i know now, from having opened it, I'll assume I could have simply heated up the sensor with a hairdrier and sprayed some silicone lubricant in there and freed up the pintle. I am not sure if there is/was an Oring at teh base of the pintle, yet.
Silicone however can do damage to the oxygen sensor, So One would not want to do this with the engine running, as an Inoperable 02 sensor reduces fuel economy by 50%, in my experience.
If there is no Oring, I think one could stick the tube of a can of brake kleen into the single snout on a sensor warmed to above 120f and free up the pintle.
I think it highly likely at 30 years old that this sensor has failed on every vehicle into which it or similar is placed and is negatively affecting highway fuel economy.
I do not know if a carb'd vehicle could be tuned so precisely as to make much of a difference in highway mpg, but these air cleaner temp sensors are on carb'd vehicles back into the 60's, and seemed to not disappear until the late 90's