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Air cleaner temperature sensor, Dodge, perhaps others
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

[-] The following 1 user says Thank You to sternwake for this post:
  • heron (02-03-2021)

in short,hot air is less dense so the computer compensates by giving less gas = better mpg 

cold air is dense so the computer compensates by giving more gas = more power
"not of the body"
The system on my engine does not alter the A/F ratio by measuring temperature, it tries to maintain a set elevated temperature, at low throttle input, by mixing in heated air captured off the exhaust manifold with air captured from in front of the radiator.

The main device for achieving this blend of hot and cold air, has been inoperable for a while, due to the stuck Pintle in this sensor.

i would have to think this is the primary failure mode of this sensor, as the only other thing to go wrong inside of it, would be the Bimetal leaf spring strip failure, which is in my opinion extremely unlikely.

Now the vaccuum modulator which lifts the blend door could go bad, and the vaccuum lines and passages in the base of the throttle body could get clogged.

Anyway, for those with these sensors in their aircleaners, and who want to achieve best possible MPG, insuring this system operates as it should is highly desirable.

Those with carb'd engines might not see as much benefit, or perhaps they might see even more.
It depends on how they are tuned.

I think I will clean this one up and if I determine the pintle's base originally had no Oring, glue it back together and return it to service. The Carter TC13 I bought is said to be for a Ford.

The TC13's little snout which allows filtered heated air into the sensor and reduce vaccuum passed to the modulator, has a slightly different inner diameter. The Bimetal leaf spring of the TC13 could be different thickness or layup, and respond to temperature differently.

The dirty area inside the sensor, below inlet snout, shows the filter is not filtering everything. Particles smaller than the filter's pores have accumulated. Not sure if those particles are the reason the pintle got stuck, or there is an Oring that partially liquified with age.
There was no gummy O ring sealing the base of the piston.

It was just grimy and caked with 200+ K miles of dust which made it through the airfilter, perhaps made worse by the oil which one sprays on K&N filters, which I regretted using many years ago when I returned to standard filters.

I have rtv'd the sensor back together and will soon have a K type thermocouple near it, inside he housing, measuring the temperature that the CArter TC13 and this original sensor allow.

[-] The following 1 user says Thank You to sternwake for this post:
  • heron (02-03-2021)
Hole drilled, grommet inserted and RTV's from underside.
K type thermocouple ( temperature sensor probe) inserted through grommet.


Data Soon.
[-] The following 1 user says Thank You to sternwake for this post:
  • heron (02-05-2021)
I love having 1 cummins diesel truck 1 month before the computers & my last year before the computer International diesel ambo. when we were married 40 years ago my wife had bought a new Cordoba. We were flat broke & the computer died, $500 which could have been $5 millian so I was walking 8 miles to work when finally they figured out it had a 5 year computer warrenty. I've hated computers since then. Vehicles ran fine without computers.
"If a law is unjust, a man is not only right to disobey it, he is obligated to do so." - Thomas Jefferson
[-] The following 1 user says Thank You to Gr8ful for this post:
  • heron (02-05-2021)
Temp range with carter tc13 sensor....once engine at full temp and at light throttle was 89f to 129f...though 129 was only once and very brief. Usual range was 109f.

It changed faster than i expected, and was only steady when idling in park or neutral, drive foot.on brake. Though once parked was 94.5 5 the other 102.5.

New front window seals are much quieter at highway speeds.
Extended.reach slightly cooler spark .plugs yield smoother idle hot and cold and better throttle response.

Ngk zfr5n 2763.
Actually same heat range as champion rn12yc plugs as specd for.this engine.
Just slightly cooler than my.previous NGK gr4gp 2763

Average air temp into throttle body with carter light my estimation is 102.5f.

Higher throttle.levels it ~19f over ambient. Perhaps.drop more.if accellerating longer or better cold.air snorkel fitted.

This same.air cleaner temp in non computer controlled vehicles as well. Carbs can be tuned for a specific air charge temp, and this sensor tries to deliver it in order for max economy at light throttle, and during warm up.

If wanting.max power, then coldest possible air desirable.
Max throttle means no vaccuum to this sensor, and no manifold heat mixed in.
[-] The following 1 user says Thank You to sternwake for this post:
  • heron (02-06-2021)
So, how’s your mpg? Or do you know , yet. I’m going to have to check this out. Although tuning a carb is not in my area of expertise. I did rebuild a Bosch one, a million years ago, and it worked, though.
Two gloriously stinkin' badges.
Official YARC ship’s navigator.
I don't yet know.

Going west to east filling up every 390 to 440 miles
I got ~14.1 with vacuum hose to sensor disconnected, from AZ border on I-8 to near the Continental divide
16.67mpg from the continental divide to Van Horn Tx with blend door propped open ~3/4" and strong tailwinds
and basically 15.15 to 15.83 mpg from Vanhorn Tx, to Southwest Florida.

During the warmer part of the day, the gas needle dropped slower than it did at night when it got cooler.

If I filled up earlier in the day, I would be happy to see the mileage accumulated by certain hatchmarks on the fuel gauge to be quite good, only to have those gains wiped out at night when it got colder, but still averaging over 15.

This is driving 65mph and with light winds or slight tailwinds or on aft quarter. This is also with LT 30x9.5x15 all terrain (loud) tires which make my speedo and odometer dead nuts accurate. The LT 235/75/15 tires I used previously would have my speedo read 64mph when I was doing 60mph , and with the smaller diameter tires, which are also lighter with less rolling resistance.

The smaller stock sized tires would inflate the mileage actually travelled and make it appear as if MPGS were higher than actual.
If you have a smartphone, use a GPS speedo and see how accurate your speedo is. There's tons of variables in fuel economy from measurement error to terrain travelled and wind direction in addition to the obvious speed factor.

I always try and fill my tank on x country journeys at tanks as much as I can, on gas pumps where the passenger side sits lower than drivers. Still this varies quite a lot in just how full I get. Sometimes i only get 11 miles before the needle falls to the very top hatchmark, othertimes i can get as many as 50 miles. i take this into consideration on each tank of gas and adjust mileage expectations accordingly.

I just filled my tank yesterday, but I only got 20 miles before needle fell to top hatchmark on the last fillup in the Florida Panhandle, and I did a lot of driveway idling when playing with my power steering system, but it calculated out at 15.15mpg.

I'm hoping to average at least in the high 15's on my return west.

If you pull off your cold air snorkel, which is just the two bolts on teh radiator support, you can see into the air cleaner snout. When the engine is cold and warming up you should see the little blend door closing off the snout, forcing the engine to feed on hotter air collected off the exhaust manifold.

Once the engine is at full temperature this blend door should drop, mixing in hot manifld air with cooler ambinet temp air .

I've been in contact with someone who has an '88 B250 extended campervan with a carb'd 360 v8. They found their aircleaner temp sensor's pintle was not stuck as mine was, but the vacuum actuator, which lifts and lowers the blend door, its diaphragm was bad and the blend door never moved no matter how much vacuum was applied.
This is also a minor vacuum leak, in addition to making this whole heated air system inoperable. The '88 b250 with a 318 has throttle body fuel injection, only the 360 still has the carb. 1989 model years both engines had TBI. 1994 was the first year of the magnum engines in Dodge vans and these have multiport fuel injection which is more efficient, and also the more rounded body style which.

They had been complaining about how crusty it ran until it got to full temperature and of very poor mpgs despite always driving slowly. They are happy to have found this system inop as it gives hope of better economy easily achieved.

When mine was disconnected it would bog down on the first few accelerations of the day.
and to complicate things more,high ethanol gasoline gets less mpg than low/non ethanol gasoline,so e85 will get significant less mpg than e10,it varies from state to state
"not of the body"

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