Air cleaner temperature sensor

[Sac79]

I recently bought a vacuum pump to test the sensor and the motor in a hope to get the air mixing snorkel to work. I was glad to find the motor works fine.

In reading the emissions manual I found that the sensor should allow vacuum through below 75F and then not bleed off until 105F. No idea how that would work, but since mine doesn't do much above 40F, I ordered a new one. After waiting weeks for USPS to deliver it, sadly it functions no better.



I can not get either sensor to work in my garage, which is around 60F. I managed to get the old one to activate the motor after placing it in the freezer... Both work outside(mid 40s), but also bleed off even at those temps. I do have the Cold weather modulator and that does work. It held the vacuum outside and even held it when I tested the frozen sensor inside. So I suppose the system would work if I were to drive the truck outside now, but for how long?

So my question is, what temperature is optimal? The 105F is just the temp listed for my original and new sensor. There are also 90F and 75F options. Since I have a snorkel without the air mixing capability in addition to the mixing one, I'm thinking I might want warm engine bay air added constantly during winter. Since the sensors aren't working as I expected them to, I'm thinking the best way forward is just bypassing the sensor or plugging the bleed off valve... But that depends on what temperature air I should attempt to provide the engine. Maybe the 105F has thrown off my thinking and 60F is fine...

[Gary Lewis]

Rob - Did you try passing vacuum through the sensor both ways?  I've not played with those much but do remember the sensor I tried working one way but not the other.

As for the temperature for the sensor, I've thought that 105 would be best.  I say that because you want your carb to "see" a constant temperature all year long, and I know that in the summer 105 would be optimistic.

[ArdWrknTrk]

It's definitely 105F under the hood on all but bitter days, so that's what Ford set the carb mixture for. (IAT)

Rob, the air flap motor sees continuous (but not constant) manifold vacuum any time the engine is running.
Believe me, there's plenty to keep the flap in position.
I think the bleed restriction is there to damp the changing vacuum the motor sees.
Otherwise it would jump around every time you stepped on or off the gas.

[Sac79]

Thanks gents. It's entirely possible that I've tried it the 'wrong way' most of the time. I'll do some more testing...

[Sac79]

Both sensors will let through vacuum regardless of how you hook them up. For consistency I've settled on connecting the vacuum source above the bleed off valve. I tested both outside in mid-30s temps. Both would get up to around 10inHg and no higher, plenty to activate the motor, which is fully open bellow 5inHg. Blocking the bleed off valve, the old sensor would allow up to 20inHg, the new one only 15. Both bleed off constantly even at these low temps. The CWM keeps about 5inHg for a short while, about a min.

Back inside, temps low 60s, the old one will only get up to about 5inHg, the new one 8. So I tried them on the motor again and the new one opened it fully and the old one managed to take the pressure off the spring, but no more. The vacuum maintained by the CWM is enough to keep the motor activated.

I don't know what's different from yesterday, but I'm going to try the new sensor tomorrow without a stove pipe on the snorkel so that I can easily check the motor's functioning.

[ArdWrknTrk]

Thank you for this detailed dive into air cleaner sensor function.

I'm following those details, Rob.

[Sac79]

Sure Jim! I'm just posting my findings though, certainly not gospel. Neither sensor works like the manual says they should, ie activating below 75F and continuing to provide vacuum up to 105F... The old one hasn't work in the truck with temps down to mid 50s, the new one I'll try in the morning when it should be below freezing.

[ArdWrknTrk]

But your personal experience is gospel..

We all have expectations, but it comes down to experience.

You documenting that is what makes this forum better than BS.  👍

[old55pete]

I have been following this with some intrest. I have a question that may add to or subtract from the discution.

Could the operating temps be rated at the under hood temps and not outside ambient temps?  I ask because I work on Semi's, over the road trucks. I know that the temp on the engine coolant temp may be at 200 deg, if you put a non-contact thermomiter on the outside of the hood, on a 90 deg day, the hood will read between 600 to 900 deg. That being said, the under hood temp could be way above that. I have read between 1000 to 1500, and I have to admit that even I dont believe those numbers.

My point being is they may not need to stay open/ closed for as long as you think because of the under hood temp by it's self.

Again, this is just my humble opnion.

[ArdWrknTrk]

Steve, I think they certainly relate to the optimal inlet air temperature.

Ford can't control the weather, but they can decide on a temperature that they will calibrate the carburetor for.

Beyond that, they will try to make sure that 105° condition is met.

With a inlet drawing from in front of the radiator support it's not often that 105° can not be met.

(Again, JMHO)

[Sac79]

I agree with your observation Steve. If I start the truck in my garage and idle it outside, by the time I'm checking the 'mixing door' an ambient air temp of 50F probably isn't cold enough. Tomorrow should be though.

But yes, the sensor is definitely activated by the air cleaner temps, which could be higher than 75F even with ambient air temps at freezing once the engine is at operating temps. I'll report back tomorrow.

[old55pete]

Jim, that was kinda my point, they MAY not get met all of the time. It may be more a matter of just close enough to make it work right.

Again JMHO

[Andrew1983F100]

Sac79 wrote

I recently bought a vacuum pump to test the sensor and the motor in a hope to get the air mixing snorkel to work. I was glad to find the motor works fine.

In reading the emissions manual I found that the sensor should allow vacuum through below 75F and then not bleed off until 105F. No idea how that would work, but since mine doesn't do much above 40F, I ordered a new one. After waiting weeks for USPS to deliver it, sadly it functions no better.



I can not get either sensor to work in my garage, which is around 60F. I managed to get the old one to activate the motor after placing it in the freezer... Both work outside(mid 40s), but also bleed off even at those temps. I do have the Cold weather modulator and that does work. It held the vacuum outside and even held it when I tested the frozen sensor inside. So I suppose the system would work if I were to drive the truck outside now, but for how long?

So my question is, what temperature is optimal? The 105F is just the temp listed for my original and new sensor. There are also 90F and 75F options. Since I have a snorkel without the air mixing capability in addition to the mixing one, I'm thinking I might want warm engine bay air added constantly during winter. Since the sensors aren't working as I expected them to, I'm thinking the best way forward is just bypassing the sensor or plugging the bleed off valve... But that depends on what temperature air I should attempt to provide the engine. Maybe the 105F has thrown off my thinking and 60F is fine...

You don’t happen to have the part # handy ?

[Gary Lewis]

Part numbers and temp ratings are shown on the page at Documentation/Fuel Systems/Air Cleaners.  And you have to click on Air Cleaners as that is an actual page.  But to make it easy, here is the chart from that page but it doesn't show part numbers.  Unfortunately the catalog doesn't have a listing for those parts, but just says which one goes for what vehicle.

Maybe I can find that in another catalog?

[Gary Lewis]

Ok, here are the real part numbers.  And we may be one of the few places on the net that has these.  I'll put them on the Air Cleaners page.

[ArdWrknTrk]

It's just awesome that you have all this documentation available!

Thank you, Gary.  

[85lebaront2]

When I had my shop a lot of this was just coming out. I found that some of the temperature sensors had an adjustable bleed fitting that could be turned in to raise the "set point". You have to be careful as most of them I worked on had it either glued or Loctited in place.

[Gary Lewis]

Jim - I have the MPCs from 1948 on trucks and 1949 on cars.  So when the 1980 - 89 truck MPC gives an earlier part number but no info, I know where to go.  

Bill - That's interesting.  I wonder about these.  

[ArdWrknTrk]

Loctite is no good near plastic.

Gary, you go back all the way to the 1940's?!?!?

It's really helpful for me because I don't have an optical drive to read my MPC.
Nor a screen big enough....

Thank you for all the time you spend helping us with parts numbers and diagrams.  

[Gary Lewis]

Welcome, Jim.  I think we have the friendliest and best-informed community on the internet.