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bimetal sensor in airbox

Discussion in 'General Explorations!!' started by punkbek3886, October 9, 2002.

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    1. punkbek3886

      punkbek3886 Active Member

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      when is this thing supposed to let air through? i thought it was when the intake temp was low but it doesnt do it even when the car is first started. will getting water in it make it go bad? i think it might be broken, but im not sure.

      if broken, what symptoms will it cause?
       
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    3. TDG

      TDG Elite Explorer

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      Well... it depends on what type of air. The bi-metal sensor controls the vacuum motor in the lower intake tube. When the underhood temp is cold it will route warm air from the exhuast manifold into the air box and as the underhood temp comes up it will begin to blend cold air into the mixture and maintian the air temp between 70 - 100 something degrees.

      I'm not sure if getting water in it will cause it to go bad, old age might but there really isn't much to it.

      I'm not sure what the symptoms are of a bad one and I don't remember ever reading about anyone on here having a bad one or noticing it. I don't think it will throw a code with the older OBD systems in the 1st gen explorers.

      I would suggest getting a haynes, ciltons or factory service manual to trouble shoot the system as the intructions are a little lengthly to type out here.
       
    4. dogfriend

      dogfriend Human-Animal Hybrid

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      On a fuel injected vehicle, you may not notice any symptoms but the emissions will be worse until your engine is fully warmed up. Ive noticed that my 97 doesn't have a heat stove (the metal thing on the exhaust manifold that the air tube connects to) or a bimetal valve (the thing in the airbox that controls the air coming from the heat stove).

      Getting water repeatedly in it may cause it to fail because it gets corroded and can't move freely. You are right that it should be opened when the air is cold and close when the air is warm. The valve uses a piece of metal (actually two metals) that move in response to the temperature.

      On a carburated engine, you would definitely notice because it would run like crap (hesitate, buck, stall) until the engine warmed up. This was particularly true in the early days of emission controlled engines (70's thru mid 80's).
       
    5. punkbek3886

      punkbek3886 Active Member

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      thanks. there are two vacuum lines coming from it, i know one of them is to the vacuum motor, but does anyone know what the second one is to? i have a haynes and a chilton's manual but they are not very specific.
       
    6. dogfriend

      dogfriend Human-Animal Hybrid

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      I'm speculating that the other one must go to the vacuum source which is on the intake manifold somewhere. You need a source of vacuum to operate the vacuum motor. I don't have one on my 97, so I can't check this out for you. Maybe someone with an early Explorer can?

      Also, you should have a vacuum diagram on the sticker under the hood. This might help.

      I'm guessing that the vacuum routing is like this: Vacuum comes from port on intake manifold (it may have a valve near intake). Vac line connects to bimetal valve which is open when cold, closed when hot. When cold, vacuum signal passes thru bimetal valve and is applied to vacuum motor which in turn opens the air duct leading from the heat stove.

      Of course, I don't have a manual or a vehicle to look at, so I could be completely wrong ;)
       
      Last edited: October 10, 2002
    7. punkbek3886

      punkbek3886 Active Member

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      at least you are trying to help. thank you
       
    8. dogfriend

      dogfriend Human-Animal Hybrid

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      I found this in my Haynes manual. If you have it, Chapter 6, Section 18, Inlet air temperature control system (1994 and earlier models).

      It does tell where the two hoses go (for the bimetal sensor) ; one is coming from the intake manifold, the other goes to the vacuum motor under the air cleaner.

      It has a section describing how to check out the system; it also describes the purpose of having the system which is to reduce emissions while warming up the engine and improving driveability. It tries to maintain inlet air temp between 70 deg F and 105 deg F. If your outside temperatures are normally in this range (likely in FL) it may not matter if it works if it is stuck closed (air not coming from heat stove).
       
    9. punkbek3886

      punkbek3886 Active Member

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      wouldnt giving it colder air boost performance also?
       
    10. dogfriend

      dogfriend Human-Animal Hybrid

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      Maybe.

      Yes, in general colder air is denser so you have more O2 available so the injectors can feed more fuel so you get more power (theoretically). With a warm engine, you generally want the coldest intake air available for max power.

      However, when your engine is cold, the fuel does not atomize as easily and may condense onto the cold engine parts (on a carb equipped car it would condense on the intake manifold walls) and not burn completely. Also, in the Haynes manual, they hint that the inlet air control allows the fuel/ air mixture to be leaner during warm up (for emissions). The PCM is probably programmed at a set fuel/air ratio which takes the inlet air valve into account. If it isn't working this would probably screw up the fuel/air ratio during warm up.

      So, in general, colder air is better except during engine warm up.
       
    11. punkbek3886

      punkbek3886 Active Member

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    12. dogfriend

      dogfriend Human-Animal Hybrid

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      Did you ever find where the vacuum line plugs into the intake manifold? If it fell off, you will have an open fitting sucking air into intake manifold (huge vacuum leak). This happened on my Ranger once and made it run like crap until I found the problem and plugged the vacuum line back in.:rolleyes:
       
    13. punkbek3886

      punkbek3886 Active Member

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      if i were to take my injectors out what would i use to clean them?
       
    14. dogfriend

      dogfriend Human-Animal Hybrid

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      :confused:



      Its not necessary to take injectors out to clean them. A shop will hook up a machine to the fuel pressure port on the fuel rail and introduce injector cleaner solvent while the engine is running.

      The only time I have ever taken the injectors out was to replace the o-rings that seal around them. If you take them out for some reason, you could soak the ends in solvent to try to clean them, but don't insert anything into the end or try to scrub them because you could damage the metering valve at the end and ruin them.
       
    15. oceanworker

      oceanworker Member

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      Those two vacuum line go to the bi-metallic sensor in the side of the air filter box. If you drive in cold weather, the sensor is important. It is basically atemperature switch which will divert air from the exhaust manifold to your air intake when the air is cold aoutside. This is an area of the air intake system which is often neglicted. Check out the intake tube from the grill to the air filter box. the heat duct valve may be stuck closed. Also I once heard a story of a friend who found a rats nest in there resulting in very bad drivability plus a CEL which no one could figure out.
       

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