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Map sensor cleaning

Discussion in 'LH: Large Cars, 1993-2004' started by movinyou, Dec 9, 2017.

  1. movinyou

    movinyou Active Member

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    Hello all, while looking up something on NAPA's website I noticed an article on cleaning the map sensor. I would think if it was causing problems, the car would pop a code. Is this a smart thing to do or is it a time waster? It was pushing better gas mileage and better engine response. Seems to me, if the air filter is kept serviced, their should be minimal dirt on the map sensor. I'd appreciate some thoughts on this. Thanks
     
  2. ImperialCrown

    Level III Supporter

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    The MAP (manifold absolute pressure) sensor should set a fault code if the vacuum doesn't match what the PCM thinks that it should be according to the throttle opening (TPS).
    It would also set a code if the MAP signal line was shorted to voltage (5v) or shorted to ground (0v). 'Shorted to voltage' faults are usually due to an open circuit. A 'real' signal to the PCM generally is between 4.5v and 0.5v and as long as the corresponding TPS signal agrees with that.
    By 'dirt' they must mean carbon deposits like what would be found in a dirty throttle body or on the backside of intake valves. It shouldn't be from dirt carried in by outside air past the air filter.
    The factory service manual gives no procedure for 'cleaning' a MAP sensor and I have never heard of a vehicle manufacturer giving a procedure for this. If the MAP has carbon deposits inside it that are affecting its performance, the sensors are cheap enough where I would just replace it. Always use an OEM sensor.
    It kinda looks like an aftermarket scam to sell more spray cleaners to me. Beware of marketing claims.
    Z_K690fo5oy.JPG

    OTOH, MAF (mass air flow) sensors have cleaners available, but domestic Chryslers don't use the MAF system.
    fa72e89a6909206997f92268b13cdb55.jpg
    Only Daimler (Sprinter/Crossfire) and Mitsubishi used MAFs on the air intake. Turbodiesel engines usually use the MAF system.
     
  3. movinyou

    movinyou Active Member

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    Hey Thanks Dude. I found it odd that even NAPA would post something that just seemed like it would create more problems than it was worth. I agree. Just a way to sell more cleaner or sensors!
     
  4. Tomguy

    Tomguy Well-Known Member

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    It'd have to get dirty to the point of throwing a code. That being said the PCV system on some of these engines (the 3.2 and 3.5, and maybe the 2.7 as well) are known to allow a lot of oil into the upper intake. Removing the upper intake on both my DD 300M (that had 170k at the time) yielded a good 4 tablespoons of oil. Same with the one from my 117k one I sold. If you see oil around the front of the manifold by the manifold tuning valve (the circle in the front with a plug), there's oil in the manifold. As well as carbon on the butterflies in the intake, and the throttle body, and the IAC. A good cleaning on these can smooth out a rough idle.
     
  5. Bob Lincoln

    Bob Lincoln "CHECK FAULT CODES"
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    Since the pressure sensor IC in the MAP sensor is under vacuum and not pressure while the engine is running, the IC can only be exposed directly to dirt and fumes when the engine is off. I believe the manufacturer would protect the die with a parylene coating or similar product to prevent harm in an application like this. In any event, a code would not be tripped unless the endpoints were out of range or there were no vacuum, with the output not matching the expected voltage.
    There are two prevalent failure mechanisms for the MAP sensor. One is a functional failure where the chip cracks. The other is drift, where the output drifts out of the linear curve in its midrange, but this does not trip a fault code. Instead, it shows up as the mixture being too rich or lean (usually too rich). I had the latter failure, and it caused the O2 sensor to throw a code, when the O2 had nothing wrong with it.
     

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