I wanted to know what the MAF sensor is responsible for. What does it measure and are these measurements affected by the outside temperature at the same RPM?
I am trying to figure out what seems to be a fairly common problem with 4.0L Ford Explorers (from complaints on different Explorer forums) producing a high-pitch whislte, during the winter season, when accelerating and the RPM is peaking just before the gear shifts.
Well the MAF sensor does exactly what it says. It converts a voltage reading into a grams per second g/s reading that is an INPUT to the PCM. Now the MAF in an explorer may or may not have an IAT (Intake air temp sensor) integrated into it. Check the intake tube for a sensor about 10 inches from the air box, if there is a sensor there than the IAT is external. If not. Internal in the MAF.
The MAF sensor helps in guiding the PCM in to a closed loop operation (this requires many many other sensors too). The MAF is also used by the PCM to diag if there are any problems with the engine. Kinda like if my rpm is 1500 than my MAF should read 12 g/s and then my SFT should be set to this if my O2S11 is reading this. Kinda an a+b+c=x, but if say there is an intake leak.
Maybe your MAF will be correct, ECT (engine coolant temp) is ok, RPM is ok BUT one of your 02 sensors is calling for full rich all the time. Well that would indicate an intake leak.
This is all alot of typing, but I think that the MAF sensor would not be causing the problem. The noise you are describing sounds like somehting I have encountered on B4000's here in Canada. Check and see if the noise is coming from the IAC valve (the silver one on the top of the intake not sure what Ford calls it)
Cosmo. Mazda TEch
January, 21, 2007 AT 5:40 PM
Thanks Cosmo for the thorough explanation. I'll check the IAC valve, but does the IAC valve control air intake when the car is in gear and moving, or does it do its thing only during idle (as its name suggests)?
Thanks again for your help with this.
January, 21, 2007 AT 5:48 PM
That's the same question I've wondered about. Every printed piece on the matter indicates that during idle the IAC valve takes over, and that while the throttle plate is open it's on standby, however why would it make the noise it does when it's dirty. Unless air passes through it at all times, and that based on the design, buildup in it causes a certain whistle.
January, 21, 2007 AT 6:45 PM
The IAC control the idle. Sometimes when they stick open they cause idle problems or stall. But sometimes they become 'fau; ty' and make a humming noise at idle that comes through the air box. Really loud 'hummmmm'