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Engine Sensors - Part 2 - Mass Air Flow (MAF) Sensor

Discussion in 'Computers, Chips & Tuning' started by Glacier991, March 13, 2006.

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    1. Glacier991

      Glacier991 EF Tranny Guru Moderator Emeritus

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      Computers now pretty much run our cars in every respect. Adjusting fuel mixtures to a degree of precision not previously attainable for one thing. They shift our transmissions and they adjust for changes in the operating conditions and aging of components. BUT... the old saying "Garbage in - Garbage Out" is still applicable. The computer needs valid accurate inputs to do its job effectively. One of those inputs is telling it how much air the engine is "breathing". This is measured by several types of sensors, depending on the manufacturer, engine and year. This thread is about the Mass Airflow or MAF Sensor... sometimes refered to as a heated wire airflow sensor (and there is a slightly different kind known as a hot film sensor which is very similar). The other kinds are the MAP sensor, which operates quite differently and will have a thread of its own, and the Vane airflow sensor, which I will not be discussing.

      The operation is thus: There are two wires suspended in the intake airflow. They are heated to a predetermined temperature (about 212 degrees over ambient). The increase in the energy required to maintain that temperature can be measured and correlated to airflow at any given intake air temperature (see now why we measure intake air temperature on these kind of engines?)

      The system is pretty ingenious, and works well. On very rare occasion the wires can get coated with soot or particulate matter affecting the performance. FORD did not plan that these sensors would be cleaned, only replaced. They did not want the weekend warrior fooling with them. SO, enter the torx security screw. This is a standard torx screw with a pin in the middle, and is used to hold the MAF in position. They look like so:

      [​IMG]

      Now you will hear that you can take a small punch and break off that post, and you can... but why? Proper bits are in the $5 - $10 (for a set) range. Do it right folks. Get the proper tools.. in this case a t-20 torx security bit... it looks like this

      [​IMG]

      The MAF is held into the air intake plenum by two of these. Remove them, unplug it and carefully pull it out of the plenum mount, and here's what you have:

      [​IMG]

      Turn it over and you get the business side. These two litle wires between the posts are the actual working part of this sensor....

      [​IMG]

      They are easily damaged, so if you find a need to get into this sensor - BE CAREFUL. Here is a closeup, not a great pic but you get the idea...

      [​IMG]

      If you have a need to check and/or clean yours (as this thread will discuss in more detail later on) you can clean them with brake cleaner, or, my preference, use electrical contact cleaner, which leaves NO residue. Here is what I used:

      [​IMG]


      Now about cleaning. You would THINK that they'd get pretty dirty being in the airflow (think about your furnace filter for example) yet they rarely need attention, why? Well a little known fact is that on engine shut down a circuit heats those little platinum elements to about 1000 degrees...CENTIGRADE!... burning off any contaminants. So, if yours is dirty, you may have lost that function... never say never but these rarely need to be a source of worry cleaning wise. There are plenty of stories where cleaning the MAF improved an idle, but ME ? I have to wonder if the self cleaning cycle was working correctly. I'm not guessing cleaning the MAF needs to be high on your Saturday automotive "to do" preventative maintenance list.

      Ok, so other than to show you my MAF, why did I even bother to pull it out of the car? In other words what symptoms might make you suspect a MAF?

      If you just think what a bad input for air might do to the ability of the computer to calculate and create a proper A/F ratio you'll have most of the "usual suspects" list down. Ex. The vehicle may be hard to start, or stall soon after starting. It could hesitate under load or surge. The idle could be rough. You may find that the engine runs excessively rich or lean. In ODB-II vehicles or in select OBD-1 (like my 93 Sable and a lot of early, pre OBD-II Chrysler vehicles) you can also observe these things directly on a scanner.

      A bad or failing MAF will NOT always set a code. Typical FORD codes related to MAF are codes pertaining to MAF voltage out of range etc.

      The beauty of ODB-II scanners is they will allow you to read a MAF output voltage. It should be smooth and vary with accelerator push. Voltage will vary in typical operation from around 1 V to about 2.5V. (See graph.)

      In my case, I had my 93 Sable, a few blocks from my house last weekend, cold, exhibit some odd symptoms. The idle at a stoplight was high. I thought maybe I had a sticky cable setup and goosed the accelerator, and the idle stayed high (1800 rpm in neutral - where I had shifted to see what was up). When I put it back into gear it died, and refused a restart. It did start when I returned later, like a flooded engine might.

      My suspicions were possible problems with TPS, MAF, IAC, then ignition fault and then gawd knows what.... so when I had time I decided to check into those things. These threads (this one the IAC and soon the TPS thread) are the result. My MAF ? On the scanner ...smooth movement, voltages in range. (BUY a SCANNER! - best tool in the toolbox these days) On visual exam, as you can see... clean as a whistle. Everything A-OK. Still.... was worth the check, and this thread was the result. (Oh.... and no code was set with my problem).

      Now we all know a little more about MAF's.

      (That is it for tonight. I will post sensor value voltages, and output graphs in the days ahead. Thanks for letting me get this started.)
       
      Last edited: March 14, 2006
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    3. BrooklynBay

      BrooklynBay Moderator & long time member. Staff Member Moderator Elite Explorer

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    4. dogfriend

      dogfriend Human-Animal Hybrid

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      I just wanted to add that (at least on my 97) Ford also adds a dab of epoxy to the recess of the Torx screw. You can chip it out (carefully) with an ice pick or other sharp instrument to allow the Torx bit to fit into the recess.

      Wikipedia also has some good info:

      http://en.wikipedia.org/wiki/Mass_airflow_sensor
       
    5. shamal

      shamal Elite Explorer

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      Thanks Glacier, you're a great help!

      read your post on cleaning the MAF, it helped me solve a riddle no one told me about! Engine idles smoother now !
      Am tracking down the software you mention a few years back, to hook up my notebook. Been flying from the seat of my pants since I was a kid, it's time to start reading the codes etc. ! No use buying another piece of hardware when I own a portable computer ! Thanks for that tip too !!
      Thanks for all the effort you put in here, it's very much appreciated !
      shamal
       
    6. chamuko

      chamuko New Member

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      thanks but also more help please!!!

      Hello guys I love this forum as it rocks I do own a explorer too 2000 6v sohc and same problem as everyone else the iddle won't stay put some day do some days don't I changed the IAC brand new one , cleaned the MAF sensor with electrical cleaner non residue and today still revs ok at start up then after a while specially after it rains or temp changes it shuts down , of course as you guys immagine after starting it again and keeping my foot on the gas pedal stay till it feels like it to iddle on its own again , so therefore please someone help any more tips greatly appreciated and keep up the good info flowing . thank you .:(
       
    7. ajay

      ajay New Member

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      Wrong thread sorry
       
    8. Glacier991

      Glacier991 EF Tranny Guru Moderator Emeritus

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      Chamuko, investigate your throttle position sensor.
       
    9. MarineSNiper217

      MarineSNiper217 B

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      anyone know if I were to buy a aftermarket universal intake, would I be able to mount the MAF sensor to it and have it still work properly? At our Advance, they sell an (I think) APC Universal AirIntake System.
       
    10. cloaked_chaos

      cloaked_chaos Elite Explorer

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      I think I have seen threads stating that it is possible to do that, but I am no professional. I am just an 18 year old who does all his own work. You may want to try the forum's search feature if you haven't already.
       
    11. daxb

      daxb New Member

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      Help please - something poured into the torx security screw?

      So I finally get the assembly out and get one screw out with the t-20 only to notice that the other had some kind of coating on and it it? It looked sort of metallic on top (silver or gray) and it slowly coming out as I chip away as some sort of epoxy or plaster. Anyone know what this stuff may be and/or how to get it out easier so I can unscrew the dang screw to clean the MAF sensor rather than buying a whole new assembly? Gahhh, would that be ford that did that? Who else would bother?
       
    12. dogfriend

      dogfriend Human-Animal Hybrid

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      From my post above:


       
    13. daxb

      daxb New Member

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      That is what I finally did

      Took forever, but I got it done and removed. The wires looked clean, but I sprayed with the electrical contact spray anyway, put it back together and into the housing then attached the wires, etc. I hope it works. I did this because my truck was chugging when accelerating (at first, at low and accelerating speeds) but now chugs at idle.

      I stopped by Autozone to pick up the right items and had them scan and the only code was my typical 402, which I think is the EGR flow excessive, which has been there forever.

      Would this issue have anything to do with the fact that I recently had my a/c recharged (would not charge when I did it manually with the RU and gauge I bought at autozone, but a shop emptied and recharged plus checked for leaks, which there were a few but quoted as expensive to fix) and have been running it as much as I can stand in these high 95+ temps in Birmingham, AL?
       
    14. dogfriend

      dogfriend Human-Animal Hybrid

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      I kind of doubt it, unless your compressor is in bad shape and putting an extra load on the engine.

      If your EGR valve is stuck open, it might explain why your truck isn't running well; it should only be open at cruising speeds with a warm engine - otherwise it will throw off the A/F ratio.
       
    15. daxb

      daxb New Member

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      The CEL for 402 has been on at least a year


      This just started about two weeks ago. Will see how it runs tomorrow since I've cleaned the MAF. After that, I guess I will try and check the vacuum to make sure a hose isn't loose or badly cracked. Not really sure how to do that, time to go check the forum. I'm not very mechanically inclined.

      I appreciate the advice by the way
       
    16. Kimiann

      Kimiann New Member

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      My 94 Ford Explorer has 200,000 miles (mostly highway), doesn't use oil and never gave me a problem til now. Just a few days ago the check engine light came on. I took it to Autozone and they said "numbers 172 & 181 is showing lean b1, number 176 is showing lean b2, number 186 showing injector pulse highes and number 332 EGR valve opening not detected". She does now start with a rough idle but warms up nicely yet she does not seem to have any power, like she is going up hill towing a brick trailer behind her. I've got no clue where or what to begin with or what the number means, could you help a gal out?
       
      Last edited: March 14, 2008
    17. Turbozombie

      Turbozombie New Member

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      MAF Screws

      The metallic top on the other screw, is it chipped off? Or are you referring to chipping away at the expoxy under the metallic top?
       
    18. kingram

      kingram New Member

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      MAF Sensors need to be fooled for hho usage

      Hey Everyone;
      It's nice to have found this forum. I appreciate all of those that participate. I'm wondering if this forum would be able to answer my question!!
      I have installed an hho water as gas device on my 1996 Ford Ranger XL, and it has improved my mileage considerably for the first week. Then after that, I think the MAF sensor caught up to the fact that there was less oxygen getting to the engine, and increased the gas flow. Now I'm back to the same mileage that I began with. I talked to others, and they told me to just wrap the MAF sensors with aluminum foil to keep the heat in.
      I was just wondering if anyone could help me in not only finding out where the MAF sensors are, but how many there are, and if you have any ideas about hooking up a device to fool the MAF sensor in what richness it is getting?
       
    19. walterGT67

      walterGT67 New Member

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      Thanks for the info...
       
    20. Colin2722

      Colin2722 New Member

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      i just wanted to thank you guys for this endless information. fixed my cel in less then 30 min thanks to this site.

      thanks again
      Colin
       
    21. 1996X

      1996X Active Member

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      Thanks you Glacier for doing a write up on this. Just got mine done a few minutes ago. Only problem I had was, same as daxb, with the covering on one screw. Just used a dremel and small cutting wheel and made a slit and used a flat head screwdriver to take out. fairly simple.
       
    22. Rigger 19

      Rigger 19 New Member

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      Thanks for posting this Glacier991 just finished cleaning now to put it back in and find your thread on the TPS.

      as for the screw with the epoxy i just used vicegrips and spun it out, worked fine :)

      Thanks again
       
    23. OneLever

      OneLever Active Member

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      Invaluable information Glacier991 thank you for posting this.
       
    24. trailertaskforce

      trailertaskforce New Member

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      Glacier,
      Thanks for the awesome info. My idle was as you described, (1800 RPM's in N) spark knocked BADD under a load, surging while accelerating, just ran like crap. I bought a can of Mass Air Flow sensor cleaner ($6.99 @ O'Reilly auto parts) Took the MAF sensor out not seeing any trash or soot I cleaned it any way. Also, i took out the aluminum housing that it sits in as well and cleaned that as well, inside AND out. It evaporated rather quick on the outside I still gave it 20 mins to dry on the inside. The directions on the can state LET DRY COMPLETELY BEFORE REINSTALLING OR ELECTRICAL SHORT WILL RESULT ON THE COMPONENT. I put it all back together, started it up, and this thing runs like a champ! The spark knock is barely noticable. Spark plugs and wires are next. To think I've had this thing to every known mechanic here and NO one knew a $7 can of cleaner and 40 minutes fixed what has been a problem for MONTHS! Thanks again, you guys absolutely RAWK!
       
    25. cknorw

      cknorw New Member

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      MAF Sensor

      I experienced a gradually worsening spark knock over peroid of 6-9 months in my Crown with loss of power. After research, found the MAF sensor was possible culprit. It didn't look dirty? I cleaned it with a (keeping in mind I wanted to be delicate with it) a feather duster as I didn't research what to clean with. Noticed an immediate diffference. No knock. Its been at least 6 months now. Never set a code.
       
    26. Amznwmn

      Amznwmn New Member

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      A Place to Start

      I just wanted to say thanks for giving me so much information here. :thumbsup:

      I've spent all day today inside the engine compartment of my Explorer, cleaning the MAF sensor, cleaning the IAF and tryingto do a tune up. My hands and arms, however, DO NOT fit down the sides of this engine in between all the other crap that is attached. URGH! :(

      CEL has been on for a couple of years (I know, I know), but couldn't get through DEQ to get new tags so I had to do something.

      Until I read all this stuff, I didn't know I could take it to AutoZone for the codes (another BIG thank you :thumbsup::thumbsup:). Found out that my suspicions were correct in that codes said either MAF or oxygen sensor.

      I think I will wait until Monday to replace the two front sensors though because I need to let all the bruises on my hands and forearms heal (from trying to squeeze them into places they don't belong!!).

      Thanks again for all the VERY helpful, useful info. Hopefully, after replacing those oxygen sensors, it will pass DEQ.

      Keep up the great posts!!
       

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