Engine Sensors - Part 2 - Mass Air Flow (MAF) Sensor | Ford Explorer Forums - Serious Explorations

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

Glacier991

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1992 XLT
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:

DSCN6384.jpg


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

DSCN6385.jpg


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:

DSCN6386.jpg


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

DSCN6387.jpg


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...

DSCN6388.jpg


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:

DSCN6389.jpg



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.)
 



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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
 






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
 






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 .:(
 






Wrong thread sorry
 






Chamuko, investigate your throttle position sensor.
 






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.
 






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.
 






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?
 






From my post above:


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.
 






That is what I finally did

From my post above:

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?
 






r.

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?

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.
 






The CEL for 402 has been on at least a year

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.


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
 






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?
 






MAF Screws

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?

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?
 






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?
 












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
 



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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.
 






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