- Joined
- February 8, 2003
- Messages
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- City, State
- Sacramento, CA 95827
- Year, Model & Trim Level
- 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:
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
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:
Turn it over and you get the business side. These two litle wires between the posts are the actual working part of this sensor....
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...
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:
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.)
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:
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
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:
Turn it over and you get the business side. These two litle wires between the posts are the actual working part of this sensor....
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...
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:
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.)