Thread: strange v8

Mmmm.....It's not possible to make any adjustments to the MAF without the right equipment and voltage tables are very often incorrect.

The 'hot wire' type (which I think your's is) has a heated wire element suspended in the air stream, as the air flows over this wire it draws the heat out. This reduces the resistance of the wire therefore allowing more current to flow. The circutry in the MAF measures the current flow and sends a corrisponding voltage to the PCM.
When you open up the accelarator, more air flows over the 'hot wire' and cools it down, reducing the resistance which allows more current flow. The MAF sends the correct voltage to the PCM, which increases the injector on time.
Here's a link which explains all the different types and how they work. [ame="http://en.wikipedia.org/wiki/Mass_flow_sensor"]Mass flow sensor - Wikipedia, the free encyclopedia@@AMEPARAM@@/wiki/File:Mass-airflow.jpg" class="image"><img alt="" src="http://upload.wikimedia.org/wikipedia/commons/thumb/e/e8/Mass-airflow.jpg/220px-Mass-airflow.jpg"@@AMEPARAM@@commons/thumb/e/e8/Mass-airflow.jpg/220px-Mass-airflow.jpg[/ame]

I'm not sure how it changes the voltage's in your case.

I would be very impressed if you have managed to get it back at it's correct voltage. The only way to know is to look at fuel trims (if possible) and the output from the Oxygen sensor....... Put that multimeter down . For that you need a scan tool or scope. A analogue multi meter may do the job, not sure. Or an exhaust gas analyser.

"so is it a case of ''if it ain't broke don't fix it or what,"

Or 'if you don't know how it works, don't fix it".


HTH.

The flapper type has a black plastic plug under which there's a socket head screw that adjusts the flap. Is that the one? A pic of the offending AFM.

If it is the 'flapper type' technically that is an airflow meter not a MAF (mass air flow). I have been pulled up on that a number of times.

The air trying to move through that sensor pushs against the spring loaded flap. The more you put your foot down the more air is pumped through the engine therefore more air trys to get past that flap and the more it pushs the flap back.
Internally there is a potentiometer and the flap is connected directly to this potentiometer. As the flap moves it creates a variable voltage on the signal wire to the PCM.

The adjustment is the 'air by-pass screw'. That mainly effects the idle mixture. Although it will effect the rest of out put voltages to a certain extent. More down the bottom end.
It works by allowing unmetered air through without passing the flap. There fore the more the screw is screwed out, the less air pushs on the flap at idle. This sends a lower voltage to the PCM which then reduces the injector on time. Which gives you a leaner mix. And vicer versa.

One problem this type of meter can have is flat spots at certain RPM (there is a post on here that suggest's this could be the fault). This is caused by the carbon track in the potentiometer being worn thin in a well used part of the track. This results in the PCM receiving a reduced voltage output. Again going lean.

Hope that makes sense.