abecedarian

In general, the dropouts will be covered by either the TPS, coolant and O2 feedback, if you happen to cross one of those under gentle acceleration (a sudden change in the AFM reading without changing any of the above will 'blend'), or the WOT map in the ECU which primarily maps RPM's and coolant temp against AFM and can interpolate rather smoothly between drops.

Not saying hooky's information won't help though, but you're better off using an analog ohm meter for this instead of a DVM- you can sneeze on the AFM and throw a DVM off just from the moisture in your sniffle.

thook

So, you're saying the fluctuations aren't that big of a deal? That they are/can be compensated for, buffered, so to speak? I'm wondering why if that's true that in the two cases with my vehicles it didn't happen that way. In both cases, when I replaced the AFM with units that did not behave in a fluctuating manner, both vehicles ran better.....as they should.

Also, I only ever use my DVM. It's all I have. In both cases, again, when I tested the new units that caused my vehicles to run right, I was able to get steady wave patterns in resistance. I may have even sneezed once.

I'm not going to argue that you and InternetRK seem to understand something more about volt/ohm meters than I do.....I'm not an engineer or technician. But, I have to compare my experience with your knowledge. There seems to be a gap there.????

buckz6319

here is something interesting


Automotive Repair Library, Auto Parts, Accessories, Tools & Equipment, Manuals & Books, Car BLOG, Links, Index



Vane Airflow VAF Sensors

Copyright AA1Car


Airflow sensors are used on engines with multiport electronic fuel injection. This is because the amount of fuel delivered by an EFI system is controlled by a computer (powertrain control module or PCM) which turns the fuel injectors on and off. The airflow sensor keeps the computer informed about how much air is being pulled into the engine past the throttle plates. This input along with information from other engine sensors allows the computer to calculate how much fuel is needed. The computer then increases or decreases injector duration (on time) to provide the correct air/fuel ratio.

On engines equipped with Throttle Body Injection (TBI) or a Speed-Density type of EFI system (most Chryslers and some GM applications), air flow is not measured directly but is estimated using inputs from the throttle position, manifold air temperature and manifold absolute pressure (MAP) sensors. But on engines with airflow EFI systems, airflow is measured directly by a vane airflow (VAF) sensor, a mass airflow sensor, or on some Japanese applications, a "Karman-Vortex" airflow sensor.

VANE AIRFLOW APPLICATIONS

Vane airflow sensors (also called airflow meters) are found mostly on German imports equipped with Bosch L-Jetronic fuel injection, Japanese imports equipped with Nippondenso multiport electronic fuel injection (made under Bosch license), and Ford vehicles equipped with the Bosch multiport EFI (such as Escort/Lynx, Turbo T-Bird and Mustang with the 2.3L turbo engine, Ford Probe with the 2.2L engine), and various other makes and models of vehicles.

HOW A VANE AIRFLOW SENSOR WORKS

A vane airflow sensor is located ahead of the throttle and monitors the volume of air entering the engine by means of a spring-loaded mechanical flap. The flap is pushed open by an amount that is proportional to the volume of air entering the engine. The flap has a wiper arm that rotates against a sealed potentiometer (variable resistor or rheostat), allowing the sensor's resistance and output voltage to change according to airflow. The greater the airflow, the further the flap is forced open. This lowers the potentiometer's resistance and increases the voltage return signal to the computer.

The vane airflow sensor also contains a safety switch for the electric fuel pump relay. Airflow into the engine activates the pump. So if the engine won't start because the fuel pump won't kick in, the problem may be in the airflow sensor. The easiest to check the safety switch is to turn the ignition key on and push the flap open. If the fuel pump does not come on, the contact inside the sensor is probably defective.

A sealed idle mixture screw is also located on the airflow sensor. This controls the amount of air that bypasses the flap, and consequently the richness or leanness of the fuel mixture.

VANE AIRFLOW SENSOR PROBLEMS

Vane airflow sensors as well as all the other types of airflow sensors can't tolerate air leaks. Air leaks downstream of the sensor can allow "unmetered" or "false" air to enter the engine. The extra air can lean out the fuel mixture causing a variety of driveability problems, including lean misfire, hesitation and stumbling when accelerating, and a rough idle.

Dirt can also cause problems. Unfiltered air passing through a torn or poor fitting air filter can allow dirt to build up on the flap shaft of a vane airflow sensor causing the flap to bind or stick. The operation of the flap can be tested by gently pushing it open with a finger. It should open and close smoothly with even resistance. If it binds or sticks, a shot of carburetor cleaner may loosen it up otherwise the sensor will have to be replaced.

Backfiring in the intake manifold can force the flap backwards violently, often bending or breaking the flap. Some sensors have a "backfire" valve built into the flap to protect the flap in case of a backfire by venting the explosion. But the antibackfire valve itself can become a source of trouble if it leaks. A leaky backfire valve will cause the sensor to read low and the engine to run rich.

VANE AIRFLOW SENSOR DIAGNOSIS

For Bosch applications, there is a special Bosch tester to check the output of the sensor. But a technician can also check a vane airflow sensor by using a multimeter to check the voltage and resistance values between the sensor's various terminals.

As a rule, the sensor's output voltage should rise from around 0.25 volts up to about 4.5 volts as the flap goes from closed to open. If the voltage reading is low, the reference voltage from the computer (VRef) should also be checked (it should be 5 volts on most applications).


Watching a vane airflow sensor's output on a digital storage oscilloscope (DSO) is a good way to detect "skips" or dead spots in the sensor's internal potentiometer. A good sensor should produce a smooth and gradual voltage transition from idle to wide open throttle. Changes in the sensor's voltage output should also produce a corresponding change in fuel injector duration when the engine is running. Injector duration should increase as the VAF flap is pushed open.

The rheostat that senses the position of the air flap most often becomes worn in the positioin just above idle to about 20% throttle. This is where most problems are likely to occur.

Vane airflow sensors are not serviceable, so must be replaced if there are any internal problems with the unit. We�ve heard of people taking the sensor housing apart and using electronics cleaner to clean the rheostat contacts. This may restore normal operation if the contacts are not worn, but it would be no help if the sensor has an electronic fault or a damaged flap.

buckz6319

delete...sorry no audio on that camera

abecedarian

Them videos got audio?

abecedarian

If you look at the schematics for the AFM, you'll see it is basically a potentiometer (variable resistor) and there is no single signal to the ECU, per se.: there are two.
The connections are 12V from the ECU- white/red stripe, two returns to the ECU- one yellow/red, one yellow/black, a ground- brown, and 12v from the circuit opening relay via green/yellow wire, which oddly enough is also the color for the ground from the TPS, and has continuity to the 'brown' wire when the AFM flap is sufficiently open.
As the vane sweeps, the resistance between white/red and yellow/red will change, and the resistance between white/red and yellow/black will change, but inversely. Between the two readings, the ECU can determine the vane position.

TinMan

Good information here, my 22re is running so rich that it is building up a lot a carbon in the exhaust system and when you start it after sitting for a few hours it will burp out a lot of carbon onto the pavement. It is also running so rich that I can not go down the road with the rear window down.

Like I said when I had the TPS off to clean the throttle body and tested it putting it back on, the sweep test reveiled drop outs in resistance, and I could not get continuity with the correct size feelers guage at the throttle stop. I stopped there thinking the TPS was bad. It sounds like I need to check the AFM before I drop the money for a TPS.

I have read the posts about how to richen or lean down the mix by rotating the gear in the AFM, and many other posts about the AFM none of them have mentioned a backfire limiter that could be leaking, or a idle air bypass set screw, are these contained in the AFM for the 22re?

Been doing house hold stuff for the wife for the last few days, and will not be able to look until monday. So any information would be appreciated. I dont think that I have air leak down from the AFM, everything is new vacume lines, new gaskets in the throttle body and such, and I am not getting a lean mix. So if it an air leak problem I would think it is around the AFM.

But like I said generally running pretty good. Set the idle up to around 900 on the dash tach, and that seemed to stop most of stalling problems when hot that I was having before. Getting almost 22mpg even with it running so rich. I dont know maybe someone has been in the AFM before and tried the adjustments and just richened it up way to much. But if someone was in it, they did a really good job with the cylicone around the cover.

abecedarian

the 'yotas don't have the backfire valve. and if I told you about the air-bleed screw, I'd have to point you at a few posts I made a while back, but you really shouldn't be adjusting that unless you've got a modified engine with abnormally low idle vacuum.

22 MPG? You're doing as good as I am, but 900 is still a bit high so maybe there's some fine tuning to be done between idle, timing, plug gaps, valve adjustments and that other thing you haven't found yet.

thook

Okay, but as far as the testing between VS (whatever colors the VS is....I'd actually have to go look) and E2/ground is concerned and not any other circuit, while there isn't one single signal, VS- E2 should move incrementally up from 60 -1200 ohms starting from fully closed position to midway of the vane's path and back down again from midway to fully open.

Though I probably shouldn't say this, I will for illustration. I had the used AFM tested at Nix99 before I purchased it. They don't normally do this, but I didn't want to buy one and then have to ship it back if the VS circuit was even remotely weak. It tested out in this manner with no dropouts: (again, arbitrary) fully close >>> 1-2-3-4-5-6 (6 being midway of the vane movement to full open)-5-4-3-2-1. <<< fully open. They tested it several times. This illustrates how the ECU will read the voltage telling the ECU at what position the vane door is at on that particular circuit. Otherwise, well.....I'm getting redundant as I've said all of this already....the dropouts will give a mixed voltage reading to the ECU. And, wherever there's a dropout in resistance there will be a dropout in voltage. I just don't think it's that small of a deal regardless of interplay between two signals to the ECU on two different circuits considering every time I tested an AFM (having gone through 4 between two different vehicles) and it had dropouts, the vehicles ran like doodoo.

I'll do some reading on potentiometers today. But, now I've gotta ready for work. Later.......

BTW, Abe.....have you ever tested your AFM on your vehicle while the vehicle was running well in this manner?

TinMan

It's pretty much just me at work this week, so this afternoon I decided to tear into the AFM, give it a good cleaning and check. I did not bring my notes home but basically everything was within specs, until I did the sweep test. On the sweep test it revieled that at approximately 5%, 20%, 60%, 80% there were OL readings on the meter.

I know that you should use an analog meter, but I dont have one. We do have the high end flukes at work, and it was reading a nice steady rise in resistance until the OL's hit. So I am confident in the meter.

I decided nothing to loose by trying to clean it, if it is bad anyway, it cant hurt right. So I gave the vane a few shots of carb cleaner, not enough to get to the resistor contacts, but after that the vane moved really freely. I tested the AFM before moving on, it was the same.

I did not have any electrical contact cleaner, but we do have some acetone, so used some and a few Q-tips, gave it a good cleaning, tested again. The OL at 5% went away.

Cleaned it again, and the OL at 80% went away.

Basically had to clean several times before I got a nice steady resistance reading up to 1K and back down again.

It does run better, much smoother out on the road. Engine seems to turn easier.

But it did not take the small stumble out. Like I said a small stumble at about 2500rpm, in both 2nd and third.

And it did not make it run any leaner. Still running to rich to go down the road with the rear window down.

But like I said I know the TPS has tested bad in both the sweep test and the throttle stop test.

I will probably order a new TPS next week, in the mean time going to redo the plugs, timing, valve lash, check the O2 sensor. Just want to be sure before dropping $120 on the TPS

thook

I have only a minute to type, so here goes.......

I pm'd Roger Brown and he was kind enough to direct me to his cheaptricks page where he already has and has had a write for this:

http://www.4crawler.com/4x4/CheapTri...tml#AFMtesting

Duh.......how did I overlook this one? I must've blinked. Anyway, as you can see by reading this InternetRoadKill was correct, Abe is correct, and I am only half correct. In other words, I did see a smooth increase and decrease in ohms as I've described on AFM's that were functioning properly. But, those units were brand new. Case in point, I pulled the AFM off my '86 22re to test now that it's been on for some time (almost a year now) and it does not test out the same as when I got it. I swear to the Universe. I know what I saw. The only way I can personally explain it is that the potentiometers had to be designed with wear to be accounted for. In other words, now that it has wear, it is having "normal" drop outs described on Roger's site........what I was thinking was not normal. But, I was correct that never should the meter go out of limits (OL) or out of spec at any point in the sweep. As Abe has so kindly pointed out in a general way, and now I understand, there is a second circuit that makes up for potential drops in voltage signal along the circuit = VC circuit (<<<this according to autoshop101).

Anyway, more later. Gotta go put the vehicles back together. It's getting cloudy again......