Air Flow Meter (VAF) resistance (ohm) values: linear or not?

[foca]

troubleshooting some rough running problems. I have checked all the obvious leak and crack issues. The VAF checks out OK by the manual's resistance checks, but I am still suspicious of it.

when I measure the resistance between the E2 and Vs terminals on the VAF's 5-pin connector, I can move the cone and see the resistance change. But the ohm readings go up and down, then up again, then down again, as I move the cone steadily from the fully closed position to the fully open posistion. I think that although my stop points (full open and full closed) are within the factory specs, my meter is still giving the wrong readings in between. I have never seen a MAF (on other cars) do this, I have only seen linear readings while going from the closed to open position (ohms increase steadily as you open the gate).

Can someone please confirm this, or check one of their known-good VAFs to see if it does the same thing. thanks a bunch fellas.

[lakersfan1]

There are no specs for in between readings. If it meets spec at both ends, it's fine.

[foca]

well, there is definitely a spec. The VAF I have even has a calibration sticker on it. so it was calibrated to some spec. apparently it is rebuilt. But, as you know, the spec is not published in the repair manual.

That's why I need someone to check one out for me, if they haven't already, and let me know what it reads.

I have been tuning cars for a while, mostly hondas and toyotas, and my experience leads me to believe that something is not right with this unit. just would like to confirm that. thanks.

[max kl]

yea it should be linear .
i have watch my vaf s on my scope and vdc goes down smothly with increased air flow.
so ohms should change smoothly and go up as you move plunger inside vaf.
the dc voltage test is preferd by snap on and you ca use a dvom if you dont have access to a scope.
vdc should be around 2+vd at idle them smoothly increase with rpm or engine load highest possable reading is 5vdc most wont hit 4.8 vdc

[Steeb]

do u know how to calibrate it?

[max kl]

nope and i dont know why you would need to.
a vaf is a mechanical air volume meter not an electrical maf sensor that cant handle drastic flow changes and need recalibration.

if you excede the flow of the vaf than you need a standalone

i suppose you could cut iy open and change the spring tension

[jschrauwen]

i suppose you could cut iy open and change the spring tension

I don't believe it's so much the spring tension but rather the contact patch along where the pick-up runs along copper windings. I had something similar fatigue on me on my 83 Celica. There were noticeable flat (or zero) spots along the contact patch. These got worn out over time (300,000 kms) and when the pick-up (which rubbed along the copper windings) reached those certain dead or (zero) spots an incorrect resistance reading was sent to the computer therefore voiding the appropriate fuel application /injection. This is the actual first time I've heard of our VAF's doing this and I'm quite surprised I never heard of it sooner. I've got a spare VAF although it's a KL02, it shouldn't be that much different. I'll try to remember to put an ohm meter to it this week. If you know off hand which are the 2 connection points on the connector to tap into - even better. Saves me going through the manual or trial and erroring it.
BTW, those flat or zero spots were usually found at the most frequently used throttle positions which for me was the usual highway speed spot so whenever I would accelerate and pass through that "dead zone the car would almost die. Hmmmm ....."Dead Zone" ..... "Die"???? Did I just make a funny???

[max kl]

alldata spesifies term a & b .
thats the two on the throttle body side or the out put of the maf.
d&e are for the iat sensor
& c is ground

abcde
big end small end

[max kl]

do u know how to calibrate it?

i think you mean so you can run bigger injectors?

[foca]

hmm, interesting. I think I will try the voltage test like you said max. go in at the ECU pins and move the cone by hand. Linear seemed like the obvious answer, so you would think that the resistance and the VAF would be linear also, but check this out. I went to the junkyard and ohm tested 2 different VAFs with my multimeter, and both did the same thing.

Now, either those could BOTH be bad also, or there is some kind of active circuitry in there that makes the output voltage linear, even though the unpowered unit reads a non-linear resistance across the potentiometer wipes. this would be possible with some transistors and diodes, but it seems more complicated than necessary. unless the engineers did it to maybe improve resolution of the signal at the different steps... but, enough theorizing.

I'll check the voltage output of the VAF tonight at the ECU. Let's hope it is non-linear and I have found the culprit. then all I have to do is find a good VAF, cause it appears the ones I found at the JY are also faulty.

thanks for the traffic guys. stay tuned.

[max kl]

dont leave out the comon denominator . what kind of thest equptment are you using. a high or low impedance dvom or an analog ohm meter will all act diffrently. and back probe at the sensor or ecm will eliminate poor connections during testing

[foca]

thanks for the heads up on my meter.

went in at the ECU and referenced to ground. voltage swepped up linearly from about .5V to about 4.5V, just like you said. so i am starting to steer away from the flow meter.

I disconnected to temp sender and the car ran much beter almost perfect, it seams someone hacked up some wires on the connector there. so I am going to fix it, but I am not positive that is the source of the problem. disconnecting it should have sent a cold reading to the ecu and it then dumped more fuel in, and made the engine run better. same thing happened when i manually pushed in the VAF cone while it was running. idle smoothed out real nice. so it appears to not be getting enough fuel for the amount of air going in.

i did a fuel pressure check and that was within spec. did a vacuum check and it came up at 17 in/hg and the spec cals for 24 in/hg. looks like it could be loosing vac somewhere, so I am going to give it another run at the vacuum leaks.

question: those plastic baffle chambers that sit under the back side of the manifold, are only connected to the plenum through that one fitting towards the front, right? they are not connected underneath somewhere or directly sealed to the plenum are they?

I knew this was going to be a challenge as 2 different shops have already looked at it and neither had any success. looks like I am in for it. can't let it win though. wish me luck.

[max kl]

[quote="foca"]t
question: those plastic baffle chambers that sit under the back side of the manifold, are only connected to the plenum through that one fitting towards the front, right? they are not connected underneath somewhere or directly sealed to the plenum are they?


no there are 2 vac lines the suply line that goes to the virs solinoids connects to the" plastic baffle chambers" and then conects to a metal vac tube that runs under the front of the throttle body to the solinoids. the other end you can see has a check valve thats on the side of the intake facing the belts.
if you havent replaced them than do it they are always cracked .
but be very carfull!!! the plastic parts are brittle dont try to pull them off cut with a razor . the check valve is the easyist to break .
ford cars use a check valve that will work if you need 1. on the ford it it used under the hood on the black vac line going into the dash.

[max kl]

well any new devlopments?

[foca]

well, i got sent on the road a few times, so I have been pulled away from this project a lot, but now I have some time to get back on it. so...

this thing is kicking my a-- now!!

- fuel pressure checks OK
- ignition timing is at spec (11 deg)
- swapped the distributor with a JY one, no change
- catayltic is not clogged
- capped off all possible sources of a vac leak
- disconnected crank postion sensor, still runs terrible
- compression is 180-190 psi on all cyl
- leak down test shows OK too
- does not overheat, no water in oil, or oil in water

If I manually move the position of the VAF the idle smoothes out nice, again adding fuel seems to make things better. part throttle is still terrible and there are dead spots all over the place. it stumbles.

Any more ideas fellas??