thook

Don't know if this has been covered in other threads before....it certainly isn't in the FSM or on 4crawler's page. (Actually, it is covered in 4crawler's page pretty well, but I completely overlooked it.........apologies).

The CEL for the O2 sensor had been coming on in my '86 for the longest time. I'd tried one thing after the other to rectify it, but even after my recent rebuild it returned.

Out of the blue, one day I decided to swap AFM's with someone nearby me(thanks....you know who you are) and the vehicle ran better. Two symptoms other than the CEL went away. One was a lagging idle on start up, and the other was a hesitation on deceleration.

So, I tested my AFM again....for the millionth time....but, it still passed on every FSM specification. Baffled, to say the least. Well, knowing what I've seen with TPS malfunctions, I decided to test the AFM for a "sweep test". I hooked the ohm meter up to the VS and E2 terminals and watched the readings as the flapper vane moved from closed to fully open.

Now, the FSM only shows to test for readings at closed and open, but says nothing for the "in between" or the actual movement of the flapper vane. According to my friend's new meter, the readings should move from low at closed to high at midway and lower again towards the wide open position. Mine did the same basically, but it had dropouts in resistance along the path.

To illustrate....
Say it starts out at 20 ohms. Well, a healthy one will move from there incrementally......20, 30, 40, 50, 60, 70, .....reaching midway....then down....60, 50, 40, 30, and so on. Mine wavered.....20, 30, 40, 30, 40, 30, 60, 70.....and then down again. You get the idea.

So, for anyone interested and suspecting an AFM issue, test yours this way.

BTW, the numbers I'm using here are irrelevant and are not actual numbers you'll see. They're just for illustration. In fact, at fully closed, my friend's brand new one showed to be at 104 ohms while mine showed at 140 ohms. Both still well within spec at that position.

mt_goat

Last I saw Cadman had one for sale:
http://home.earthlink.net/~cad_man/id5.html

thook

Hmmmm......for whatever reason I can't open the file. I mean, it'll open, but all I get is code.

And, thanks, Dale.

mt_goat

Yeah its not working for me now either, I'd just send Cadman a PM.

thook

The site seems to be under construction. If you were to click on the home page, that's what comes up.

If you find out when he's up and running again before I do, let me know. I'll keep checking back periodically, though.

thook

Oh yeah....update.

Got a reman'd Denso unit at Auto Zone for $170. Works!

InternetRoadkill

The zig-zag ohms reading as you move the flapper is normal. The best way to test the AFM is to hook power to it and measure the output voltage which will (or should) move smoothly.

thook

What makes you say that? I'd tested a brand new one off a friend's vehicle and it did not zig zag. I tested mine.....which I suspected was giving me my problems, just didn't know how....and it did. I bought a new one and it did not zig zag. Now, my issues are gone. So, please explain what makes you think that's normal.

InternetRoadkill

Because the FSM says so. Also, it's because of the way the yota AFMs were calibrated. It's too complicated to detail here, but in short the toyota AFM used a complicated resistive ladder network which allowed them to laser-trim the AFM across different portions of the AFM band. An ohm meter would see the ladder steps because it only measured part of the circuit at a time.

As I mentioned before, the best way to test the AFM is to power it up and measure the output voltage since this activates the entire ladder network. The ohm meter is nothing more than a spot check.

FYI: I you have a newer AFM or a clone replacement unit that doesn't zig-zag, it means that the unit is using a different circuit than the original OEM AFM. This is not a bad thing, but don't make an apple vs. orange comparison.

mt_goat

That's a good explaination, Roadkill must be a EE or ME.

InternetRoadkill

EE for almost 30 years.

mt_goat

Wow, an old experienced one, even better.

thook

Okay....I see what you're saying. It says a "wave pattern" in the FSM, but that's all it says. Unless you have an FSM that goes into more detail, this to me doesn't necessarily mean drops out along that wave pattern to be normal, though. And, if you'll notice in my lame description, the ohm readings did follow a wave pattern. Gradually up and then gradually down again....atleast on the new unit.

While I'll agree testing using the voltage function is more accurate (that has been explained to me by a mechanic), I still don't see what makes the ohm drop outs normal. To explain......the ECU, as you know, sees input from the AFM circuit in voltage. But, it's been my understanding that the amount of resistance directly correlates with the amount of voltage that a circuit would see......and, consequently the ECU.

For example, the coolant temp sensor....as resistance decreases the amount of voltage decreases. This is explained in the FSM for testing complete with a diagram.....which I didn't see one for in the AFM testing. To me, this would mean if there was faltering in the amount of resistance in the coolant sensor, the amount of voltage would be directly affected at the point of falter. Another example is Rogers Brown's explanation of the TPS "sweep test" he performed on his cheaptricks web page. This is where I got the basic idea to test the AFM in this way. I dunno....Roger seems to know what he's talking about. He is an engineer when it comes to electronics. Am I just comparing apples and oranges, again?

Regardless of the extrapolations I've made on my part, when I tested my original AFM it passed every initial/standard test procedure. Yet, the CEL continued to come on flashing a code 5 for the O2 sensor. (And, it wasn't the O2 circuit or the sensor itself....checked both by the FSM). Then, when I replaced the AFM with the new unit, the CEL finally went away. This is after over a year of trying to track it down including numerous standard tests of the original AFM and a total rebuild.

I still have an original OEM airflow meter on my '92. For the sake of comparison (apples to apples), I will test it at some point soon in the same way I did for the '86. Maybe then....since I tend to understand better hands on.....I can wrap my little noggin' around what you're trying to say. I just don't think it's correct. I'm willing to be wrong, though.

thook

Incidentally, my wife's '92 was having problems and checked the AFM the way I've described here. It behaved the same way on the meter. Fluctuations.

Because of roadkill's input, I figured I've been wrong before and could be wrong again. So, I asked the head tech at the local dealer about my findings and said definitely it should not be doing this.........confirming my suspicions and previous finding on the '86.

So, went to auto zone and got another reman'd denso unit for the '92, stuck it in, and viola!...problem gone.

So, so......if anyone reading this suspects their AFM to be the culprit, do run a test this way.

That is all.....

buckz6319

thook...here is my testing of the VAFM on my 3.0

I need to know if this is what your referencing in your post about sweeping of the measuring plate
my ohms meter on Auto Ranging onms
[youtube]QTD2561oY_k[/youtube]

buckz6319

thook....I'm doing more trouble shooting again...just shoot me hehe......here is another video of me moving the VAFM measuring plate with engine at idle....when I move the plate about 3/4" in the vibration, rough idle and misfire smooths out quite a bit (BUT NOT TOTALLY) and when I release the arm and back to idle and vibration, rough idle and misfire...I think there is something going on here....not quite right or is this a normal thing?....any suggestions?...sorry no sound on this camera
[youtube]RHGWJ-plljE[/youtube]

TinMan

When I bought my truck it ran really ruff at several different areas of the driving range.

After a good all around tune up, and throttle body cleaning, few bottles of fuel injector cleanner, new vacume lines, and a free flowing exhaust, it runs pretty good.
22 mpg but does not run perfect.

When it is cold the only problem I have is during excel between 2nd and 3d, 3rd and 4th it will give one little stumble. Then it is fine.

After it warms up and has been driven for a while, when I come to a stop the idle will periodically drop down and have really ruff time of it, but not all the time. When it does this I can give it some throttle and it will go back to normal, but it does not have any drivabilty problems after that, until maybe the next time it goes to idle.

When I had everything apart doing the throttle body cleaning I checked the TPS by the FSM and 4crawler site. Everything checked out fine, except for the last test inserting a .022" feelers gauge between the stop screw and the lever it should get continuity. Going up and down in thickness between did not give continuity at any point.

So at that point I figured it was the TPS bad and causing those problem.

The truck is not throwing any CELs.

Does anyone here think it could be the AFM.

Can you apply power to the TPS and check the voltages out? If so what connections do you apply power to, and what reading should you get out.

Sorry for the book

thook

If you have your meter on the VS (third terminal from the right) and the E2 (second from the left) and you're moving the measuring plate slowly from closed to open, the reading I'm seeing on your meter means it's bad. Number one.......never should the resistance your seeing go out of range of the specified ohms regardless of the wave pattern. And, never should the meter even read "OL", or out of limits. This means at that point on the track, the ECU is getting no signal.

Just for the sake of doubt, I'd contacted mechanics previously mentioned.....even though I hated to bother them with this once again.......and they said the same thing. This means it's bad. You never want to see drop outs. And, using the ohm/resistance method is valid enough for this kind of testing. And, it will reflect the same way (albeit in a different way, you understand) testing for voltage. With both mechanics they said,"I'd condemn it". I'm only relaying this because I did have my doubts and questioned my own understanding here.

Incidentally, Dwayne........the way you did it (with the cover off) is not the way I did it. I merely disconnected the airflow meter/top portion of the airbox from the assembly, stuck my finger in to move the plate/flapper door thingy, and took my reading. The way you did it was fine.....just not necessary.

thook

You can test for voltage certainly and it may be argued that's "the better way" to do it. But, since I've been working on my own EFI's, and for the purposes covered here, I've not found it necessary. I've been able to successfully diagnose TPS and AFM issues using the ohm function.

I'm assuming your vehicle's an automatic? It could be the throttle sensor or the AFM given the symptoms. But, if you're not getting continuity where you should, that would have to be the TPS. Also, run a sweep test on your TPS. Same concept as the AFM test gone over here, but your meter probes will be on the VTA and E2 terminals. Slowly move the throttle plate while your meter is hooked up and watch the resistance. It should move as described with the AFM. You'll get different resistant readings, but again the idea is the same.

TinMan

Thook, I did the sweep test on the TPS and it has drop outs, at that time, and from reading other posts, I thought it was normal. I'll test it again this weekend, and the AFM. Would not supprise me if they are both bad, but I hope not. the combination of the two would be just about the cost of the head I want, and need.

My runner is a 5 speed. But I appreciate your info.

Last few fixes before I can really start to customize, TPS, knuckle rebuild(ordering tomorrow), OME 2" lift. It has come a long way in just a few months. Mostly because the wife has allowed a monthly truck payment to the old 4runner.