JacobLoren

Adjusting the spring tension on a S4 AFM (which also calibrates the voltage)

Ok so this is what I did....

You will need a 10mm wrench, a flat blade screwdriver, a volt meter, and silicone sealant.

1. Warm up the car.

2. Remove the air box, Three bolts hold it down and four bolts hold it to the AFM

3. Remove the black plastic cover on top of the AFM. Do not disconnect the AFM from the ECU, you will need it connected to calibrate it. You will see a few small wires, some metal tabs, the resistor plate, and a coil spring with a metal ring around it. Note that the ring has small teeth on it. There is a small retaining tab on one side of the ring that keeps it from spinning backwards, DO NOT BEND OR BREAK THIS TAB!

4. Connect the positive of the volt meter to the second connection in from the air outlet side of the AFM, or with the connection side of the AFM facing you it would the second pin in from the right. (its kind of hard to miss... its the longest metal tab coming from the connector. it spans about half way across the spring area) and ground the negative of your volt meter.

5. Turn the ignition on but do not start the car. Verify that the AFM closed is reading the proper voltage, 4 volts. If it is not reading 4 volts there is something more wrong and you should remedy the other problems before you bother adjusting the spring tension.

6. Start the car and check the output voltage of the AFM. It should read between 2.5 and 3.5. If it does then you don’t need to adjust your spring.

7. If your voltage is reading to high you will need to release tension on the spring then bring it back into spec. If your voltage is to low then you simply have to bring it back to spec.

7a. To release the tension on the spring, put a small amount of pressure on the retaining tab to separate it from the teeth of the ring. The spring will unwind quickly so use the flat blade screwdriver you keep if from going to fast.

7b. Bringing it back to spec is fairly easy. You simply rotate the ring in the clockwise direction to add tension to the spring. Use the flat blade screwdriver to rotate the ring, and watch the volt meter until it is in that range of 2.5 - 3.5 volts.

8. All that’s left is re-assembly. Re-install the black plastic cover and seal it from the outside with the silicone sealant. Re-assemble the air box.

Any questions... just let me know
Jake

RETed

Why would you want to do this and risk damage of the airflow meter?
Isn't it easier to just replace it with a good used unit?
This can't be a performance gain, as an AFC would do this better and easier.


-Ted

JacobLoren

This process will not not damage the air flow meter... and in my case I needed to do it because my spring had lost some tension and was causing problems with my idle.

a poorly calibrated AFM can cause rich or lean running conditions.. so yes if it is out of spec it could be a proformance gain. Though its not really intended for that... its intended to be an easy fix to a simple problem.

WAYNE88N/A

Because I planted the idea in his head, Ted, and damn if he didn't do a hell of a job with it

He was going to get another AFM anyway, because we knew from the numbers that his was crap, so he had nothing to lose...

Why do you take anything apart and risk damage? To see if it can be fixed and returned to service, it's that simple. He wasn't doing this for a performance gain, but to get the voltage inputs to the ECU back into range...

Good job, Jake, I wish more guys displayed the drive and motivation to help THEMSELVES fix their car instead of wanting someone to "hold their hand" over the forum...I'm impressed

JacobLoren

Thanks Wayne,

The problem is still not totaly fixed but I am getting closer.. I almost got to idle steady tonight.. damn it was rough ... but hey it was an idle.

I am going to go out and pull the voltages from every part of the ecu tonight.. just to see what is out of spec..

can you believe I have only had this car for 2 weeks?

-Jake

WAYNE88N/A

Perform a very thorough search for vac leaks now...

The roughest idle (if you want to call it that) I've ever had was due to an injector being totally rusted shut & useless. Are we talking that "rough" on yours? Engine trying to break free of the mounts, that kind of thing?

JacobLoren

LOL no not THAT bad... I am honestly just thinking about buying a **** load of vac lines.. and changing them ALL.. just for ease of mind...

So let me ask you why you would want to add tension to your air flow meter?

WAYNE88N/A

The ONLY reason I would even think of messing with it is if a scenario popped up exactly like yours- the key on voltage was good, the door sweep voltages were good, just lower (or higher) than specs, the obvious solution is always the simplest- tweak the spring until the voltages are in line with FSM expectations, then run road tests on her to verify everything's good, as far as the ECU is concerned...

It has occured to me that if you had a fairly large vac leak, it would throw your AFM outputs off, in relation to the ECU's fuel scheduling (the engine's getting more intake air than the ECU thinks it is), but by how much, I dunno...

JacobLoren

Thats the path that my mind was headed down.. I still cant see how i can go from running perfect one day to having such a bad problem the very next day....

But alwell.. I will get it fixed

eventually.

WAYNE88N/A

My point exactly- make sure the tweaking of the AFM isn't covering up a far more sinister problem

JacobLoren

I know I am Bias cus I wrote this.. but I think it should be archived.. for those rare occasions that some one is in that kind of situation..

BTW thanks for the diag from the ecu link.. :-) that is some damn good info

WAYNE88N/A

Yes, you're biased, lol

Yeah, all the guys chipped in some damn good info & jpegs to make that ECU writeup a useful tool for a lot of guys...

HeffBoost

Excellent information. Kudos for posting it.

Long before I knew what I know today I adjusted my AFM via trial & error to get the car lean enough to pass emissions. It worked.

JacobLoren

I think acouple pics would be of good help.. so I will try and snap acouple soon.

RETed

The problem is that I HAVE seen people posting about messing with the airflow meters, and they usually end up killing them.

I'm sure a competent person would have no problem messing around with it, but that assumption is a bad one.
I wouldn't trust the majority of the people in here trying to do this.

The airflow meter is usually not at fault, and there are a lot of other things that can cause headaches.
I dunno if I missed something, but did this fix the original problem?



-Ted

JacobLoren

My problem seems to be more and more involved.. no it did not solve it compleatly but it did help. I am closer to having an idle and the car doesnt surge as bad while driving.