Re: AFM Question (archive)

I recently spent a lot of time and money trying to get a MAF conversion kit from Modern Performance to work. It similar to Split Second's kit but not nearly as adjustable. The initial unit that was sent to me had some kind of problem so they sent me the upgraded model which was suppose to be easier to adjust. In the end, it just wasn't smooth enough for me to live with. I had several spots from 1000-2800 rpm where the car surged and hesitated, slightly. compared to stock, I just couldn't stand it so I returned it. The cost was $575 but I spent another $700 on valve adjustment, spark plug wires, cam & rotor, breather hoses, etc. to make sure the engine was running as smoothly as possible. None of the above made a lot of difference, though some of the work was a needed due to mileage.

Danial
Thanks Todd.

Yes, I agree. It needs to be smooth. Mine was jumping around a bit so I bent the copper "U" shaped piece that rides on the carbon track to apply more pressure and in a slightly different part of the carbon. The retest showed the reading to be smooth and stable. Upon close inspection of the track there were a couple of divits or rough spots which caused the needle to loose contact a bit. The only question that still remains is whether there should be a specific resistance curve.

I did put the AFM back in and did not notice the hesitation as before, but I had by 3 year old in the car and although she's a trooper I didn't want to jump on it. Eventually I'll go with the MAF, I was talking to split Second and they have a new fuel-map controller coming out that allows for greater control. Software driven I believe. If anyone knows of a good MAF conversion other the the Split Second or RMS units please post them. I'm evaluating these and will probably convert this summer.

Philo.

Although i've seen some things that say it's supposed to be smooth, in my experience they are not. Yours sounds similar to mine. If you look at the circuit board in there, you can see why it might go in a step pattern. I think the only red flag when doing this is if resistance suddenly goes to zero or very high somewhere along the track. Swap an AFM if you want to confirm. If your fuel pressure and vacuum leaks check ok, maybe pull the injectors and have them cleaned. Can't hurt, other than the $150 dent in you wallet.

Ive been chassing a hesitation and decided to full the AFM and test it. I know I didn't ha ve to pull it but i wanted to pull the air filter and it's just easier to yank the whole AFM and air box out. Anyway, I put the AFM on the ohm meter and here's what I got for a reading.

Oh yes, I know nothing about electronics so bare with me.

With the ohm meter on pins 4&2
* Closed gate = 0.2 ohms
* As I open the gate just off closed position it bounces slightly .01 ohm to .04 ohms.
* As I open it some more, about 1/4 open gate it runs up quikly to 1.2 ohms.
* From 1/4 to 3/4 gate it varies between 1.2 and 1.4 ohms.
* As I approach WOT it ramps up suddenly to 1.8 ohms.
* Then just before it hits the WOT stop the ohms drop back to 1.8 ohms.

Now I'm not a master tech but as I was opening the gate and watching the ohm meter I felt as though I was witnessing the hesitation when applying throttle but only on an ohm meter.

Can anyone tell me what the curve or reading should look like as the AFM gate is opened. Maybe it's time to drive over to Armando's house..., I'm buying the beer Armando,don't worry !

If the AFM checks out I guess I'll start looking at fuel pressure, vacuum pressure, leaks and so on. Wish I was a master tech in my past life.

So should the AFM curve be smooth and progreesive or should it jump to specific readings at specific gate openning points ?

Philo.

Follow Ups:

[ Follow Ups ] [ M5 (E28) Message Board ] [ Msg. Board FAQ ]

Questions, comments, or problems, please visit the Roadfly help desk.