Miller MAF


Update on the Miller MAF testing. We tried the MAF in 4 cars at CMP. It goes into a car in about 15min, less so if you’re prepared (see link below). Wasn’t a complete success. We found pretty much what the Aussies told us we’d find…the MAF and it’s chip are more sensitive to engine management problems (mostly vac leaks & failed TPS), then the OEM hardware. If your shit is good, the MAF is fabulous. But not of all of our shit is good. So altho the MAF makes the AFM madness go away, just like the Aussies learned, it’s a transition with some teething pains as unrealized problems all the sudden become visible.

I get occasional CELs in my car, but they go away on their own, giving me not much to chase after. With an AFM, my car seems to run fine. But it looks like I’ve an underlying problem, prob a vac leak, that I’ve not found. The throttle response with the MAF was amazing. I didn’t expect to be able to notice the faster throttle response, but it’s very apparent and can’t help but bring a big grin to your face. But about once/lap at mid throttle, I’d get about a half second of hesitation.

We put it in Barry’s car and he absolutely loved it. No problems at all. Then we put it in Arjun’s car and his experience was like mine. Fabulous, but occasional hesitation. Finally we put it in Emmanuel’s car, which we knew had engine management issues, and altho he got the fabulous throttle response, none of the car’s larger problems went away.

The MAF will go to Road Atlanta next for more track testing in anyone’s car who’s interested. We’ll also be doing a bunch of dyno testing on it. Then it will go to MidAtl for a couple events so they can test it.

I think that what we’re all going to find is that the MAF is fabulous. But is the hassle of fixing pre-existing vac leaks (etc) worth the benefit of making our AFMs go away? I don’t know. Personally…I have a good AFM, so for now, I don’t have a problem that needs fixing. At some point the bitching re. the availability of good AFMs will drown out the bitching re. changing to a MAF. My sense is that the latter group is louder right now. But at least the community knows that there is a solution to the AFM problem if they want it.

What I would ask is that people listen to each other. Those that have not experienced AFM problems should listen to the anecdotes of those who have. And those who have experienced AFM problems should listen to those that have dodged the bullet. Learn from each other’s experiences. Don’t build a wall of certainty around your experience.

Link to thread showing how to mod your AFM cable to allow quick install of the MAF. Testing Miller MAF


This is easy. Just segregate the throttle body from the engine by running a catch can and plugging all the exits on the throttle body except for the IACV or Brake Booster. Otherwise you will dependent on getting a good seal on the valve cover gasket, dipstick O-rings, crankcase to intake hose, crank vent tube O-rings more then with the TB segregated.

On a similar note, I recently replaced my AFM with a rebuilt from Cardone A1 and was lucky. Also I take back saying the O2 not being that important, I gained significant power from a good O2 that and that result was verified on a Dyno & my racing results this week-end on a Horsepower track after battling the lack of power this season.


My weekend test with 2 refurbished Bavarian Motorsports AFMs yielded 158hp and 160hp.


I once was unable to find/fix a vacuum leak until I did an engine swap. Ain’t always easy.


I am not saying that it’s easy to find. I am saying it’s easy to segregate the evap system so that you have basically you have no reason to have a vac leak

In the end, we should just go MAP…


I’m going to ask what is probably a dumb question. How does a vacuum leak cause engine operability issues? Is it the FPR that goes off kilter or something else. I know it is abig issue with these engines and know about the smoke test procedures, just wondering what part of the engine management systems gets affected. This is just a general knowledge question as my engine is still in pieces.


The DME is trying to control the ratio of fuel to air. Lets say optimum for WOT is 12 bits air to 1 bit fuel. A vac leak means that maybe 14bits of air gets in. So the DME ends up having to puzzle out what is going on. It knows only 12bits of air is supposed to be going in, but the crappy narrow band O2 sensor is saying that the mixture is too lean (too much air). So the DME will try to adjust the mixture (and ignition timing) in order to make the O2 sensor happier in this clearly screwed up situation. Adjusting, in this case means richening the mixture by increasing the duration of the injector spritze. Lean means too much air. Rich means too much fuel.

Why does this matter. Well, I don’t know. This kind of thing is a specialty area and my knowledge of all this shit, ALL this shit, is pretty superficial. My Bosch book says that Motronic 1.3 ought to be able to adjust by about 25% from baseline. Of course, if you’re already at 20% adjusted because of {whatever}, then your DME can only adjust 5% more.

My guess is that all aftermarket chips get more power by exploiting that 25% adjustment that our engine management will support. So maybe a chip consumes 15% of the system’s ability to compensate for problems, and therefore it’s ability to adjust to problems is reduced by > 1/2. That’s all conjecture tho. Rob Eskew works with a guy named Markert. That guy knows E30 tuning. He’d have good answers for something link this. Find Rob on the fb page.


Thanks Scott,
I get it now. The leak allows more air into the intake track than the AFM reports with causes the system to go closed loop to compensate. When the command authority of the DME is saturated, then engine operation is effected. I was of the vacuum as an actuatiion device for external controls, not thinking about intake air volume.


My experience with Miller MAF - the thing is fantastic. Made a bigger difference in driving enjoyment than the new springs. But your mileage may vary. I’m generally against rule changes, but assuming there is a general dissatisfaction with the availability of good AFMs (I personally have two that seem good), I would be in favor of the switch. The throttle response is incredible and my butt dyno told me that the thing kept making more HP past 6000 RPM in 3rd gear whereas with the stock AFM the power curve flattens out.