MAF Clamp

If you use the MAF in the system for whatever reason, i use the IAT sensor and let the MAF do it’s thing or everything else.  I have always wanted to know how to clamp the MAF voltage as when it reads too high, it freaks out and closes up the throttle, screws with cam timing among other things.  I researched some simple methods as to create a MAF clamp. THE AEM EMS lacks the 0-5 volt programmable output which left me SOL there.  I researched the old Audi forums and found the zener diode mod to prevent them from hitting boost cut. this is a similar application though for a MAF instead of a MAS, but the same principle.  I played around with the idea and made some easily reversible changes to my MAF wiring in the jumper harness to incorporate a zener that is grounded to the chassis off the MAF signal wire – and it works wonderfully. there is no effect to the signal under the specified voltage of the zener diode and it clamps the voltage perfectly.  The car runs fine without the MAF, but then the gas gauge goes all crazy, so I decided to leave it in and see if I could come up with a system to do this.  Bottom line, connect the zener diode (voltage will vary – I used a 4.3v) (stripe towards MAF signal wire) and ground the other side.  If you want to be safe, put a big resistor between the diode and the chassis to prevent current overload which will eat your MAF.


Items I used to make it easily reversible:

  1. Male/Female Insulated Quick-Disconnects (8-Pack)
  2. 4.3V-1W Zener Diode
  3. Ring Terminal
  4. Wire
  5. (optional) A high value resister (10kohm 1 watt)

Usually get my stuff from Fry’s Electronics, but I have seen them at RadioShack.  The zener just needs to be 1 watt, 4.3v-5.0volt. I wouldn’t go much less or much more. I would really try and stick to 4.7 or 4.3 volt.  I used a 4.3 because that’s what I could find.

Cut the MAF wire(c27 green wire with black stripe in the 3rd connector from the front) and put in a quick disconnect butt connector so that you can reconnect it.

Now for some making stuff:
Use the hookup wire (only really need about a 2″ piece) and strip both ends and a small section in the middle. wrap the end of the diode around it that has the stripe closest to it. Solder it together. Other end of the diode solder on a length of wire (I used a good bit so that it could reach a grounding point) use heat shrink where possible and tape up any exposed areas.

The long wire crimp on a ring terminal and on the short wire use quick disconnects (so that they correspond with the cut MAF wire).  Now ground the ring to the lug holding in the ECU, and put the wire in the quick disconnects and you are all set.

For added safety i recommend using the resistor between the diode and the ring terminal, this can help protect the MAF sensor. 

(I’m no artist, so don’t make fun…)


If you want to connect it to your AEM take the ring terminal out and wire it to the corresponding pin in the AEM for a low side driver.

I used LSD#1 for my fuel pump switch so I used #2 for this piece.  Then you just need to program it to come on at over 1 psi of pressure in the “Configure Outputs” panel. Grounding it essentially turns it on or off so you can see the differences, in how it drives. I haven’t had any issues and it pulls good and hard all the way through the rev range.  If you don’t like it you can always disconnect it using quick disconnects and reconnect the MAF signal wire without tools (except for getting the cover off).

I will build a few of these and put them in the store to purchase.  It is an easy modification with some pretty profound results in the right application.