MAP sensor MOD...

So I figure with my 2.5 bar MAP, I am looking for a zener diode of about 3.3V. I measured the current going through the pressure output wire (placing the multimeter in series in the yellow/black wire) being about .015 milliamps (mA) at idle and up to .060 mA at 20psi.

In varying schematics, i have seen resistors before and after the diode, potentiometers before the diode, or high resistors with no diode at all. Being that I want normal MAP operation below 3.3V, I think a diode is the best option...

So what does the adjustment of the potentiometer before the diode have to do with voltage setting???

The potentiometer in my previous post regulates how much the signal is changed. If it is lower resistance to ground (better conductivity), the diode will pull the MAP voltage down more- fooling the ECU to make more boost.

Ok that makes sense, the 10K pot accordingly limits the rate at which the sender voltage is bled off, affecting the voltage that makes it back to the ECU.

Now robnitro, trying to understand your schematic a little better. You state that R1+R2 is 10K ohm, and that you are using a 10K pot. So are there actually 2 resistors (pot + resistor) or just 1 pot that you display as R1 and R2 for calculation purposes? Your Vout wire also seems to connect at the middle of the resistor(s), between R1 and R2. It has been a while since my electronics class, so what does this positioning indicate in the wiring setup?

BTW, thanks for posing that graph of MAP voltages, its been a great help!

R1 and R2 are both variable in this potentiometer, I meant to indicate it as a resistance, not a physical single resistor.
The middle is the wiper the other two are the ends of the variable resistor. So, if the wiper is all the way near the ground, its 0 ohms to ground, and 10,000 ohms to the other side. This acts like a voltage divider.. but its requires tweaking as I haven't found an exact formula that matches it perfectly.

Here is a good website I googled for you to check out: http://www.allaboutcircuits.com/vol_6/chpt_3/6.html

If this is hard to get, the easiest way to get more boost would be to do the other schematic where you are clamping the voltage so the ecu never knows it is overboosting. Then you can use a boostvalve to mechanically limit the max boost via vaccuum but be careful!!!

My have installed the setup I listed above (3.3v Zener Diode going between the signal and ground wires) and it paired with the evry mod gives a pretty awesome power gain without the smoke .

But if I hold full throttle for more than a few seconds, it throws the car into limp mode, spitting out a code for "turbo/supercharger underboost".

Now I thought I just had too low of a zener diode. But when I put a scanner on the car tonight, it read that the MAP sensor clearly hits its upper limit at 114 kPa (16.5 psi). Before the mod it was pushing out a max of 12 PSI.

So any clue why my car is now declaring that the boost is lower than expected?

I am not sure, but the way you explain it, seems like you are clipping the max boost seen by the ECU, which would make it think that it never reached top boost. In fact, I would never recommend that setup because it means no ECU control of boost past that MAP voltage besides a boostvalve.

A voltage divider setup would be less drastic. But that takes more time to tune and figure out.

You are correct, I am only controlling the max boost via the mechanical boostvalve.

And nevermind on my question. My gauge is reading absolute pressure, so I am actually reading about 4.4 psi, which is indeed an underboost . So time to change diodes and maybe throw a resistor in there

Please guys, can you briefly explain what is this Mod for? There is a lot of posts about it, but for the public, you forgot to tell what is this Mod objective.

It looks possible and cheap to do. So it is interesting to learn about it.

Thanks.

Oldbeaver

The objective of this mod is to fool the ECU into thinking it is receiving less boost than it actually is, and as a result not moving the VNT adjuster to reduce the boost. This means that you can achieve higher boost pressure (the Manifold Air Pressure). I achieve this by a 3.6v zener diode between the output wire and ground of the MAP sensor, and controlling the upper boost limit with a boost valve (aka dawes device). Robnitro has better way of controling it via circuitry at the MAP sensor.

This will not really have an effect on performance, though, if you have not done a mod (chip, nozzles, evry, ect) that will increase the fuel, since more air alone doesn't mean more power. And too much boost pressure on a stock turbo can mean over-spooling at altitude, or too high of cylinder pressures.

A picture is worth a thousand words.

hi. wil this mod. work on my 1994 audi 100 2.5tdi? and do any of you know witch wires to splice in to? and is the diode neccesary?
sorry about the english, but im from norway

saab9turbo said:

hi. wil this mod. work on my 1994 audi 100 2.5tdi? and do any of you know witch wires to splice in to? and is the diode neccesary?
sorry about the english, but im from norway

Click to expand...

Great country!

I don't know which wires you use, but you can check it with a meter. Skin the wires coming out of the connector a bit. Start car, take voltmeter, put one side to something metal on the engine or body. The other, you test to see which wire is which.
A wire that gets around 1-2 volts is the pressure.
A wire that gets 5v to chassis ground, that is the power.
Another wire with a different positive reading is the temperature.
And the last wire that gets around zero is the ground.

On our connectors, it may be similar to yours: Pressure, 5v, Temp, Ground. So if you find the ground you should know the other ones.

You don't need the diode, but it prevents the circuit from modifying the sensor output voltage until a certain range.

thanks the engine code is aat, and the conector to map sensor only has 3 wires, if i have the time i wil try this tomorrow, i need all the power i can get to keep up with my mates a8 3,3tdi and bmw 530d 04my

I think a 3 wire map is one that doesn't have the temperature sensor integrated. You can see if one wire is 5v, one is x.xx V and the third would be zero to ground. The diagram I made is the same for that. Be careful though, you need to have a boost gauge and know how much boost your turbo can take safely. Being that you have a wastegate turbo, it might make sense to do what some do, use the diode to fool the ecu (somewhere in this thread), and put a boostvalve to control the wastegate.

Well that's my head popped lol, interesting stuff but my brain isn't puting all together yet

Have bought the variable resistor, so maybe i wil try this on friday but i have to chek for errors, i only got 0.5-6 bar now, used to have 0.9-1.0 bfore, any ideas?

What kind of map sensor is it? Hmm, perhaps you have the map sensor inside your ecu instead like the older TDI?

External, on the bulkhead, i moved the hose for my boostgauge to the hose for the map sensor, and now it runs on 0.9-1.2, so now it runs nice adjust diesel tomorrow, and maybe do the map sensor mod