Three bar map wiring question.

[jeff1234]

When wiring the three bar map plug on a logic module controlled system using a Mopar performance based custom cal is a diode needed to prevent overboost similat to when using the stock map sensor?

[shadow88]

I'm not sure I understand your question.
You're adding a 3 bar map sensor to the factory style Logic Module with a MP based program?

If that's the case, unless it's a super 60 based tune, (made to work with a 3 bar sensor) it will need some way to prevent overboost. Maybe restate what you have and go from there?

[83scamp]

First off, your custom cal needs to be a three bar cal, other wise it won't work. The output voltage on a 3 bar MAP is exactly the same as a 2 bar, it's just re-scaled to cover the wider presure range. If your cal isn't set up the same way, it won't work. Well, let me clarify that... it will "run", but the ECU will have no clue what boost you are running because the scaling is all wrong. Fuel will be wrong because it will think you are running less boost than you are. A perfect situation for melted pistons...

As I understand it, the zener diode is used to "clamp" the max voltage a 2 bar MAP sensor can put out so the computer never goes into overboost shutdown. It's an old school way to up the boost without freaking out the ECU. If you have a propperly tuned ECU and a 3 bar MAP, the diode shouldn't be necessary. If your over-boosting a 3 bar, and going into shut down, you are producing some very serious boost, and the rest of the engine better be up to the task. Remember, overboost shutdown is there to protect your engine in case something goes wrong.

The diode doesn't prevent overboost, it prevents the ECU from seeing the overboost condition. Two very different things. And unless you really know what you're doing, very dangerous. Clamping the MAP voltage, and not having a way to control fuel will lead to things going BOOM! in a hurry... In the old days, that was the only way to do it. But they did other things to make sure they had fuel to match the boost. Now with folks like Boostbutton who can do cutom ECU tuning, the diodes are pretty much dead...

[jeff1234]

Thanks guys, 83scamp answered my question, I need one in this particular case. My understanding of the zener diode is that it shunts any voltage over 4.6 to ground preventing the l/m from going to over boost. I have all of the needed accessories on my engine.

[shadow88]

Nothing wrong with the "old fashioned" way of upping the boost as long as precautions are used. My smec knows about 12 of the 32 psi boost my engine sees.