Hello everyone,

I had looked into doing the diode mod last summer but never got around to it, I even have the zener diode in my garage. I have a few questions about it first. Mainly I am a bit confused about what exactly happens when you have the diode installed. I understand that it tricks the ECU into reading the voltage from the diode etc but my question is whether that will change the boost in itself or will it simply allow me to change the boost with an MBC?

Second question is as to whether the stock map on the ECU will handle the new boost properly, I understand a chip changes the AFR etc...If I just change the boost with this little mod is my engine going to run nicely or will it have some bad spots?

Thanks

N.B. I don't have the cash for a chip right now, I know it is a better choice.

 

With the mod you mess around with the wires on the map sensor, pretty much it allows you to over boost without going into limp mode. Ive seen people run this mod for ages with no issues and ive also read about horror stories. I personally would not do it knowing how sensitive our cars are. When people chip a car the software usually involves changes in the air/fuel rayio and timing to compensate for the extra power, with the mod all you get is extra boost. If you are going to do the mod atleast upgrade the diverter valve.

 

There's information about this mod in the FAQ sticky at the top of the B5 forum.

All the diode does is limit the voltage seen by the ECU from the MAP sensor. There's a safety feature built into the ECU that will kick you into limp mode if the MAP sensor sees more than a certain threshold for boost pressure. (I forget exactly what that number is offhand, but I believe it's someplace around 11.5psi.) By limiting the boost pressure perceived by the ECU, it allows you to run higher boost with a MBC without going into limp mode. This mod is only safe up to about 15psi. After that the stock fuel pump, injectors, and timing/fuel map can't keep up with the volume of air being metered by the MAF sensor and you run lean and stuff breaks. I've been running this mod almost since I bought my car two years ago with no issues.

 

How does it feel when it kicks in? Is it smooth and even or just pushes you into your seat after a certain point?

 

Being a manual boost controller, it definitely isn't the smoothest thing ever. The added boost definitely makes the car more fun, but it's not as good as a proper chip. Incidentally I had to turn the boost down lower than stock because my clutch started to go.

 

sorry to dig this up after a few months, but i just have one question before i start buying a MBC and a diode...
do i need to mess with timing, or can i put the diode and MBC in, set it at 16 psi and call it a day..?

 

you cant mess with timing. you are best off skipping the diode business and waiting for another group buy for speedtuning chips. it will run you about 125 and it will be much better in the end

 

I've heard mixed responses about speedtuning chips. some people seemed to love them but others seemed to have had problems, so i figured this would be an easy way until i can save up for an apr or giac chip. unless i'm misunderstanding about the speedtuning chip.

 

i had speedtuning. not a thing wrong happened.

 

Yeah I just last week swapped out my diode/mbc stuff for a new ECU with a proper tune. MUCH better than the diode. I also couldn't run 16psi because the AFR would lean out above about 13psi. I'd be very careful with that.