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Old December 9th, 2005, 11:37   #5
cathalferris
Member
 
Join Date: Jun 2005
Location: Limerick, Ireland
Fuel Economy: Typically thirsty 2007 3.0 v6
Default Success!

Alright!

I now have a MAP that is reporting to the ECU the way that I want it to. It reports as normal for the low boost conditions, but it will only report a constant medium value once the real values go above what would previously have caused a code to be thrown and limp mode engaged.

Monitoring vag-com controller 1 (engine) block 11, I can now see that at idle, the MAP reports the exact same that it always did. However, once the actual MAP pressure goes above a certain limit (1350mbar for a 2.7v zener diode and 300 ohm resistor) the MAP sensor only reports that clamped pressure of 1350mbar. I have a dawes device controlling the higher pressure region the way that I want it to - spike to an indicated 1.15 bar on my boost gauge dropping back to 1.05 bar constant. I think I'll play with the dawes device to get it to hold at 1.15 constant - the spikes are so short and so small that I'm not worried about them.

My circuit is so simple. I have from the yellow-green wire, a 2.7v 0.5W zener diode with the band towards the sensor, in series with a current limiting resistor of about 300ohm, connected to ground. No connection of anything to the yellow-blue sensor wire.

I'll be trying different values for the zener diode when my electronics shop gets them in stock, I think the ideal value will be either with a 3.0v zener or else with a 3.3v zener. I'll have to experiment and see, but I have a feeling that the engine will limp mode on me with the 3.3v because at high revs it'll be showing 150mbar too high from the sensor when compared to the requested at 4300rpm.

My turbo pressure control piping is like this:
Banto bolt on the gt15
Short tube from there to the tee for my gauge
Short tube from there to the tee for the dawes device.
Longish tube from there to the N75.
I have the second connector from the dawes device put in close to the wastegate controller.

I'm happy with the way that this works, and it looks like I'll be able to make it switchable also.
I have to go and mount the menagerie of cables and free-hanging components down onto a little breadboard in a little tidy plastic box to hide in the dashboard.

I'm all ready now to have those pp520 injectors in and performing without smoke! I'll have some pics up soon, but the wire work is certainly not pretty and I'm not proud of how it looks. I could go and get the proper VAG connectors and splice in correctly, but that would take a while for them to come in.

I'll have to be careful though, as masking the higher MAP values from the ECU removes one safeguard from the system. The ECU cannot know if there is an overboost condition... so if the N75 fails or a pressure control pipe comes loose, it could be a bad day. I'll just have to monitor the boost gauge religiously.



I've driven with this in for 200 miles today in various traffic conditions comparing to the output from the vag-com to the boost gauge. I'm not throwing any codes, but I can feel the little loss in horsepower from putting that little bit more energy into the turbo than before.

My reference links include:
MAP reference
and various threads here on MAP clamping.

My way will not cause a CEL because of differences in the idle values reported, and I think that it would also be applicable to those that are unchipped with the newer two-pin MAP sensors (chips will need to see the higher MAP).

What do you lot think?
__________________
Current: 2007 Audi Q7 S-Line Sport 3.0 tdi, Mugello Blue, Stock, 215,000km
Scrapped:- 2002 Audi A4 variant PD100@140+, 245ft-lb. Atlas Silver, 350,000km at time of engine death.
Sold:- 1998 Passat variant, AHU, GT15, @120 bhp (VAG-COM butt-dyno), Boost sensor cap, boostvalve at 1.2bar. 203,000 miles. Based in Limerick, Ireland.
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