sa52

Just finished up installing an OTS Cobb AP stage 2 tune to my car and noticed when looking at the Boost Pressure Gauge on the AP it was reading around ~ 5 PSI at idle. Then when going for a short drive it got into the 20+ PSI range without even being full throttle. Is this some kind of calibration error for the boost readings or do I have some kind of setting wrong on the AP? I did a couple of searches and could not find anything related to this on here or Cobbs website. Anybody have any ideas?

Not sure if this matters but this was a used AP and it seems the previous owner was using a 3 Bar map sensor in his car, would there be changes I need to make because I am still using the stock map sensors?

Ruskiy

Most of these MAP sensors use 0-5V values to spit out kPa or PSI value. So yes it must’ve been programmed within COBB to support a specific make and model MAP sensor.

I’m not familiar with COBB interface but with stand-alone ECUa like Haltech or AEM Infinity you’d need to select a specific make MAP from an already available (pre-calibrated) list or enter your own values based on MAP manufacturers values.

5V is 10.98PSI on my Honda OEM MAP sensor. With 3BAR sensor that 5V limit is now 29psi.

Call Cobb and ask how to recalibrate.

powdrhound

MAP sensor reads manifold absolute pressure. At sea level it will read 14.7 psi or 1.0 bar with the engine off which will equal atmospheric pressure. At higher elevations like Denver a MAP will read about 12psi or about 0.82 bar. With the engine running at idle, vacuum in the manifold will pull the reading down substantially which is probably what you are seeing. At full boost you need to add whatever max boost you run (for example 20psi) and add it to the atmospheric pressure reading in order to get a MAP value. An engine running 20psi gauge manifold pressure at sea level standard atmosphere conditions will show a MAP reading of 34.7psi. Most people confuse the value you see on the dash boost gauge with MAP. They are not the same. I suspect in Cobb access post the MAP value is a modeled number as it is on the 996.

Ruskiy

^ I would hope that a reputable tuning device would display actual (not modeled) Manifold Absolute Pressure data.

Also, what’s up with Porsche “modeling” #s? I’ve heard of it but I don’t get it.

TT.BRN

AFAIK 997.1's have the modeled channel, the 7.2's have a second MAP sensor in the manifold ... Also when going tohe 3bar boost is logged from the "boost corrected" channel and the stock sensors on the regular boost channels ...

good luck

powdrhound

I don’t know about 997.2, but 997.1 and 996 only have a pre-throttle body boost pressure sensor which is not really all that useful as it indicates Y-pipe boost pressure and not true manifold absolute pressure (MAP). The factory pressure sensor references boost relative to atmosphere static pressure and not absolute pressure. As such, it can not display a vacuum condition. We installed a Bosch Motorsport true post-throttle body MAP sensor in my application in order to get accurate MAP data. Unfortunately Cobb and other tuners can only get modeled MAP numbers as there is no true MAP sensor data available on CANbus. I believe the modeled number is calculated from the Y-pipe pressure sensor in conjunction with the atmospheric pressure sensor in the ECU. It baffles me why Porsche would not instal a true MAP sensor on these cars from the factory.