MAP vs MPG incorrect

[Turbo.Tim]

I have an evo 8 with the Link plug and play (E-throttle) ecu.  I have the car started and did most of the cruise tuning.  Yesterday I started to get into boost and around 15 psi the car completely cut out.

After reviewing the log I can see that the MAP was reading 30.2 psi even though the MPG was reading 15.8.  My Fuel table is set to MPG so luckily that is all in line but I assume the boost cut is set to map.

Why would these be reading different?  I have tried to recalibrate the map sensor.  Map attached.

Turbo.tim.pclr

[Confused]

MAP = Manifold Absolute Pressure, which starts at 0 for a total vacuum, and is only ever positive.

MGP = Manifold Gauge Pressure, which starts at 0 at current atmospheric pressure, no matter where you are. Positive values are "boost", negative values are "vacuum".

The MAP limit is, as you suspected, using MAP rather than MGP, so assuming you're at sea level, 0 MGP = 14.7 MAP. As you increase your altitude, the cross-over point with MAP decreases.

So - for your limiters etc, you'll need to start thinking in absolutes rather than what you see on the gauge.

[Turbo.Tim]

Thanks for the quick response.  Other than the map limits, is there anywhere else that I need to keep this in mind for?  It scared the crap out of me

[Adamw]

8 hours ago, Turbo.Tim said:

Other than the map limits, is there anywhere else that I need to keep this in mind for?

MAP is the main factor that effects engine combustion pressure (or torque/power) - which is usually the limiting factor that causes knock or mechanical engine failure.  MGP or "boost" is irrelevant in many cases as at the same boost the load on the engine will vary with altitude or baro.  For this reason, engine safeties and Closed loop boost control should also generally use MAP instead of MGP.