Jump to content

MAP vs MPG incorrect


Recommended Posts

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.



Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...