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map value of non running engine
omega0684 - 17/2/09 at 01:00 PM

im just reading through the MS manual again and it says


quote:

Connect your laptop to your MegaSquirt using a DB-9 cable, turn the ignition to run (do not start it), and verify that all the sensors give reasonable values. The MAP should be about 100 kPa, the coolant and intake air temperatures should be approximately the same as the outside air, and the TPS should read from 0 to 100% as you open the throttle.


is this right, the MAP sensor should read 100 kpa?

britishtrident - 17/2/09 at 01:03 PM

P Atmos

MAP = manifold absolute pressure

adithorp - 17/2/09 at 01:06 PM

100kPa is about 1Bar so... yes.

adrian

mcerd1 - 17/2/09 at 01:12 PM

quote:
Originally posted by adithorp
100kPa is about 1Bar so... yes.

adrian


1bar is exactly 100kPa which is roughly 1 atmosphere

omega0684 - 17/2/09 at 01:28 PM

so am i correct in saying that the faster you go the lower the kpa reading should get? im a little confused.

vinny1275 - 17/2/09 at 01:37 PM

if you're using speed-density rather than alph-n, you'll find an ideal MAP - as you tune the engine the MAP will go lower and lower - then you'll get to a point where whatever you do (fuel up / down, spark earlier / later), the MAP will go up again...

Did you get the msq last nite btw?

MikeRJ - 17/2/09 at 01:56 PM

quote:
Originally posted by omega0684
so am i correct in saying that the faster you go the lower the kpa reading should get? im a little confused.


No, if you think about it the maximum pressure you could possibly see in the manifold is atmospheric pressure i.e. 100kPa (unless you bolt a supercharger on it!). You will only see this with the engine stopped or at WOT. With the throttle mostly closed, the engine is pulling a vacuum in the manifold, so you see less than atmospheric pressure. i.e. the higher the manifold pressure, the greater the engine load (as long as it's running).

David Jenkins - 17/2/09 at 02:05 PM

I got myself a headache the first time I had to think this through for Megajolt...

Engine stopped - MAP will be around 100kPa (atmospheric). Engine not sucking in air.

Engine ticking over, foot off throttle - MAP will be very low at around 20kPa (high vacuum). The engine will be trying to draw air in past the closed butterflies.

Engine running fast, foot hard down - MAP will be approaching 100kPa (near atmospheric). The engine will be sucking in air, but the butterflies will be open so very little restriction and no chance to build up a vacuum.

omega0684 - 17/2/09 at 02:15 PM

CHEERS GARAFE MAN, that makes it easy to understand.

David Jenkins - 17/2/09 at 07:15 PM