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GM 3-bar map sensor accuracy

Car-specific questions and tuning advice for the Lancer Evolutions. EVO 8 and 9 mostly, but earlier models welcome.

GM 3-bar map sensor accuracy

Postby rogersmith » Sat Feb 10, 2007 2:01 am

I've read of people getting different readings from their MAP sensor and boost gauges. I was wondering which one is more accurate.

I don't have a boost gauge but I'm going to be installing a GM 3-bar MAP sensor and tuning my boost according to the sensor.
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Postby honki24 » Sat Feb 10, 2007 11:49 am

I assume the GM is more accurate than the guage. The guages are all calibrated to read "0" when off, even if you are on the mountains, where it should read a small bit of vaccuum. I see a 2psi difference between my (expensive) Apexi guage and my GM. I'm tuned at 26psi on the GM, but my Apexi shows closer to 28-29. lol, it's a good show for the riders.
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Postby rogersmith » Mon Feb 12, 2007 11:12 am

Well I got my sensor hooked up and had another question in the same area as this topic.
On my ECU+ log my boost numbers jump up and down constantly, so it comes out to a jagged line.
Is this normal? If it is then what numbers should I go by? the minimums of the curves or the maximums? or maybe draw a median line through the curve?
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Postby honki24 » Tue Feb 13, 2007 2:49 pm

I "draw a line through the spikes", because the electronic sensor is picking up the varying pressure changes due to valve openings, which are pretty much irrelivant to you for general tuning.
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Postby tlcoll1 » Wed Feb 14, 2007 12:55 am

Yes - draw a mental line between the jaggies. The next release of the software improves this a bit.

As to who to trust - I'd say trust your boost gauge first. MAP sensors read absolute pressure, and you're normally interested in boost as a relative-to-atmosphere pressure. For the next software release, one of the to-do items is a enhancement that'll let you tweak the ECU+ settings for the MAP sensor so it agrees with the gauge.

Tom
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