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Old 03-30-2010, 08:38 PM   #1
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Default Reasons this would be off?

My car idles at 25kPa or around 19-20 in vacume according to migasquirt tunerstudio

my boost guage is showing that im pulling about 15 in of vacuum

I am hitting about 170kPa in boost, and because its roughtly 88kPa here at 4400ft above sea level so its about 10-12 psi, but my boost guage is only showing 5psi?

I have the MSPNP for my year, 97, and it came with e 400kPa sensor

Both guage and megasquirt are running of the same source, so what one sees, so does the other

If there some setting that is causing it to be off so much? or something is not scaled correctly?
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Old 03-31-2010, 01:07 PM   #2
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I haven't had my morning coffee yet, so I may be doing the math wrong here...

Let's assume your boost gauge is roughly accurate. I assume it's a relative-reading gauge, meaning that it shows 0 when the engine is off. According to my book, 4,400 feet ASL should be about 86 kPa.

The 5 PSI of boost your gauge shows is about 34.5 kPa of boost. 86+34.5 = 120.5.

At 120.5 kPa, an MPX250 sensor would be putting out 2.4 volts. The scaling for a 4 bar sensor would interpret 2.4 volts as meaning ~ 190 kPa. Close enough to 170 that it makes me a little suspicious.


Maybe your boost gauge is just fubar. If you want to verify it, you can buy a genuinely accurate pressure gauge for only $6.15 here: Enco - Guaranteed Lowest Prices on Machinery, Tools and Shop Supplies or you can really splurge (for $9.62) and get the liquid-filled version guaranteed to 2% here: Enco - Guaranteed Lowest Prices on Machinery, Tools and Shop Supplies
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