bluehawk2

iTrader: (74)

My friend has been helping me tune my car and we noticed a problem with the map sensor. The map sensor is saying that i am running 55-60 kpa at idle. Then when I drive down the road it drops to around 40-45. Is my map sensor going bad or is there some other explanation for this?

Thanks

bluehawk2

iTrader: (74)

hmmmmmmmmmmm stumped me too

2xLS1

iTrader: (25)

Those are normal MAP values for those conditions.

txhorns281

iTrader: (12)

Cam = reduced idle vaccuum = increased idle MAP

bluehawk2

iTrader: (74)

Thanks, that's one less problem for me to worry about.

bluehawk2

iTrader: (74)

So, when i get out on the road an increase vacuum the map sensor reads less. map an vacuum are inversly related?

2xLS1

iTrader: (25)

Depends on the units you are reading MAP in.
High kPa = Low in Hg
Low kPa = High in Hg

ChrisS@sdpc

This is one place were metric units are really nice. ~100kPa is atmospheric (standard) but your specific atmospheric condition is affected greatly by your elevation. 100kPa is sea level, but in Denver you may only see 85kPa.

If MAP reads
0 - 100kPa = vacuum
> 100kPa = boost

Or you can substitute in your kPa value for your specific atmospheric conditions above. No more 10inHg of vacuum here, 7psi there, etc.

jimmyblue

iTrader: (11)

Cams depress vacuum / raise MAP especially at lower RPM,
at cruise you are up in RPM and the available overlap-time
that makes for vacuum loss (drawing from both intake and
exhaust, whichever is "cheaper" for pressure) is cut back.

Vacuum =(BARO-MAP) in PCM-world.

bluehawk2

iTrader: (74)

Thanks, it's making better sense to me now. I really don't know a lot about tuning at all, so thanks for explaining.