my cheapie autometer boost gauge does not register the same readings in vacuum as does the VAFC, which obviously reads from the stock MAP sensor via the ECU. the map sensor and the boost gauge are plugged into the same source, essentially.

at idle, warmed up, no load on the engine, the boost gauge sometimes reads as much as 20"/hg, but more often around 18.5. at the same time, the VAFC NEVER reads less than 535mm/hg, which is 21"/hg, and usually at idle it's more like 570mm/hg, or 22.5"/hg.

i only ask because the <20" reading gets me worried about a vac leak every time i see it. then i look at the VAFC and there's more vacuum.

is the autometer gauge just not all the reliable down there? when i expose it to atmosphere it it goes nicely to 0.

 

My autometer gauge is off by 2 inches under vacuum and 1 psi under boost. I'm comparing it to the readings from my Hondata logger which reads the MAP sensor voltage. Ie, if the gauge shows 18" vacuum, Hondalogger reports 20". If it shows 9psi, Hondalogger shows 8.

Sonny

 

sounds like yours is off in the exact same way as mine. at full boost mine reads high too... although how high is hard to see since when i'm at full boost, my eyes are on the road!

 

Anyone having this problem with any Greddy gauges?