Question on intake MAP readings

[hunterdan]

Had my obdlink hooked up and was watching some of the functions (including the intake MAP). How accurate are those readings? What should they be reading at idle? According to that live read, it was reading 8.6 in-hg at idle. Which seems kind of low to me. Truck is running really well, no codes stored or pending. I didn't pull that sensor when I did the intake cleaning, so I'm wondering if maybe it got damaged when I did the cleaning or if it's still dirty and not getting an accurate reading. I have a vacuum tester coming to manually check the vacuum level at idle.

 

[HEMIMANN]

There used to be some Techs on here that would know. Or retired vehicle engineers.

 

[hunterdan]

Yeah, I would think a map that was reading way off would throw a code and have drivability issues, because I certainly don't have any at the moment.

 

[pacofortacos]

What was the baro reading?

 

[Ken226]

8.6 is normal

About 30 is normal atmospheric pressure at sea level.

At idle, with the throttle blades closed, there will be quite a bit of vacuum in the intake.

 

[hunterdan]

8.6 is normal

About 30 is normal atmospheric pressure at sea level.

At idle, with the throttle blades closed, there will be quite a bit of vacuum in the intake.

Appreciate the reply, I had ordered a vacuum gauge to double check to make sure, but I know some of these readings don't directly correlate to numbers we expect to see.

 

[Ken226]

Appreciate the reply, I had ordered a vacuum gauge to double check to make sure, but I know some of these readings don't directly correlate to numbers we expect to see.

Normal atmospheric pressure at sea level is 14.7psi, or 30 in-hg.

@ Idle, the engine running and the throttle blades almost completely closed generates quite a bit of vacuum inside the intake. Relative to 1 standard atmosphere, (30 in-hg) a map sensor reading of 4-1/2 psi or 8-1/2 to 10 in-hg is normal.

To confirm my own best guess, I asked Google Gemini to look it up: