11th Gen Civic Forum banner
1 - 11 of 11 Posts

· Registered
Joined
·
7 Posts
Discussion Starter · #1 ·
23 Civic Si here, bone stock, 700 miles. At idle, boost fluctuates from -9 to -10 continuously. Doesn’t really stay on one or other but changes every second. If I remember correctly, it usually would sit at idle at -10 and not fluctuate, sometimes bumping up to -9 with a/c, but never the fluctuation. Can’t get it to stay at -10 with or without a/c.. Anyone else experienced this?
 

· Registered
Joined
·
9 Posts
No boost without load, as rpm increases thru powerband, air density, air temp, timing, injector pulse and duration, exhaust temp, oxygen sensors, fuel pressure, vtec on exhaust side, load, are directed thru computer in micro seconds which ultimately command turbo boost. To add on there are many more parameters, the end of the day a lot of things happening and a pretty good job by Honda making it work! I am amazed at the fuel mileage, guessing on a regular Civic with the 1.5 and taller gears must be crowding 50 mpg at times.
 

· Registered
Joined
·
152 Posts
The negative (-10) indicates it is vacuum, not boost. All engines run with some degree of vacuum when the throttle is closed.

Look up engine vacuum or how throttle works on YouTube, probably some good explainers on there.
 

· Registered
Joined
·
5 Posts
Chiming in on the fluctuating comment you had made: I am not sure what the idle target is on this engine but I would guess the ECU is likely targeting 20 in-hg of vacuum which converts to -9.85 psi. Any type of load change on the engine, especially the alternator, may cause the engine to pull more or less vacuum momentarily leading to the fluctuating on the gauge. I am not sure if this is something you're concerned about but if so, I do not think this is anything to be worried about :)

Congrats on your new car! Hope it makes you smile like mine does.
 
1 - 11 of 11 Posts
Top