Bad boost gauge?

JGDogg10

Active Member
Established Member
Joined
Aug 3, 2012
Messages
105
Location
San Diego
I’m just now getting a startup tune for my car after about a year of sitting, still dialing it in. While it’s trying to idle, the boost gauge is reading 5-10in of vacuum and if I tap the gas it actually goes down showing more vacuum. It will go to around 15-17in of vacuum if i tap the throttle or hold it steady around 2500rpms. Has anyone experienced anything like this? It’s an electronic autometer c2 gauge. Checked vacuum lines and nothing seems out of the ordinary or leaking.
 

robvas

Well-Known Member
Established Member
Joined
Sep 8, 2020
Messages
1,317
Location
MI
Rough idle is going to show less vacuum. Have you smoke tested it or tried starting fluid? Mine idles around 20 in.
 

DSG2003Mach1

Well-Known Member
Established Member
Premium Member
Joined
Apr 15, 2004
Messages
15,910
Location
Central Fl
what blower is on the car? have you checked the bypass valve is functioning and not stuck open?
 

01yellercobra

AKA slo984now
Established Member
Joined
Oct 5, 2005
Messages
21,126
Location
Cali
Sounds like the sensor is going out to me. But as mentioned I wouldn't worry about it too much until the idle is dialed in better.
 

SVTdreamin04

What's a "Termi"???
Established Member
Premium Member
Joined
Sep 20, 2015
Messages
2,536
Location
America
Get a mechanical gauge and compare the two. That will tell if it is off or not.


Sent from my iPhone using Tapatalk
 

JGDogg10

Active Member
Established Member
Joined
Aug 3, 2012
Messages
105
Location
San Diego
I smoke tested it not too long ago and nothing has changed as far as vacuum lines. It has a Vortech YSI on there now. Bypass valve is functioning, if I blip the throttle it closes, but the car is on jack stands still so haven’t gotten so do anything but start it and try to get it to idle. I’m going to buy a mechanical gauge today just to see(cheaper than a new sensor from autometer lol) but this is my second autometer electric boost gauge.. first one wouldn’t calibrate to 0 anymore and now the new one is doing this. I feel like it is a good thing though that when I can hold a low rpm steady throttle it holds down around that -20in vacuum?
 

01yellercobra

AKA slo984now
Established Member
Joined
Oct 5, 2005
Messages
21,126
Location
Cali
You should only see the full 20" when it's at idle. That's when the throttle blades are closed and the vacuum is highest. As soon as you open the throttle the vacuum should move towards 0.

It still could be a tuning issue since the IAC could be affecting things. But as mentioned get a mechanical gauge to compare. FWIW I've only used mechanical and have had good luck with them.
 

JGDogg10

Active Member
Established Member
Joined
Aug 3, 2012
Messages
105
Location
San Diego
Well I’m an idiot, stuck my hand down to check the back fuel injector on the passenger side and my finger was sucked to a nipple off the throttle body that had a vacuum line missing.... got a nice new gauge out of it hah. Gonna switch the other gauges from the C2 to the new Cobalt series one that I bought. Idle is still rough because I am still tuning, but at least the gauge part is fixed.

On a side note, my idle is way up high and I’m trying to figure it out to get it back down to normal. Short trims are spot on up to 3k so far, and idle is set around 850, but I just can’t get it to stay there. Throttle position absolute looks good, anyone else ever have this problem? It’s all through SCT
 

01yellercobra

AKA slo984now
Established Member
Joined
Oct 5, 2005
Messages
21,126
Location
Cali
If there isn't anything mechanical holding it up then double check the tune settings. Especially if you've been tuning with a vacuum leak. You might have to go back a few steps and start over now that the leak is fixed.
 

Users who are viewing this thread



Top