Cold vs warm expected vacuum readings?
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Joined: Dec 2013
Posts: 126
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2005 CL65
Cold vs warm expected vacuum readings?
Hey all, I have an 04 g55 with an aftermarket supercharger (unsure on brand). I ordered a mechanical boost/vac gauge that should be here tomorrow and I'll see what my readings are. I was thinking there may be a vacuum leak somewhere as the truck will jump up in idle when warm and put in park (about 1500 rpms). Idle doesn't jump around at all when in gear and doesn't seem to be as high when cold (cold start idle will be a bit above 1k rpms). I pulled the air box to look around the back of the intake for possible loose lines.. One came off very easily just below the maf sensor and I put this back on but am sure I popped it off while feeling around..
I'm curious what range I should be looking for at idle on this truck. It is tuned with the supercharger and has never thrown a check engine light or anything just the high idle when warm (in gear stopped with brakes it is around 700-800rpms..go to park and it jumps up to around 1500rpm). I'll get the gauge in tomorrow and drive around a bit to see what I'm getting for readings as well to see how much boost this blower actually makes.
Thanks all
I'm curious what range I should be looking for at idle on this truck. It is tuned with the supercharger and has never thrown a check engine light or anything just the high idle when warm (in gear stopped with brakes it is around 700-800rpms..go to park and it jumps up to around 1500rpm). I'll get the gauge in tomorrow and drive around a bit to see what I'm getting for readings as well to see how much boost this blower actually makes.
Thanks all
Thread Starter
Member
Joined: Dec 2013
Posts: 126
Likes: 12
2005 CL65
Well through the gauge in but I don't think I'm using a good manifold source. There was a t that was capped off by the brake booster so I tried that.. With the gauge on it never really went below 10 vacuum.
Also at idle the gauge was reading about 25 and when put in park it would jump up to about 30 and rpms would raise to about 1500rpms.. When cold the engine revs sit just above 500rpms..ill play around a bit more and see if the tps is showing the throttle opening slightly when warm and put into park.. Not sure why it would but also not sure what the tunning is like on the truck..
Is there a good easily accessible manifold line I could use to see boost pressure? My plan is to just run the line through the window and into the truck to monitor boost and see what it makes (I am not planning on permanently installing the gauge).
Edit: went out again tonight and I found my map sensor was relocated due to the supercharger install and tapped off that line to fine the same readings.. It was late and it was kind of hard to see where that line is tapped into but really not sure what's going on (unless the truck isn't making any boost at all?).. Very odd but ill look into it some more when I'm not slammed at work..
Thanks
Also at idle the gauge was reading about 25 and when put in park it would jump up to about 30 and rpms would raise to about 1500rpms.. When cold the engine revs sit just above 500rpms..ill play around a bit more and see if the tps is showing the throttle opening slightly when warm and put into park.. Not sure why it would but also not sure what the tunning is like on the truck..
Is there a good easily accessible manifold line I could use to see boost pressure? My plan is to just run the line through the window and into the truck to monitor boost and see what it makes (I am not planning on permanently installing the gauge).
Edit: went out again tonight and I found my map sensor was relocated due to the supercharger install and tapped off that line to fine the same readings.. It was late and it was kind of hard to see where that line is tapped into but really not sure what's going on (unless the truck isn't making any boost at all?).. Very odd but ill look into it some more when I'm not slammed at work..
Thanks
Last edited by eaks; Mar 16, 2025 at 11:55 PM.
