Where to check for vacuum leaks?

[Juiced 66]

Need some help guys, I'm working with Lund getting my Paxton car tuned, and I sent some logs Friday, and he sent a revision this morning. Well I did more data logs, and he just emailed me and said the idle trims cleaned up, but that now the neutral rev trims are off, and suspects I have a leak.

Nothing has changed since I sent the last data logs, heck the car hasn't even been driven. The car drives fine, and has had the blower on for a thousand miles and was tuned by another tuner, and seemed to run fine, and I never suspected any leaks.

So where all should I check around the manifold for leaks?

Also, could my breathers on the valve covers be causing it?

 

[FiveLeeter]

for the valve cover breathers, did you cap off where they connect to the intake?

Start the car, let it idle, spray carb cleaner around the base of the intake (anything you removed during the install). If it bubbles or the idle changes, you found your leak.

 

[NoSlo5oH]

FWIW, I logged a couple of tunes and sent them to Bama in an effort to fine tune my car. The response I got back from Bama was that I had an exhaust leak in both banks. They even found that the car was adding 30% more fuel at idle. The big kicker was the car never threw a CEL. I probably never would have known about this had I not data logged the car. I checked the headers and found that all of the flange bolts were slightly loose. I tightened the headers, logged another run and sent it back to Bama to see if there was an improvement. Bama said that made a huge improvement, but suspected that I still had leaks at both header collectors. I ordered aluminum gaskets for the collectors, but haven't installed them yet. I will before I drive the car again though.

 

[Juiced 66]

Thanks guys, it looks like it may be the breathers on the valve covers that are causing the rev logs to act funny sometimes. I went through the car, checked throttle body, intake, blower piping, etc.. I couldn't find anything loose. Tuner said the breathers can cause it.

for the valve cover breathers, did you cap off where they connect to the intake?

Start the car, let it idle, spray carb cleaner around the base of the intake (anything you removed during the install). If it bubbles or the idle changes, you found your leak.

Yes, everything is capped off like it should be.

 

[onebadgsx]

I run breathers and lund has never complained. What vacuum are you seeing at idle. Should be -10 to -11

 

[Juiced 66]

I'm showing -14/-15 idle is still a little high right now though. Right at 1000 rpm.

Lund didn't seem to be really worried about it after I told him it had the breathers. He just said they can cause that sometimes with the neutral revs.

 

[Phuck Phace]

Do you have any friends with an auto shop? If so see if they have a smoke machine and you'll find those leaks easy as pie.

 

[Juiced 66]

Do you have any friends with an auto shop? If so see if they have a smoke machine and you'll find those leaks easy as pie.

How does this work?

 

[Phuck Phace]

How does this work?

Pumps smoke through everything. When you see the smoke, you found your leak. Found 2 on my car that were causing surging issues around the Throttlebody and at a weld on a custom made pipe. The machine costs 1k, that's why hopefully you have a friend with an autoshop that may already have one. If you google "smoke machine automotive" you can find more info.

 

[Juiced 66]

Cool, thanks man

 

[86GT351]

THis is a great diagnostic tool. Use one regularly for Check Engine light work,

 

[CPRsm]

Smoke machine is easiest. Or you can use carb spray or another flammable liquid. Spray on joints, vacuum lines and connections. A change in idle will signal a leak