Using EFILive to Help Check for Vacuum Leaks

[ferocity02]

What tips and tricks are out there using EFILive to help us search for vacuum leaks? I once tried the trusty propane method, but the idle didn't change in the slightest bit even when I was pumping propane straight into the intake through the PCV port. I was told that the IAC is compensating too quickly (maybe the IAC needs to be unplugged?). Other suggestions were using carb cleaner or WD-40 but what a mess and I can't see carb cleaner being good for the intake gaskets.

What I'm imagining is logging some parameters (not sure what) while I go around the intake with propane or something else. And if there is a vacuum leak, there would be an obvious change in the data. For example, maybe the O2 sensors would flatline with propane, or maybe there would be a slight drop in MAF... I also have oxygen and acetylene I could try if those would yield better results.

Anyone know how we could better utilize EFILive to search for vacuum leaks?

[joecar]

Yes the front O2 sensor voltages trend higher (possibly breaking out of switching) and the LTFT's go negative when propane is introduced (regardless of IAC compensating idle speed back to desired).

Brake cleaner leaves no mess (but be careful not to spray it on painted surfaces).

[Gregs]

What tips and tricks are out there using EFILive to help us search for vacuum leaks? I once tried the trusty propane method, but the idle didn't change in the slightest bit even when I was pumping propane straight into the intake through the PCV port. I was told that the IAC is compensating too quickly (maybe the IAC needs to be unplugged?). Other suggestions were using carb cleaner or WD-40 but what a mess and I can't see carb cleaner being good for the intake gaskets.

What I'm imagining is logging some parameters (not sure what) while I go around the intake with propane or something else. And if there is a vacuum leak, there would be an obvious change in the data. For example, maybe the O2 sensors would flatline with propane, or maybe there would be a slight drop in MAF... I also have oxygen and acetylene I could try if those would yield better results.

Anyone know how we could better utilize EFILive to search for vacuum leaks?


What I've done before is had someone watch the fuel trims while I sprayed brake clean on hoses and gaskets and stuff. It works like a charm. When you see a sudden change in fuel trims you'll know you found the leak.

Someone wanted you to spray wd40? That would be a mess! Use brake clean!

[ferocity02]

Will the LTFT's react fast enough, or should I monitor the short term trims?

[joecar]

LTFT's.