2nd Generation GE8 Specific DIY: Repair & Maintenance Sub-Forum Threads discussing repairs and maintenance you can do yourself on the 2nd generation Honda Fit (GE8)

Vacuum Leak

Old 07-06-2013, 03:23 PM
Thread Starter
Join Date: Apr 2010
Location: Louisville
Posts: 1,302
Vacuum Leak

I'm pretty sure I've got a leak in my intake system and need some advice about how to proceed.

First, here are my symptoms.
  1. According to my UOA, I've got high silicon and aluminum in my oil. This might still be from the last of wear in, as the engine only just has 15,000 on it (with 3 oil changes).
  2. According to my ultragauge, my fuel trims are high. under most driving conditions, they sit at about +7ish but vary as high as +10 or so, but never below +5
  3. Fuel economy is a but lower than I would expect, but that's very subjective and hard to evaluate. But even just driving 65ish on the interstate will average low 30s. Absent the other two I wouldn't mention it, but its still an anecdotal data point.
No codes/mil, so I can't take it in for warranty work. The extra wear and silicon points to unfiltered air getting into the intake system. The higher fuel trims indicates that it's getting in after the MAF, so probably not a filter problem. Are those guesses reasonable? (FWIW, replaced the air filter just to be sure. No obvious holes.)

I have no experience checking for vacuum leaks. Is it really just a simple as spraying carb cleaner around (being careful of sparks obviously) or is there an easier way?
Old 10-12-2013, 05:38 AM
Join Date: Oct 2013
Location: PA
Posts: 201
I know this post is a few months old but I would like to share some thoughts. While carb cleaner has been used for many years as a way to check for leaks it can be very dangerous.

We have a propane leak detector at the shop that is basically a small propane bottle with a valve, some hose and an aluminum probe that disperses propane. The aluminum is non-sparking and the probe is small enough to fit into small places. We hook a scanner up and watch the short term fuel trims for changes when the vacuum leak sucks in the propane. You can hear the engine raise a few RPMs too. Its way safer than carb cleaner since the propane's auto ignition temperature s 1004 degrees F and Gumout carb cleaner is 392 degrees F.

The other method is with a smoke machine that pressurizes the intake system with harmless smoke while the engine is not running. The leak can then be spotted when the smoke is seen. Obviously the cost of the machine is way more than would be worth spending to find one leak.

In a pinch I have taken a small propane tank and put a soldering tip on it with the torch tip removed and replaced with a long rubber vacuum hose. I then started the engine and just barely cracked the valve and ran the hose along all gasket edges to find the leak. Much safer than carb cleaner.

Hope someday somebody can use this tip when they need it!
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