That is typical. They use a galvanized steel line but then route them close to the frame or other items and that creates pockets where dirt and moisture collect and they rust out. Have replaced thousands of feet of fuel and brake lines over the years. Normally the leaks are not that hard to locate. You put the car on the lift or slide under it and look for stains or moist areas. Some vehicles are well known to have issues in specific areas so you look there first. Like the S series Blazers where they have a bent spot on the frames just in front of the rear tires. GM ran the fuel and brake lines in a cluster in that spot. They collect mud and dirt there and probably 90% of leaks happen in that spot.
If you have something like an EVAP line that only carries vapors you can use a smoke machine to pressurize the system slightly (less than.5 psi) and use soapy water sprayed on it, or look for the smoke. There are a lot of ways that work and you learn over the years. Then you learn bending and forming new lines out of steel, stainless or these days NiCopp line, or buy one of the kits that is available out there.
As for accurate, a modern leak detection system can detect holes down to.03 inch (almost 3/4 of a millimeter) and set a code and the test gear we use can find even smaller ones.
Monday, February 23rd, 2026 AT 1:19 PM
