Case Studies

BMW Z3 M Convert – Evaporative Emission System Fault

Most late model cars are equipped with a system to both capture and recover vapors from the fuel system. In the past these vapors were often vented to the atmosphere, not exactly an environmentally friendly approach. The evaporative emission recovery systems are usually reliable, but from time to time, as cars age, problems do occur. In our workshop we’ve chosen to efficiently diagnose these problems through the use of a machine that creates a low pressure smoke containing a UV dye. By the use of this system, even leaks as small as a pinhole can be located.

We’ve all seen the ubiquitous P0455 – Large Evap Leak or BMW Fault Code 251 – Minor Leakage, pop up on the diagnostic computer. Often it is a loose fuel tank cap, or a deteriorated evap hose, both common for the age and mileage of most of these cars. But how many times have you found the photos below? One of our skilled techs, in process of diagnosing the leakage in the system, noted diagnostic smoke coming from the fuel tank area. On the Z3 this is no small challenge, as the entire rear suspension must be dropped to remove the fuel tank, not an easy task. But as you can see from the photos below, our techs observations were right on! A large rodent nest was found on top of the tank, and the rodents had gnawed through the evap and fuel recovery lines.