Our Experts At Work

We deal with a large variety of automotive issues at the shop. Some issues such as tire patches are simple and daily occurrences. Sometimes we take on classic cars that need regular repair and overhaul. Sometimes we take on "headaches" that other shops just could not figure out. This is a story about one of those times. 

We recently had in a 10 year old Chevrolet Colorado, 4 cylinder and four-wheel drive. It had been throwing lean condition codes, this means that the engine was getting too much unregulated air into the engine. As a result, the engine computer was forcing the injectors to stay open longer causing gas milage to plummet. Upon looking under the hood, it appeared to have had the "throw a part at it and see if fixes it kind of look". After looking at the scan data, the computer indeed displayed to us it was lean, the mass air flow sensor was reading lower than expected. This is likely due to a component failing causing air not seen by the mass air flow sensor to enter the engine. The air/fuel sensor (oxygen sensor) sees the excess after combustion and then the computer adds more fuel to the engine until it sees a proper mixture at the oxygen sensor in the exhaust. 

So how do we find air entering the engine? We check obvious components such as intake tubes and hoses for cracks and holes. If nothing is obvious, then it is best to hook up a smoke machine and fill the intake with smoke. Smoke machines are primarily used for fuel and evaporative emission leaks; however, they can be used for situations such as these. Expert technicians know that tools can always be used for more than 1 situation. The smoke machine showed us the leak. Within minutes, the air intake resonator box was smoking out of the seam.  The resonator box appeared in physical good health; however, it clearly was not. 

Unfortunately, the air resonator box was not available anymore as GM had discontinued it and it is not a commonly sold part by a junkyard. Our only choice of repair was to physically seal the box with adhesive and a plastic weld compound. After resealing the box, engine fuel trims came back to normal. The check engine light issue was resolved. The truck could then pass inspection and gas mileage was restored to normal.