How to get started diagnosing real-world problems
Part one in a series
Alex Portillo is the head technician for Car Clinic, an advanced repair shop in Mahopac, N.Y. He has received much of his training from Technicians Service Training and is a pupil of automotive trainer G. “Jerry” Truglia.
In the following case study, we aim to give a good overview of how you can get started diagnosing real-world EVAP problems. In the future, we will cover more advanced EVAP problems.
A 2005 Mini Cooper rolled into the shop with a check engine light. After scanning the codes we saw that what we were dealing with was a small Evaporative Emission Control System (EVAP) leak.
Now, the first thing we do as a matter of protocol is check the fuel cap, delete the code, and send the customer on his way. After all, half the time the customer simply did not tighten his cap or the cap itself has an obvious defect.
Customers do not like paying for a $100 diagnosis in order to find out that all they needed was a $15 part, so we deleted the light and told him to get a cap. So, when he comes back, the cap won’t figure into the diagnosis. When you are doing this, it is also good to take a peek at the fuel filler neck. Is there excessive rust where the cap meets the seal on the cap? Is it a Subaru? These are things that are worth investigating.
After having followed this protocol, the car came back, so now we knew it was time for a serious diagnostic checkup.
So, we got all my “go to” EVAP tools out in preparation for our work. This includes a smoke machine, BMW fuel filler neck adapter (there are a different sizes), smoke machine and CO2 tank. It is good to use CO2 gas instead of shop air as not only a safety precaution, but also so you can find leaks on top of the gas tank or those you cannot see with an emissions analyzer.
Because we were working with a European vehicle, my weapon of choice was the Autologic.
This scan tool has the ability to run tests that the factory scan tool can, and a lot of factory scan tools have an EVAP leak test. This test is useful to run before a diagnosis, because if the vehicle fails it confirms that whatever is setting the check engine light on the vehicle is still present.
After all, do you really care that the vehicle has an EVAP leak? No! You care that the PCM thinks the vehicle has an EVAP leak!
Smoke the car
The Mini failed the test, so we knew it was not an intermittent problem or PCM issue. Now it was time to smoke the car. The Mini, even though it is European, is an LDP system, meaning it uses a leak detection pump on its system. A lot of Chryslers and Mazdas (among others) have this, so we had no reason to be intimidated working on this vehicle.
This is how an LDP system works: it has its own motor (on this vehicle it runs on engine vacuum) that pumps pressure into the system, and sensors measure how long the system can hold pressure. If pressure is lost too quickly, there is a leak somewhere.
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