Where There’s Smoke... There’s Learning

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Where There’s Smoke... There’s Learning

Mike Joachim • Dec 11, 2020

It’s no secret that students need help

to make the leap across the gap between information and understanding.

It’s also no secret that “doing” bridges that gap. ATech’s faulted trainers include “real world” system electrical faults designed to give students the opportunity to acquire and practice troubleshooting skills by “doing”.

The ATech EVAP trainer takes this concept even further. The GM enhanced EVAP “plumbing” system has been replicated on the trainer and is fully functional, allowing students to become familiar with EVAP system testing, troubleshooting, and diagnosis.

This trainer emulates the GM enhanced EVAP system from a 2003 Chevrolet Impala. Courseware, which includes an Instructor Guide and Student Manual, provides on-trainer and on-vehicle activities.

How much time and effort are required to use a live vehicle for EVAP diagnostic exercises? GM’s scan tool-driven EVAP Service Bay Test, which is used to verify both existing conditions and completed repairs, will only run if the vehicle’s fuel level is between 15 and 85% and the engine coolant temperature is below 158°F (70°C). This test has to be performed with the vehicle’s engine running. How many times in a row can this test be run before the engine temperature gets above this limit? How long will the vehicle take to cool back down enough to run the test again?

The 2003 Impala sets the following EVAP “plumbing-related” DTCs:

- P0440 (Large EVAP Leak)

- P0442 (Small EVAP Leak)

- P0446 (Blocked Vent Solenoid / Path)

- P1441 (Vacuum detected during non-purge)

Do your students currently practice diagnosing these DTCs and pinpointing their causes? Faults that set all of these DTCs can be inserted on the EVAP system trainer. Students can practice troubleshooting all of these faults via GM Service Information (SI) procedures. The EVAP system trainer also has faults related to EVAP system monitoring and control. The goal is for more student learning to occur in less time.

Let’s preview the on-trainer diagnostic process for a small EVAP system leak with DTC P0442 set. The instructor inserts a small leak into the EVAP system trainer either via the built-in keypad or the ATech Instructor Management Program.

As noted in previous Newsletter articles, the trainer will run the complete GM EVAP Service Bay Test from either the trainer’s internal scan tool, or from a Tech 2 scan tool. Since there’s no engine on the trainer, this test can be run as many times in a row as necessary.

The student begins by running this test which fails and causes DTC P0442 to set as shown in Figure 1.

OBD II regulations require that EVAP system leaks as small as .020” (.51mm) be detected. How does the vehicle (or trainer) PCM determine that there’s a small EVAP system leak? From the DTC P0442 System Description for our 2003 Impala in GM SI:

“This DTC tests the evaporative emission (EVAP) system for a small leak. The control module monitors the fuel tank pressure (FTP) sensor signal to determine the vacuum decay rate. At an appropriate time, the control module turns the EVAP canister purge valve ON (open) and the EVAP vent valve ON (closed). This allows the engine to draw a vacuum on the EVAP system. At a calibrated time, or vacuum level, the control module turns the EVAP canister purge valve OFF, sealing the system and monitors the FTP sensor input in order to determine the EVAP system vacuum decay. If the control module detects a leak larger than a calibrated amount, this DTC sets.”

The GM SI diagnostic table then lists a step-by-step procedure for locating the leak via visual inspection and the use of their Evaporative Emissions System (nitrogen/smoke) Tester. Specifically, GM’s procedure directs the technician to introduce smoke into the EVAP system by connecting the tester to the vehicle using a Fuel Tank Cap adapter.

Most working technicians would dispute this procedure. What if the fuel tank cap itself was the source of the leak? If the root cause of this DR really was the proverbial “loose gas cap”, would this method of testing pinpoint the location of the problem? The first step in troubleshooting typically is to verify the problem. The student should use the correct procedure when practicing troubleshooting. Part of teaching the diagnostic process should include the opportunity for the student to practice verifying the problem.

The EVAP system trainer’s small leak fault gives that opportunity. Just like on the car, the trainer’s internal scan tool or a Tech 2 can command the normally-open Canister Vent Solenoid closed to seal the EVAP system.

There are several nitrogen/smoke EVAP system testers available which incorporate a calibrated nitrogen flow meter. The tester is calibrated and then used to lightly pressurize the sealed EVAP system with inert nitrogen through the EVAP Service Port. Higher than standard flow under pressure is verification that there is in fact an EVAP leak.

Note in Figure 2, the greater flow rate indicated by the ball floating above the marker arrow on the flow meter. At this point, the PCM has “seen” a small leak, and the student has verified it with minimal EVAP system disruption.

Smoke can now be introduced into the system to locate the source of the leak. Note in Figure 3, the visible smoke both in and under the fuel tank.

What would you have to do to create and insert a small EVAP system leak on a live vehicle? How long would it take each of your students to correctly diagnose and locate it?

And don’t forget about the safety aspect either. Pressurizing an EVAP system with a leak on a live vehicle forces gasoline vapor out through the leak path. If students pressurize the system multiple times while practicing diagnosis, the quantity of gasoline vapor emitted could potentially be significant. There is no gasoline in the EVAP System Trainer to create flammable vapor.

-Mike Joachim

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Engines of the Future are Already Here!

By Jeff Bogue • 12 Dec, 2023

I have been dreaming about and studying engines and engine performance of cars, trucks, and motorcycles for the better part of 45 years. It’s a hobby. It keeps me busy on cold winter evenings. It’s something that has become a large part of my life and, like playing with dogs, is something I love to do. I have written about engines and the engineering that is involved in them for the last 15 years, and I have always been forward-thinking. When a new engine is being lauded by the manufacturers as the next big thing, I read all about it and report those findings here. In the past, I have written about every one of the engines in this article at one time or another, and each one was glowingly revealed by the engineers with the statement “We can expect these engines in our cars in the next few years”. Well, a few years have passed and now most of these engines ARE in our cars and trucks and should be reaching repair shops and dealerships now. We just haven’t heard that much about them because people, as a general rule, really don’t care that much about which engine is in their car if it gets good gas mileage, is reasonably reliable, and has a little umph to get on the highway. Well, that is not us. We care. We study it. It’s what we do and why you are where you are reading this article. Without further ado, let us look at the “Engines of the Future” that you can buy (and service) now.