This article will span over two months. We will solve a problem this month, but I will write a separate article to conclude solving some others.
An existing customer called us and asked to bring in their 2014 Acura MDX. The customer stated that the check engine light was on. We asked the customer if there were any symptoms, and they said no. We scheduled an appointment and saw the car a few days later.
Once the car was in the shop, we connected the scanner and pulled codes. The engine control module had stored a P1454 FTP (fuel tank pressure sensor) circuit range/performance problem. The code was stored as temporary and permanent. We also pulled a P2422 EVAP, CVS (canister vent solenoid) stuck closed in permanent memory, and code P0452 FTP, sensor circuit low voltage.
Before I get started, I will do a quick refresher on EVAP or fuel evaporative systems. The two gases that create the most visible smog we see in the atmosphere are hydrocarbons (HC) and nitrogen oxide (NOX). The engine, engine management system and catalytic converter controls nitrogen oxide. Hydrocarbons are unburnt fuel or fuel vapors. Hydrocarbons are contained in the fuel tank and its delivery system. This fuel delivery system is quite large. It spans from one end of the car to the other. The fuel delivery system consists of the fuel tank, fuel filler tube, fuel evaporative system (EVAP), fuel pump, fuel lines, fuel rail and injectors. The EVAP system is constantly testing the fuel system for leaks. It does this by pressurizing the fuel tank and fuel lines and checking for leaks. If there is a leak, HC will escape into the atmosphere. The EVAP monitor will then set a code and try to help the technician find the problem.
This is where EVAP system diagnostics become extremely difficult. The system is so large that the problem(s) can be anywhere. We have seen problems as simple as a loose gas cap and as difficult as a pinhole leak on top of a fuel tank. Even with advanced tools and expertise, troubleshooting evaporative problems is extremely difficult.
We then performed the troubleshooting procedure per the factory test. We first checked for visible leaks in and on the EVAP system. No leaks were found. We then ran a system-wide test on the components of the EVAP system. All of the components tested operational. While looking at the live data of the fuel tank pressure sensor, we saw a reading stuck at -.13. The spec is -.63 to +.63. We then removed the gas cap, and there still was no change. We then checked for vacuum at the fuel tank pressure sensor and found no vacuum. We then checked the vacuum line from the fuel tank pressure sensor to the EVAP canister filter, and still, there was no vacuum. We then opened the EVAP canister filter and found a piece of plastic that was blocking the vacuum line.
We removed the piece of plastic and then ran the test again. During the test we could see the fuel tank pressure sensor fluctuating between -.60 to +.20. We cleared the codes. Then, we ran the EVAP test, and it passed. This was great, yet we still had a problem. During the diagnostics, we can force a manual test to be run on the EVAP system, yet we need the car to pass the EVAP test on its own. For the car to pass on its own, it has to complete several drive cycles. The fuel tank also needs to be above one quart and below three quarts of fuel. This is because too much fuel will cause an inconclusive test, and insufficient fuel makes it difficult to test.
At this point, we had solved an EVAP problem, but the customer’s fuel tank was full. We needed the customer to pick up the car and burn off half a tank of fuel or so. In doing so, the car will get multiple test drives and hopefully pass the onboard EVAP monitor. The question I will leave you with is where did the plastic piece come from?
Matt Pataky owns Sunnyvale Foreign Car Service, 15 Pioneer Way, Mountain View. For more information, call (650) 960- 6988, email [email protected] or visit sunnyvaleforeigncar.com.
