30 March 2014
WHAT S NEW IN EVAP Photoillustration: Harold A. Perry; images: Thinkstock & Ford TESTING BY BOB PATTENGALE Automotive technology evolves. Changes may improve the ownership experience or allow the vehicle to comply with new regulations. Either way, these changes may directly affect service techniques. Don t touch the gas cap, don t touch the gas cap and don t let your buddy touch the gas cap. Why? If someone tightens the cap before you test for leaks, how will you know if that was the source of the leak? The good news is that the gas cap is disappearing on many new vehicles. Chrysler, Ford and General Motors have started building some of their vehicles with capless fuel systems. The two capless designs being used today single-door and double-door are shown in Fig. 1 on page 32. What are the benefits of a capless design? From a consumer perspective, the obvious benefit is not needing to interact with the gas cap, which sometimes can be a messy job. From a diagnostic point of view, we can focus on finding the leak without blaming the cap. The days of tightening the gas cap and clearing the fault code(s) are gone. One issue for many techs will be not having quick access to the filler neck for leak-testing (more on that later). The final benefit relates to limiting the quantity of fuel vapors that escape from around the open filler neck while the gas cap is off. Think about the March 2014 31
process of filling up at the pump. Some consumers remove the gas cap even before beginning the payment process, which means fuel vapors are escaping the entire time the gas cap is off. The capless design eliminates this, since the fuel filler flap is closed until the fuel nozzle is inserted into the filler neck and is immediately closed again when the nozzle is removed. This is a great idea, and a growing number of vehicles will eventually have this feature, which means you need to be prepared to service these systems. Let s take a closer look at the singledoor design (Fig. 1 below, top photo). The photo on the left shows the front of the filler door where the fuel nozzle is inserted. Two aluminum release tabs are depressed when the fuel nozzle is inserted. The photo on the right shows the rear of the filler flap, with tabs on each side of the flap. The photo in the middle is a close-up of the face of the flap. The illustration at the bottom of the page shows that there s a rubber seal attached to the flap which seals the fuel vapor system. This is a very clever design, but creates some challenges if you want to use a test adapter from the filler neck area. Now the million dollar question: Has anyone invented an adapter that allows you to seal and test the fuel vapor system from the capless area in a capless system? The answer is no for the singledoor design and yes for the double-door design. Fig. 2 on page 34 shows the Redline Detection EasyEVAP capless adapter (top photo), which is designed to work on capless systems, but does not Fig. 1 The images above (three views) are of a typical single-door capless fuel system design. The left photo shows the filler door where the fuel nozzle is inserted, the right photo (taken from the rear of the filler flap) shows the aluminum tabs (arrows) on each side of the flap and the middle photo shows the face of the flap when closed. The illustration below shows the double-door capless concept with a test adapter installed. Ford, Chrysler and GM are beginning to use capless systems on their vehicles. Expect other manufacturers to follow. Rubber Compression Seal distinguish between single-door or double-door designs. The bottom photo shows the Pop-it Capless Double-Door Fuel Neck Adapter from Smoke Wizard (also available from Vacutec). Let s take a look at the EasyEVAP adapter. The first step is inserting the aluminum tube, which opens the door but cannot seal the fuel nozzle inlet area. The next step is installing the universal gas cap adapter with double-sided tape, which in theory should seal the fuel vapor system. Now we can introduce smoke and look for leaks, but this is where we find the system is not really sealed. The photo on the left in Fig. 3 on page 36 was taken from a 2012 Dodge Charger with the cover around the filler neck tube removed. It clearly shows smoke coming out of a vent hole molded into the filler tube area. The vent is located between the universal gas cap adapter and the aluminum tube inserted to open the fuel filler flap. The top right photo shows a red wire inserted to demonstrate the path the smoke travels between the universal gas cap adapter and the aluminum tube. The photo on the bottom right is of a filler neck tube from a 2012 Ford Fusion. With this design, if you had access to the molded vent tube, you might be able to plug the end and seal the system. This is not an option on the Charger. At this time I m not aware of any adapter that will work on a single-door system, so what is the best method of testing single-door systems? If we still had test ports, this would be easy, but for most vehicles it s still fairly simple: Locate the purge solenoid (normally accessible under the hood), disconnect the hose going to the charcoal canister and introduce the smoke vapor. If you see smoke coming from around the fuel filler flap, you either have debris around the seal or the seal is damaged. If smoke is not coming from around the capless filler neck flap and the flow ball is floating, start looking for a leak in another area. The good news: The Smoke Wizard, Vacutec and Redline Detection adapters worked on the 2013 Ford Escape with the double-door system I tested, so this issue will be short-lived if more vehicle manufacturers adopt the double-door design over the single-door. 32 March 2014
What s different with the doubledoor design? Number one on the 2013 Ford Escape I tested, the vent area just mentioned has been eliminated. The bottom photo in Fig. 2 shows the Smoke Wizard Capless Double-Door Fuel Neck Adapter, with a rubber compression seal in the middle that expands by rotating a sealing nut clockwise. The top photo shows where the compressed rubber seals around the first door inlet area. The Redline Detection EasyEVAP adapter utilizes the aluminum tube to open the doors and the universal gas cap adapter with double-sided tape to seal against the face of the filler tube. The 2013 Ford Escape utilizes a vent solenoid, which must be closed with a scan tool to complete the fuel vapor system seal. Vehicles without a vent solenoid generally require you to locate the vent hose and plug it to seal the system. You probably won t see these systems for a few years, but at least you know they exist. In May 2007 I wrote an article for MOTOR entitled Evaporative Emissions Revisited, which focused on the most common evap issues technicians were struggling with at the time. In preparing for this article, I once again reached out to STAR EnviroTech to review the technical calls they were receiving on their toll-free tech hotline, used by customers who purchase their evaporative emissions testing equipment. As I suspected, three of the four Fig. 2 The photo above is the Redline Detection EasyEVAP capless test kit adapter, which can work on either single-door or double-door capless systems. The photo below is the Smoke Wizard/Vacutec double-door (only) capless adapter. questions we covered in 2007 are no longer an issue, but the Chrysler leak detection pump (LDP) system is still very confusing for technicians and is now the number one tech hotline question, which goes something like this: I m working on a Chrysler LDP system and need to know how to test it and close the vent for leak-testing. Hotline calls for Chrysler s newer natural vacuum leak detection (NVLD) system or Ford s engine off natural vacuum (EONV) system are on the rise, so our next evap update will likely focus on these systems. Let s try to clear up the confusion about Chrysler s LDP system. Fig. 4 on page 38 shows the LDP and its main components. In the rest position, the diaphragm spring keeps the vent plunger open, which allows the LDP to act just like a normally open vent solenoid-operated evaporative emissions system. As the fuel temperature increases, vapors from the tank are collected in the charcoal canister and the expanding gases are allowed to vent through the vent plunger. When the fuel temperature decreases, fresh air is naturally drawn back through the vent plunger, equalizing the pressure in the fuel tank. Fuel vapor purge is performed in the same manner. When it s time to purge fuel vapors, the purge solenoid opens, pulling fresh air through the vent plunger, through the charcoal canister and into the engine. The primary purpose of the LDP, obviously, is to check for leaks in the fuel vapor system. Put another way, if the LDP never operated, the diaphragm spring would keep the vent plunger open and the fuel vapor collection system would continue to function. The sole purpose of the LDP is to look for leaks in the system. Now let s get to the reason for the tech hotline phone calls. This usually begins when a technician encounters a P0455 (gross leak) or maybe a P0456 (small leak) trouble code and is trying to figure out if the code is due to a faulty LDP or a leak in the fuel vapor system. Looking for leaks in the system is really very simple (we ll get to that shortly), but how do you know the code is not caused by a faulty LDP? 34 March 2014
Spot for Plug If Easily Accessible Fig. 3 The single-door capless system on the 2012 Dodge Charger (above and top right photos) has a tricky design. The photo above shows smoke exiting from a vent hole molded into the filler neck. The red wire in the top right photo indicates the path the smoke travels between the universal gas cap adapter and the aluminum tube. The photo on the right shows the Ford vent outlet design. The powertrain control module (PCM) electrically and mechanically tests the LDP prior to performing any leak checks. If the PCM detects a problem with the LDP, it will not proceed to leak-testing and one of two fault codes may be set. P1494 (LDP switch or mechanical fault) or P1495 (LDP solenoid circuit fault) tells us the LDP is not functioning properly. Once again, the PCM will not perform a leak test if the LDP is not functioning properly, so if you have a leak code, with the exception of a few unique issues, you re looking for a leak and not a faulty LDP. The PCM LDP monitor begins with a check of the vacuum solenoid shown in Fig. 4, which can be performed KOEO or KOER. If the PCM detects an open or short in the electrical circuit, the P1495 code will be set and the electrical circuit for the vacuum solenoid will need to be tested. The PCM will not perform a leak test if P1495 is set. Next, the LDP monitor will check the mechanical integrity of the pump diaphragm and reed switch. Fig. 5 explains this process. KOER engine vacuum should be available at the vacuum solenoid port (1). The PCM now sends a controlled pulsewidth-modulated (PWM) signal to the vacuum solenoid (2). When the solenoid opens, engine vacuum begins pulling the diaphragm (3) upward. In the center of the spring just above the diaphragm is a centering rod (4), which moves with the diaphragm. A cutout just above the rod serves a dual purpose travel space for the rod and operation of the reed switch. To the left of the opening is SN and to the right is the drawing of the reed switch (5). Both of these items represent reed switch operation. The reed switch is normally closed in the LDP s rest position. It s not a physical contact switch; it s an electrical switch operated by an applied magnetic field. As the centering rod passes through this area, the magnetic field changes and the reed switch opens, telling the PCM that the vacuum solenoid opened, engine vacuum was available and the diaphragm is able to move upward. If the PCM sends the PWM signal to the vacuum solenoid and the reed switch doesn t open, the PCM will set a P1495 for a faulty LDP. At this point, you must determine the cause of the code broken vacuum line, ruptured or stuck diaphragm, stuck vacuum solenoid, etc. Again, the PCM will not perform a leak test with this fault code present. The next phase of the LDP monitor checks the diaphragm vent hose (6), which is vented to the atmosphere. When the vacuum solenoid is closed, sealing off the engine vacuum source, the area above the diaphragm is exposed to the atmosphere, and with spring pressure the diaphragm should move downward. Once the centering rod leaves the cutout area, the magnetic field changes and the 36 March 2014
Engine Vacuum From Charcoal Canister & Fuel Tank Vent Plunger Fig. 4 This illustration shows the critical components of the Chrysler LDP. reed switch closes. If the PCM does not see the reed switch close, this would indicate the LDP is stuck in the upward position and code P1495 would be set. If the LDP passes these functional tests, the PCM will cycle the LDP a calibrated number of times to determine if there s a restriction on the pump side. There are two one-way valves (7, 8) at the bottom of the LDP. The first (7) opens when the diaphragm travels upward, drawing air in from the vent area, 11 1 2 8 Vacuum Solenoid 3 Reed Switch LDP Diaphragm & Spring Vent to Atmosphere and closes when it travels downward. The one-way valve labeled (8) opens when the diaphragm travels downward, which creates the pumping effect, and closes when it travels upward. In the monitor test mode, the number of pumping events will not be enough to build pressure. If the LDP stalls, it s because of a restriction in the pressure side of the LDP, and a P1495 would be set. Keep in mind this all happens within a few seconds after the vehicle is started, Fig. 5 The powertrain control module (PCM) performs a comprehensive LDP check prior to testing the system for leaks. The numbers indicate the parts that are tested during the test sequence, which is explained in the text. 7 6 10 4 5 Illustrations courtesy STAR EnviroTech so the PCM knows right away if the LDP is not capable of performing a leak test. This means that if you have a leak code you should be looking for leaks, not focusing on the LDP. Is it possible for the LDP to be the source of the leak? Yes. Fig. 6 on page 39 shows the LDP in a stalled position, with the pressure gauge (12) getting close to the maximum pressure of approximately 7.5 in. H 2 O and the reed switch (5) in the open position. In the stalled position, the PCM will wait a predetermined period of time while performing a leak-down test. If the reed switch closes, leak-down has occurred and a P0456 (small leak) code will be set. Most likely you ll be looking for a small leak in the fuel vapor area, but the LDP diaphragm (9) and vent-side valve (7) could be possibilities. Here s the fastest way to deal with leak codes on a Chrysler LDP system. Note, however, that this method does not test the vent plunger seal, LDP diaphragm or vent-side diaphragm valve. Pick the quickest spot to connect the smoke machine the test port, if the vehicle is so equipped. If not, find the purge solenoid and connect the smoke machine to the hose going back to the charcoal canister. If this isn t possible, you can use the gas cap area. Turn the smoke machine on and follow the smoke to the LDP vent plunger outlet area (10). At this point you need to plug the vent hose to quickly seal the fuel vapor system and monitor the flow meter. If the flow ball is floating, start looking for leaks; if the ball goes to the bottom, no leaks are present. You still need to consider the vent plunger seal, LDP diaphragm or vent-side diaphragm valve. One thing to keep in mind when using the LDP testing method just described is that it s possible to see smoke or have a slight leakage from the vent side of the LDP that would not set a leak code. Going back to Fig. 5, if we plug the vent outlet (10), smoke vapor will be able to travel into the hose (6), vent check valve (7) and around to the rear of the suction side of the diaphragm (3). It s not uncommon to see smoke coming from around the LDP electrical connection; this would be normal. Once again, this is not the source of your leak code. If in doubt, remove the hose to the 38 March 2014
12 11 9 Fig. 6 Small leaks can occur within the leak detection pump, but only on the pressure side. If you can t find a leak in the fuel vapor system, it s a good idea to check the LDP diaphragm (7) and vent-side diaphragm valve (9). 7 10 5 must run to test the system. For example, if the fuel gauge reads half a tank but the actual fuel level is a quarter of a tank, it will take longer for pressure to build. The PCM sets the LDP pumping time for half-tank volume and when the pressure does not build in the expected time, the PCM has only one choice it sets a leak code. Here s a critical tip: If your leak code keeps returning and you can t find a leak, try thinking like the PCM thinks. What s the logic behind how the test is performed and what are the limitations? Evaporative emissions testing is not complicated, but you need to understand the system you re checking, review the specific recommendations for the code and have the right tools for the job. If you have a leak code, always start with testing for leaks and use the least intrusive method possible. charcoal canister (11) at the LDP, plug it and test again. If the ball still floats, look for leaks on the fuel vapor side. One final note about LDP systems: Fuel level accuracy is critical for the PCM to calculate how long the pump This article can be found online at www.motormagazine.com. Circle #18 March 2014 39