Fuel Systems and EVAP Functionality

Today’s fuel system is responsible for evaporation emissions control as well providing fuel storage and delivery. One major requirement for proper function of the EVAP system is for this system to be completely sealed.

Repairs made to the fuel system need to maintain the integrity of this sealed system and restore any lost performance and functionality. The technician is still required to “drop the tank” to gain access to the fuel pump module, more often than not, and that requires disconnecting the fuel lines as well as the filler neck.

As the technician is now left with an immobilized vehicle, usually tying up a lift and a service bay, this is the “point of no return”. Aside from the correct fuel pump module, the technician may require additional parts or repair pieces before this vehicle can leave the shop again under its own power.

Most pump assemblies feature replacement wiring harnesses, new sealing rings, and quick-disconnect clips, but items such as the fuel tank locking ring, fuel pump relays and in-line filters are available separately and at extra cost. The sealing surfaces inside quick-disconnect fittings on fuel lines under the vehicle are especially vulnerable to being compromised.

Missing or distorted seals may cause serious leakage that will only be evident after reassembly and startup. In the long run, close inspection of these small items beforehand may save your customer large trouble. Complete repairs of EVAP and fuel lines are made possible by aftermarket companies offering repair solutions for steel and nylon lines.

Most of today’s fuel systems are returnless, with internal fuel pressure regulators, adding another element to the in-tank module. The module is now responsible for passing vapor along to the EVAP system, pumping, filtering and regulating the flow of fuel.

Some returnless modules also feature a fuel tank pressure sensor, which monitors pressure for the on-board EVAP system self-diagnostics, as well as serves as input for the PCM to vary fuel pump speed. The presence or absence of this sensor also is one of the key visual elements used in selecting the correct replacement module for many vehicles. Other systems use an external fuel pump driver module to vary the speed of the pump, maintaining proper fuel pressure.

This failure-prone driver module has gained popularity as an aftermarket part, but too often, it is discovered after a new fuel pump has been installed and the truck still has a no-start condition. This module is exposed to moisture and corrosive road salt due to its location on the frame rail.

In the northeast, shops see more rust than some areas of the country, so straps, tanks, and steel fuel lines are more popular replacement items here than in some other markets. They also see a more cases of filler neck failures due to rust-through.

The dreaded P0442 code, “small leak detected,” is often caused by tiny pinhole leaks like these can lead to which often leads to multiple component replacements and frustration when the actual source of the leak isn’t found until much later. Aftermarket or salvage yard filler necks may only be supplied as partial units, without rubber fill and vent hoses.

Old hoses are prone to cracking and dry-rot and should be replaced, as they are a potential source of liquid and vapor leakage. Replacement hoses should be rated for fuel or fuel vapor; coolant hoses will not hold up to long-term fuel exposure.

The fuel cap should also be checked for fitment. If the cap does not fit the replacement filler neck correctly, or is in poor condition, it should be discarded in favor of a new cap. In some cases, these recommendations are simply suggested as convenience items when replacing a failed pump, but sometimes they prove to be necessary items to maintain or restore system integrity.

For a parts specialist, providing the “correct” parts should be considered a minimum qualification. Sometimes, the thing that sets you apart from your competition is being able to provide the “extra” parts to complete a job when it becomes a larger repair than anticipated, or when something goes unexpectedly wrong.