Abstract: The present invention provides a malfunction diagnostic apparatus for an evaporated fuel purge system in an internal combustion engine, capable of detecting abnormalities such as looseness or clogging in the purge line between a purge valve and an engine intake passage. An electric pump 14 is turned on when a purge valve 5 is in a closed state and a selector valve 20 is in an open state. After the lapse of a given time period Tref, a load-current initial value I1 of the electric pump 14 is detected at the moment switching the selector valve 20 to a closed state. After the lapse of a given time period Tpump, the purge valve 5 is switched to an open state, and a load-current final value at the moment after the lapse of a given time period Tpurge. As in the curve A, when a load current final value I2A is equal to or less than the load current initial value I1, it is determined that the gaseous communication state in the purge line between the purge valve 5 and the intake passage is normal.

Abstract: The present invention provides a malfunction diagnostic apparatus for an evaporated fuel purge system in an internal combustion engine, capable of detecting abnormalities such as looseness or clogging in the purge line between a purge valve and an engine intake passage. An electric pump 14 is turned on when a purge valve 5 is in a closed state and a selector valve 20 is in an open state. After the lapse of a given time period Tref, a load-current initial value I1 of the electric pump 14 is detected at the moment switching the selector valve 20 to a closed state. After the lapse of a given time period Tpump, the purge valve 5 is switched to an open state, and a load-current final value at the moment after the lapse of a given time period Tpurge. As in the curve A, when a load current final value I2A is equal to or less than the load current initial value I1, it is determined that the gaseous communication state in the purge line between the purge valve 5 and the intake passage is normal.

Abstract: A system for diagnosing evaporation control system failures repeatedly introduces pressure, positive or negative, into the evaporation control system and closes up it hermetically, a plurality of times (for example two times), and detects changes in internal pressure in the evaporation control system. An average value of the internal pressure changes is compared to a threshold value so as to judge whether there is leakage of fuel vapors of the evaporation control system. When a difference between the internal pressure change is greater than a specified value, the evaporation control system failure diagnosis is interrupted.

Abstract: A valve operation verifying system for making verification of valve operation of an EGR valve of a type having a diaphragm elastically deformable according to operating conditions of an engine to admit controlled amounts of exhaust gas that is recirculated into an intake air stream which verifies, on a basis of gas pressure in an EGR passage, whether the diaphragm remains elastically deformable as specified and whether a pressure sensor remains free from freezing, and executes the verification of valve operation of the EGR valve on a basis of a change in the gas pressure in the EGR passage when the EGR valve opens and when it closes, and when the temperature of ambient air is lower than a critical point, verifying that the diaphragm remains elastically deformable as specified and that said pressure sensor is free from freezing.

Abstract: A leakage diagnostic system for making a judgement of leakage of a fuel purge system, which has in order from the side of a fuel tank a control valve, a canister and a purge valve disposed in a purge passage and a relief valve isolating the canister from the atmosphere, based on a rising rate of pressure in the purge passage between the fuel tank and the intake system isolated from the atmosphere after lowering and keeping the interior of the purge passage below specified negative pressure level for a specified period of time. When the interior of the fuel tank increases above a threshold level after a specified period of time, the leakage diagnostic system delivers a judgement of leakage of the purge system.