perform unwarranted repairing.
When ignition is on, DO NOT remove any electrical devices to avoid electric components
being damaged by inductive electromotive force generated in circuit.
6. Electric fuel injection system faults and repairing
1. Basic knowledge for electric control fuel injection system repairing
The electric control fuel injection system is a complicated system. Operational person
should have a good command of system theory, structure, repairing procedures and tester
using methods. When repairing an engine problem, which may has relation with electric
fuel injection system, determine if the problem related with electric fuel system first. If
engine fails and indicator does not light, it is generally not related with electric fuel
injection system and should be checked and repaired as a carburetion engine.
When checking and repairing, some instruments and gauges are often used. Frequently used
instruments and gauge include special scan tester, circuit test light, voltmeter-ohmmeter and
oscilloscope etc.
Main methods for checking electronic controlled components includes ohmmeter, voltmeter
method, scan tester methods etc. Ohmmeter is often used to measure electronic controlled
components resistance under all conditions. Voltmeter is often used to measure electronic
controlled components voltage under all conditions and scan tester is used to determine if an
electronic controlled component operative upon indicated value on display (such as
monitoring coolant temperature sensor, air intake temperature pressure etc.)
2. Electric control fuel injection system problem diagnostic precaution
(1) No matter engine is running or not, when ignition is on, any electrical units absolutely
CAN NOT be removed, such as any battery lead, idle control valve, fuel injector, electric
fuel pump, ignition system cable, ECU circuit, A/C circuit.
(2) When checking ignition circuit, fuel pipe and electrical circuit to be tested must be
disconnected before starting engine. Disconnecting ignition wire is absolutely forbidden
when engine is running.
(3) Ohmmeter and indicator used to check sensor and electric controller resistance
must be over than 10kΩ, otherwise sensor and ECU may be damaged.
(4) ECU is a high quality integrated circuit, the failure ratio is very low, and do not suspect
its failure.
(5) Preventing water splashing to system wiring harness and sensor which will cause short.
(6) Before welding vehicle circuit, removing battery negative terminal.
(7) Electrical arch welding operating must be far away from ECU and sensor
3. Electric control fuel system fault and repairing
(1) Engine does not start or hard to start
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