[Repair Case] Chevrolet sports car cannot start

Posted by Tony Brown on

Issue: The car was towed to the repair shop for maintenance because it wouldn’t start. The preliminary inspection result showed that there was a high-pressure fire, but there was no fuel injection.


 The engine is equipped with a HEI-EST ignition system, which stands for high-energy electronic ignition. For the fire test, we unplugged the sub-cylinder high-voltage cable to test for firing; the sparks were very strong. Next, we used chemical cleaner into the intake manifold, and the engine could barely operate. We used an external pump instead of the fuel pump of the original car to build up the fuel pressure, and the car still wouldn’t start. We then unplugged the fuel injector harness plug, conducted a test run, started the vehicle; the test light illuminated; the engine can run; however, the test light goes out after 2 seconds, and the engine shuts down. Following the aforesaid examination, it was established that the defect is caused by an interruption of the injector grounding circuit's control signal.

 The power system is self-diagnosed because the injector grounding circuit is directly controlled by the power system control module. Short-circuit the diagnostic sockets A and B pins, turn on the ignition switch, observe the flicker frequency of the engine fault light on the instrument, and then check the fault code table, it is learned that the content of the fault code is that the coolant temperature is too high. The abnormal signal of the coolant temperature sensor will not cause the fuel injection to be interrupted, and the coolant temperature sensor failure factor can be ignored, based on previous maintenance experience.

Measure the connection between the wire harness plug pins and the injectors on the power system control module, which is located on the inside of the front passenger's foot guard. The four injectors in the engine's left cylinder were discovered to share a ground loop control. Another grounding circuit control wire connects the four injectors on the right row of cylinders. To put it another way, the engine employs grouped fuel injection, and the measurements reveal that the two ground loop control lines mentioned above are well connected.

 A distributor is included with the HEI-EST ignition system, which houses an ignition control module and a crankshaft speed sensor. The engine control module is connected to the ignition control module through four wires. EST output, reference input, bypass control, and reference signal are their names. When the vehicle is started, the ignition control module controls the ignition timing if the engine speed is less than 400r/min; if the engine speed is greater than 400r/min, the power system control module controls the ignition timing. The 0V of the bypass control wire becomes 5V, and there is voltage on the EST output wire, which is the conversion sign of ignition timing control. The mechanic leads out the two injector grounding circuit control lines, lightly stepping on the accelerator pedal during the startup process, and then manually regulating the two injector grounding circuit control lines to execute intermittent grounding, according to the aforementioned operating principle. able to keep the car in good working order, simultaneously, the voltage on the bypass control wire is measured, and the result is changed from 0V to 5V, indicating that the power system control module has received the reference input wire's crankshaft speed signal. Since this signal determines the control of the power system control module to close the injector and the fuel pump relay, and the fuel pump of the vehicle is running, there are two possible causes for the failure to be judged. One is the fuel injector drive circuit of the power system control module being damaged, the second is that the anti-theft function of the engine is activated and the fuel injection function is interrupted. The power system control module was disassembled for inspection, and no signs of damage were found.

 Continue to check the engine anti-theft system. The automobile has a PASSKEY II anti-theft system, which consists primarily of an ignition key and an anti-theft control module. The ignition key contains a black resistance block, which is how it works. It is necessary to employ the anti-theft identification element. The anti-theft control module reads the resistance value of the resistance block using the two wires on the neck of the ignition switch, and then compares it to the resistance value stored in the internal memory. If the values match, a pulse wave of a specific frequency is triggered and released. The fuel injection locking function of the power system control module allows the engine to start and run. If the values do not match, the fuel injection function is locked.

 The ignition switch was removed for investigation, and the wiring was discovered to have been changed. With an original car ignition key in between, locate two resistance block detecting signal wires from the anti-theft control module. The original car's ignition key was removed, and the sliding rheostat was repeatedly tried to debug, all of which failed. Inside the instrument panel, the anti-theft control module was discovered and disassembled for inspection. There was no anomaly discovered. A dark blue cable connects the anti-theft control module to the power system control module, according to the necessary circuit diagrams, and the anti-theft data cable is this wire. Can the anti-theft data cable be used to start the engine? The author devised a simple method: identify a bolt, thread one end of the iron, and trace the anti-theft data line through the threaded area while starting the vehicle to simulate a set of 5V pulse signals. The engine was ultimately turned on after repeated tests. This indicates that the power system control module and the anti-theft control module are both in good working order, and the issue is with the line connection. The line was returned to its original state, the test was completed, the failure symptoms vanished, and the inspection job was completed.

 Summary: The key to troubleshooting in this case is determining whether the power system control module and the anti-theft control module are normal. Furthermore, the engine may be turned on by replicating the anti-theft pulse signal using a simple approach, demonstrating that the PASSKEY II anti-theft system lacks the code-changing feature and is readily cracked.

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