Q: I have a 1992 Chevy 1500 two-wheel-drive pickup with the 5.7L V-8 and an automatic. It idles rough, gets poor gas mileage, and pings. I have to use at least 93 octane to stop the ping. It's not the EGR valve, and I've already replaced the plugs, ignition wires, distributor cap, and rotor. I retarded the timing a little, but I want to put it back. Where is the wire I have to disconnect to set the timing? What can be causing these problems?
A: It's a good idea to get the ignition timing correct before going any further. There should be a black connector joining a single tan and black wire that breaks out of the wiring harness under the battery-junction block in the rear center of the engine compartment. Once disconnected, the electronic spark timing will go into bypass mode. This means the timing is no longer computer controlled and can be adjusted at its base setting by rotating the distributor. You should line up the timing marks with a timing light to 0* BTC, shut down the engine, and reconnect the set timing connector before restarting. The symptoms of rough idle, poor mpg, and spark knock can originate in a number of different areas that may require a qualified tech to diagnose properly. I would double check on the exhaust-gas recirculation-valve operation along with closely inspecting the knock sensor. The system should be gone over with a scan tool checking for trouble codes and proper sensor inputs to the electronic control module that manages the system. You should also check with the dealer for any computer calibration updates for your particular application. It could even boil down to an internal engine problem.
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