99 Chev.2500 5.7 L engine I is blowing 20 amp ecm fuse when you turn ignition switch on
Your 1999 Silverado has two ECM fuses in the underhood fuse block, the ECM 1 fuse which feeds power to the ignition coil, ignition control module, crankshaft position sensor, and fuel injectors and the ECM B fuse which feeds power to the fuel pump via the fuel pump relay before the engine starts and the oil pressure/fuel pump switch after the engine starts. Depending on which ECM fuse is blowing, look for a short in the circuits it powers by unplugging those items, replace the fuse, and then plug each item in until you find the circuit which is blowing the fuse.
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