The firing order for an internal combustion engine is the sequence in which each cylinder delivers power in a multi-cylinder reciprocating engine. Gasoline engines and diesel engines accomplish the correct sequence is different ways. In a gasoline engine the distributor rotor delivers the high voltage from the ignition coil to each individual spark plug. In diesel engines it is the sequencing of the fuel injectors that establishes the firing order. Correct firing order is important for balancing the engine, minimizing vibration and keeping the engine running smoothly. All of these directly contribute to the life of the engine, the comfort of the driver and passengers, and the reduction of overall wear and tear on the engine. Firing order is one of the primary influences when mechanical engineers are designing the crankshaft of a given vehicle, which is what translates the linear motion of the reciprocating pistons into the rotational motion of the crankshaft.
GM firing orders
All General Motors engines, including the Chevy 350, have the same firing order. The firing order on the Chevy 350 engine can be found stamped or molded into the stock intake manifold (the one from the original manufacturer) toward the front of the engine, usually between the outlet from the water pump and the carburetor. The correct firing order or sequence is 1-8-4-3-6-5-7-2.
Locating the cylinders
When referring to cars, the left-hand side of the car is the side that corresponds to the driver's left, as if you are sitting behind the steering wheel in the driver's seat or standing behind the vehicle facing forward. When discussing the engine of a vehicle, the front of the engine is where all of the pulleys for the various accessories (alternator, power steering pump, water pump, etc.) are located. The rear of the engine is where the flywheel or flex-plate is located.
Cylinder numbers-and, therefore, firing order--start at the front of the engine. Given the firing order of 1-8-4-3-6-5-7-2, that would mean that the first cylinder that fires is the #1 cylinder located on the left, front end of the engine. The odd-numbered cylinders (1-3-5-7) are on the left side of the engine, and the even-numbered cylinders (2-4-6-8) are located on the right side. The only exception to this in General Motors vehicles is the Cadillac Northstar engine, which is exactly the opposite.
Replacing plug wires with correct firing order
Finding the appropriate insertion point for each spark plug wire on the distributor cap is relatively easy. Replacement caps usually have the #1 position molded into the cap itself immediately adjacent to the corresponding port. Number one usually sits at approximately the 6:30 position if you are looking down at the distributor cap and envisioning a clock face. Number eight will be at approximately the 7:30 position, number four at the 8:30 position, and so on in a clockwise rotational pattern.
If the distributor has been removed, the engine needs to be rotated so that the piston in the #1 cylinder is at top dead center (TDC) and the distributor re-inserted so that the striker for the rotor sits at approximately the 6:30 position. If the motor spits, pops or backfires, odds are pretty good you have the distributor inserted 180 degrees out of time. If this is the case, remove the distributor cap and return the #1 cylinder to TDC with the distributor rotor pointing away from #1. Lift the distributor back up and rotate the shaft so that the rotor is pointing at #1. Replace the distributor cap and replace your spark plug wires on the cap.