Firing Order for small block chevy engines
OK, so you've done a tune up on your chevy small block V8 in your classic chevy and now it runs really bad. In fact it is missing so bad it will barely run and you suspect the firing order is off. You are sure you moved the spark plug wires from the old distributor cap to the new one, one-at-a-time. What could be the problem?
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How to correct firing order on your chevy small block
First, this document assumes you have not removed the distributor from the engine. If you have, you will need to bring the engine to TDC or "Top Dead Center" in the firing position for the number one cylinder, then reinstall the distributor so that the striker on the distributor rotor is in the 6:30 position, detailed later in this document. There is a trick to this, but that is another document altogether.
Something for you to note. The firing order for the classic chevy small block with a breaker points ignition is no different than the newer HEI electronic ignition. The only difference is that the number one firing position on the HEI distributor is in the 5:30 position such as the one on my 86 GMC pickup with a chevy 305 small block.
Well, it makes sense at this point to just run through a systematic check of the distributor wires on your chevy small block V8 engine to be sure the firing order is correct. We may run into the cause of the problem by simply verifying the spark plug firing order on the distributor cap. Most likely there are two spark plug wires in the wrong position on the distributor cap and now the firing order is off.
Which chevy small blocks does this work on?
This method is good for the firing order on all chevy small block v8 engines from 265 cubic inches to 400 cubic inches. This would include 265, 283, 305, 327, 350, 400 cu. in. chevy small block v8 engines.
Let's cover some safety concerns first. If you try to troubleshoot a mixed up firing order with the engine running, you could be in for a serious shock,.. literally. You can do it, with certain precautions, but you really don't need to check the firing order with the engine running. You definitely don't want to try checking the firing order if you are wearing any kind of pacemaker or sensitive electromechanical prosthesis. The voltage coming out of the ignition coil is in the thousands. Common sense dictates that you wouldn't stick a knife in an electrical outlet, so you wouldn't want to take chances with being shocked by the electrical discharge from your classic chevy's ignition coil either.
How do I find the distributor?
For the sake of beginners, let's take a look at the orientation of the chevy small block distributor in relationship to the motor. You can refer to the drawing below. The chevy small block motor has the distributor at the rear of the engine, nearest the firewall, or closest to the car's interior. The front of the engine is nearest the car's bumper of course. If you are standing at the front of your chevy small block motor, you can imagine that the back of the chevy motor would be at 12 o'clock and the front is of course 6 o'clock. If you are really new at this and you don't know how to identify the distributor, it looks like the bottom of a large bell pepper, except that it is not green, with a bunch of wires coming out of it.
What is the chevy small block firing order?
The firing order, which should be cast into the intake manifold, for the chevy small block V8 is 1-8-4-3-6-5-7-2. The firing order is the numerical sequence in which the spark plugs are fired. The insertion position of each spark plug wire around the circumference of the distributor cap can be found according to a clock face. The insertion sequence determines the firing order. The firing order is followed clockwise around the distributor cap starting from the 6:30 position with the 6:30 position being the number one cylinder spark plug wire.
On classic chevy small block engines that use ignition breaker points instead of electronic ignitions, the number one cylinder is the one immediately clockwise of the small metal sash cover on the distributor cap. The firing order starts here. There is no sash cover on the distributor cap for GM HEI electronic ignitions, and the firing order is the same, but starting at the 5:30 position.
The firing order makes sense if you know how the cylinders are numbered. The number one cylinder is the front most on the drivers side and 2 being the front most on the passenger side. From front to back, the cylinders are odd numbered on the drivers side, and even numbered on the passenger side.
See the diagram; Click to open a printable larger image in a new window. The firing order starts with the number one cylinder. We would connect the number one spark plug wire to the distributor cap terminal in the 6:30 position.
Since the next cylinder in the firing order is 8 (passenger side rear), we connect the number 8 spark plug wire to the next distributor cap terminal (approximately 7:30 position) in the clockwise direction from number one. You need to be sure you continue the firing order in the clockwise direction around the chevy small block distributor cap from the last installed spark plug wire. Setting the rest of the firing order is just a matter of repetition. Be sure to count the spark plugs from front to back on each side of the motor to identify the correct cylinder number in the firing order.
The rest of the firing order wiring process is a matter of tracing out the spark plug wires and connecting them to the correct terminal. If you find it difficult to trace the spark plug wires you can use a little bit of tugging back and forth on each end of the spark plug wire. Simply pull the spark plug wire off the spark plug for the cylinder number you are working with, and while looking down the side of the motor, tug or jiggle the wire using quick short tugs without pulling it taught. Find the other end of the spark plug wire near the distributor, using the other hand, and you can then tug back and forth to be sure you have the right one. Don't pull them tight though. This exercise can be a little challenging since the front 2 spark plug wires on each side should be routed between the small block chevy motor mounts and the engine block and then through some spark plug wire clips at the bottom of the engine block, but at the top of the oil pan, then around the back of the cylinder heads and up to the chevy small block distributor cap. They won't be in your immediate view.
As a general rule, as I said earlier, follow a clockwise direction around the distributor cap when setting the firing order. This is much easier than following the cylinders along each side of the chevy small block motor, and trying to skip terminals on the distributor cap while locating the correct distributor cap terminal. It can get too confusing. If you get it wrong, you will likely have to pull them all out and start over to correct the firing order.
Being systematic about it and following the 1-8-4-3-6-5-7-2 firing order around the distributor cap is the best way to be sure you complete the job correctly.