A wrong firing order means that the spark plugs are firing out of sequence, causing major ignition timing problems. The pistons will be in the wrong position when a spark occurs, leading to inefficient combustion or no combustion at all. It won't be a simple every-other-cylinder misfire; it'll be more chaotic and unpredictable.
If you've wired your engine with this firing order, you need to rewire it immediately using the correct firing order (double-check the correct one for your specific engine - some variations exist, but 1-3-7-2-6-5-4-8 is most common). Continuing to run the engine with this incorrect firing order will likely cause serious damage.
