Thanks for your help. I haven't gotten any codes in a while. But sometimes they would come and go. Its just odd the mower would start shortly before I unplugged and plugged in the oil sensor and then after it will not start. The oil sensor plug and harness appears fine. So I will be trying to unplug those three or 4 pins this afternoon on the ECU harness. Just not sure how to get them out I assume I need a long thin flat head to push a locking pin after removing the pin locking tab? According to the flow chart it's definitely speed sensor related because the MIL does not turn off when cranking and now that's its a new properly gapped speed sensor the only thing it could be is this harness or ECU unless the speed sensor came loose again but I doubt it.Without realizing or checking actual pin functions, it is obvious the two most problematic issues through this whole thread were spotted in my red arrow pic. Speed sensor and oil sensor. Talk about chasing tails around the yard....
Really the smarter the ECU, the easier this gets but I recall working on my best friend's prize 1969 Camaro show car with crate EFI engine. Guy helping with the body work was good with that work but other work, not so much. From the first key turn car had a code for an OPEN injector circuit. Open meaning not connected. It went through 3 ASE mechanics before I got into it.
I am not trying to toot my horn here but man, you gotta let the brain think! OL means open, means if you probe the injector and the coil reads fine, you got other issues! I determined the body guy jammed the plug on that #7 injector and totally killed the pins on the injector. I was able to recover the pins and that car is still hitting shows 8yrs later with no other faults.
A "code" does not always means a device is bad, it means there is an issue in that circuit. Revolve in your thoughts and usually ideas come to mind in how to find the issue. SEND IT!