First problem is 12.2 volts is bad. Will it charge to 12.5 or higher? Try a fresh battery.
Is battery in trunk or underhood?
Possible problems:
Advanced timing
Bad cables
Bad starter
Not enough ground cable-needs to flow same amps as positive. If batt in trunk you need a large ground cable from engine to frame/body.
Yes batt is in trunk but initial start up is easy … engine cranks over no problem. I’m will try what you suggest, but I’m wondering whether timing is implicated as well