My friend borrowed my f150 and after a very loud backfire it will not start. It gets a spark, has between 90 and 100 lbs of compression in all cylinders and when cranking around the dampener it appears the rotor is at cylinder 1 at TDC. I have also dumped a little gas in the carb to no avail. The interwebs seem to point to a timing gear skip. What should I look at for this? without removing the timing gear cover?