1970 Ford F700

The engine had at least one misfiring cylinder, so I inspected the sparkplugs and did two compressions tests on each of the eight cylinders. All the sparkplugs' tips were covered in oil. The compression test results are in the table above and are within spec according to the truck-shop manual. I also tested for sparks on each cylinder and was shocked in the process... I'm pretty sure that was part of the problem, as that cylinder would prematurely spark inside the cable rather than at the gap of the plug. The engine was also making a tapping sound, so we removed the rocker cover and found that a rocker arm had slipped off the valve stem. We repositioned it, and the tapping stopped :).