My father was driving my 78 superliner yesterday with an endt 676, 10 minutes after he left the pit loaded, he said the exhaust sound changed and there was slightly less power, he though he had an exhaust leak, but when he pulled in our yard I could hear the difference in sound, almost sounds like one cylinder dynatard was on, parked it at our shop overnight, started it this morning and same sound cold, pulled the valve covers to check and every thing looks right, everything is tight, no cracked springs, started it and everything is moving(not a wiped cam). Leaning towards cracked valve or bad injector, my question is what is the best way to check the injectors before is start pulling the motor apart, thanks (last over head was ran about 8 months ago, truck runs about 3-4 days a week)