1966 Crown Coupe, 2016 200 S AWD, 1962 Lark Daytona V8.
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17,277 Posts
If it hasn't set a misfire fault code yet, it still might. There may be a one trip or pending fault set that would best be read with a scan tool. An intermittent or historic misfire may be read with a scan tool that has the capability to read the misfire counter in 'real time', like the DRB III or equivalent. Knowing which cylinder is misfiring would greatly narrow the field of possibilities and simplify diagnosis.
Spark, fuel and compression are possible culprits. A spark plug, plug wire or injector could be swapped with a known good cylinder to see if the problem follows the component or stays with the failing cylinder.
Cold misfire may be a fouling spark plug, fuel delivery or cylinder compression issue. Low engine speed misfire could be a vacuum leak or leaky valve (loss of low speed compression) as well.
Even though they are 100K mile platinum plugs, one may be failing early. If you do, go with the plug type and gap listed on your underhood emissions label. Might as well do wires at the same time too.
Spark, fuel and compression are possible culprits. A spark plug, plug wire or injector could be swapped with a known good cylinder to see if the problem follows the component or stays with the failing cylinder.
Cold misfire may be a fouling spark plug, fuel delivery or cylinder compression issue. Low engine speed misfire could be a vacuum leak or leaky valve (loss of low speed compression) as well.
Even though they are 100K mile platinum plugs, one may be failing early. If you do, go with the plug type and gap listed on your underhood emissions label. Might as well do wires at the same time too.