Hi all, have a head scratcher I've been dealing with. Originally came in for a misfire, found low compression on a pair of cylinders. Recommended that the customer replace the engine as an assembly per mileage and cost and time effectiveness. Replaced engine, all good on test drives, customer takes vehicle. Back about a month later, misfire. Find swapping plugs moves misfire. Replace with motorcraft plugs, send again. Another month goes by, and customer is complaining of misfire under load and intermittent cel. Misfire codes again. Moving coils/ plugs has no effect. Will move injectors in the morning. PIDs look good, fuel trims look great during freeze frame data. Compression is 140 all cyl. Any ideas? Only under load, no misfires at idle.

Andrew Alves
Technician
Tim Dahle Ford
Spanish Fork, Utah, USA