2013 Ford F-150 3.5L EcoBoost - P0306 Misfire under heavy load/acceleration

Question

My 2013 EB has developed a nasty shudder whenever I try to pass someone on the highway. If I'm light on the throttle it's fine, but the second the boost kicks in and it drops a gear, the whole truck shakes and the Check Engine Light starts flashing. Usually, the light goes back to solid after I let off the gas.

It feels like a massive misfire. I've had the truck for about 40k miles and haven't done much to it other than oil changes. I'm worried it's something expensive like a turbo or a head gasket, but there's no smoke out the back and my coolant levels look perfect. It seems strictly related to high-load situations.

JeepJunkieJoe · Accepted Answer

✅ Confirmed fix: On these EcoBoost engines, the spark plug gap is critical. Even though the plugs looked okay, the gap had eroded to .045". I replaced all six plugs with Motorcraft SP-534 (now SP-580) and gapped them tightly to .030".

I also found a tiny carbon track on the porcelain of the #6 plug boot. Replacing the plugs and ensuring the boots were clean with a dab of dielectric grease fixed the high-load blowout completely. These engines are very hard on plugs due to the high cylinder pressures.

ACAceAdam · Answer

Check your intercooler for moisture buildup. These early 3.5 EcoBoosts are notorious for 'intercooler condensation.' Under low load/high humidity, water pools in the CAC. When you go wide open throttle, that water gets sucked into the intake and causes a quench misfire. Ford has a TSB for a plastic shield to prevent this.

2013 Ford F-150 3.5L EcoBoost - P0306 Misfire under heavy load/acceleration

Suggest a repair