Misfire under hard acceleration in damp weather

The truck stumbles or briefly loses power when you accelerate hard after a long run, and only in humid or damp conditions. Water collects inside the intercooler and gets drawn into the engine in one go. NHTSA investigated, Ford fixed it with a deflector rather than a recall, and the investigation closed — so on a used truck the question is whether the deflector was ever fitted.

Symptoms

Ford's own description, quoted in the investigation file: "an intermittent engine surge during moderate to light loads at cruise, stumble and/or misfire on hard acceleration after an extended drive at highway speeds during high humid or damp conditions." The conditions are the whole tell — a dry test drive round the block will not reproduce it.

Likely cause

Named directly: "condensation could form and accumulate on the inside of the CAC tubes which could then be ingested into the engine during particularly hard acceleration." The charge air cooler is the intercooler that cools the compressed air from the turbochargers; on a long motorway run in damp air, water condenses inside it and sits there until a hard throttle application pushes it through in a slug. What happens next is deliberate, not a fault: the engine software "will disable up to two of the misfiring cylinders for no more than 30 seconds and until the driver tips out the throttle in order to protect the catalytic converter from damage." That is the loss of power drivers report — the truck protecting itself.

How should it be checked?

Ask whether the charge air cooler deflector shield was fitted. Ford's remedy was a technical service bulletin rather than a recall, so it will not show on a VIN recall check — a dealer service history is the only record. Ford told NHTSA the fix was "100% effective" on 2013 trucks and "95% effective" on 2011–2012, so on the earlier two years a fitted deflector improves the odds rather than closing the question.

How can you check it yourself?

You need the right weather and the right road. After a sustained run at motorway speed on a damp or humid day, accelerate hard from around 50 mph and see whether it stumbles or briefly flattens. A short dry test drive proves nothing either way, and it is fair to say so to the seller.

The question to ask the shop

Has the charge air cooler deflector shield from Ford's bulletin ever been fitted, and is there a dealer record of it? Has the truck ever thrown a misfire code, and if so which cylinders?