I have a 2006 ford f150 with the 5.4L v8. Recently I had the same flashing light, my local dealer told me that I needed a new catalytic converter. ok well about 25000 km's later my new converter came in it was installed. Still experiencing the same shuddering under heavy acceleration. So I called the dealer and they told me all is fine it will work its self out. So today I was on the highway go to pass same shuddering I think all right the usual look at my dash the engine light is flashing. So ok I go home check my manual it says experiencing hard miss fire may cause damage to catalytic converter. Know I think that ford just fixed what the problem not the problem hoping that my warranty would be up before i take it back in. know my warranty is up in 5000
what happends if i still have this problem once the warranty's up and i have all ready brought it to there attention.

 

Sounds like a bad O2 Sensor.Get the engine code read.

 

Have them fix the misfire. If it persists, it will ruin the converter again. Make certain you tell the service writer about the flashing MIL as the mechanic needs to know that detail.

It is NOT an O2 sensor.

 

x2 missfire. Bad coil plug or injector..

 

Well I had a flashing check engine light on my 4.6 when you where at higher speeds, code was bad O2 Sensor of right bank 1.Changed it and it fixed the problem.