I have a 2007 f150 5.4 lariat that misses when floored , 93,000 miles , just changed fuel filter (had black trash in it), added lucas injector cleaner to full tank and ran tank to neer empty, filled tank , added lucas again and burned half tank then changed fuel filter again . still has same problem , gave a code one time, turned off truck and code went off. never gave code again . engines runs great at normal driving speeds , has anyone had this problem ? I can turn some wrenches, but would like to go straight to the problem if i could and not spend a weekend finding the problem. Any ideas
Thanks in advance

 

What code did you get when the check engine light came on? It will still be stored in the PCM so you can read it and post the EXACT code number we can search it for you and lead you in the right direction.

 

I did'nt know it kept it stored , I'll check.

 

checked for codes , none , everything reads normal I thought these new computer systems could tell you everything about your engine
way2old the check engine light was blinking until i turned off the engine, but i did'nt count the blinks . I really don't want to bring it to the ford garage they are super expensive , any thoughts ?

 

Go to Autozone, Pep Boys or Advance Auto. They have a loan a tool program. Or they may read the codes for you. If the light was blinking, it is probably an engine misfire. But you need a scan tool that will read the codes. So have the codes read and see what they are. If it is a P03xx code(P0300 to P0308), that is an engine miss. However, if you have the 5.4 3 valve engine, I would not recommend that you replace the plugs yourself. They were a poor design and break off in the head. A 1 hour plug swap can become a major nightmare. We had one break off and the tech trying to remove it broke off the extraction tool, so he had to pull engine and remove head to get it out from the bottom. So think very carefully before replacing the plugs yourself.

 

ok the check engine came on and stays on now , the code is P0420 catalyst efichincy below threshold , engine only seems to stumble when cold . check fuel pressure and reads 32 to 35 lbs at idle ,to the floor jumps to 40 to 50 , what is the pressure supposed to be on this engine ?

PS thanks w2o ,it is the 3 valve, I won't attempt that job if it turns out to be the plugs .

 

Your fuel pressures are right in the area they need to be in. You will probably need to replace the converter. I have tried many different repairs to repair the 420 code and it always comes back. Replacement of the converter is just about the only cure.

If you get an estimate on the plugs, be sure to get a maximum dollar amount. If they don't know the plugs break, they will try to burn you after the repair. Go into the repair with a dollar amount that you should not exceed. Good luck.

 

W2O the only thing that stumps me is the engine was doing this a few weeks before the engine light came on , do you think something else caused the converter to give this code ?

 

A cold stumble could be a mis reading Coolant Temperature or an Air Temperature sensor. Also a dirty throttle body can cause your problem. Get a can of throttle body cleaner and spray the throttle body while giving enough throttle to keep it running. Let us know if it helps. The P0420 is more than likely a converter that is not working. It is the on the passenger side. It is warranteed for 8 years, but just 80K miles. Thanks for working with me.

 

Thanks w2o I'll try that .