I have a 2005 5.4 supercrew. When i stomp on the gas at highway speed it revs up until 4300ish and then cuts power and the check engine starts flashing. This does not happen when I stomp on it from a standstill it will rev all the way to redline no problem, no code. The code is a P0303, cylinder #3 misfire. I've read this is the third back on the passanger side. I swapped the coils and it still happens, then I replaced the plug(old plug looked fine) and it still happens. What is going on??

 

Injector maybe. 2005 had the recalled injectors you might have one failing. I'd swap it with another one.. they are covered by an extended warranty I think.

 

Replaced the injector, still the same problem. So I've replaced injector coil plug, and the problem is still there? Anyone have any ideas what could be wrong?

 

did you clear the code? do that and see if it comes up again. whats the mileage? maybe needs all new plugs. how olds the fuel filter? if the code doesnt come back then it may just be as simple as changing the fuel filter.

 

If that's the case truly and the SAME thing happens. You need to compression test IMO. BUT , make absolutely sure you have tried everything you said I did with the same result. Compression testing might open a can of worms with that year 3 valve. You might be better off taking it in.

I would definitely exhaust all other possibilities thoroughly first. Fuel filter, Regulator, pump, leaks, tune, MAF etc.

4300 rpms? What are you doing way up there anyway lol. I didn't think they rev-ed that high on the downshift? Maybe they do, not sure - I'll have to try it lol.

 

It has all new plugs and the cam phasers were replaced less than 4k ago. I also have a scan tool and clear the code with it.

As for reving that high I don't usually either, thats why I've had the truck 2 months and this is the first time I've noticed this. Thought I would see how well it would go and this is what ended up happening.

Anyone ever seen anything like this before? Could it be CAT related? Its really weird it always happens at the same RPM and only when at highway speed and not from a standstill.

 

Call up Ford and see if there's a recalibration for the PCM. Definitely look at the TSB's for that model year - all of them. They tell you allot.

Try the 2004 and newer forum on this site as well.

 

Here are some possible casues.
Possible Causes:

Fuel injectors, related wiring, sensors and computer issues
Running out of gas, or poor fuel quality
Evaporative emissions system (EVAP) concerns: fuel vapors leaking into engine
Incorrect Fuel Pressure
EGR system concerns: leaking EGR valve or restricted ports
Base engine concerns: low compression, valve train problems and timing issues
Ignition system concerns including, but not limited to:
Faulty spark plugs
Faulty coil or related wiring
Ignition module or related wiring issues
Ignition related sensor faults or wiring issues
Faulty oxygen sensor(s)
Burned exhaust valve
Faulty catalytic converter
Poor compression
Defective computer

 

According to your statements failure only occurs when at speed and you hit 4300 rpm. When you start from a stand still and rev through 4300 rpm it doesn't happen. This will eliminate any engine mechanical problems because low compression or burnt valves don't care how you got to 4300 rpm the failure will occur all the time. For that matter the coils and injectors should fail at the 4300 mark too...... I suspect a PCM issue that is shutting off the injector or coil but not keeping track of it and setting the misfire code.

 

Hello, My 2005 F-150 lariat with the 5.4L engine is also doing this!!! what is the fix please help before I spend pointless money! I need my truck! I have tried nothing yet and would like to do it right the first time.

 

New to the page, hate to bring up a old dead post but this is what my truck is doing. Hell this could be my truck with what is going on, would love to know what the fix was/is

 

It ended up being a plugged cat. Replaced the cat and everything worked fine. Sorry for not posting the follow up!

 

adam ty for the reply man, i have tried everything but the cat.. looks like the truck is gettin a new one.. fun fun

 

Could anyone help with a more comprehensive explation about the "plugged cat". I am new in this fórum, and not a mechanics expert. But I am driving a F150 / 2005, with exactly the same behaviuor. I can suspect your are talking about the cathalitic converter or something similar, but, just guessing. Thanks in advance.

 

Noerazo you are correct sir, talking about a catalytic converter they get plugged time to time and can play hell with obd codes