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Let me paint a picture here. I have a '05 Superduty 5.4 Triton 3V (of course), with a 146,000 on the clock. I purchased it new, and have truly taken impeccable care of it. Up until recently it has not given me a days headache. This past weekend i was taking a field trip about 50 mile away from home. I was running 60-65 on the interstate hit just a slight grade, CEL came on, and i backed of it until I completed the grade. Got back on the gas after leveling off. She did not like that at all. Started getting the dreaded flashing CEL (limp mode i'm guessing). Immediately got off the interstate to turn around for home. Stopped for a moment in a parking lot, and the truck was idling and you could defiantly feel it misfiring. Nursed it back home, but not being able to go faster than 45 with out the CEL flashing at me again. Once home check tail pipe, no fuel or other liquids coming out. Next I read the codes, and had the P0300, and like a P0301, and P0305.

Now up to this point in the trucks life out side of typical routine maintenance (oil, filters, tires, shocks, ect.....) I did a plug change in the fall of 2013. (I broke two). Installed the E3 plugs, and they run great, maybe felt a little healthier too. So I'm thinking maybe it's time for some new cops. So after taking some time for researching parts. I have now installed new cops, the new Champion 7989 one piece plug(got a story on those), new injectors, Maf sensor, new fuel filter, cleaned the throttle body and PCV, and reset the PCM/ECM. Now I did not do this in one sitting, I do not believe in just throwing parts at it. One thing I won't learn anything, and I won't really know what might have fixed it. So cops, and plugs where first. with test runs, with A LOT of forum readings in between each. As soon as you would start it though you could hear the ruff idle. Since it has never had any injector issues, I have never changed them. Now ever since the love affair with my truck began I have always run a quality injector cleaner regularly. They got swapped. I have double, and triple checked my work, but still every time the P0300 would come back, with random cylinders filling out a few more codes.

So now I'm hunting for a more mechanical cause of the failure. I my long ago past a ruff idle usually equaled a vac leak. A big dose of carb cleaner around the intake, and throw some starting fluid in there to. Yet no change in the idle. Did the tail pipe trick to see if it is trying to suck you hand back a little for a burnt exhaust valve, nothing.even misted water all around in the dark looking for power jumping around. Now I'm not saying I have ruled anything out, I have done the tricks a guy in his home garage would do.

So I'm losing sleep racking my brain, reading any thread on the internet I can find to rule out something. While at that, I'm reading a lot of negative feed back on this Champion plug I used. Burning up, faulting, just name it.
So lets put another plug in it. How about the Original Motorcraft plugs. I do have to say, these Tritons like them the best. After that I got a little break.
It idle a little better, and first time with no codes. Still idle like a dog sh****** razor blades though, and rpm bouncing around, but no pretty orange light on the dash (yet). So getting to the present now. Since I can drive it to the end of my street, and around town while not producing any codes. I decided latter tonight (traffic light) I'll do a hit on the interstate to see what shakes out. So on the highway running 60, I can still hear, and feel the shudder in it. Pulled a pretty decent grade with the cruse set. Power seems there, but I know all of it's not. So I jump on it, got the passing gear to kick in, and held it there for a little while. (level ground now). Sounded good, pulled hard, but just after I got my foot out of the loud pedal. The CEL started blinking, and buy the time I got off,and turned around at a exit it went out. Same result on the way back home. Got codes out of it and sure enough P0300, with 1, 5,and 6 showing misfires.(again not always the same cylinders).
So right now I see my options as replacement intake, even though I can't prove a vac leak, and have no fluids showing up on the heads or in the oil, and no steam from the tailpipe. Replacing both VCT solenoid, I'm sure they need it. I want to check the cylinder compression, and seal(looking for a burnt valve), but I don't have a 16mm fitting with my compression kit. I need to make one at work this week. I'm even toying with the idea of a blown head gasket, but have no typical signs of that either. Since Ford found it funny to remove the fuel pressure port. I don't know how to check fuel pressure now.

Sorry for going long, but I just wanted to try to paint a clear picture of what is what. So please someone help, and ideas, or checks would be great.smilieFordlogo


Tonto Papadapolous
Have you checked your battery voltage? Have you checked for a restricted catalytic converter?
Well I'm not quite ready to drop the exhaust, not going to go easy on a ten year old exhaust, but I know it could be it.
Now I've been thinking about the battery. It is two years old, and with the high demand of voltage these systems take today. It could start it, but not be able to supply the voltage demand.
Could this be possibility, week voltage at the battery, starts truck but trouble with voltage supply, truck runs ruff, but no codes yet. Drive around town ruff, but still no codes. Get on the highway at speed where systems get more demand on them. forcing engine to work at high RPM's, overwhelms the already low voltage issue, cops start breaking down on creating correct spark at the right moment, even though you don't really feel it, but more shudders at the crank sensor, PCM reads that as a P0300.


Tonto Papadapolous
I am not a mechanic, but the two I mentioned seem to be a common thread with other people, along with the long list that you have already thought about or tried. A coworker/friend had some similar issues, requiring a tow to the dealer. The problem was solved by replacing the battery.

The battery would be simple to eliminate, if you have a Volt meter.