stew47 wrote:
Lol helps greatly. Sensory overload! Makes me think I might drop off to mechanic so I don't start the costly process of changing parts. I bought with 169000 and I have 174000 on the odometer now. No idea when plugs were replaced or if any cops have been changed out. Since its at full throttle what do you think about fuel filter as a first step? I guess I could pull a plug out and look at the general condition. I've watched the videos about using carb cleaner to dissolve carbon on plugs first but still scares me
Thinking further about when lights went off the truck didn't seem to have quite the power as normal which I guess could be starving for fuel or a cylinder dropping out.
Fuel filter is a cheap part, good idea to change as preventative maintenance since you do not know the history of said vehicle.
Since you bought it used, there are a few things that may need to be addressed.
Plugs, might want to change them, not sure if 2008 used the infamous two piece plugs (2006 5.4 did), this plug style has a bad habit of getting stuck and breaking off.. There is a special removal tool that is needed if this happens.
IF for any reason the previous owner had a plug eject they may have used a "timesert" or "Helicoil" to fix the damaged threads.. Sometimes that fix may cause intermittent issues with the strength of the spark.. That may need attention if that is the case.
If for any reason the previous owner changed the plugs and did not use a torque wrench to set the plugs, you could have LOOSE PLUGS which can cause random miss fires.
The torque specs have changed over the years so you will need to get that info most likely from a Ford mechanic.. I can tell you this, for our 2006 5.4 the factory torque was 33 ft lbs and the replacement plugs are supposed to be set to 27 ft lbs.
Additionally, Oxy sensors are a "wear item", if those are the originals they HAVE done well and are most likely end of life. As the sensors age they tend to react slower and they often do not respond fast enough under hard acceleration.. A code reader with live data function can easily see the speed of change on the oxy sensors.
The upstream oxy sensors handle the fuel mixture settings (these are before the Cats) and the downstream sensors are mainly for emission performance checks..
With the miles you have, I would highly recommend a good cleaning of the Throttle body. Most likely this has never been cleaned.
You should have electronic drive by wire throttle body, unlike the older throttle bodys that had a direct connection to the foot feed you can not feel the throttle plate sticking.
Ford has the PVC valve vented directly under the throttle body, this allows oil vapors to collect on the throttle body and the throttle plate.
Over time this builds up until the throttle plate starts sticking..
This can cause stalling, extremely slow idle and when it gets bad enough you will lose complete throttle control (nothing happens when you step on the go pedal).. This condition will be indicated with a little "wrench" Icon on your dash.
I would try filter, but plugs would also be good to get done but at the same time check all the vacuum lines for breaks or cracks. When changing the plugs, inspect the COP boots for damage, cracks, dirt.. Replace them if they do not look good.
If you find antifreeze in one of the plug holes or on the COP boot, you may have a cracked intake manifold. This is a common problem and can cause random misfires.
Otherwise, might want to see if your mechanic is familiar with Ford modular engines.. Much easier and cheaper if you have a good mechanic.. I wasted a lot of money at my local Ford dealer, they caused a lot of problems, changed a lot of parts and wasted a lot of my time by just guessing and randomly changing parts..
Took me a few searches on the Internet with the symptoms I was having and I solved all the problems that my dealer caused plus figured out the original problem..
