Embarrassed to say I haven't been taking good care of my truck.. Appreciate any help.

I have a 2006 King Ranch 5.4L with 157,000 miles. At least 18 months ago the car developed a significant misfire that I misdiagnosed as a slipping torque converter.

I went on deployment 12 months ago and got back to the truck this January. The symptom is a significant loss of power under certain loads, as well as significant hesitation, generally resolved by disabling overdrive. It seemed the higher RPM kept the motor/transmission pulling strong. There have been times where I have felt the hesitation in lower gears and lower load settings more recently. Again, it looks like I just misdiagnosed this one. CEL would also set but my scan tool wouldn't full the code at the time. The light would "flash" when the symptoms were at their worst.

I dropped the truck at a transmission shop this week. They road tested the truck and gave me the bad news. Oil was 2 quarts low and the CEL was for a misfire on cylinder 4. Is there a CEL for loss of compression? He mentioned a possible loss of compression on that cylinder and I can't remember if he got that from the CEL code. He couldn't find anything wrong with the transmission. I had trouble believing the guy because I was so convinced the transmission was the problem! He was nice enough to road test it with me and talk about it a bit.

Sure enough, topping off the oil reduced the loss of power. The truck idles smooth and has good drivability at low load. I can't feel a mis with low load. The loss of power gets worse with increasing load. When road testing I was pretty aggressive with the truck. At times it would respond OK under heavy acceleration from 20-30 mph and even 50 mph on the highway. But also about 50% of the time it feels like the acceleration is sluggish, occasionally a significant hesitation, and at least once or twice I heard a pretty loud knock/metallic noise under my feet that went away when I came off the gas.

I believe I had checked the oil within the past 1-2 months. I am guilty of not changing the oil since before deployment. Lesson learned. The truck needs a tune-up as well.

I'm planning to try and do this myself, beginning by changing the oil as soon as I get the truck home from the shop. Then I was considering a compression test on cylinder #4 and exploring ignition and fuel for this misfire. CEL seems to consistently point to the same cylinder.

Any direction would be greatly appreciated! I actually love this truck and need to take better care of her. Hopefully I can dodge a bullet here and keep driving her for another 5 years.

 

Change all the spark plugs, and do a compression check on all the cylinders while you have the plugs out. Also replace the coil boots and springs.

NOTE the spark plug breakage issues with the 5.4 3 valve, know what you are doing and have a Lisle extractor tool available.

The reason you had a loss of power with low oil is low oil pressure, the variable cam timing system uses oil pressure to advance and retard the cams.