I've been reading posts on this forums for a few months now and this is my first real post (I posted in the Introduction thread). I recently purchased an 06 Lariat and have been slowly working on tackling some of the issues it had. It had a ticking noise, which I thought was for sure the cam phaser, but the ticking was gone after I changed the plugs and coils. Anyway, I won't ramble.

The real issue I'm still having is while driving, I have a slight loss of power coupled with a grumbling (instead of normal engine revving while driving). If I let off the accelerator and get back on it, the car functions normally again (until the issue happens again a few seconds later). If I don't let my foot off and push it harder, the engine will come out of the grumble with a high rev and the car will continue to function normally. This will happen a few times each drive. In addition to the plugs and coils, I changed the fuel filter and the throttle body (not for this reason...tps was shot). The fuel pump control module was changed by the previous owner (it's a Dorman).

Could this be an issue with the fuel pump and/or the injectors?

 

Check my posts on other threads, DO NOT ignore this as this is the exact same thing that just happened to me but it did not stop...Injector was stuck and wiped out the engine by the time I could pull over....pretty much grenade the motor short of poking a hole in the block, even broke the motor mounts!

 

My bet is a faulty coil.
The only way you see which cylinder it is is by using a Scanner to look in mode 6 at the test that contains the misfire counts for every cylinder.
The one with the high counts is suspect.
The reason is does not set a code is because it's not a hard fault but comes and goes. The PCM cancels the misfire counts when it goes away.
The cause usually is a coil with shorted turns. The coil still fires but is low in output.
Good luck.

 

I was actually leaning towards the fuel pump. So you had these exact symptoms? Any chance a faulty pump caused the issue with the injector?

I checked this already. No misfires. Looked at the count. Every cylinder is at 0.