I am trying to diagnose an intermittent powerloss on my F150.
History: 5.4L FX4. Have replaced Cam Phasers, O2 sensors, plugs, injectors, and throttlebody. (Some of these were done for other reasons, but all within the last 40k miles) Engine has no mods, chips, intake or exhaust modifications. Runs reasonably even, but intermittently it has a mostly flat accelerator where you push it but little happens. Sometimes it is ok and accelerates normally.
I have run the full gammet of tests at the dealership and they can't figure it. Computer says everything is fine. Also ran injector flow test and was right in the middle.
Two notes here: firstly, most of the time when you are trying to accelerate and it is dogging, if you let up on the throttle just a little, it begins to pull harder. Also, there is a very notable increase in overall power using 93 octane gas almost immediately. I'm thinking there is a sensor failing somewhere, but I am at a loss as to which one, and why does the 93 octane gas make such a dramatic improvement? It's almost as if the timing is off or something.
I'm going to replace the MAF sensor tonight to see if that is the problem, but I have already replaced a lot and I have not impacted the issue at all, except with the 93 gas.
Other than the O2 and MAF sensors, what would evenly impact the entire engine?
Thursday, May 24th, 2012 AT 3:17 PM