2005 Ford F-150


May, 24, 2012 AT 3:17 PM

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?


11 Answers



May, 24, 2012 AT 4:49 PM

Check yoru vacuum at idle, if it's 15" or below suspect a catalytic converter problem. Also check crank sensor for ohms, it may be to hoigh causeing this as well. Also when was the last time the fuel filter was changed. There is a tsb published in 2009 for a lack of power but it's the torque converter clutch tip in at 2nd gear and it's an unintended tip in. I can't think of much more.


May, 24, 2012 AT 11:55 PM

Thank you for the prompt reply, I will check it this weekend, but the cats are most likely ok. Once you are out of the powerloss range, above 3500 rpm, it will wind right up to 5k without even thinking about it. Trans and torque converter were just rebuilt for a broken low/reverse band, and it made no change at all (other than the fact it will go backward now).

Fuel filter is only about 40K miles old, and the fuel pump control box in the rear was also replaced due to corrosion.

I can't help but think the 93 octane gas is the clue. Would the crank sensor cause early or late timing?

I'll check the crank sensor, do you have any idea what the reading should be? I hadn't considered that.



May, 25, 2012 AT 12:04 AM

I can't get to the ford site to get resistance but I thinkit's like 400-600 ohms. You could always go to an auto parts store and check a new one with an ohm meter. Normally they would allow you to do that especially if you buy parts from them all the time. Who rebuilt the trans? Because the tcc swithc inadvertenly applies and there is a check ball that needs to be taken out to cure it. 93 octane is only for high performance motors and really sholdn't make a difference with that vehicle. When a crank sensor goes bad it screws up the cam and engine timeing. The pcm really doesn't know where to go with it. Also if you have asomething near the knock sensor that is banging it is going to retard the spark and when you let off the gas, it may quit rattling and let the spark go wher eit is supposed to be. So check by that for a loose shield hitting the block etc. But other than thati cannot think of anything else, especially if it's intermittent like you say. Maybe you could do a freeze frame and see if it picks soemthing up.


May, 25, 2012 AT 12:27 AM

Trans was rebuilt by the dealer, believe it or not, they have a very good tranny guy. Moderate price, but if it goes as long as the original I'll be happy.

I'll put an ohm meter on it this weekend and see what I get. Would it cause late or early timing if bad?

I know what you mean about the 93 octane. It should actually make the situation worse, but it was unreal. Not only was the change in power almost immediate (almost as soon as it hit the engine) but it added about 1 mpg on that tank. The only reason I can think of that that would happen is if the timing is too early. Could the pcm be confused?

Unfortunately, I don't have the capability to get a freeze frame. I'd love to find the diagnostic software for my laptop and a cable, but I cannot find anything that is not associated with a chip. Do you know where I could get it? I also have an 01 Mercury Grand Marquis so I could also use it there.



May, 25, 2012 AT 1:58 PM

When teh tcc applies it drags the engine down when it s' not supposed to giving you a feel of loss of power. If the kock sensor is activating it will retard your spark cause it hears what it thinks is a spark knock. Any auto parts tore have these scanners as long as you get theo ones over $100 they will tell you if it has freeze frame or not. All cars since 95 or 96 have the same connection so it will work on ANY OBD2 system. Mine is an actron, cheap but works ok but won't do alot of other diagnostics. Some have abs capability as well.



May, 25, 2012 AT 2:21 PM

Ord recommends changing the fuel filter every 15k. 40k is to long on ford filters. A very co min problem with fords is the maf sensor. Some times cleaning ti will help.



May, 25, 2012 AT 5:07 PM

What djcl has just said makes alot of sense, as it may be running just a tad lean and the 93 octane will give it a little more boost to stoop knocking from running lean. It's a cheap fix if it cures your problem and stopps you from beating your head against a wall because of being irritating.


May, 25, 2012 AT 5:44 PM

The tcc (I'm reading torque converter clutch) is operating normally and disengages when it should. I replaced the maf last night. Seems better, but I'm reserving judgement for a couple days until I see what it is really doing. Iknow maf affects timing among other things. Tried cleaning the old one and it made no difference at all. We'll see what a replacement does.

I thought about the knock sensors retarding the timing but I don't hear any knocks at all. If it is, I will need to determine if the knock is real or sensors are bad or hearing something else. Engine compartment is tight with nothing loose.

I'll replace the fuel filter out of policy, but I believe fuel delivery and exhaust are good as after about 3500 rpm it takes off right up to max shift. Also a fuel delivery issue would seem to be soft to me. This comes and goes like a switch. It is intermittent and in mid range.

I think the timing is the area, though. Does anyone know if you can get to the knock sensors without removing the intake?


May, 30, 2012 AT 1:08 PM

It wasn't the MAF, replaced it and nothing changed. Crank sensor is ok, and replaced fuel filter. No change.
Went to the dealership and flashed the PCM and that made a remarkable change. Not perfect yet but much improved. Apparently the PCM is learning (or has learned) something bad from one of the sensors. I'll update again when I know more, I'm going to look at the cam solenoids.



September, 11, 2012 AT 1:51 AM

Fuel regulator

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