Vehicle: 2007 F150 SCAB 4x4 5.4L 85K miles.

So I started noticing a "thud" occasionally from my drivetrain last year. I thought maybe it was transmission related because it was hard to nail down when it was happening.

Well, it's gotten worse over the last three months or so to the point that I have nailed down exactly when it happens. It happens at 40-50 MPH with the truck at 1150-1300 RPM, at light throttle tipin (about 1/4 throttle).

It seems at that speed the truck is in top gear, with the converter locked, so it'd be much easier to feel misfires.

Then recently I dumped the remaining 3 gallons from an old outboard in my truck. Stuff looked like tomato juice. Probably not a great idea in retrospect, but then the truck REALLY felt like it was missing and idling rough. Added a fresh tank of gas over the top and the problem went away, which indicates engine more than drivetrain.

At 85K I'm sure the factory plugs are probably not in great shape. And I have the dreaded factory ready-to-break plugs, so not a trivial task to change them either.

My question: does this sound like an old plug misfire? Just checking with some people that have been through it before I pursue changing them.

 

Yep, that's a classic low grade misfire. Plug time.

 

I have been trying to nail down a similar problem. It started out with the same problem. Happened maybe once a month about a year ago. Now it's almost constant. The more things I change the more it changes. Had some misfires so I started with the COPs (motorcraft). The problem seemed to move so it replaced all of them. Next I replaced the plugs (motorcraft) as they were cheap. I replaced the TPS but that failed after 2 days. I have since received a motorcraft unit but have not put it in yet. Next, I replaced all fuel injectors (motorcraft). It's gone from misfire to stumble, cold verses hot, and comes and goes. The dealer ran a test early on but only saw misfires. A trans shop said it not the transmission.. As of yesterday, it seems to be stumbling in light acceleration after foot is off the gas pedal 5-10 seconds. It stumbles at 45 and all the way up to 75 mph. Reading up on some posts suggests o2 sensors and maybe egr valve. These Issues can be tough and throwing parts at it may seem silly. I look at it as early preventive maintenance verses dropping big bucks at the dealer and ending up with the same result. I am wondering if it's some type of fuel pressure problem. All the normal maintenance is up to date. Oh, 2002, 5.4, 143k miles.

 

I had the same issue with my 02 screw with 5.4 ..... I had the plugs changed and it quite doing the studder , misfire thing . Mine use to do it on semi bumpy roads at first ... when i finally decided to do something .... It was doing it on all the roads .. of coarse We don't have many smooth roads in Ca , some are just better than others .... Its what happens when STUPID(LIBs) spends all its money on a train track to now where
One other thing you might check is the cat converter ... my buddie said thats how they fixed his studder , misfire on his 2000 5.4 .... Have fun changing the plugs .....you should check this out on youtube : Ford master mechanic tells how the dealership changes the plugs real fast and not one broke .... wish Id seen it before I spent 400.00 on mine ...

 

I did not plan on hi jacking this thread. I just wanted to add a few more things that I went thru. Hopefully along the way I would get some more ideas. The cat? Well that's not on the top of my list due to cost. I'll put it at the bottom with the trans and torque converter.

I'm still thinking fuel delivery or o2 sensor. It really has to see foot off the gas to ack up. Unfortunately, that's daily traffic here.

Replacing the plugs is not all that bad. A couple of right tools help along with patience. Much easier the second time around. My buddies shop quotes $1000 for plug changes just incase they break or strip.