Have a 2004 Fx4. Lately its been shaking violently when i accelerate. when i turn the overdrive off it stops. Any thoughts?

 

Mine did the same thing and ended up being the spark plugs misfiring. Have the plugs been changed?

 

Not yet. That was the first step I was going to take. Why would it only shake when overdrive is on?

 

Failing plugs usually will misfire when under load only. Does it get worse as you hit a hill? Mine shook like crazy in O/D going up hills at 45-50 MPH and when I took it out of O/D to take low RPM load off of the engine, it cleared up right away. I can almost guarantee your issue is the same one I had. I replaced my spark plugs and it hasn't happened since. That was 44,000 miles ago.

One thing I want to mention; If you're not familiar with the spark plug design on these year 5.4s. These are not your regular spark plugs. They have a 2 piece design and the bottom piece of the plug is a porcelain shell that can break off in the head during removal due to carbon seizing it into the well. There is an extractor tool by Lisle part #65600 to extract the shell. There are some good videos on YouTube showing proper procedure for spark plug removal, shell extraction with the Lisle tool, etc. I also recommend running a few tanks of Chevron Techron before tackling this job, which will help to break loose the carbon from the porcelain shell.

 

It does get worse going uphill. In fact it starts to shake on the exact same spots on my way home which are hills. Thanks a bunch for the input!

 

No problem! Hopefully should fix your issue. Pretty confident it will.

 

I had the exact problem a few months ago. Changed the plugs and all has been well for 4,000 miles. I used original motorcraft plugs as i read here that after market plugs xometimes failed...good luck.

 

Yep, plugs should clear you right up. I bet if you hooked up an obd reader and observed misfires, you'll see the counts increase as it shakes. Plug change out is a piece of cake just take your time and keep the beer cold and plentiful!

 

Would this throw a code? My is doing the same thing but doesn't show problem codes. I cleaned throttle body and MAF, changed fuel filter, cleaned air filter, etc. and it still shudders under acceleration.

 

Not necessarily. You may see Misfires on your scanner. The plug change isn't the nightmareiit's made out to be.