2003 5.4 2v with 164000 miles. Have had a rough idle issue since I purchased it a month ago. After throwing some parts at it, I finally took it to ford for evaluation. Tech found poor compression in all the cylinders in bank one. Anywhere between 60 and 95 percent. They went right to head replacement for 3500 or used motor for 3900. On the way out, I heard the lead tech say he thought it was unusual for just one whole side of the engine to have poor compression and the other side to be normal (or better than normal).

Would it be possible for a cat to be so clogged that it would cause poor compression? In other words, could it be so clogged that it actually pushes the exhaust back through the cylinder?? The only problem that I have is rough idle. The truck runs smooth on the highway, I am really not sure if I have power loss, because my last truck was a 6.8 v10 that wasn't as torquey as this 5.4, so I don't really have much to compare it to.

Has anyone had this issue before?

Happy Thanksgiving!

Scott

 

the 6.8 has gobbs more torque than the 5.4 any day. It does sound like a blown head gasket. They are known to pop 4 ways. Oil in coolant, Coolant in oil, cylinder to cylinder, or cylinder to cooling system. Have a block test done first.

 

I unfortunately had the 99 6.8, which wasn't quite as torquey as the later models. But thats not my point here.

The only thing it could be if it is the head gasket is cylinder to cylinder. I have no oil leaks, no coolant smell in exhaust. No white smoke.

I had a friend suggest I loosen the bolts holding the exhaust manifold to the cat on the side with the pressure issue and see if this improves power. I just wanted to know if anyone had tried this before successfully

 

a clogged cat will cause poor performance, but will not cause poor compression via a compression test. Do you have any coolant loss?

 

None at all. As far as I have found, motor is tight. Just the rough idle and rich fuel bank one code. Compression on driver bank is better than 125 percent each cylinder. Getting 60-95 on passenger side cylinders. There are cats coming off of each manifold.

Just got a text from a friend who had the same problem and he did loosen the cat from the manifold, relieving the pressure from the blocked cat. Cylinder pressure returned to normal and ended up buying a new cat conv.

I am praying this is the answer to this problem in my case.

 

You can loosen the manifolds and check it out. But your dynamic compression should be in the 165-180. But being you have high mileage you should see anything from 145-160 psi and it should hold it. If your truck has been running extremely rich or lean for a extended period of time it can cause ring wear, valve sealing issue and will cause compression to be low.