jdinner

bought a 2006 5.4 four months ago and it had a stumble at full throttle. I didn’t think much of it because I had planned on changing the spark plugs as soon I could. I changed the spark plugs 3.5 months later and it made no difference whatsoever. In fact, the stumble was progressively getting worse over the months. The truck has 140,000 miles and these were the first set of plugs going into it. All had broken and I had to use the Lisle tool.
I tried some injector cleaner in the fuel just as a test, no difference.
I was now getting P0300 and random specific cylinder mis-fires(P0305, P0308…).
Truck was now shaking at idle and I could only use about half throttle. After half throttle it would pop in the intake and the engine would slow down then produce a flashing engine light with more mis-fire codes.
Luckily I have my 4.6 Mustang in storage for the winter and I borrowed all 8 coils from it as a test to see if that would change anything. No change.
I tried Seafoam spray upper engine cleaner into a vacuum line as per the instructions. I let it do its thing and took it for a test drive. I was now worse. 50mph was my top speed and I could only feather the throttle. The next morning 40mph was my top speed.
I scanned the fuel pressure and then changed the fuel filter again, no change. Fuel pressure was 40psi.
I pulled all the injectors out and cleaned them one-by-one. All looked very clean with the identical two nozzle spray pattern. Reinstalled, no change. Problem is even worse now.
As a mechanic for over 30 years I was stumped. I took it to a local garage and they checked it too. They were stumped also but suggested I noid light the injector circuits. I did that and they all checked great.
Yesterday I had a truck that I could barely drive and I didn’t know what was wrong with it.
I have been pouring over this forum for two weeks trying to find a solution to my symptoms and all the threads I found did not have a ‘solved’ post. This thread does have a solved sentence!
Purely by running out of ideas I heated the exhaust pipe/manifold nuts and dropped the exhaust system down before the catalytic converters. Test drive - PERFECT POWER and really loud.
Both converters were plugged and not giving me any codes or tail pipe indications that there is/was a problem.
I’m welding in new catalytic converters today but I just thought I’d share my experience with this hair pulling process.
Dropping your exhaust costs $0.00 and is an easy check. I wish I had found a thread that had a conclusion with my symptoms.

Summers22

iTrader: (2)

First of all, it's great to hear you got it running good again. But this is a known problem with our trucks, the converters melt down, usually to a stuck open injector and it robs power.

jdinner

Now I know. However, I searched for weeks with queries like:
"popping in intake"
"no power"
"random mis-fires"
"popcorn under the hood"

I did not ever get a P0420 or P0430 code so it didn't even dawn on me to think about clogged cats.

So many of the threads I searched just ended without a solution. Very frustrating.

Summers22

iTrader: (2)

I agree, so many threads end without a resolution. Generally its people that join a forum to ask questions, then when they get it fixed, never come back. They are not true enthusiasts, just someone trying to fix something as cheap as possible.

techrep

iTrader: (1)

especially when you dont change your plugs for 140K miles.

LEN671

First off, thank you for stating your solution for this issue. I have been having this same problem for a while now, which got worse after I did a tune up, Oil change, the whole shebang.

I was thinking of just cutting the catalytic converters completely out of the equation, but it seems most people are just replacing them.

jdinner

Replaced my converters on Monday. What a difference!! Runs better than I expected with a smooth idle and so much power.
I had a problem with both converter mounted O2 sensors galling the threads off. Now I'm looking at 2 new ones but since I'm really cheap I made a fix and it works great.
I welded two 5/16" X 1" bolts to the convert body so I could clamp the O2 sensors in place with a large washer. With a little muffler cement on the gasket I have no leaks and I still retain the new converter threads in case a sensor needs to be replaced.

Mod (Ret.)

True. In many cases, a forum such as this one is a source to obtain information and get that magical "quick cheap fix", then do not return or take the time to post their results.

Kudos to jdinner for providing a diagnosis, a fix, and positive results.

Mod (Ret.)

The reason for this is federal laws, and not your local laws. Many owners will cut them off when the fail, or they want a loud exhaust.

What they fail to realize is that even if there are no local sniff or visual inspections required in their state, there is a federal law that supersedes any state law. Simply put, you cannot operate a vehicle on public roads without its federally mandated smog equipment. Lucky for many, the police are simply too busy to stop you and issue a citation for this. Should you go and sell or trade in the vehicle without this equipment, it's illegal, no matter if you sell it with an "as is" clause in the paperwork or not. A dealer/used car lot or private individual cannot sell a vehicle without this equipment. Huge fine if/when caught.

I mentioned this before in other threads: my son got nailed when he sold his Subaru WRX STi without the cats. He sold it privately, with an 'as is, no warranty' in the bill of sale, and the buyer signed. Two weeks later my son was served papers, as the buyer lived in a state that had state inspections. It failed the visual test. He had two choices: full refund, or install the cats at his cost. If he refused, he was going to have to pay a huge fine, more than the sale price of the vehicle.

thebluesbox

thanks for the cat problem solution, I'll remember this if I ever have any issues like it.