I replaced the knock sensors, and repaired the fuel line going into the fuel rail with the Dorman Fuel line kit. I have checked that no fuel is leaking where I fixed it. Here is the problem:

Startes and idles very smooth.
Driving slow, like under 1600 rpms, everything seems OK
When stepping on the gas, the engine is smooth and rpsm go up smooth, but no power
At about 2000 RPM's seems there is some kind of "shake"
Transmission seems to be shifting very smooth
The engine check light is on, but but only flashes once in a while
The truck will not accelerate normally unless I am "very light touch" on the gas pedal, then it kinda takes for ever.
Have normal brake pedal and did connect the vaccum line below the air intake manifold

Any ideas how I can run down what the problem with power is?

Thanks!

 

Sounds like you have a misfire which caused the cat converter to melt down. The shaking and flashing CEL indicate the misfire. You need to get the codes read and prob put a set of spark plugs in and the coil for whatever cylinder the code is for. Then once the misfire is fixed loosen the exhaust pipes at the manifolds and drive it. If the power is back then a converter is clogged.

 

OK, thanks...went and got codes read and here is what they wrote down:

po316 misfire on start up

po300 random misfire

po303 cyl 3 misfire

po305 cyl 5 misfire

po325 knock sensor 1 circuit ..bank 1

po308 cyl 8 misfire

po171 system too lean bank1

po174 system too lean bank 2

Does any of this help your analysis? They told to try resetting the computer. The way I set before was to disconnect from battery for 10 minutes...hooked up and let idle for 1 minute....turned on ac and ran for 1 minute, then ran truck up/down drive way for about 5 minutes. What is weird is sometimes the engine light will flash then it stops flashing, then back.

Thanks for help !

 

I would start with a tune up and coils for 3,5,and 8. The lean codes can be caused by misfires. Since 5 and 8 are on the same side it's safe to assume the converter on that side is melted down causing your low power problem. After the tune up loosen the driver's side exhaust pipe and drive it. Make sure there is a gap between the pipe and manifold to let the exhaust out. If the truck has good power then the driver's converter is clogged. Once you get the misfires and converter sorted out retest it to see if the lean codes come back. The knock sensor code is prob caused by the wires rubbing through on the IMRC linkage at the back of the intake. Most people don't route the wires properly when they take it off and it rubs through. The wires shoyuld be routed between the intake and IMRC linkage. You will need a flashlight and a mirror to look behind the intake.

 

Ok I've got several things over a period of time that I feel are somehow related. I'll keep it as brief as possible.
07 F15O King Ranch 5.4
8000 miles on the plugs
New fuel filter

It all started with the typical IWE noise/rattle. I saw it on my last truck, so did the usual. I replaced the vacuum solenoid for the 4WD, no change, replaced both IWEs and still had the noise.

I suspected a vacuum leak, or low vacuum condition. Didn't get a chance to troubleshoot further before I went on a road trip, about 1000 miles over a 5 day weekend.

On that trip, it would accelerate like a Yugo pulling a camper, and I was getting a whopping 11.2 MPG. At low speeds, sometimes I would hear a clunk from the front end like the 4WD was kicking in, and other times the typical IWE rattle. Switch it to 4 hi, all noises would go away.

Adding all those up in my head, I came to the conclusion I had a stopped up cat. No acceleration, bad gas mileage, and presumably low vacuum. This is where it gets weird.

When I got back to town, I was going to take it to the exhaust shop on Monday. They were closed. I was getting on the interstate, and I felt it accelerating pretty well. I nailed it, and when I hit about 70 mph, WOT, it nosed over, and check engine light started flashing. I pulled over, shut it off, started it up, CEL was off.

I reset the trip meters because it seemed to have the power back, gas mileage was up to 16.5 MPG.

Took it to my mechanic, he pulled a PO308 code. I replaced the COP on cylinder 8.
Took it to the exhaust shop on Tuesday, he said cats are fine, no rattle, engine is breathing, no codes.

Yesterday, I was getting on the highway and nailed it. When I hit about 70 mph, CEL came on. I now have a blue tooth OBD2 reader, so I read the code, and again it was a misfire on cylinder 8.

It does seem to idle a little bit rough, but not real bad.
It seems to have decent power right now, but my gas mileage isn't quite where it should be, but it's not terrible either. Between 14 and 15 mpg.

No I don't make a habit of driving it like a hot-rod, but I have nailed it a few times trying to monitor the fuel trims and O2 sensors to figure out what isn't right.

Any ideas???? The intermittent misfire on cylinder 8 is bugging me.

Sorry for the long winded post, but it all seems relevant to me.