Hey, my truck has recently lost a bunch of power, mileage has dropped from low 12s to mid 10s and it has picked up some low rpm knock. It also hits a big flat spot right at 5k rpms, I can feel a hesitation in the motor. The setup is in the sig, I tried cleaning the MAF, and I replaced the Air filter as it was somewhat dirty. I originally thought it might have been a bad tank of gas, but I have run several tanks since the this started and nothing has changed. Any ideas on what could be causing this??? I'm really at a loss, and I don't want to drive it much with all the Knock that it is getting down low, It is not false knock, as I can hear and feel it.

Thanks

 

check the injectors,plugs and wires
idk what it would be but thats my 2 cents

 

id get a couple cans of seafoam, pour a full can in a tank of gas, and run a half a can threw the vacuum line.

 

Cats?

 

Could be a number of things...the knock may be an indication of a lean condition, excessive spark timing, excessive cylinder temps, etc. I'd check for vacuum leaks, check fuel pressure, etc. If you have scanning software, check out your O2 sensor activity and long term fuel trims. Clogged or partially clogged cats, like therock mentioned would cause a loss of power, spark knock, and possible misfires, as well as affect MPG.

 

I ran a can into the vacuum line, but when i removed the TB to clean it I found this big puddle in the J-tube which I started cleaning up, only to realize that it was all of the seafoam, so I guess I can give it another shot.

I've been thinking fuel issues, or a clogged/melted cat, whats the easiest way to determine Cat problems I still have stock manifolds/cats

I will take a log today driving around and maybe that will show something.

 

I have HPtuners, and I scanned the other day, but apparently forgot to save it, so I'll do another one today, all the long term trims were in the -5, to -8 range which I thought was a good range??

Anyway i'll take another log today and we'll see what it comes up with.

 

You can do 1 of 2 things to check the cats...you can either remove them and drive and see if the problem goes away, or you can check with a vacuum gauge. With the truck in P or N, hook a vacuum gauge to a good port on the intake and rev the engine to about 2500 RPM. Snap the throttle shut, and vacuum should immediately jump up over 20 mm/hg (probably more like 25). If vacuum creeps up slowly, the exhaust is restricted or a cat is clogged.

 

My 8.1 was doing similar things..ended up being the plugs...also noticed a couple wires got alittle close to the headers so I threw a set of plugs in (TR6ix's) and a set of wires from MSD that have the heat sleeves on them and all was good.

 

Fuel or cats gets my vote.