Engine Knocking on deceleration (btwn 800-2000 rpm)

Good Morning/Afternoon/Evening to you all.

I'm dealing with an engine knocking on deceleration.

Taco Spec:
- 2005 Crew Cab V6 4.0L TRD Sport Manual 6SPD
- 117k miles.
- Only maintenance done has been oil changes. (I accept blame for this)

Symptoms:
- Knocking has been occurring for about a month now.
- Knocking occurs only when engine is warm. (no engine knocking on cold start)
- After engine is warm, knocking is somewhat audible at idle.
- After engine is warm, knocking is very audible when decelerating (take foot off the gas) between 2000 down to 800 RPM.

Actions Taken:
- Been using 91 octane for a little over a year.
- Replaced spark plugs with iridium plugs (

$6 NGK LFR6C-11 V-Power Spark Plug, Pack of 1

NGK LFR6C-11) properly gapped.
- Cleaned MAF sensor.
- Added a can of seafoam to gas tank.
- Added seafoam to crankcase and ran for approx 100 miles.
- Then changed oil (Mobile1 Synthetic) and added Lucas oil heavy duty oil stabilizer.
- Belts look good no cracking, stripping.

Symptoms remain the same.

About to take the taco in for proper diagnoses, but wanted to see if anyone has any additional input that I may have overlooked.

 

From the symptoms. Sounds like it may be a rod knock. Get under the engine and have some rev up and let off. You can prob hear it better from below if it is a rod knock.

 

When is the last time you lubed the driveshaft u joints? Check the center bearing, too

 

Thanks for your response. Got under the engine after the truck was warm and rev'd the engine. It seems like a rod knock for sure. What is a ballpark on the amount that would cost to replace? $1K or higher?

 

Thanks for responding. I will be honest. I have never lubed the driveshaft u joints. So guess what I will be doing today

 

Don't jump to the worst conclusion yet. Get it looked at by a pro. "Rod knock" is extremely unusual, more so for a 117K mile engine.

 

Just wanted to update the forum.

Took the taco to a mechanic and it is the driver's side catalytic converter that is rattling. The mechanic stated that it is not affecting the engine as there is no 'check engine' light at the moment. Since there are no codes being thrown, the mechanic could not guarantee that replacing driver's side cat would resolve the issue. The reason given is that is might be a different cat. The part alone was $800-$850 and i would have to leave it over night.

How many labor hours to replace a driver side cat? I would assume about 3hrs, if the part is available.

 

What exactly is rattling? The material inside the cat or is it just loose somehow? Maybe it's just a heat shield or something and you can get under there and replace a bolt/tie it off with the bail wire and call it good. Go tap around with a mallet and see what's actually rattling.

 

It is something inside the cat that is rattling. I checked the heat shield before I took it in. Heat shield wasn't loose at all.

 

Thats way better than a rod knock then! Theres a honeycomb looking partition inside the cat. Rare but they do come apart inside as it degrades over time. Ive seen some where it causes poor engine performance and driveabilitly due to the pieces inside clogging the flow of exhaust. My shop charges 4hrs labor to replace one cat. So 3hrs aint bad.