i have a 2008 TL, V6 engine. i have about 155,000 miles on my car. Now i am starting to hear Engine Knock noise when i press on the Accelerator. It doesn't do it all the time but it does it enough where it is bothering me. Is this case of Bad gasoline. i always fill with Premium grade. Is this normal for car of this age and miles ?

 

IMO: NO, it's not normal, at any mileage. My 2003 TLS, has 241K+ miles, and the engine runs like a fine Swiss watch, with no abnormal noises. If, as you state, " It doesn't do it all the time " , it's most likely NOT a rod, or main bearing knock! Invest in a $5.00, Harbor Freight style stethoscope, and try to pinpoint, the general source area, of the noise. Could be any number of things. If possible, please post a VIDEO, to better describe the noise your hearing, as well as, under what condition, you normally hear it, "ie" cold start, etc. Normally, poor fuel, creates more of a PING, than a knock.

 

At first i thought it was my loose heat shield. but then this is different noise, more like a true knock noise. i may have to take it into dealership again. i think it is worse when cold start, but i am not certain

 

Any chance U could post a video? If, it's truly a knock, that's Very serious.

 

yes, i can try to record the video or sound and post. today it was making the noise like 99 % of the time.

Can old bad spark plugs cause this kind of knocking noise ?? because i may have skipped getting the new spark plug when i was doing timing belt 40,000 miles ago. They did recommend getting new spark plugs back then but i decided to put it off and must have forgotten about it.

 

No, spark plugs will not cause the type of knock I think you're describing. Now if you have detonation, which is often described as "pinging", yes, it is possible for an old damaged spark plug to cause that, in rare circumstances, however, given how long modern plugs last, I would be hard pressed to think a plug with 145,000 miles on it would be that far gone.

 

I also skipped out on Valve timing adjustment service they told to do. and they said if my valve timing is off, it can harm the engine or it won't perform very efficiently. is this true ?

 

Harm the engine (specifically the cam, cam followers, and valves), yes; impact performance, meh, maybe a very little (until the damage gets bad enough to notice). That said, what you've described doesn't really sound like a valve train issue.

 

( " I also skipped out on Valve timing adjustment service they told to do. and they said if my valve timing is off, it can harm the engine or it won't perform very efficiently. is this true ? " ) FWIW: Valve lash, "ie" adjustment, and engine timing, are two distinctly different things! Yes, if the timing is off, the engine can't perform efficiently! A noisy valve lifter, normally, is not a serious issue. A TIGHT valve, will not make any noise, and is a serious issue. It's unlikely, that your engine, has suffered any ill effects, resulting from declining the 100K valve adjustment!

 

Well, i am trying to post a video but it is not easy. It will do it sometimes and sometimes it won't. and it isn't always when i press on the accelerator either. It is also doing it sometimes when the engine is idle. and this is some type of clicking noise more than knocking noise. Not sure if it is ping type of noise, more like Click Click Click definitely sound like coming from the engine. Can noisy valve lifter make this kind of noise ? If i went ahead and did the Valve timing adjustment like they recommended, would it help ? I do remember doing the Spark plug replacement because they told me if that goes bad, my engine won't start at all.

 

I googled bad valve timing symptoms and this is what i came up with. How can i tell this noise is "Spark Knock" or "Pinging" ?? and i have been noticing some bad gas mileage lately on the car, or is is cause i have been using my AC more lately ? not sure....

"What are the symptoms of a bad timing?
Symptoms of incorrect ignition timing are poor fuel economy, sluggishacceleration, hard starting, backfiring, or "pinging" or "spark knock". Too littlespark advance will cause low power, bad gas mileage, backfiring, and poorperformance. Too much advance will cause hard starting and pre-ignition."

 

First comment, it sounds like you are confusing or conflating ignition timing and valve timing; the two are very different conditions.

I'm not sure of what your source is and how relevant it is to the engine in your car, but I'm not even sure it is possible to screw up the valve timing short of having the timing belt jump a tooth. As for the comment which says, "Too much (spark) advance will cause hard starting and pre-ignition." Whatever that source was, you can discount it as irrelevant. Why? Because too much will cannot possibly cause pre-ignition, at least not directly. Consider the term "pre-ignition", this means the ignition event happens before the spark event. That said, too much spark advance can (and typically will) cause severe detonation/pinging, which in turn can damage engine components and the spark plugs themselves, and the damage can cause pre-ignition.

 

With the description so far being all over the place on being a knock, to a click, to a tap and no idea what part of the engine...

1.) Check all of your plugs to make sure they are all still snug.
2.) Work to get a video posted
3.) Continue to work to better isolate what part of the engine the noises are coming from (top, bottom, driver's side, passenger's side, front, back,etc)

At idle, you won't have spark knock (detonation) unless something is really wrong. Valve adjustment shouldn't throw your timing off either...they usually just get louder.

 

It could be something with the timing belt parts. My moms odyssey made a terrible knocking noise, it turned out to be a bad timing belt tensioner so my friend changed the belt, wp, and that tensioner. Now good as new.. Its actually a pretty common failure. The noise for that would be on the passenger middle side of the engine bay. Good luck