2008 M35 Knocking Noise Help

[M35Squirrel]

Hello guys, new forum member here. I have a 2008 M35 with 51k miles and the only mod is a 5/16" plenum spacer.

Started about a month ago the engine developed a knocking noise that follows the RPM (the frequency increases as rev goes higher, and when it shifts into next gear it starts from low again). What makes this very strange is that the noise only comes on when engine is warmed up and under load, in both drive and reverse. No noise in park or neutral or coasting when in drive. No noise when engine is not warmed up.

I put in a fresh tank of premium gas and a new oil change, nothing helped. I drained and filled 6 qts of fresh Matic S 1 year ago, and the fluid still looks nice and pink. I am out of ideas of what this noise can be! Can you guys please help or chime in your $.02?

Thanks in advance!

[EniGmA1987]

Well hopefully it isnt "rod knock", since that means some major $$$, but sine it doesnt make the noise when idling or coasting it could be something else.

Here is rod knock:
https://www.youtube.com/watch?v=NsCb0auCDWI
https://www.youtube.com/watch?v=DfJIpiQZtR4

[M35Squirrel]

Well hopefully it isnt "rod knock", since that means some major $$$, but sine it doesnt make the noise when idling or coasting it could be something else.

Here is rod knock:
https://www.youtube.com/watch?v=NsCb0auCDWI
https://www.youtube.com/watch?v=DfJIpiQZtR4

Yeah I saw that video too when I googled M35 knock. Since the knocking doesn't come on when car is stationary, this is really difficult to diagnose, unless I have my friend drive with the hood open and I run along side. But I sure don't want to get run over by my own car......

Someone suggested idler pulley, but that is still illogical since there is no noise at idle.

[zerg711]

It's been about a 9 months since I've lemoned my M35, but I had a knocking noise which lead to short block replacement twice.... long story short, they were unable to fix the knocking sound which lead me to lemon my car.

You should probably take your car in and have the dealership perform a cylinder deactivation test to figure out which cylinder the problem is associated with. On my first short block, one of the cylinders failed.... O and by the way, don't let them tell you that the knocking sound is normal. The dealership telling me that the sound was normal felt like they thought I was an idiot which led me to hire a lemon law attorney...

[M35Squirrel]

It's been about a 9 months since I've lemoned my M35, but I had a knocking noise which lead to short block replacement twice.... long story short, they were unable to fix the knocking sound which lead me to lemon my car.

Did your knocking noise also only come on under the same condition as I have?

In my case I am pretty sure the noise is from the engine area and not the transmission. But it just baffles me of what part of engine could produce such noise only when the engine is fully warmed up and accelerating......

[lovemycarM35]

I had the same issue is zerg711 about two years ago I went through hell to get the dealer to fix my car. They replaced the short block lucky for me the tech that repaired my car did a really good job I've had zero issues after that all under warranty but the tap I had was only heard around 1500-1900 rpm's after warmed up


Side Note ...I do know that the belt tenser can cause a knocking noise you may want to do a search on that

[M35Squirrel]

I had the same issue is zerg711 about two years ago I went through hell to get the dealer to fix my car. They replaced the short block lucky for me the tech that repaired my car did a really good job I've had zero issues after that all under warranty but the tap I had was only heard around 1500-1900 rpm's after warmed up


Side Note ...I do know that the belt tenser can cause a knocking noise you may want to do a search on that

Hmmm I heard the noise around that same rpm range, because after 2000 rpm the frequency gets so high it becomes difficult to pick up......

Unlucky for me, my car is now out of warranty......

[svard75]

Start with the cheap stuff first before assuming it's the worst.

1. Have someone perform a fuel injector cleaning and check to ensure each fuel injector is working. I would disconnect the power leads to each and reconnect just to re-seat the power connectors. You would be surprised what corrosion does and makes you spend so much money thinking the sensors are not working. Rotten mechanics almost always take advantage of this issue.

2. Next check the spark plugs, regap and again re-seat each coil pack connector.

3. Perform an engine oil flush with seafoam and run the engine till it's NOT (Normal Operating Temperature) for at least 3 fan cycles. Rev it a bit to get the solvent up into the heads. Before you refill let the oil drain a good while and watch the oil coming out of the pan. Use a magnet to fish around in the oil and see if there are any metal bits in there (Bad sign). When you top up the oil make sure it's not more than the manual states. Too much engine oil causes excessive frothing from the crank and can cause engine starvation.

4. Get one of these http://images.palcdn.com/hlr-system/Web ... 110847a5a6 and have someone rev the engine while you're listening.

[M35Squirrel]

Start with the cheap stuff first before assuming it's the worst.

1. Have someone perform a fuel injector cleaning and check to ensure each fuel injector is working. I would disconnect the power leads to each and reconnect just to re-seat the power connectors. You would be surprised what corrosion does and makes you spend so much money thinking the sensors are not working. Rotten mechanics almost always take advantage of this issue.

2. Next check the spark plugs, regap and again re-seat each coil pack connector.

3. Perform an engine oil flush with seafoam and run the engine till it's NOT (Normal Operating Temperature) for at least 3 fan cycles. Rev it a bit to get the solvent up into the heads. Before you refill let the oil drain a good while and watch the oil coming out of the pan. Use a magnet to fish around in the oil and see if there are any metal bits in there (Bad sign). When you top up the oil make sure it's not more than the manual states. Too much engine oil causes excessive frothing from the crank and can cause engine starvation.

4. Get one of these http://images.palcdn.com/hlr-system/Web ... 110847a5a6 and have someone rev the engine while you're listening.

Thanks for the tips! I had 1/2 can of seafoam in the oil for about 400 miles before the oil change, too bad I didn't change my oil this time and the mechanic didn't mention any metal debris. I will need a stethoscope for sure since I can't pick up any noise with my ear during idle. I will also get new plugs and see if they help, but I just need to find a good 2 hour slot in my weekend since this isn't a 5 minute plug job (insert that's what she said joke) like my Civic!

[svard75]

... since this isn't a 5 minute plug job (insert that's what she said joke) like my Civic!

Not like this eh? http://www.hairtransplantnetwork.com/ha ... -front.jpg

[lovemycarM35]

dude this has nothing to due with the plugs!! can you take a sound clip I'd like to here it

[M35Squirrel]

dude this has nothing to due with the plugs!! can you take a sound clip I'd like to here it

I will try to take a video this weekend, but this will not be easy because I will need to be driving while filming......

[M35Squirrel]

Took my car to the dealer last week for a diagnosis, the mechanic told me the noise is from "carbon knock." There is carbon deposit on the valves and pistons, and he recommends a fuel induction service plus timing adjustment. The weird part is the timing adjustment. I asked him if he meant updating timing in the ECU, but he said no, the timing will be adjusted mechanically. Not sure how that works......

[svard75]

dude this has nothing to due with the plugs!! can you take a sound clip I'd like to here it

Hair plugs, spark plugs same idea right? haha JK a bit of baldie humour.

[lovemycarM35]

That May be what's going cause I had that same issue with my car a few years ago they did the y fuel cleaning and It was fine I forgot to tell you about that