View Full Version : Strange ticking sound -- need help

08-29-2010, 11:29 PM
Hey folks,

So today I finished applying anti-seize to all my spark plug threads. Once I finished and started up the van I have a new ticking/tapping sound coming from what seems to be the top, driver's side of the engine. It's audible from the passenger compartment and I'm certain it's never done that before. Also, there is a definite rhythm to it.

I have no idea what might be causing this. Removing and re-installing the spark plugs is about as straight forward a job as one can come up with. If anyone has suggestions for what I can check or what might be wrong I'd really appreciate it.

I drove it out on the highway, and it doesn't seem to be lacking power and there isn't a strong unburned fuel smell from the exhaust. If one of the cylinders is mis-firing I'd expect it to be more significant than a ticking/tapping. I'd also expect a check engine light. I know it doesn't take long to plug a catalytic convertor, so I definitely want to get this addressed ASAP.

Any suggestions, especially from the professional mechanic types? Thanks.

08-29-2010, 11:37 PM
are you quite certain one is not cross threaded and thereby not sealed?

08-30-2010, 12:37 AM
Plug wires (whatever they are) are all pushed down tight ? no arcing ?

Coil wire seated at both ends ?

Does clicking follow with RPM changes ?

That's all I've got for now.


08-30-2010, 12:38 AM
No, nothing's cross-threaded. Actually, it would be near impossible. The spark plugs are in a tunnel that prevents the spark plug from being anything but straight inline with the axis of the hole. Plus I threaded them by hand with my finger turning an extension until I did the final tightening with a torque wrench.

I will say I went out and listened with a engine stethoscope (well, strictly speaking it was a long funnel for changing oil and ATF). It seems sounds like the sound might be fuel injectors. It's coming from a few inches above the spark plugs. And seems quite a bit faster than the engine speed.

For the life of me, I don't remember hearing this previously, but then again, I couldn't bet money against it. Any one out there have a Mercedes 3.5L V6 that they can say if they hear a medium-high pitch ticking/tapping sound coming from the top of the engine?

My current next best idea is to take it to the Mercedes dealership and ask one of the tech's there if this is a normal sound I just happened to never notice before until I became hyper-sensitive following my spark plug job. Again though, any other suggestions would be greatly appreciated. Thanks.

Aqua Puttana
08-30-2010, 12:49 AM

My current next best idea is to take it to the Mercedes dealership and ask one of the tech's there if this is a normal sound I just happened to never notice before until I became hyper-sensitive following my spark plug job. Again though, any other suggestions would be greatly appreciated. Thanks.

FWIW. That sounds like a good plan. I know there have been times I've noticed something after doing a job that ended up unrelated. As you've said, too soon to panic yet. I hope someone has noticed a similar noise and relates their experience to put you even more at ease. Good luck. vic

08-30-2010, 01:19 AM
It's possible you have a bad new plug that is leaking. You could try re installing one old plug at a time on the side that is ticking.

08-30-2010, 03:41 AM
Thanks for the suggestion Bruce. Actually I didn't change any of the spark plugs. Just unscrewed them, cleaned-up threads, applied thin coating of anti-seize, and screwed back in.

After thinking about it some more, I'm fairly convinced the sound is the fuel injectors. It is present equally on both sides: distinct and out of phase. It's local to the area of the intake manifold and not near the spark plugs or combustion chamber area. There's really nothing else it could be, and for the life of me I can't imagine I did something to the plugs that a) would cause a strange tapping sound and b) not throw a check engine fault.

I'll call and see if I get anywhere talking on the phone with a service manager tomorrow, but I'm ready to chaulk this up to hyper-vigilance and selective memory on my part. Thanks for the consideration those that responded. I hope to have a write-up with pictures soon.

08-30-2010, 04:38 PM
I think my 3.5L engine has the same noise for about couple years now, but I don't have a stethoscope to check so I'm not sure where it comes from, but with bare ears I think it comes from the passenger side of the engine compartment.
At first I thought it was valve knocking, I use Costco gas and I thought maybe it's lower than 91 octane and may cause valve knocking, but tried Chevron, Shell, Arco, and Valero did not eliminate the noise. I could not find 93 octane gas to try.
Noticeable when accelerate from stop, I did not hear the noise at high speed 65mph or higher, maybe road noise masked it.
Mentioned this noise to the Dodge dealer several times, but as always they did not hear it. Please post what the result of your finding.


08-31-2010, 12:54 AM
So I stopped by the dealership on my way home today. I was on my bike and didn't have the van for a tech to listen to, but one of the desk guys did start a CLK350 that was dropped-off for something or other and sitting right there in the garage. Listening closely with the hood up, I could hear the same tapping/ticking sound coming from the passenger side. The driver's side had a lot more stuff in the way so it's possible I just couldn't get in close enough to hear. The desk guy also agreed with me that there was virtually nothing I could do changing spark plugs that would result in a tapping/ticking sound.

One final thing, double07, you mention having something similar and trying gasoline from different stations. I can't imagine knocking would occur at idle in a cold engine, but I did buy a full tank of gas from a station I don't usually patronize the day before doing the job. I'm still going to assume this is injector actuation noise, but the next fill-up will be from one of my typical stations. If the noise does go away I'll let the forum know. Again, thanks everyone that responded.