Been chasing a tapping noise, when using a stethoscope appeared to be coming from the top of the engine. Seemed like it was dirty fuel injectors. Engine also felt a bit sluggish. No codes present.

The valve cover gaskets were seeping a bit, so changed all of those during the tensioner updates and decided to replace the spark plugs to rule out any potential issue.

Someone previously installed Autolites, and I thought it was odd that they seemed to come out almost by hand. Very little resistance to get them out and definitely looked like they needed to be replaced.

Cleaned all areas and coil boots as best as possible to remove any leftover oil/debris. Installed the NGK Iridiums, hand tightened with just the extension and then tightened to 1/2-2/3 turn as indicated on the box.

After this, the car ran amazing. I couldn't believe the difference. The engine was smooth and very powerful again.

Well a week and 100 miles or so passed, and now the tapping is back and the engine is back to feeling a bit sluggish again.

Any suggestions? I'm wondering if the spark plugs might need to be re-torqued down properly (Did not want to over tighten). And while I would love to remove the plugs to inspect, because of the crush washer, I'd have to buy all new plugs to install again. I'll also be installing a new fuel filter soon.

Intermittent Coil? Coil Boots not fitting properly?

Thanks for any ideas!

 

I think your injectors need to be cleaned: Sea Foam, or Gumout's Best.

 

Thanks -- Ran a bottle of Techron through, but didn't make much of a difference. Might try a can of BG44k in the tank next too...

 

BMW V8's which also have a aluminum dohc cylinder head are notorious for a misfire and noise when Bosch plugs are used because they back out.

You can check the plugs again except that you need to know that using the turn method, the spec on a used plug with crush washer is 1/16 turn after seated. Alternatively, just check that they are still tight.

Also check for oil in the sparkplug wells and on the coil boots. Check for cracked coil boots.

 

Good to see you are using decent plugs! ;o)
These should be tightened to 18-22Nm and yes, it always pays to check retightening after a week or so.
They should always be installed with a dab of nickel ant-seize.
It's quite common in any modern alloy head for the plugs to lose their tension.
The tappety noise will have nothing to do with your plugs.
It will either be the injectors (which don't produce a loud sound anyway) or possibly valve shims in the buckets.
What distance has this engine covered?

 

63k miles.

Thanks for all your replies and advice

 

Torquing the spark plugs to the recommended (25-29nm) with my new digital torque wrench fixed the issue. Much smoother now and no tap. Go figure.

 

If the plugs were loose, the tapping sound was compression/combustion leaking past the plug seat.