Strange Intermittent Tapping Noise

[Jhalsey]

1989 930, 34k miles, stock.

There is a tapping noise at idle similar to loose rocker arm type tapping in a pushrod motor. It is not present at cold start or fully warmed up, just from about 5 minutes to 20 minutes of running. Seems to be coming from the top center of the engine but very hard to tell. Engine has had recent service with new plugs, valve adjustment etc. Leak down #'s are very good at 1-2% each cylinder. Noise was present before the service. My shop has not been able to determine cause. Engine runs great otherwise so am reluctant to tear into it looking for cause without at least a theory.


Welcome ideas on the possible cause. Thanks.

[M5guy]

Noisy injector?

[torresmd]

Did this noise start after the valve adjustment? If so I would have them check them again. Beautiful car and I love the wheels.

[Jhalsey]

Noise was present before valve adjustment.

Not sure what a noisy injector sounds like but the character of this noise seems to be a heavier metal on metal rotational sort of sound.

[gsxrken]

Might want to remove your air pump belt and see if the issue still persists, assuming as you stated that the car is still stock.

[kojo911]

probably terminal, will cost $$$ to fix. Cut your losses and sell me the car. JK

[Groovie Ghoulie]

are you running the proper weight oil? silly question I know, but light oils make mine have louder tapping sounds. (Was in a pinch and had to put whatever synthetic oil i could find in it to get it a few more miles for the good stuff).

[JFairman]

Originally Posted by Jhalsey

Noise was present before valve adjustment.

Not sure what a noisy injector sounds like but the character of this noise seems to be a heavier metal on metal rotational sort of sound.

The K-jetronic or CIS injectors that come origonal on your car don't make any clicking noise at all. They spray fuel continuosly and silently like a garden hose set to cone spray pattern and sometimes one might make a little squeak like sound.

Some old Bosch EFI injectors make a light ticking as they open and close. It's most noticable at idle speed if a quiet muffler is still on the car.
Newer EFI injectors seem pretty silent to me.

If you post a recording or video with sound maybe someone can make some educated guesses.
If your mechanic has any experience on these cars and he can't figure it out then the rest of us can only guess.

[WERK I]

Originally Posted by Jhalsey

1989 930, 34k miles, stock.

There is a tapping noise at idle similar to loose rocker arm type tapping in a pushrod motor. It is not present at cold start or fully warmed up, just from about 5 minutes to 20 minutes of running. Seems to be coming from the top center of the engine but very hard to tell. Engine has had recent service with new plugs, valve adjustment etc. Leak down #'s are very good at 1-2% each cylinder. Noise was present before the service. My shop has not been able to determine cause. Engine runs great otherwise so am reluctant to tear into it looking for cause without at least a theory.


Welcome ideas on the possible cause. Thanks.

How old is your fan belt? After thousands of heat cycles and millions of revolutions, the belts get hard and begin to crack. That's one area.

Exhaust leak. Linking Header/manifold gaskets will seal until things heat up and then begin "ticking". Look for carbon tracks on any of the sealing areas and joints.
Exhaust ticks sound very similar to an out of adjustment rocker arm.

[JFairman]

WERK I is on to something!
Good one on the exhaust leak!

When I first got my car it had a tick tick tick noticable at idle for about 10 minutes after a cold start and then it would go away.

It was louder when sticking your head down under ths car and I could feel a little puff puff puff exhaust leak next to one of the exhaust port to header flange points.

When I removed the B&B headers that were on the car when I got it I found that one of the exhaust port studs had pulled from the head so it was leaking there and when the motor got hot the expansion of the headers sort of sealed up the leak to the point you couldn't hear it anymore.

I timeserted the 8mmx1.25 exhaust port stud threads in the head and that fixed it.
It's best to just timesert all the exhaust port stud threads as they are hardened steel so it never happens again.

I'll bet thats it!

[mooney265]

Originally Posted by M5guy

Noisy injector?

I don't think our injectors make any noise... they're not electronic, but simply a nozzle for a hose... oops, just saw Post #8, sorry for duplicate response...

I would guess exhaust leak...

[LOWFAT]

Possibly the alternator,mine does the same thing at times. Diagnosed by removing the belt and running for a very short time.It seems to come and go but makes more noise with the lights on under more load.I replaced it with a new one and the new one does the same thing, weird.

[afterburn 549]

Will it go away with clutch pedal dwn ? ??? try that

[Jhalsey]

Thanks for all the responses, except for the one from kojo911 of course. I will try to make audio recording of the sound. The weird thing is how it is absent at full cold and full hot. Exhaust leak could maybe fit that characteristic, not so sure the others (alternator, air pump belts, oil viscosity). Well see.