129 relay chatter

[ricmerc]

The car is an SL 320 1994

I've noticed in the past few days that on start up there is, what sounds like, a relay chattering somewhere behind the passenger side facia/footwell. It stops when the engine revs get above around 1K. Sometimes it returns when the engine is on tickover, sometimes not.

I've not noticed it before, but then I wasn't listening for it, so can anyone tell me if it's normal or what might be happening. Any help greatly appreciated.

 

[grober]

Possibly the Solenoid valve which opens to allow the inlet manifold vacuum to evacuate the fuel tank evaporative control charcoal cannister. Its controlled by the engine ECU and dependant on engine temperature and vacuum in the manifold. They can get noisy but as long as they are operating correctly with no leaks nothing to worry about.

 

[alexander patie]

interestingly i heard EXACTLY this noise on a 320sl last week, p reg. relay chatter definately, ns footwell definately. it was not a concern of the customer so i did not investigate, but having a curious mind i would love to know the answer. i can say for certain that the one i heard was not the evap purge valve, and i would know. however that was a good suggestion and could be the answer to the o/p's question, but i doubt it.

 

[Sp!ke]

I get the same noise but only on a really frosty morning for the first two minutes or so.

Sounds like its coming from behind the glovebox.

 

[Dieselman]

That's Wife's teeth, outside on ice scraping duty.

 

[Smiley]

Possibly the Solenoid valve which opens to allow the inlet manifold vacuum to evacuate the fuel tank evaporative control charcoal cannister. Its controlled by the engine ECU and dependant on engine temperature and vacuum in the manifold. They can get noisy but as long as they are operating correctly with no leaks nothing to worry about.

Exactly right - my 129 SL500 did this sometimes - when I first heard it with the bonnet open my heart missed a beat - it sounds like a noisy tappet; really nasty. But as Grober says you can just leave it - or replace the solenoid - about £100 IIRC.

 

[ricmerc]

Thanks very much grober (et al), doesn't sound like too much to worry about. The chattering stops once the engine idle speed reduces as it warms up.

The sound does come back occasionally once the engine is at running temperature and comes down to tickover (at traffic lights, for example), I assume that fits the same scenario. (Excuse my lack of knowledge but the height of my mechanical achievement was rebuilding a 105E engine in 1970).

Oh, and Dieselman, thanks for the suggestion but I can eliminate that as I like to keep the old girl snug and warm on frosty mornings.