rbeggs

I'm hearing a sound I haven't heard before. It seems to be coming from the expansion tank in the luggage compartment, directly ahead of the drivers seat.
The sound is a constant pitch, hum/buzz, around 120 Hz. It comes on with the engine and varies little, if any, regardless of what the car may be doing. I can feel the vibration when I put my hand on the tank. It will sometimes stop, only to return the next time the car's started. Looking at the PET I can see no motor or device associated with the tank that would make that sound. I thought maybe a stuck solenoid for a valve could be the culprit but the documentation is not clear. It could well be that it's coming from an adjacent area. The vibration transmission thing can be ambiguous.

Any ideas as to what this might be?

Thanks for any thoughts you may have.

-rb

bcameron59

Brake pump. Comes on when pressure in the system drops, and runs for a few minutes until the system is re-pressurized. Mine comes on briefly most mornings after sitting overnight. It will come on and can be heard clearly with key in position 1, ie before engine is started.

I believe this setup is standard on the C4/C4S (option code M339) but not on C2/C2S (maybe an option on the latter?)

I believe it is #17 below but might be #1

JPS

Post a vid?

rbeggs

Thanks for the thinking Bcameron. That made a lot of sense but that's not it.

I've localized the sound. It's coming from the area of the fuse box. I banged on it and the sound changed. I removed the cover and started wiggling the relays, thinking it sounded like a stuck solenoid vibrating. Sure enough, the DME relay was hot to the touch and the noise would change as I tapped it. I removed it and what do I see but a very corroded, discolored pin #4 and the base of the DME is charred and melted around the pin. I replaced the DME with a spare. The noise persists and I can feel the relay heating up.

Does this sound familiar to anybody, and if so, what's going on?

Thanks,

-rb

bcameron59

Whoa, something is definitely not right with that DME relay. Never heard of anything like that. Wondering if this could be manifestation of a fuel pump issue?

911PERVY

DME relays do run very hot, thats why Im switching to the solid state version

HalfGerman

That's what I did, all the posts about DME scared me, so I put one in shortly after I got the car last year:
http://www.ftech9.com/new-products/993-ssr

rbeggs

The current thinking on this mystery is that it is likely a fuel pump issue. It's working but on it's way out and it's pulling to much current. This is stressing the relay.

Does this make sense? I hope so.

Anyone have an argument to the contrary?

Thanks in advance.

-rb

user 723923490

Sounds reasonable.