Frequency valve buzzing loudly

[Szabi]

hi DMC-experts, I found info about frequency valve not buzzing, but nothing about this issue: the frequency valve is buzzing loudly. A loud, resonating noise started in the engine compartment, that I identified as it may came from around the air filter box. It seems it was generated by the frequency valve that is located under the air filter and its bigger (than earlier) resonance was somehow transmitted to the air filter box, that boosted the noise level.

I made sure the frequency valve`s lines/wires can not touch the air filter box, now the big noise has gone, but the buzzing from the frequency valve is still noticeably louder than what I remembered. As a new part costs 430 EUR (590 USD) at our European DMC dealer, I wonder if there is something I can try or check, to fix it or to make sure it is still working well. Thanks

[Bitsyncmaster]

You can run the FV by just jumping on the RPM relay connector the double yellow/red wire pin to the large brown wire pin. You don't need the key on for that test so it's easy to hear if that is your noise.

The FV will make the most noise when it's running at 50% duty cycle (cold engine). It also can change loudness depending if you have rest pressure or not.

I do that jumper test to eliminate rest pressure in the system if I need to pull a fuel line. Run it for a few minutes and it will drop the rest pressure to zero.

[Tillsy]

Mine buzzes loudly too Szabi - no idea whether its loudness is louder than one would normally expect though, never remembered to cross-reference with another owner. Regardless I'd love to reduce it someday - must investigate whether any of the compatible cross-overs might be quieter.

[Szabi]

You can run the FV by just jumping on the RPM relay connector the double yellow/red wire pin to the large brown wire pin. You don't need the key on for that test so it's easy to hear if that is your noise.

The FV will make the most noise when it's running at 50% duty cycle (cold engine). It also can change loudness depending if you have rest pressure or not.

I do that jumper test to eliminate rest pressure in the system if I need to pull a fuel line. Run it for a few minutes and it will drop the rest pressure to zero.
Thanks for the advice, I`ll try that. Good to know that the noise level can change, I did not know that. I did a 15-mile test drive yesterday, I checked the noise at the end, and it was not bad.

[Szabi]

Mine buzzes loudly too Szabi - no idea whether its loudness is louder than one would normally expect though, never remembered to cross-reference with another owner. Regardless I'd love to reduce it someday - must investigate whether any of the compatible cross-overs might be quieter.

Ahh, ok, it is always reassuring to hear that others have the same issue and it does not cause further problems for them. Yes, I also plan to compare it to another car, but it is not easy when there are only 3 functioning Deloreans in the whole country :)