Humming and revs dropping

Humming and revs dropping

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Markjag12

Original Poster:

45 posts

82 months

Friday 26th May 2017
quotequote all
I drive a S-Type diesel automatic. Recently I have been experiancing a humming noise which last around half a second. And can be a one off or it comes in short bursts right one after the other for 10-15 seconds. Each time the noise comes it feels as though the car slows momentarily. Like there is a loss of power for a second or the brakes are being applied. At the same time the Rev needle drops a few hundred revs and when the noise stops the Rev needle returns to where it was and the braking sensation goes away. Any ideas ?

GreenV8S

30,150 posts

283 months

Friday 26th May 2017
quotequote all
Does that engine have a DPF clean cycle?

Markjag12

Original Poster:

45 posts

82 months

Friday 26th May 2017
quotequote all
I assume so. Honestly not sure though. Why do you ask ?

GreenV8S

30,150 posts

283 months

Friday 26th May 2017
quotequote all
I was thinking that the symptoms indicate a brief drop in power and either EGR or a DPF cleaning cycle might be causing that.

stevieturbo

17,229 posts

246 months

Saturday 27th May 2017
quotequote all
It could be, I'd presume the owners manual could give details ?

littleredrooster

5,523 posts

195 months

Saturday 27th May 2017
quotequote all
Hmmm...mine did something similar one very cold morning (-12deg). On a steady throttle just after starting, the revs started fluctuating very slightly and the engine note changed as the revcounter moved.

I suspect a lazy injector coupled with very cold diesel was turning it into a V5 rather than a V6 for a few moments at a time. It's never done it since the weather warmed up. Have you had the fault codes read?