Fuel pump humm?

[911hillclimber]

987.2 2.9 with 92k on the clock.
Runs very well and smoothly.
Anyone had a pump humm when car running, esp the high pressure pump on the engine?

 

[malarcy]

Don't think the 2.9 has a high pressure fuel pump - that is on DFI engines only isn't it?

 

[911hillclimber]

Hope and think you are correct. No such pump on the humble 2.9 engine.
The rear humm I’m trying to identify on the car sounds just like a fuel pump, hence my suspicions of the pump on the engine, if it has one.
Thank you for the reply, it all helps me.

 

[malarcy]

Have you considered anything on the serpentine belt - a/c, power steering, alternator, waterpump - or the pulleys themselves - you can remove the belt and run the engine briefly to see if the noise goes away ( only if you can reproduce stationary of course) - or manually spin the various bits to see if you can feel any roughness in the bearings ?

 

[911hillclimber]

The humming chimes in at 40 mph no matter the gear/ revs, does not change with road speed until 60 and then drowned out by tyre and engine general noise.
Belt changed last service.
Many think it is tyre noise, can’t get to the bottom of it.
Ruins a good car.

 

[Motorhead]

As Paul has indicated, only the 3.4L engine in the 987.2 series had the DFI engine with a high pressure fuel pump Graham, so you can discount that as being a source of your problem, although a pump of some kind could be a source since it seems as though it’s a constant frequency, which would rule out anything engine-related like ancillaries.

Definitely I reckon that it would be worth trying a nitrogen fill for the tyres, the rears at least. It shouldn’t be too expensive and I’m sure that you can find a tyre shop in your area which offers the service if you look online. For context I think that Lexus was the first manufacturer to use it for their first car, the LS 400 which was noted for its refinement, and maybe in part to overcome an NVH issue. If it doesn’t work then I guess that a tyre-related source would drop down the list of possible sources even if it couldn’t be ruled out completely, and a nitrogen fill has other benefits including a more consistent tyre pressure with temperature and better pressure retention.

Jeff

 

[911hillclimber]

Thanks Jeff and Paul too.
Im a bit of a dog with a bone on these things, got to find a solution but the simplest way.
Nitrogen fill is easy I think, lots of industry round here and big tyre fitters.
Will try it when back off holiday.
I think my long long suffering wife is ready to give a permission for 2 new rear tyres just to shut me up…