N54 Rumbling at WOT Mystery

[thetaobear]

Hi everybody,

I am need some help here. I am experiencing a strange rumbling when flooring my car. It happens very obviously at roughly around 2.5k RPM to 3.5k (yes, I know down shifting is the key, but this is bad when I'm just cruising on the highway and just want to push the peddle while at 5th or 6th). Vibration becomes less obvious above 3.5k. This problem becomes very bad with a tune- the rumble really sounds like something is wring.
Rumble and vibration isn't obvious when cruising, only when accelerating.

I already done an alignment (alignment helps a bit), my drive shaft was replaced with a brand new one (helped a bit), walnut blasted, and sent logs to terry with no misfires, etc.

Any ideas?

Thanks!

[ShocknAwe]

Stress on drivetrain. Higher TQ levels when tuned, just downshift to 4th. Much easier on the car.

[bNks334]

Originally Posted by thetaobear

Hi everybody,

I am need some help here. I am experiencing a strange rumbling when flooring my car. It happens very obviously at roughly around 2.5k RPM to 3.5k (yes, I know down shifting is the key, but this is bad when I'm just cruising on the highway and just want to push the peddle while at 5th or 6th). Vibration becomes less obvious above 3.5k. This problem becomes very bad with a tune- the rumble really sounds like something is wring.
Rumble and vibration isn't obvious when cruising, only when accelerating.

I already done an alignment (alignment helps a bit), my drive shaft was replaced with a brand new one (helped a bit), walnut blasted, and sent logs to terry with no misfires, etc.

Any ideas?

Thanks!

Stock DMFW?

I had a terrible drive-line vibration on decel right at 3k rpms until I replaced my flywheel. DMFW fatigue shouldn't be written off.

Also, did your shop properly pre-load the Driveshaft Center Carrier?? It should be pushed toward the front of the car before being bolted down.

This is also assuming you have an actual problem and you're not just overreacting about noise from high gear high load stress (downshift to pass).

[thetaobear]

Replaced DMFW at around 20k miles ago- but will have the shop look at it this Monday.

I will have them check the driveshaft center carrier.

Thank you for the reply! Yes, the vibration has gotten worse over time. Hopefully it is nothing too serious.

[thetaobear]

I found the problem.

I installed an OCC. And during a walnut blast session, the OCC was moved a bit, which caused pressure onto the Crankcase vent PVC part that I re-used.

As a result, after a track day, the PVC part is loose and causing air to leak (oil is present around the area).

After adjusting the length of the silicone pipe to the PVC, it applies a lot less pressure. However, it seems like it is still a bit iffy. The PVC portion seems to move a bit freely? The vibration is *greatly* reduced but still present- I'm pretty sure the PVC is leaking some air after a few movements from the car.

Any ideas on solutions?

[ShocknAwe]

thanks for updating the thread.

If you suspect the PCV is contributing to your vibration, I'd look into the upgraded PCV options. I know RB makes a variant that folks have been quite pleased with. Not sure on others, but there are a few options.