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350matt
350matt, Mechanical Engineer
Category: Porsche
Satisfied Customers: 23886
Experience:  BEng Hons, worked in the car industry for the last 22 years
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Porsche cayenne 2011 petrol 4.8 v8 While turning left or

Customer Question

Porsche cayenne 2011 petrol 4.8 v8While turning left or right i hear a dry grinding noise but cannot figure if it is in the front or rear end.
Also while driving during acceleretion at any speed the car seems to jerk, while it jerks i can some noise as if hard shifting of gears from under the car.
Please help in finding what kind of a noise is this
Submitted: 7 months ago.
Category: Porsche
Expert:  350matt replied 7 months ago.

Hello and welcome to Just Answer

I'd say that this sounds like a worn drive shaft joint - typically these won't produce any vibration unless badly damaged but they can be noisy or 'clonk' for a long time beforehand, turn the steering to full lock and look at the drive-shaft rubber boot there should be no rips or tears in it and the suspension should be clean and dry of any grease. If you reverse at a reasonable speed with the steering on full lock a worn joint will 'click'.

you can also inspect the rear joints but obviously steering won't have much effect

If these are OK then I'd suspect that the propshaft either has a worn joint or the centre bearing is worn or its out of balance

you can easily check for for any slack in the propshaft joints by twisting either half by hand and feeling for any play as there should be virtually none

the centre bearing is quite loosely mounted so this can be moved normally but if you can run the car in gear with the wheels off the ground and then feel the centre bearing housing for vibration if there's any then consider replacing the unit

and then look along the propshaft for any signs of a missing balance weight as these take the form of little 3/4" squares that are welded onto the shaft - as they are only tacked on they can sometimes come loose and be lost resulting in the shaft being out of balance - if a joint is worn this can also shake them loose

so if a joint is replaced its good practice to have the shaft re-balanced afterwards

Expert:  350matt replied 7 months ago.

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Thanks Matt

Customer: replied 7 months ago.
The car jerks a lot only while acceleration.
You can drive upto whatever speed no issues but you can feel the jerk while accelerating.
This jerking is surely not because of fuel or power, it is a mechanical jerk as if the gears are not shifting properly and during this jerk you can feel something is getting locked and releasing.
Expert:  350matt replied 7 months ago.

Hello

well that's why I 've suggested checking mechanical aspect 1st, run through what I've mentioned and let me know what you find

Customer: replied 7 months ago.
Propellar shaft checked, balance in place, no play in joints, drive shaft boot not broken, no leakage of oil or grease
Diiferential checked
Expert:  350matt replied 7 months ago.

Ok

in that case I'd check that all the wheel bearing are OK

- jack the car up so the wheel is off the ground (you’ll need to do this for all 4 corners) and shake the tyre from top to bottom and from side to side (with someone holding the steering wheel on the front) there should be no play in either direction. Any play in 1 direction will usually require a joint to be replaced, if there’s play in both directions then the wheel bearing may be at fault

If this is OK then I'd check the front and rear differentials oil level and condition

Expert:  350matt replied 7 months ago.

Hi
do you still need help?
Bear in mind that the site takes a deposit from you at the beginning and this is held by the site until you rate my answer at which point the cash is split between the site and the expert. I am only paid for my work on this question if you rate my answer, using the star system at the top of the screen. Please do not forget! If you're not pleased, also let me know because rating bad does not result in a refund, there are better options. Rating now will not close this post nor prevent further replies
Thanks Matt

Customer: replied 7 months ago.
Hello.
Hope all is well.
Every end is checked, also noise of visible damage from transfer has been checked but solution found so far.
Car still continues to jerk despite all checks.
I went to the point of changing plugs and ignition coils but no resolve .
Any other suggestions?
I have no issues in giving u the best rating only after i am to resolve this issue with your help.
Expert:  350matt replied 7 months ago.

Well its possible that the jerking is an engine issue such as an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out and can also allow the engine to rev up when not desired causing rough running.

As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running.

Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.

The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane or brake cleaner around each joint in turn. If the engine rev's up you've found your leak.
Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.
Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.

Air leaks are very temperature dependent as gaps can open up as things expand with temperature so depending on how the leak occurs ( on a hose joint with a clamp expansion will help seal and on a vacuum hose expansion will make a leak worse) so leaks can be better or 1 vacuum leak path that you won't find with the above test is if the brake servo is leaking
so try clamping off servo hose to see if this has any effect