06 Cayenne s 4.5 no compression cylinder 5 need help!

[motorworx12]

Hey everyone im new to the boards im always on hear reading stuff and theirs so much help on hear i love it! anyways ive got a cayenne s 4.5 non turbo. Ive had trouble starting the car and running really rough after letting my cousin drive it and it comes back misfireing! Found codes for misfires cylinder 1 and 5. after cross swapping coils problem still there. So i decided to check compression and cylinder 5 was dead! i had between 180-200 psi on all cylinders except 5. so i bought a boroscope to see if i could see any damage on top of the piston. I found a nice big indent from the valve on the intake side!!! what could have caused this? Anyways ive been looking at repair instructions on all data and it says to remove the engine for taking out the timing chain cover? does this sound right to you guys? ive built many bmw engines so im not mechanically a tardo, just wondering if its necessary to remove the motor for pulling the head off. any help/ input would be greatly appreciated! thanks

[wvicary]

Possible bent valve due to over rev. I would first do a cylinder leak down test to confirm it is an intake at fault. Sorry I don't know if you can remove the heads with the engine in situ.

[hahnmgh63]

If indeed it is a Valve indentation then I would also agree on an Over rev. Relatives.... Be sure what you see in an indentation caused by the valve and not a relief cut in the piston for valve clearance, not a bad idea to scope another cylinder so you can compare it to what your seeing. There are valve clearance relief cuts in the tops of the pistons for valve piston clearance under normal valve train timing (high lift valves). Out of timing the valves may still contact the pistons. If a piston has a noticeable valve dent in it then the piston strength is also compromised.

[bigbuzuki]

How can you over rev the motor in the Cayenne since the DME controls the max revs?

Only way I can see this happening is if your going downhill, you have selected a manual gear selection and the car speed increases to a point that over speeds the engine.

The DME in this instance has no control over the revs.

If the valve impacted the piston it too would have sustained damage.

Any valve damage visible with the scope?

Edited May 27, 2013 by bigbuzuki

[gkwong]

I have an 04 cayenne s and had both head gaskets replaced as they were leaking to the outside of the head. big job but the mechanic I used managed to do it with the engine staying in the car. he really didn't want to deal with taking the engine out. porsche dealer said it was not worth trying and wanted to replace engine. also replaced water pump while I was in there. car is now running great now. there is a mechanic in Ohio who does lots of cayenne rebuilds and has some interesting you tube videos, he seemed pretty reasonable but it was hard to get my car to him so I found someone near me.

[motorworx12]

Thanks for the replies everyone as it has been most helpful. Im going to try to take the head off with the engine still in the car. if i get stuck then ill take it out. My scope can take pictures ill try to get one loaded up. ill take some pics to keep everyone posted on whats happening. I have used engines before where the valaves hit the piston. Although if the piston is cracked thats a whole other story. thanks again.

[hahnmgh63]

As Bigsuzuki said, I would question your cousin about shifting it in manual mode. Did he possibly downshift a little too aggressively? Do you have the mirror attachment to see the underside of the head to inspect the valves? Like I said, it would be great to inspect two cylinders so you have a visual comparison of the two. I have the Snapon BK5500 and it is a great analyzing tool.

[deilenberger]

If it's an automatic - chances are it isn't an over-rev. The DME is smart enough to not downshift into a gear that would cause an over-rev.. even in TipTronic mode. I seem to recall cylinder #5 being the problem one for the wall coating breaking down, or the ring scoring the cylinder wall..