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No pressure Cylinder 8 2003 Turbo


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Hi, I have an issue with 2003 Cayenne Turbo which started after filling up car in France. Shortly afterwards car started shaking with little power. Was ok on motorway going 70mph max but any faster, or up hills, shaking returned. Similar thing happened a few years ago which was resolved with new ignition coils and spark plugs. However this time this has not solved the problem and porsche in Germany did compression test and found no pressure in cylinder 8.

Car has now been towed back to UK and i'm hoping to find a way to diagnose the problem without taking the engine out. Porsche in Germany put a camera in the cylinders and they are not scoured but spark plugs were all black.

I can't find any similar problems but hopefully someone will be able to point me in the right direction.

The engine management light is on permanently orange now.

Car has done 98,000 miles and otherwise great.

Any hints would be greatfully received...

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This does not sound overly well. While the lack of compression is most probably a mechanical rather than an electronic issue, I would not be running the engine and would get the vehicle scanned with a Porsche specific diagnostics tool (PIWIS or Durametric) to find out what codes are triggering the MIL. To make a long story short, if you have suffered a mechanical failure, the engine is most likely going to have to come out.

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Hi, i don't think Porsche in Germany generated any codes (or atleast they did not share them with me if they did). I did see the results of the presseure tests with the graphs showing cylinders 1-7 and then cylinder 8 being blank. I think i will try to find an independent specialist in NW uk to take the engine out & tell me whether it is worth reparing.

Cheers

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Hi, i don't think Porsche in Germany generated any codes (or atleast they did not share them with me if they did). I did see the results of the presseure tests with the graphs showing cylinders 1-7 and then cylinder 8 being blank. I think i will try to find an independent specialist in NW uk to take the engine out & tell me whether it is worth reparing.

Cheers

It would still be very useful to know what the codes are before going further.

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Codes are always useful, but here is my take....

no compression in a single cylinder can only be mechanical. the codes can help you figure out what happened, but at the end of the day you still have a mechanical failure. Long story short.....you will have to pull the head....or the entire motor.

Not sure if you have tools or not, but here is what i would do:

move #8 to TBC

get a pressure tester, or take an old sparkplug and weld an air fitting to it

install and pressurize to 5ish psi

Take the oil cap off, if you can hear it coming through the cap then you blew a hole in the piston, ring damage, or a combination

Open the throttle body and take the y pipe plenum off the TB, if you hear air from there, you busted up an intake valve.

If none of that occurred, then it most likely is an exhaust valve. You MIGHT be able to hear it in the exhaust pipe, but it's unlikely.

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Codes are always useful, but here is my take....

no compression in a single cylinder can only be mechanical. the codes can help you figure out what happened, but at the end of the day you still have a mechanical failure. Long story short.....you will have to pull the head....or the entire motor.

Not sure if you have tools or not, but here is what i would do:

move #8 to TBC

get a pressure tester, or take an old sparkplug and weld an air fitting to it

install and pressurize to 5ish psi

Take the oil cap off, if you can hear it coming through the cap then you blew a hole in the piston, ring damage, or a combination

Open the throttle body and take the y pipe plenum off the TB, if you hear air from there, you busted up an intake valve.

If none of that occurred, then it most likely is an exhaust valve. You MIGHT be able to hear it in the exhaust pipe, but it's unlikely.

What you are describing is very similar to a leak down test, which would be what most competent shops would do next, as well as checking the codes. A leak down provides a direct reading of the percentage loss of seal for the cylinder; anything much more than about 10% would mean dropping the engine for a further look. You could also bore scope the cylinder at the same time, again looking for anything out of the ordinary.

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  • 4 weeks later...

There are a few threads on here about CTTs dropping pressure in a single cylinder. Have any of these issues ended up as a pattern of anything but scored cylinders?

Anyway, what about a blown head gasket? These don't always display white smoke or rapid coolant loss. There are testers that check for compression gasses in the coolant; it's a quick and easy test that could rule this out. These testers are quite inexpensive. They look kind of like a clear chambered turkey baster with special fluid that changes color to dark blue if the head gasket is blown.

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  • 7 months later...

I have finally managed to getsome additional diagnostics done.

When testing pressure in Cylinder 8 managed to get upto 50% from arounf 20% initially.

Further camera work displayed pitting, discolouring & scoring on Cylinder 8.

Andvice from the independent garage is that i should look for a new engine.

Does anybody have any experience of someone who can re-engineer such a problem (In the UK)?

I'm wondering now whether to look for a replacment engine or just to sell the car as is (which i am a little reluctant to do)

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I have finally managed to getsome additional diagnostics done.

When testing pressure in Cylinder 8 managed to get upto 50% from arounf 20% initially.

Further camera work displayed pitting, discolouring & scoring on Cylinder 8.

Andvice from the independent garage is that i should look for a new engine.

Does anybody have any experience of someone who can re-engineer such a problem (In the UK)?

I'm wondering now whether to look for a replacment engine or just to sell the car as is (which i am a little reluctant to do)

 

Have you verified the conditions of the valves?  Make sure you've ruled out all other options.

 

Assuming it is scoring you have very few options other than pulling the engine, unforutunately you aren't mechnically inclined but here are some options:

 

1.  Remove head and pan, pop the rod cap off and pull the piston/rod out.  Hone out all the damage (this will only work with minimum depth damage), gap and install new rings and reinstall.  Break in, change oil, and go to town.  I've had success with this in the past on light damage.  I've also been able to do this without engine removal.

 

2.  With heavy damage, you will need to recut the cylinder, the challenge will be seeing if Porsche had plus sized pistons/ring sets.  VW generally always had 3 plus sizes for rebuilding purposes.  Engine will definitely need to be out for this.

 

3.  Buy a used engine and have it swapped in.  The core value of your engine is something you will want to pay attention to.....the shop will probably tell you the core is worthless.....with is not generally true.

 

All in all, if you aren't doing any of this yourself, then my guess is the cost of the labor alone is going to make this painful and force you to think about just moving onto another car.  You put the P name with this and the cost goes through the roof.

 

my guess is the fact that you have 50% compression of the other cylinders means you can salvage this with a hone and a new ring set.

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