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Yesterday we changed de spark plug & coil pack on cylinder 5.

The car still has failure on idle.

I did notice that the old spark plug was black on the tip & smelled of gas.

Why is this happening? What could be the failure the car is having?

I would appreciate all of your feedback.

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Since you mentioned fuel and you've already swapped the spark plug and coil pack, you could try to swap the fuel injector from cylinder 5 to 6 and see if the misfire follows.

Here's a link to the misfire troubleshooting guide:

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Today im going take out all the fuel injectors and take them to be cleaned.

I'm going to make a mark on the injector on cylinder 5 to keep an eye on it.

When I put them back in I'll let you know how it worked.


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I checked the compression on the cylinders and this was the result.

Cylinder 1: 220

Cylinder 2: 220

Cylinder 3: 220

Cylinder 4: 205

Cylinder 5: 178

Cylinder 6: 210

I'm worried with cylinder 5.

How can I solve this issue?

I would appreciate all your feedback.


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If you repeat cylinder 5 test and add a little oil into the cylinder and the numbers improve then it could be due to worn compression rings and or cylinder wear. Lokasil is known to oval, how many miles on the car/engine?

If the numbers are the same it could be due to valve seat issues.

You might want to consider performing a leak down test which will help pinpoint whether air is leaking through the intake/exhuast valves and/or crank case (through the piston rings).

Comparatively, 4 is also a little low.

Is that a reason to not drive the car and worry about it though? I don't think so.

Edited by logray
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Well I've read from a worldwide renown reputable engine builder that he has seen "ring seal loss" in as little as 25,000 miles.

Some off the top of my head ideas:

Perform the leak down test and compression test as per my advice above. Perhaps the test results were skewed and before you start taking action or going further....

Perhaps try running straight SAE30 break in oil for 200 miles. Drain, and replace.

Or just drive it without worry?

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A leak down test is performed with a 10 gallon or larger air compressor.

The engine should be warm, the intake blocked open, and all spark plugs removed. Open the oil filler cap. The engine set to TDC and locked with the pin (to prevent from turning over).

Start with cylinder 1.

Connect the leak down meter between the air compressor and cylinder.


The leak down meter has two air gauges. The first gauge is the input gauge, which should be provided 100psi. The second gauge reads the percentage loss. For example, if the second gauge reads 90psi, there is 10% leakage.

Listen by ear for where the air is leaking, place a piece of paper over, or blow smoke around the exhaust, intake, and oil filler tube.

Depending on where the air is leaking will tell you where the problem is.

For example if the air is leaking at the exhaust, then the exhaust valves could be a problem, leaking through the throttle body, intake valves. Oil filler tube (through the crankcase), piston rings.

Repeat the test for the remaining cylinders in the firing order, ensuring the cylinder you are testing is at TDC (no valves open). To do this you will have to rotate the crankshaft and lock it at the proper position. Record the results.

Depending on how much leakage there is will also tell you approximate condition of the engine.

"No engine will have perfect sealing with zero percentage loss. Five to 10 percent loss indicates an engine in great to good running order. An engine between 10 and 20 percent can still run okay, but it’ll be time to keep an eye (or ear) on things. Above 20 percent loss and it may be time for a teardown and rebuild. Thirty percent? Major problems. The percent of leakage should also be consistent across the cylinders. Any great differences indicate a problem in that cylinder."

However with compression numbers that you are providing, my guess is there is very little leakdown. However it might provide you with an indication of what the problem with #5 is.

More information here:



Edited by logray
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I havent been able to do the leak down test. But as soon as you start the car it smells a lot like gas.

And when I use it, it has lost a lot of power!

Does this symptoms tell you something?

What could be the problem?

I changed coil packs, spark plug & cleaned all the fuel injectors.

The next thing to do is the leak down test.

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With those types of compression numbers on the remaining cylinders you are going to have great power, despite having one cylinder that is 19% off from the other healthy cylinders. The limit for healthy typically being less than 10-15 psi of difference between cylinders.

As mentioned previously a compression test with a little oil put into the cylinder, if by doing that the compression test shows improvement you could be looking at a problem with the piston rings in that cylinder, or the cylinder itself (for example scoring or oval/warped).

Smell of fuel could be related to the work you just did on the fuel system? These cars have a lot of "normal smells". Sometimes one is a fuel smell on cold startup, especially if the car is just idling and hadn't been driven hard.

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Yesterday we did the test on cylinder 5 adding a little bit of oil and doing the compression test.

The psi value went up to 215 psi.

But we did the same test like 4 times and the values went from 215 to 190.

Could this be the piston rings?

Tomorrow we are doing the leakdown test . But I think it's an air leak problem.

Give me your feedback on this.


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Yes based on the better test results after adding oil, that typically means the piston rings are not sealing as well in cylinder 5.

The leak down test should help confirm where the problem is, whether it would be with the valve seals/guides/seats or the piston rings.

I have been told though by a few reputable engine builders that you cannot expect typical results from the Lokasil cylinder wall material, although your tests are following convention.

What year is your car?, if it is a 3.6L then the cylinder walls are slightly improved over older 3.4L models and the piston ring problem could be a symptom of another problem (such as clogged fuel injector/bad spark/etc.)

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The issue I see here is that the misfire(s) or poor fuel or spark delivery could have already caused a problem with piston rings or ring seal in that cylinder. It could have been that the rings were not seated well in the first place and had nothing to do with spark/fuel and this cylinder has always been down on power.

In any case, if there are no problems found with the valves, and you are still seeing low compression on that cylinder, then the only things left could be problems with the cylinder itself or piston rings. The damage is "done" so to speak. About the only last possibility aside from tear down and rebuild might be trying an oil change with straight break in oil, for example "SAE30 break-in motor oil" for a few hundred miles and trying to get better ring seal by following a procedure such as this: http://www.mototuneusa.com/break_in_secrets.htm. It might be worth a few compression points, but would it be enough to bring that cylinder to within "healthy engine" status, I'm not sure.


Have you used a boroscope on cylinder #5 to see if there is any cylinder wall damage (for example scoring)?

A car with such low miles though, if it is under warranty and Porsche is willing to replace the engine: that would be about the only way I would consider repairing this. I have read about warranty replacement engines for cylinder wall scoring or other issues similar to this.

Sine the car has great power still, and the cost to rebuild the bottom end and replace the piston rings is very high...

If the car is out of warranty, I would just continue to drive the car until it really does need a new engine or major rebuild.

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