Question about 2005 Porsche Cayenne Turbo

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Posche Cayenne Trubo 2005 cylinder 5 gives only 20 compression what could be the reason, no overheating nor overrev If the cause is a valve, how could have happened?

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You could have a cracked block or worn rings. Even with no over-revving or overheating bad oil or low oil can cause this to happen. Could also be a defective part.

Posted on Dec 16, 2013

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Have a spark plug not firing.


Are you sure it's actually a plug?
Are you getting oil on the plug?
The plug may be firing but you may be losing compression which gives the symptoms of a misfire. As you've changed the plug, lead and coil this points to to a problem elsewhere.

Your first course of action should be to get a mobile mechanic carry out a diagnostic check for you.

To put your mind at rest, do a 2nd compression test using a light oil squirted into the bores:

Doing a Compression Test
Warm the engine. Remove all the spark plugs.
Get a pencil and piece of paper to note down the readings.
Put the compression tester into the No1 cylinder and crank the engine for 10 seconds.
Note down the compression reading.
Repeat process for all cylinders.

Here's an illustration of what you may expect on a 4 cylinder engine:
Cylinder 1 2 3 4
psi 125 122 120 124

125 is the uppermost figure for that engine. Here, this engine is fine. There's a slight variation in psi figures, but that's perfectly normal.

Here's the same engine:
Cylinder 1 2 3 4
psi 110 112 114 112

The psi reading is down. However, as all the figures are pretty much equal it doesn't indicate head /gasket problems. It may point towards worn pistons or burnt valves.

Now consider these psi readings:
Cylinder 1 2 3 4
psi 125 84 86 124

There's more than a 10% drop - a difference - between cylinder 1 and 2, and cylinders 3 and 4.
The compression readings for cylinders 2 and 3 is down; low. There's something clearly wrong.

It suggests that there is a defective head gasket between cylinders 2 and 3 or a crack in the cylinder head. The rising piston compresses the gases which escape into the adjoining cylinder via the defective gasket or cracked head.

However, it could also mean that there is a problem with the valves (burnt/not seating properly) or perhaps piston / ring problems.

A burnt valve - it's usually the exhaust valve as they bear the brunt of the combustion - can cause a reduction in engine power simply because the combustion process isn't occurring properly. Compressed air/fuel gets squeezed out of that cylinder because of the damaged valve . There even may be a misfire - a surge as the car runs.

Worn or broken piston rings allow compressed gases to leak past into the crankcase. A compressed crankcase can force oil out of the dipstick tube. The pressure in the crankcase will leak to atmosphere anywhere it can find an outlet.

The 2nd Compression Test
The second compression test is known as a 'wet test'. The first compression test was the dry test because no oil was added to the bores. The second 'wet' test can give an indication of whether it is the rings or valves at fault (though bear in mind rings and valves do not cause overheating or water in the coolant symptoms).

Spray a liberal amount of light penetrating oil into each cylinder - aim for the cylinder walls, not the centre of the piston. You want the oil to run down the cylinder wall and around the piston to form a seal.

Place a rag over each spark plug hole and spin the engine to eject the surplus oil.

Then carry out a full compression test noting down the results.

Here's the previous results with the 2nd compression readings added:
Cylinder 1 2 3 4
psi 125 84 86 124
Wet 128 112 110 126

The readings have increased. This because the oil sprayed into the bores has formed a temporary seal around the piston, thereby enabling the compression to be raised. It also indicates that the bores/rings are worn on cylinder 2 and 3 - the 'oil seal' has increased the readings but is still low in comparison with cylinders 1 and 2.

This could also indicate that in addition to worn rings there is also burnt valves. Oil cannot form a seal around a valve. A worn or split valve will cause a low compression reading and misfiring symptoms.
Compressions readings should be taken in conjunction with other symptoms. It will help you identify the problem:

Low compression readings between two adjoining cylinders point towards a head gasket/head fault if your vehicle has shown signs of coolant loss, coolant in the oil system - mayonnaise, overheating, rough running and lack of power.

If those symptoms are not present it points towards burnt valves/piston rings. A worn engine may be difficult to start and pressurise the crankcase, but it doesn't cause overheating problems.

Feb 09, 2016 | Cars & Trucks

4 Answers

Holden viva 2005 wagon auto electrician said there is no compression in number 4 cylinder and not much in number 1 and maybe the valve could have been damaged? Advice appreciated please.


The valves allow air and gasoline to enter the combustion chamber, to be ignited by the spark plug, and to allow the burned gases to be exhausted from the chamber.

When the valves do not work, a mechanic needs to remove parts of the engine, to see what's wrong, and to make repairs.
It could cost you $500 to $1000 US dollars.

Maybe, time to "junk" the TEN-YEAR-OLD vehicle, and buy another one ???

Apr 20, 2015 | Holden Cars & Trucks

1 Answer

Mis fire on cyclinder one and overheating for an 2005 Chevrolet equinox


You are describing the classic symptoms of a blown head gasket from the cylinder into the water jacket. This causes loss of compression in the affected cylinder and also injects hot gases into the cooling jacket resulting in overpressure and overheating of the coolant. Perform a compression check of all cylinders and if any are appreciably lower than the others, you are looking at some major engine work.

Aug 02, 2014 | 2006 Chevrolet Equinox

1 Answer

Ford escort 1996 1.8i - running on 3 cylinders, changed leads have spark


Determine what cylinder is misfiring and do a compression test on that cylinder. Compare it with a cylinder that is not misfiring. You should have no more than 20% difference between the good cylinder and the bad cylinder. If it is low on compression, suspect a burn valve or bad valve seat... and it will require cylinder head repair. If it is good on compression, then look for a faulty injector or some other reason for the misfire on the dead cylinder.

May 13, 2014 | 1998 Saturn SL

1 Answer

93 Ford Ranger 4cly. running rough and back firing out exhaust, has had a tune-up. Could the Mass Airflow cause this problem, no change in engine when unplugged.


Timing may be off. Have you checked it? Back firing could be valve timing problem; could also be too much gas-check injector spray pattern-should see a cone shaped pattern of fine mist on the throttle plates when cranking engine-this is if you have throttle body injection.
For $20-$30, you can buy a compression gauge tester and check engine compression. On a warmed up engine, pull all spark plugs, disable ignition and fuel delivery (pull injector fuse or unplug injectors), hold throttle wide open, and check compression on each cylinder by cranking engine over about 7-10 revolutions-the same amount for each cylinder, about 4-5 seconds each. All cylinders should be nearly even and balanced. Lowest cylinder should be at least 75% of highest reading cylinder. For any low reading cylinder, put a squirt of oil (about a tablespoon) in that cylinder and retest compression: if compression rises, rings are worn. If compression does not improve, valves are the reason for low compression-valves may be burnt or not sealing good.
I would do the compression test-on an engine that old, before putting expensive parts into it, you should know if the engine's internal mechanical condition is good first.

Oct 13, 2013 | Cars & Trucks

1 Answer

1993 accord has dead cylinder


I have seen many of those years Accords with a burnt intake valve, from too much EGR gas entering only one cylinder, overheating and eventually burning and breaking that valve. This causes the valve to not be able to seal the combustion chamber, resulting in no compression and no power from that cylinder. You will have to remove the head and change out the broken valve. When done replacing the valve, clean out the EGR ports in the intake or the valve will be damaged once soon. Those blocked EGR passages are what cause the burnt valve problem in the first place.

Jul 14, 2012 | 1993 Honda Accord

1 Answer

No compression and turns over fast, but wont start on terracan 2002


Have you performed a compression check on all cylinders? Possible reasons for no compression are: Blown head gasket, No valve clearance. Valves stuck in open position. Collapsed piston rings from extreme overheating of engine.

Mar 12, 2012 | Hyundai Terracan Cars & Trucks

2 Answers

Low compression in cylinder 4


When an engine has a cylinder with low compression it will be caused by a mechanical malfunction, and the reasons for low compression in a cylinder can be a bent or burnt intake or exhaust valve, or a valve that is not closing all the way because of a piece of carbon or an improper valve adjustment, the head gasket could be faulty around the compression sealing rings, or the cylinder head could be warped or even cracked, and the piston for that cylinder could be damaged with a crack or a hole, or the piston rings could be worn out or damaged.

The cause of the low compression can be determined without having to dis-assemble and inspect the engine by a "Compression Leak-Down Test" and a good repair shop or someone with a compression leak-down tester and a good air compressor can perform that test.

Jun 19, 2010 | 1983 Ford Ranger

2 Answers

Loss compression


How to Test Engine CompressionAn engine depends on an equal compression reading in each cylinder to run smoothly. If poor compression exits in one or more cylinders it can cause a rough idle condition and low power. A compression test can be performed to check wear or internal damage. To start a engine compression test gauge is needed. There are two types of gauge styles, one threads into the spark plug hole which is more accurate. The other style of gauge is constructed with a rubber plug that is meant to be pressed against the spark plug hole, this style of gauge is difficult to use. To perform a engine cylinder compression test follow the steps below.
  • Remove ignition coil connector or ignition system fuse to disable power to the ignition system
  • Test ignition system to ensure that the power to the system has been disabled
  • Remove #1 cylinder spark plug and insert compression gauge, most gauges have a hose attachment that is installed into the spark plug hole with the gauge connecting to the gauge hose.
compression_gauge.jpg
Engine Cylinder Compression Gauge
  • After the compression gauge has been inserted, use the starter to crank the engine over for about five seconds. Use about the same five seconds to test the remaining cylinders.
  • Record the compression reading as each cylinder is tested
  • Remove the compression gauge and reinsert the spark plug
  • Follow this procedure until all cylinders have been tested
  • Compare cylinders compression reading, all readings should be within about 5% of each other
If low compression exists a cylinder malfunction exits and further inspection is required. Possible causes for a low compression condition are: burned intake or exhaust valve, broken piston or piston ring, broken valve spring or a blown head gasket.

May 31, 2008 | 2000 Hyundai Tucson

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