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Audi A6 The mid-sized Audi A6 model offers more room to the driver and passengers over the A4 line.
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Old 12-12-2010, 11:56 PM
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sooo the A6 wont start, it tried to start the first time and idled (really roughly) for about 10 seconds and died. I pulled off the timing belt cover and the belt is still intact, I have both fuel and spark, but the engine has zero compression... any thoughts?

I was thinking that either it jumped time or that the engine was flooded (I read a few things about the thermostat crapping out and causing the engine to flood).. any ideas are appreciated, the car is a 99 a6 2.8L 30v
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Old 12-13-2010, 07:49 AM
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Assuming you pulled all the plugs and cranked the engine to test the compression, you would have cured any flooding issue. 0 compression means valves have hit pistons. Ouch!

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Old 12-13-2010, 08:16 AM
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Is that 0 compression in every cylinder? It is likely the timing belt is intact but a tensioner has failed and let the belt slip, either damaging the valves or just skipping time. Thsi is the only way all cylinders could lose compression all of a sudden. Suffice it to say, with no compression, you are in for a major repair.
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Old 12-13-2010, 12:47 PM
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well we pulled everything apart today, and got down to the timing belt, and its still in time, and the belt is still intact. so what now? is it possible that if it had flooded that could give me a reading of zero compression?
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Old 12-13-2010, 01:04 PM
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Once again, are you saying 0 compression on all cylinders or just a couple? Do you really mean 0? Or is there residual pressure. What values are you getting?
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Old 12-13-2010, 01:18 PM
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i would like to know how you are measuring your compresion . Flooding has nothing to do with compresion. if you have 0 compresion the valves are not sealed when you crank the engineon the compresion stroke. I think we need more details of your analytical process to help you .
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Old 12-13-2010, 03:54 PM
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well I just went through and retested the compression on all 6, and there must have been something wrong with the guage, because it was reading 0 but when we took the guage off you could feel that there was some compression when cranking, but not near as much as there should be. So I guess after some reanalysis, its not that I have 0 compression, I have some but the tester wasnt getting a reading.
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Old 12-13-2010, 05:28 PM
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after you get a new guage -- repost
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Old 12-13-2010, 08:18 PM
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I watched a tech I used to work with tear down an engine because it had "0 compression on all cylinders". Had a no-start condition, had spark, fuel pressure, etc. His gauge was bad. The car had a rotor (inside the distributor) that got loose, so as it cranked, the rotor free-wheeled, giving it the illusion of having proper spark. It just wasn't at the right time. Couple that with a bad compression tester...

Anyways, moral of the story: Think about it first. Will an engine ever have 0 psi all cylinders? Not likely. Possible, not likely. When it cranks (full battery charge, all spark plugs installed) does it sound the same as it used to? You can hear an engine with low compression. It'll crank really fast, and won't sound like it's "pumping". It'll just make a "weeeeeeeee" sort of noise. Not a "na-na-na-na" sound.

Flooding does affect compression. Fuel can wash the oil away from the piston rings. The oil actually is what keeps compression. This is especially true on rotary engines, but not as big of an issue with piston engines.

Here are some simple diagnostic procedures you can do.

Does it have fuel in the tank? Fuel pressure? Spark? How do the spark plugs look?

Last edited by AGreen; 12-13-2010 at 08:25 PM.
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Old 12-14-2010, 12:58 AM
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Sounds like a typical coolant sensor problem now that the weather is changing. They go bad quite often and can prevent your car from cranking when cold and would cause a rough idle for several minutes if you can get it cranked when cold. Definitely do a proper compression check to verify that you don't have the proper compression, that can rule out the coolant temp sensor.
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Old 12-14-2010, 12:58 AM
 
 
 
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