Intermittent miss on a IX...advice???
Jun 12, 2008, 05:58 AM
#31
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Yes the car would stumble if blipping it while cold. Turned out the be a bad valve seal or burnt valve I guess. I Really dont see how that would happen. I bought the car basically new and I know the previous owner babied it like no other. I get the car back tommorow though from the dealer. I guess they have seen a few cases of this on very early IX's as mine was one of the first IX's in the country.
I was under the impression that if a compression and/or leak-down test was good then everything would be fine. If this fixes your issue I guess that isn't the case.
Jun 12, 2008, 06:50 AM
#32
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I feel the need to clarify something here for those that don't know,
Compression and leak down test are indeed two very different tests.
Compression test= cranking the engine with a pressure gauge inserted into the spark plug hole. The gauge has a one way valve in the hose between the cylinder and the gauge. As you crank the engine over with the starter, the gauge will measure the maximum cranking cylinder pressure. This is a good indicator of general engine condition. But a small leak may be missed due to the fact that there is a 10% difference in cylinder pressure allowed. You also (usually) can't hear air leaking from different places.
Leak Down Test = Using an air compressor to fill the cylinder with air through the spark plug hole. There is a valve in the hose between the compressor and and the gauge. You shut off air to the gauge when the cylinder is at shop air pressure and measure how fast the air leaks out of the cylinder.
Now here is where a leak down test will identify a bad valve if done properly. When that cylinder is full of air, you will here air leaking out of the intake manifold if there is a bad/leaking intake valve. If there is a bad/leaking exhaust valve, you will here air leaking out of the exhaust.
In the 16 years I have been building and repairing engines, I have never seen an engine with a bad valve pass a leak down test. If someone told you guys it did, then maybe it's time to find a better mechanic. Did the dealer show you the results of the leak down test? Ask them to show you, then post it here. We can then see the results and analyze them. Since the dealer is doing the work for free
, let them do it.
I'm really curious to see the results now. Please keep us posted.
Compression and leak down test are indeed two very different tests.
Compression test= cranking the engine with a pressure gauge inserted into the spark plug hole. The gauge has a one way valve in the hose between the cylinder and the gauge. As you crank the engine over with the starter, the gauge will measure the maximum cranking cylinder pressure. This is a good indicator of general engine condition. But a small leak may be missed due to the fact that there is a 10% difference in cylinder pressure allowed. You also (usually) can't hear air leaking from different places.
Leak Down Test = Using an air compressor to fill the cylinder with air through the spark plug hole. There is a valve in the hose between the compressor and and the gauge. You shut off air to the gauge when the cylinder is at shop air pressure and measure how fast the air leaks out of the cylinder.
Now here is where a leak down test will identify a bad valve if done properly. When that cylinder is full of air, you will here air leaking out of the intake manifold if there is a bad/leaking intake valve. If there is a bad/leaking exhaust valve, you will here air leaking out of the exhaust.
In the 16 years I have been building and repairing engines, I have never seen an engine with a bad valve pass a leak down test. If someone told you guys it did, then maybe it's time to find a better mechanic. Did the dealer show you the results of the leak down test? Ask them to show you, then post it here. We can then see the results and analyze them. Since the dealer is doing the work for free
, let them do it. I'm really curious to see the results now. Please keep us posted.
Jun 12, 2008, 07:23 AM
#33
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I 100% agree with you that a leak down test will show if a valve is leaking where the valve seats against the head.
However if it is the valve seal that is bad the leak down test wont show crap. The car will only throw the P0300 after it is warm. I was under the impression that for the valve seal to be the culprit there would be visible smoke. My car has visible smoke, but only when you first start it and blip the throttle. Once the car is running for more than 30 seconds there is no visible smoke.
However if it is the valve seal that is bad the leak down test wont show crap. The car will only throw the P0300 after it is warm. I was under the impression that for the valve seal to be the culprit there would be visible smoke. My car has visible smoke, but only when you first start it and blip the throttle. Once the car is running for more than 30 seconds there is no visible smoke.
Jun 12, 2008, 08:53 AM
#34
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Yes, you are correct. A bad valve seal will leak oil into the combustion chamber while the motor sits over night. Yes, this can cause an intermittent miss at start up, that will blow some blueish white smoke. Usually the smoke will dissipate shortly after start up. A bad valve guide could also cause this situation. It stinks that our ecu's will detect a miss at start up.
Just for my info, how long does it take for your car to clean up after you start it up? Everytime it is about 30 seconds?
Just for my info, how long does it take for your car to clean up after you start it up? Everytime it is about 30 seconds?
Last edited by turboracer; Jun 12, 2008 at 11:08 AM.
Jun 12, 2008, 11:23 AM
#35
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Our ECU will not detect a miss at start up. The coolant has to reach a certain temp before the car will throw a P0300 code.
If I do not blip the throttle within the first 20-30 seconds of starting there will never be any visible smoke. At least not enough to notice in the rear-view. I will have to get out real quick after starting it tomorrow morning to look.
If I do blip the throttle it will last for just a few seconds.
If I do not blip the throttle within the first 20-30 seconds of starting there will never be any visible smoke. At least not enough to notice in the rear-view. I will have to get out real quick after starting it tomorrow morning to look.
If I do blip the throttle it will last for just a few seconds.
Seems that is has turned out good.
Jun 14, 2008, 06:58 AM
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Jul 25, 2008, 12:03 PM
#44
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?
I have a similar problem but no code. I have slow throttle response and rough idle. And the car stumbles if blipping it while cold. No boost leaks and I put new spark plugs and car still runs like ****.
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