The customer reported that the car starts, runs for a few seconds and then shuts off. The Check Engine light is on. Pulling codes revealed a P0341 CMP/CKP (camshaft/crankshaft) synchronization error. The computer constantly looks at the camshaft sensor waveforms, and compares them to the crankshaft sensor wave form to make sure that the camshafts are in time. In the event of a mechanical failure and the waveforms get out of sync, the computer shuts the engine down to try and prevent further damage. The customer reported that several people have already looked at this, including removing the valve cover to inspect the timing ,marks and failed to find the cause of the problem.
Since the car runs for a few moments that's plenty of time to get a compression waveform.
The cursors mark the two compression peaks, so between them is all four strokes of the engine starting with decompression, then the exhaust, intake, and the next compression stroke. By measuring the time in between the cursors, you can divide by four and then mark the individual strokes of the engine and see if the camshaft is in time or not.
The total time between the cursors was 99.2ms, divided by 4, that's just about 24.9ms, so the one cursor gets moved to first display the decompression stroke which is when the crankshaft turns from TDC (top dead center) to BDC (bottom dead center) and then the second one gets moved to show the exhaust stroke as the crankshaft turns back to TDC.
See the rise in pressure at the end of the exhaust stroke? That means the cylinder pressure was rising when the exhaust valve should have still been open during the overlap of the intake valves and exhaust valves. You can see the pressure start to drop just before TDC, that's the intake valve opening.
So when did the exhaust valve open, and how far out of time is the exhaust camshaft?
The waveform is created by two full revolutions of the crankshaft, so that's 720 degrees of rotation that took place in 99 ms. Dividing 720 by 99 gives us just over seven degrees of rotation per ms.
The point where the waveform stops dropping on the decompression stroke shows us when the exhaust valve opens. By placing a cursor at that point, and multiplying the time elapsed from TDC you can see that the exhaust valve opened up about 56 degrees after TDC, that's about 90 degrees early! That also explains why the exhaust valve closes to soon.
So it's confirmed that no matter what we see with the timing marks when we get this apart, the camshaft is out of time, and the computer is correct in setting the P0341.
Questions?
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