Exhaust Camshaft Timing Errors

Scott Manager Claremont, California Posted   Latest   Edited  
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Driveability
Propulsion
2004 Mazda 6 S 3.0L (D AJ) 5-spd—1YVFP84D845N94129
P0300 - Random/Multiple Cylinder Misfire Detected

This vehicle arrived with the MIL on and a complaint that the engine performance seemed to have dropped off. Customer has been driving this vehicle for 300k+ miles. FF Data

After investigating, we found that the bank 2 exhaust camshaft had jumped time in the advance position. We didn't see this at first in our cranking compression test where using the Pico Diagnostics app but the bump between the compression strokes should have been a clue. Figured that we'd share this data here hoping in can benefit someone in the future.

Initial running compression test on Bank 2 (Faulty)

Post repair running compression test on Bank 2 (Good)

Here are the Pico Data Files:

diag​.​net/file/f4789x9mh…

diag​.​net/file/f2jyikwkf…

diag​.​net/file/f1jkul3gn…

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Bob Owner/Technician
East Longmeadow, Massachusetts
Bob
   

Exhaust cam is very advanced. As the piston rises on the exhaust stroke, the ex valve closes early which traps some spent exhaust gases. This causes the pressure to rise as the piston is rising on the exhaust stroke. Hence the pressure spike near the 360 deg mark. As soon as the intake valve opens the pressure in the cylinder drops. If there were a transducer in the intake you would see a

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Scott Manager
Claremont, California
Scott
 

Thanks for chiming in here Bob. Yes you're right and as you can see we didn't have a sample signal in the intake but I wish we would have. However I believe that in some cases this intake signal disruption might be hard to see depending on manifold design. One thing here that I wanted to emphasize is that we performed the relative compression test and failed to recognize the small bump in this

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Bob Owner/Technician
East Longmeadow, Massachusetts
Bob
 

I understand. I have been know to miss little details like that when I'm in a rush to get the work out the door and I don't take the time to "analyze" my test results.

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