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Toyota Service
Toyota Service, Toyota Expert
Category: Toyota
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Toyota sianna: 2007 Toyota sienna v-6 little or no compression

Customer Question

2007 Toyota sienna v-6 little or no compression in rear bank. What could cause this
Submitted: 2 years ago.
Category: Toyota
Expert:  Toyota Service replied 2 years ago.
Hello. Welcome to Just Answer. Please allow me to assist you.
Since you have decent compression on the front bank, I would not thing the timing chain has slipped. If that were so the compressions would be down on all 6
What you most likely have is either a faulty VVT control valve or a failed VVT controller gear assembly on the rear bank. If the oil control valve is sending pressure to the controller gear, it will advance the timing. If the controller gear is stuck, the timing will stay in advanced mode. This will kill the compression as the valve are staying open too long. Ok when running hard, but not ok to start the engine
Based on experience with this issue, I am inclined to think that the VVT controller gear is stuck in the advanced position. Replacement of this unit is a very labor intensive job. The intake needs to come off, the front of the motor needs to come off and the camshaft with the VVT controller gear needs to be removed from the engine in order to replace the controller gear. This is about an 8 to 10 hour minimum job for someone who is not familiar with the disassembly.
If you have any questions, please feel free to reply.
Customer: replied 2 years ago.

We are already "stripped down" to the point that the controllers for the rear bank are easily accessible. Any way to check and/or confirm which component is faulty, oil control valve or controller gear itself? What would happen if we simply pull out oil control valves and rechecked compression?

Expert:  Toyota Service replied 2 years ago.
If you pull out the oil control valves you will have full oil pressure to the controller gear. That advances the timing on the gear. That will not do you any good. If your vehicle was in my shop, I would recommend we replace the controller gear and the oil control valve.