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VANOS System And Its Effect On Emissions Testing

2K views 2 replies 3 participants last post by  cvx5832 
#1 ·
Discussion topic.

From Wiki ...

VANOS is a variator system that varies the timing of the valves by moving the position of the camshafts in relation to the drive gear. The relative timing between inlet and exhaust valves is changed.

At lower engine speeds, the position of the camshaft is moved so the valves are opened later, as this improves idling quality and smooth power development. As the engine speed increases, the valves are opened earlier: this enhances torque, reduces fuel consumption and lowers emissions. At high engine speeds, the valves are opened later again, because this allows full power delivery.
As an assumption I would expect the rest state of the VANOS solenoids to be at engine idle ie: lowest RPM = de-energized VANOS solenoids. The default position of all components. That makes sense to me.

At some point, as the engine speed increases, the DME energizes the VANOS solenoids pushing the solenoid pistons forward applying hydraulic pressure to the back of the VANOS pistons and advancing the camshafts via the helical gears to which they are attached. This reduces fuel consumption and lowers emissions according to Wiki. I prefer to think of this in terms of improving fuel consumption efficiency because the phrase is less ambiguous.

So here's the thing. During the emmissions test a gas analyzer is shoved up the tailpipe and the gases are analyzed.

The test is conducted in two phases. At idle and at 2500 RPM and the vehicle has to pass both tests.

It is reasonable, given what I have just laid out, to assume that the emmissions recorded during the 2500 RPM test have to be less than those of idle.

In which case if the VANOS isn't working as it should, advancing the camshafts, then it is going to impact on the emmissions readings of the 2500 RPM test, leaving them more in line with teh idle test, and therefore may impact those readings to the point where the emmissions are greater than expected resulting in the car failing the second test.

How does that sound? Does that make sense?

More importantly, has anyone had an emmissions failure that has been corrected by a VANOS rebuild?
 
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