Volvo’s Variable Valve Timing

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What VVT actually does

When Volvo switched to the ME7 engine management system in 1999, they added variable valve timing. At first, only the exhaust cam had it, but after 2005, both intake and exhaust cams employed VVT. The exhaust-only implementation of VVT was primarily for emissions compliance, as it allowed for the removal of the EGR and SAS systems. The intake side VVT was added to increase engine performance.

Cam timing controls when the valves open and close. Retarded timing means the valves open and close later; advanced timing means they open earlier. Each setting favors a different part of the rev range:

  • No power to the VVT solenoids (cams retarded): maximum peak power at the top end, but at the expense of low-end torque. This is why an engine without working VVT feels noticeably flat below roughly 4000 RPM.
  • Power to the VVT solenoids (cams advanced): the cams advance, restoring strong low-RPM power.
  • With VVT working: the VVT hubs position the camshafts dynamically, so you get the best of both – greater torque down low and more peak power up top. In short, VVT widens the powerband and increases the usable power of the engine.

How M4.4 controls VVT and where it differs from ME7

The VVT routine we’ve added to M4.4 is open-loop control: the ECU tells the solenoids what to do, but never checks where the cams actually are – there’s no feedback from the cam sensor. ME7, by contrast, monitors cam position and corrects it live (closed-loop control). So M4.4’s cam control isn’t as refined as ME7’s, but it still gives a significant boost to the width of the powerband.

Why cam timing must be spot-on with a VVT head

When you fit a VVT head to a non-ME7 car, getting the cams timed perfectly matters more than it does on ME7:

  • ME7 forgives small errors. It dynamically corrects for cam timing deviation, and only sets a fault code (DTC) if the timing is off by more than 11º.
  • M4.4 can’t adjust at all. It has no ability to dynamically correct the cam angle – what you set at install is what you’re stuck with.
  • Using a cam lock tool isn’t a guarantee. Even when using a cam lock tool, it’s still possible for the timing to be a bit off.

That’s why, when using a VVT head on an M4.4 car, I add a few extra steps to the normal timing belt process. Here’s a complete breakdown of the timing procedure that guarantees the VVT cams are timed perfectly:

  1. With the timing belt fitted and tensioned, rotate the crank to the reference position (indicator on the block pointing to the valley between the crankshaft teeth) and lock the back of the cams in place with the Volvo OEM-style tool.
  2. Take the timing belt off.
  3. Rotate the crank 1/2 tooth counterclockwise. The indicator on the block should now be pointing directly at the notch on the crankshaft pulley tooth.
  4. Rotate the VVT hubs clockwise until they reach their limit position.
  5. Loosen the three cam gear bolts (10mm, or 8mm on some cars) just enough so that the gears can move independently of the cams.
  6. Rotate the cam gears so that the reference tick is approximately at the 11:30 position.
  7. Install the belt, starting at the crank and working your way clockwise. With the cam gears free to rotate, the timing belt will easily line up with the gears while the hubs stay fixed in place.
  8. With the belt in place, tighten the three perimeter cam bolts on both cams to 10 ft-lbs. Use of blue thread locking compound is advised, but not necessary.
  9. Set the tensioner so that the indicator points slightly to the right of center.
  10. With the cams still locked in place, rotate the crank clockwise until the free slack in the belt is taken up and you can no longer rotate the crank.
  11. The crank should now be exactly at the reference position.
  12. Inspect the tensioner and retighten if needed – it usually is.
  13. Remove the cam lock tool, rotate the crank four full revolutions, ending at the reference position on the crank.
  14. Verify your work – if the timing is set correctly, the cam lock tool will bolt back in place without having to move the cams at all.

Timing the motor this way guarantees the cams end up in exactly the right place. Having done many timing belt jobs on ME7 cars and noting the cam deviation each time, I’ve found this procedure gets the cams to within 1º of spec.

Never rotate the engine counterclockwise once the belt is fitted – this removes slack from the VVT hubs and will throw off your timing.

For those using a VVT head without VVT control

When a VVT head is used without VVT control, the low-end torque of the engine will be greatly decreased. To alleviate this, the static timing of the cams should be set so they’re centered in their total range of adjustment. While this does decrease peak power, the increase in torque is well worth it.

When in its default, unpowered state, the VVT hub is dragged to its most retarded position. To set the cams in the middle of their range, the cams need to be advanced (rotated clockwise).

Volvo used hubs with varying degrees of adjustment, but the majority of gray exhaust hubs had a total adjustment range of 16º and the blue intake hubs had a total adjustment range of 28º. While the timing belt is off, confirm the total adjustment range of your cams – divide this number by 2 to determine how much to advance your cams.

To accurately advance the cams, you’ll need a magnetic digital protractor, like the Klein 935DAG. The process:

  1. Time the cams to factory settings using the procedure outlined above.
  2. Remove half of the cam locking tool from the intake cam, leaving the other half still bolted to the back of the exhaust cam.
  3. Set your reference 0º datum by zeroing the magnetic protractor on the flat spot on the valve cover, between the two cams. Then move the protractor to the ‘arm’ of the cam locking tool still in place.
  4. Loosen the three perimeter bolts on the VVT cam gear.
  5. Rotate the cam clockwise, using the interior T55 bolt directly screwed into the cam (not the center cap for the hub). With the cam gear loose, the hub and cam will be free to rotate while the belt and gear stay fixed in place. Sometimes, due to friction, the cam gear and belt will want to rotate with the hub. If this happens, you’ll need someone to hold the gear and belt in place while you turn the hub – a strap wrench works well.
  6. Using the digital protractor as your reference, rotate the cam to half of the hub’s total range of adjustment.
  7. Once the exhaust cam is adjusted, remove the cam locking tool, and if your engine has dual VVT, install the intake side of the tool.
  8. Reset your protractor and repeat the same operation on the intake side.
  9. Due to the greater adjustment range of the intake hub, you’ll advance the intake cam a bit more than the exhaust.
  10. Torque the three perimeter cam gear bolts to 10 ft-lbs. Use of blue thread locking compound is advised, but not necessary.