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post #23 of (permalink) Old 15th September 2011
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Re: Renault - Laguna II - dci Engine Management Light *Fixed*

The MAP sensor (adjacent to the air-box) is used for the fuel control, and is more important to running the car than for turbo control. If the car runs, then the MAP sensor is not affecting the turbo .

Logically, the air filter is ambient, the MAP sensor similar, then the compressor makes the air hot and compressed, the inter-cooler makes the air cold and compressed, and then the engine uses all the lovely oxygen to go bang. The waste gasses power the turbo , (and hence the compressor) before exiting back to ambient.

So the turbo has two control systems; the vacuum one (which is reasonably immune to vibration and heat, so controls the turbo VVT via bellows) and the electrical one (which appears to be a bit delicate).
From this forum, it pays to check the wiring as well as the sensors and actuators, as corrosion of the harness as well as the connectors is not as rare as it should be.

The pressure sensor is on the plastic duct running up from the inter-cooler (radiator area at the front of the engine compartment) to the inlet manifold (at the top rear of the engine).
(The plastic connection to the metal manifold is the shut-off valve; it actuates by vacuum when the engine is turned off, and helps stop over-run; the vacuum runs out after about 20 seconds, releasing the valve, and as such is a useful check of your vacuum system)

Note that it is possible to check if the VVT actuator moves on the turbo under control when the engine is running; similarly, with the engine off, if you squeeze it by hand, you may hear air escaping from unexpected locations. It should be slightly damped (not instant) when squeezing and when releasing.
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