TD5 D2 engine - Wastegate Modulator (1)

Td5 Discoverys are fitted with a Turbocharger Wastegate Modulator controlled by the engine ECU.

It allows greater control (modulation) of the air pressure applied to the Wastegate Actuator mounted on the Turbocharger. In doing so it allows greater control over the generation and delivery of max- boost pressure which benefits the performance of the engine. 

The Modulator is bolted to the side of the engine block behind the water pump. Removing the turbo intake hose will allow easy access to the Modulator body. The four connections are as follows..

(1)  -  Hose connection to the air intake downstream of the MAF sensor. Used to evacuate or 'bleed' the applied turbo boost pressure that builds on the Wastegate Actuator. 

(2)  -  LOWER - Hose connection from the turbo outlet pipe. This supplies the turbo boost pressure used to control the Wastegate Actuator. 

(2)  -  UPPER - Hose connection to the Wastegate Actuator. This hose supplies the turbo boost pressure direct to the Wastegate Actuator. It is the pressure in this hose that is 'modulated' by the solenoid controlled internal valve of the Modulator.

(3)  -  Electrical connector (C0629) connects to the vehicle loom and engine ECU. Supplies live reference and control signals to the internal solenoid as required. The internal valve controls/modulates the connection between (1) and UPPER (2).

(4)  -  Locating bolts x2 (10mm)

Two views of fitted Modulators.

Td5 Defenders are not fitted with the boost modulator and rely on a direct small-bore hose connection from the turbo outlet hose direct to the Wastegate Actuator.

Routing the pipework 'direct' on a Discovery and in effect by-passing the modulator is a workable option, but it will allow 'Wastegate Creep' to develop and compromise delivery of the available boost pressure.

MODULATOR PERFORMANCE  - 

Road Testing

Driving on an 'open' road going uphill will put the engine under max load. The Modulator is designed to assist the engine performance by allowing the turbo to maintain its maximum safe boost level for longer.

Beyond a certain engine rev/boost level (c.2500rpm), the ECU begins to send a variable modulated signal to the Modulator that controls the opening and closing of the internal solenoid valve. 

This has a direct effect on the developing Turbo boost pressure which will begin to stabilise in order to prevent the engine over-boosting. 

If the modulator valve does not operate and stays closed, the turbo boost pressure will continue to build and operate the Wastegate actuator directly. 

Depending on the setting of the Wastegate actuator, this condition will mirror the Defender Td5 set-up and could lead to Wastegate Creep. If the modulator valve fails to close completely when requested then the turbo boost pressure inside the modulator will leak away and potentially full boost or indeed 'overboost' will be achieved before the wastegate valve opens. 

If the engine develops enough Turbo Boost to achieve a dangerous overboost condition, this will be detected by the engine ECU/sensors and trigger a cut-back on the fuelling of the engine. This is a safety measure and it will be felt by the driver as 'hesitation' and the power will seem to cut-off and then return and repeat at the same engine rev. range. LR designed this as a safety feature to protect the engine and its occurrence should NOT be ignored.

MODULATOR PERFORMANCE  -  

Using a 'Nanocom' diagnostic reader

The Nanocom offers a system check that will operate the solenoid when the engine is stationary. The operation of the modulator can be determined by listening for the 'click' of the solenoid.

There is also a number of read-outs on the Nanocom that can be used with the engine running to determine the performance of the modulator.

'DIAGNOSTIC CAPABILITIES  -  SETTINGS' Wastegate Modulator (%) measures the 'duty ratio' of the Modulator as a %. The readings range from 0% to 40% and indicate how long in a given period that the solenoid is active and thereby modulating the Actuator pressure supply.

The Nanocom has a one second sample rate, whereby the Td5 ECU can sample data many hundreds of times per second. 

'DIAGNOSTIC CAPABILITIES  - INPUTS' 

 Wastegate Modulator - as above but shown next to 'manifold turbo pressure'

'INSTRUMENT MODE' - screen 5 - wastegate % Also - screen 1 - engine speed - Turbo pressure

I need to connect the Nanocom to Hx and record these values while driving around to get a better idea of how the engine is currently operating. 

I recently cleaned/replaced the MAP and MAF sensors which each brought big improvements and I have confirmed that the Wastegate Actuator and valve are physically free to move.

REPAIR / REPLACE.

There are no user-serviceable parts inside the Modulator and replacement is the only real option....

The Modulator Solenoid is readily available and it's replacement is an easy task. 

I have read many online comments that speak of the benefits of replacing the unit, but most seem to be related to issues of hesitation or lack of boost which could well be symptoms of a faulty Modulator. Bear in mind that the unit operates by modulation of the control signal meaning it can be cycled open/close very rapidly. After many years use it could well be getting tired, leaking pressure, or sticking.

In the case of Hx, I have noticed how oily deposits from the turbo outlet have been ingested by the modulator, and passed through the wastegate actuator and then deposited into the turbo intake hose. While this could well provide a degree of lubrication, it could also interfere with the internal electrical contacts...

Further reading.

DiscoTd5.com   -  In-depth explanation of the workings of the Modulator.

Discovery2.co.uk  - Good description of the Modulator and its replacement