The UK quattro Network
The UK's mobile Audi 5-cylinder mechanic - 07833 654800, 24x7
Specialist in turbos, quattros, electrics and non-starts

Audi WR ur-quattro and Audi 200 KG full throttle fuel enrichment

The ur-quattro and Audi 200 KG engine has four modes of operation:

• Off
• Idle - throttle and idle switch closed.
• Cruise (stochiometric mean - 14.7 air to 1 fuel)
• Full load (maximum power - 12.4 air to 1 fuel, i.e., enriched) - throttle and full load switch open.

The only air/fuel adjustment available is the 3mm Allen mixture screw between the metering head and the paddle's plenum chamber - this is adjusted at idle using a long 3mm Allen key (Audi tool P377). The WR engine has no feedback to the ECU on achieved lambda levels and no way of controlling fuel mixture in any case - mixture levels for all other spheres of engine activity are determined mechanically. The various mechanisms are:

• The paddle in the air mass sensor moves a specific distance for a specific amount of air entering the engine. This movement is controlled by the shape of the cone within which the paddle moves - a Golf GTI cone will not work properly.
• The system pressure applied to the metering head. This is set by a valve in the metering head itself - the valve is easy to replace and adjust (using shims supplied in a kit) as long as a fuel pressure gauge is available.
• The control pressure applied to the top of the metering head plunger by the control pressure regulator (sometimes erroneously called the "warm-up regulator").
• A pneumatic switchover solenoid mounted on the rear bulkhead (19 in the diagram - N54 in the wiring diagrams) energised when the ignition is switched on and de-energised by the upper throttle body switch when the throttle is opened beyound a cruise setting. Note that the wiring diagrams erroneously show this switch as normally open. There are two connectors at the back of the engine bay that will fit on the solenoid - the correct one has a black/green and a brown wire. The other connector has a green and a brown wire and is normally cable-tied towards the right of the engine bay.
• A thermopneumatic valve mounted on side of the head towards the rear of the engine (24 in the diagram).

Only the mixture screw and the system pressure regulator are adjustable. However, it is easy for the enrichment system to fail and reduce high-end performance without this being noticeable to either the driver or unwary mechanic.

Assuming that the system pressure and mixture settings are correct:

• Control pressure should be 1.2 bar with a cold engine, rising to 3.4 bar when the engine is fully warm.
• The throttle body switch connections are physically interchangeable between the idle and full load switches (the latter is the upper one) and these are often found switched around. The black/blue and black/green wires go to the upper switch. Opening the throttle to between 50° and 55° (with the ignition switched on (the engine does not need to be running) should cause the solenoid on the bulkhead (19 in the diagram) to disengage with a distinctly audible click. It should not re-engage even if the throttle is opened to the stop.
• All hoses (and the functions of the solenoid and the thermopneumatic valve) should be checked with a MityVac. These hoses must be airtight for both idle adjustment and full throttle reasons. It is rare to find a WR engine without a fault.
• The thermopneumatic valve (24 in the diagram) should be open below 58°C +/- 3°C and closed above 58°C +/- 3°C

Wholesale hose replacement is usually more cost-effective than detailed debugging.

Single ear clips can be bought from most motor factors and from larger branches of B&Q - take the hose in for them to select the right clips. T-pieces can be bought from the same place. The plastic spigots - especially on the thermopneumatic valve (24) and the solenoid valve (9) - are very fragile and it is recommended that the other end of the existing hose be detached and the component removed from car for the clip to be cut off carefully. The thermopneumatic valve is used on many Audi 100s and 200s, and will be found on the rear of the head. Only the one-way valve (18 on the diagram) is directionally sensitive - the white end connects to the solenoid valve.

Kerbside Motors Home Page and Contact Information