Rover SD1 Efi Archive - Overrun Valve - The Simple View
At it's simplest level the Rover SD1 Efi Overrun valve merely corrects the fuel/air mixture during rapid deceleration with throttle shut so unburned fuel cannot pass through to the exhaust manifold.
However the complexity of the science involved in establishing how this is achieved made for an obsessive wild goose chase that the reader will find either fascinating or totally boring.
Whatever? The simple explanation does not do justice to the technical elegance of the solution so
For my amazing, fully researched scientific analysis - Click Here:
Click any Image to Enlarge
VH - Valve head
VD - Valve disc
SP - Spring
SS - Spring seat
N - Nut
IP - Inlet pipe
CF - Connection face
Mounted on the side of the plenum chamber at the rear of the engine, the connection face (CF) must be airtight. A trace of "instant gasket" when fitting may be used. Sufficient air is provided by this valve during engine Overrun conditions to ensure good combustion.
This is necessary because the very high vacuum during rapid deceleration of the engine causes any residual fuel condensed on the inlet manifold and plenum chamber walls to evaporate and create an over rich mixture.
The pressure differential acting on the valve head (VH) compresses the spring (SP) centralised by the spring seats (SS). Thus, the head moves away from the valve disc (VD) which is trapped by the connection faces.
This allows metered air to pass from the air rail into the inlet pipe (IP) and through the valve into the plenum chamber to optimise the combustible mixture.
A nut (N) adjustment controls the spring tension, which is preset during manufacture and should not be altered. However, if it has been disturbed, acceptable conditions can be restored with the nut approximately 5 turns out from fully closed.
Because the above short explanation does not do justice to the technical elegance of the solution:
My amazing, fully researched scientific analysis is a must read - Here:
The Diagnostic Challenge Continues
This above article is one of fifteen or so presentations on the key components making up the Electronic Fuel Injection System fitted to Rover SD1 Vitesse and Vdp Efi.
Pulling all these components together is the Efi Operations, Test and Instruction Manual enabling Home Enthusiasts to better understand its Purpose, Function and Maintenance.
Click here: for more information
A Major Review of Rover SD1 V8 Electronic Ignition System
Description & Analysis Here:
Components & Testing Here: