When the Rover SD1 Efi engine is started from cold the initial requirement is to provide a rich mixture to make the engine snap into life. The colder the engine the more time may be needed to allow the engine to fire and run.

Uninformed mythology surrounding the thermotime switch and the cold start injector would have one believe that they are collectively responsible for all sorts of fault conditions, when in truth, both components are relatively benign. Indeed, in a mild climate like the UK, the cold start system can be permanently disconnected without much adversity and many owners choose to do that

Yes! On a very cold morning the cold start system will encourage a properly tuned engine to fire up quickly but the same effect can usually be achieved by giving the accelerator a couple of sharp boots-full during cranking. After that the system is self-redundant when restarting a hot engine.

Yes! A faulty thermotime switch can cause uncontrolled over-fuelling during cranking if the internal contacts are permanently closed. Also the cold start injector can cause over-fuelling if its injection orifice is corroded or contaminated causing it to leak fuel continuously.

As with most components of the Rover SD1 Efi System, substitution of the thermotime switch and the cold start injector can be an alternative (short cut) route to fault diagnosis although this does not detect any supply, wiring or connector problems.

On the other hand, the key to successful fault analysis is a practical understanding of the components and the effect that fault conditions have on system operation. This article explains the nature and operation of the cold start process and how to carry out approprate tests.

The contents of this article are listed above. Read or download it in PDF format here (61kb)

Please advise of errors and omissions.