Fuel Injection
Cold Start Valve
A cold start valve, sometimes called a cold start injector, sprays extra fuel into the intake while a cold engine is cranking. We list 5 cold start valves from $109 to $226, all from Standard Motor Products, for 1975-2006 vehicles including the Lexus ES300 and GS300, Nissan 280Z, BMW 530i and Geo Prizm.
What the cold start valve does
A cold engine needs a richer fuel mixture to start because fuel does not vaporize well on cold metal. On many older fuel injection systems, the cold start valve adds that extra fuel during cranking only, usually controlled by a temperature sensing switch. Once the engine warms up, the valve stays closed. Later systems handle cold starts through the main injectors, which is why the part is mostly found on older vehicles.
Symptoms of a bad valve
A valve that does not open can cause long cranking or hard starting on cold mornings while the engine starts fine when warm. A valve that leaks or sticks open can flood the engine, causing hard hot starts, black smoke, a fuel smell and rough running. Because a timer or temperature switch often controls the valve, test that switch and the wiring along with the valve before replacing parts.
Fitment and safety
With only five valves in this category, check the fitment table carefully for your year, model and engine, and compare the part number on the old valve. The valve sits on a pressurized fuel line, so relieve fuel pressure as described in your service manual, disconnect the battery, and keep sparks and flames away. Use new seals or washers where the instructions call for them and check for leaks with the key on before starting.
Cold Start Valve questions
Can a bad cold start valve cause hard hot starts?
Yes. If the valve leaks fuel after shutdown, the engine can flood while it sits warm. That can lead to long cranking, black smoke and a strong fuel smell on a hot restart.
How do I test a cold start valve?
A service manual procedure usually checks the valve's resistance and the voltage it receives during cold cranking. Many also check the thermo time switch that controls it. Follow the procedure for your engine.
Does every fuel-injected vehicle have a cold start valve?
No. It was used mainly on older injection systems. Many later engines handle cold starts by adjusting the main injectors through the engine computer, so they have no separate valve.