BMW E60 diesel runs rough on a cold start
My E60 diesel runs rough for the first few seconds when cold, what is wrong?
Most commonly the glow plugs or the glow plug control unit, the unit that controls the glow plugs. The glow plugs can be dead even though the glow light flashes normally, and the control unit's power cable can be worn. First make sure from the fault codes that the glow plugs and the control unit are intact.
Why does a diesel start more easily warm than cold?
A warm engine cranks faster on the starter, so the high-pressure pump pressure rises and the injectors open. A leaking injector can keep the pressure too low, so starting fails. A stronger battery or auxiliary power makes it crank faster.
What should you check in the glow plug control unit's connector?
Poor contact in the control unit's power connector can melt the connector and ruin the control unit and the glow plugs. When replacing the control unit, contact paste can be added to the connector. At the same time check the glow relay's wires and connectors, and replace an old relay.
Is rough running normal in freezing weather?
Sometimes. The 3-litre 535d with piezo injectors can run unevenly for the first few seconds in freezing weather, which can be a characteristic rather than a fault. If the running stays rough for long or it smokes, a fault is more likely.