Why Is My Diesel Engine Turning Over But Not Starting?

You turn the key, the starter spins strong, and the engine cranks just like it always does. But it never catches. A diesel engine turning over but not starting is one of the more unsettling problems you can run into.

The good news is the causes are predictable once you understand how a diesel actually starts.

How Diesel Starting Works

A diesel engine compresses air inside the cylinder until it gets hot enough that injected fuel ignites on its own. For that to happen, four things need to line up: the engine needs enough cranking speed, the air needs to be warm enough, fuel needs to reach the injectors at high pressure, and the computer needs to allow injection.

Fuel Delivery Issues

Fuel starvation accounts for the largest share of no-start cases. A clogged fuel filter, air in the lines, a weak lift pump, or contaminated fuel can cut off the steady supply needed to fire.

Glow Plugs and Cold Weather

In colder conditions, glow plugs preheat the combustion chamber so injected fuel can ignite properly. When glow plugs fail, you are left with a no-start, especially after the truck has sat overnight in cold weather.

Compression and Injection Pump

If fuel and glow plugs check out, low compression becomes the next suspect. A weak injection pump can produce a similar result since it cannot build the pressure needed to atomize fuel.

Avanti Fleet diesel technicians diagnose no-start conditions for trucks throughout Vancouver and Portland. Contact us the next time your truck cranks but will not catch.