Why Won't My Engine Start?

Michael Borg — 10 September 2015

An engine basically needs five main ingredients to run correctly – air and fuel to burn, compression to prepare the mixture for ignition, spark to ignite the air/fuel mixture and the correct timing to make sure it all happens at the right time. So, when it comes to diagnosing a problem, the very first step is to find out which ingredient is missing.


You’ll want to ensure fuel is getting from the fuel tank to the engine. So try disconnecting the main fuel line after the fuel pump either from the carburettor or injector rail inlet and crank the engine over to see if any fuel comes out. Don’t attempt this if you own a common-rail diesel engine as the fuel system operates under mind-blowing pressure (well over 20,000psi), and can be extremely dangerous if you’re not familiar with these systems.

The most common causes of failed fuel flow are a blocked fuel filter or a failed fuel pump, but don’t forget the simple things like simply running out of fuel (maybe a leaky fuel tank?), or the fuel pump can’t pick up the fuel while you’re on a steep hill.

If you’ve just fuelled up the tank, grab a sample of the fuel in a clear container and check it’s not stale or contaminated with water.


Next up, check you’ve got spark. The most common spark-related problems in the bush are usually getting water in the distributor, having loose wiring to the coil or having fouled or worn spark plugs.

To check for spark, you’ll need insulated holding tools to avoid electrical shock. Remove the spark plugs, and check for a bright blue spark jumping from the end of the high-tension lead held close to each sparking plug cap terminal as you crank the engine. A weak spark is often yellow in colour.


Your engine needs plenty of clean air to run properly. So make sure the air intake system is clean and free from any debris. Pay particular attention to any sticks or twigs that may have clogged up your snorkel, and make sure the air filter isn’t blocked or soaking wet.

The easiest way to check if this is the problem is to remove the air intake tube from the carburettor or throttle body and see if it makes any difference.


First things first – you’ll want to make sure the battery is fully charged and able to crank the engine over with enough speed. A good indication that the battery is a bit low is when your interior lights or headlights dim as you crank the engine over. It’s also worth checking that any earth points, starter solenoid wiring along with any other starter connections are still nice and tight and free from corrosion.


This problem is usually either a bad wheel bearing or tyre noise. One way to distinguish between the two is to drive the vehicle at around 80km/h, and swerve from side to side. If the noise goes away or changes pitch when you swerve, there’s a good chance the wheel bearings are buggered. The change of pitch is actually due to the weight of the vehicle transferring as you swerve.


1. Air in the fuel system

One problem that can stop a diesel in its tracks is getting air in the fuel delivery system. In this case you’ll need to bleed the system for air, but it’s worth trying to figure out how it got in there in the first place. A faulty fuel filter seal, damaged fuel hose or loose injector are the most common suspects.

2. Fuel cut-off solenoid

To turn your diesel engine off, a fuel cut-off solenoid basically cuts the fuel supply to stall the engine. So, if you don’t have fuel getting to the injectors, check that this solenoid has power when the ignition is on and the solenoid is open. Also check the wiring is not damaged or the vacuum lines are in good condition if vacuum operated.

3. Slow starts and glow plugs

Glow plugs are used to pre-heat the combustion chamber before you try starting the engine. If they’re faulty, it makes it very hard for the engine to start when cold. So, check the glow plug fuse is okay, and there’s power to the glow plugs.

Three common offroad problems

1. Squashed exhaust

The last loud bang you heard underneath your 4WD could well have been your exhaust. So make sure it’s not squashed and blocked, which could cause problems like a lack of power. 

2. Scrapping brake shoes

After clawing your way through a couple of creek crossings, it’s fairly common for rocks to get caught up between the brake linings and brake drum. So, if you hear a squealing noise from your brakes, there’s a good chance that’s the problem. It’s a good idea to clean the rocks out before they damage the brake linings too.

3. Drowned distributor

Petrol engines can begin to cough and splutter after bonnet-deep water crossings. If this is the case, pop the distributer cap off and see if any water has got inside. Also check the high tension leads and coil plugs while you’re there.

Check out the full feature in issue #92 September 2015 of Camper Trailer Australia magazine.


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