A Guide to Diesel Engine Problems

Do you know what to do if your diesel engine exhaust is giving off black or white smoke? What about blue smoke? These smoke signals are your vehicle’s way to communicate its needs to you. If your diesel engine is experiencing problems, this guide can help you interpret what it is trying to say.

What could be happening when a diesel engine is hard to start or won't start at all?

• The fuel supply could be low or blocked, and the filters could be to blame.
• The fuel could be contaminated.
• The fuel pressure could be low, or there could not be enough fuel supply at all.
• Check for air leaks in the vacuum in fuel supply.
• Check the crank sensor in the cam.
• The glow plugs could be faulty.
• The diesel injector (or injectors) could be damaged.
• The engine could have low compression.
• The pressure regulator might have a faulty sensor.
• The engine might have low compression.

Steps to follow if your diesel engine won't start:

1. Check the fuel level. If necessary, add fuel.
2. Make sure the fuel cock (the fuel valve below the diesel reservoir) is adequately open.
3. If the engine attempts to start but then immediately stops, it is probably a high pressure injection pump or nozzle malfunction. Replace or clean the diesel injection nozzle and try again.
4. Ensure the speed control lever is well in the "RUN" position.
5. If the engine cranks poorly, check the battery. If it is not charged, recharge or replace the battery.

What if the diesel engine lacks power?

• The fuel could be contaminated.
• The fuel pressure may be low.
• The fuel supply may be low.
• The fuel supply may be blocked.
• The fuel pressure supply pump may be damaged.
• The engine might have air leaks.
• The high pressure pump may be bad.
• The injector blow-by seat may be leaking.
• The turbo may have a problem.
• The air intake may be restricted.
• The internal engine may have problems.
• The pressure regulator may have a faulty sensor.
• The diesel injector may be bad.
• The engine might have EGR problems.

What to check when a diesel engine runs at a lower RPM?

• The high pressure pump may be bad.
• The low pressure supply pump may be bad.
• The air intake may be restricted.
• The diesel injector may be bad.
• The injector wiring harness may be bad.
• The engine may have low fuel pressure.
• The fuel may be contaminated.
• The engine may have air leaks.
• The pressure regulator may have a faulty sensor.
• The crank sensor on the cam may be faulty.
• The injector blow-by seat may be leaking.
• The internal engine may be experiencing issues.
• The fuel supply might be low.

What to check if a diesel engine is knocking or pinging?

• Assess for fuel contamination.
• The injector blow-by seat may be leaking.
• The diesel injector may be bad.
• The fuel supply may be blocked (so check the filters).
• The injector wiring harness may be bad.
• Check the crank sensor in the cam.

What could be wrong if the exhaust is giving black smoke?

• The engine could have low fuel pressure.
• The air intake may be restricted.
• The diesel injectors may be bad.
• The engine may have EGR problems.
• The turbo may have problems. Check the waste gate.
• The injector wiring harness may be bad.
• The crank sensor on the cam may be damaged.
• The high pressure pump may be bad.
• The injector blow-by seat may be leaking.

What could be happening if the exhaust is giving white smoke?

• The turbo may have problems. Check the waste gate.
• The engine may have low compression.
• The fuel may be contaminated.
• The injector wiring harness may be bad.
• The fuel pressure may be low.
• The glow plugs may be faulty.
• The cam may have a faulty crank sensor.
• The engine may have EGR problems.
• The diesel injectors may be bad.

What could be going on if the exhaust is giving blue smoke?

• The turbo may be having problems. Check the waste gate.
• The internal engine may have problems.

As you can tell from this list, multiple problems could have multiple sources, and the same source can cause multiple problems.

If this list is overwhelming, have a trusted mechanic take a look at your diesel engine. If you are able to troubleshoot your own problem and are looking for the parts to fix the engine yourself, you can find any diesel part you may need, from diesel fuel injector pump parts to a camshaft for sale on our website.