DIESEL ENGINE PROBLEMS

The innovation of the computer-generated fault diagnosis has led us to lose sight of the basic operating principles of the diesel engine. Unfortunately, the fault codes don't always pinpoint the problem but rather bring up an array of codes that could be either this or that. Being told: "we have tried this and it has not helped" or the best one, "sorry there are no fault codes so we can't find anything", is extremely frustrating and can be costly. Main Dealers, specialists and garages equipped with expensive and sophisticated diagnostic equipment still seem to struggle.

We have put together this guide to assist you with faults regarding diesel fuel injectors and pumps, DPF diesel particulate filter cleaning and other faults relating to diesel vehicles.

Subscribe to Our Newsletter for updated Troubleshooting Tips.

THE ANSWER IS IN THE SMOKE

We can generally understand what is wrong with a diesel engine by the colour of smoke emitted from the exhaust. There are three basic colours - black, white and blue.

Black Smoke

This is due to an air to fuel ratio imbalance, either the fuel system is delivering too much fuel into the engine or there is not enough clean air (oxygen ) a few things to look for:

  • Faulty injectors (injectors need attention at about 100.000 to 120 000 miles) check for injector blow-by.

  • Faulty injector pump, this is more relevant to pre common rail systems.

  • A dirty air cleaner or restricted air inlet, check swirl flaps if applicable.

  • Turbocharger or intercooler faulty

  • Problems within the cylinder head, valves clogged up due to faulty EGR (exhaust gas recycling unit)

  • Engine timing problems, check cam to crank timing.

White Smoke

Normally means that the fuel injected into the cylinder is not burning correctly. The smoke will burn your eyes.

  • Engine/pump timing out

  • Fuel starvation to the pump causing the timing of the pump not to operate correctly

  • Low engine compression

  • Water/petrol in the fuel

  • Injectors dribbling.

Blue Smoke

The engine is burning engine oil

  • Worn cylinders or piston rings

  • Faulty valves or valve stem seals

  • Engine over full with engine oil

  • Faulty injector pump/lift pump allowing engine oil to be mixed with the diesel

DIESEL TROUBLESHOOTING

Engine not starting


With modern day engines try and obtain live data when cranking, things to check are, Low Fuel Pressure Modern fuel injection systems are all about pressure and volume of fuel. Many running problems could either be inadequate fuel supply to the high-pressure pump/rail/injectors or the rail/injectors are not holding the fuel within the system. The best way to diagnose this is as follows:

  1. Check that it is diesel in the tank and not petrol/contaminated fuel, also the level of fuel.
  2. Does the tank have an internal electric feed pump, or is there an in-line supply pump?. Feed pressures from the tank to the filter can vary from .20 to 5.0 bar. Find out what yours should be and CHECK IT with a pressure gauge. Don't just do a visual check as this does catch many mechanics out.
  3. From the tank, the fuel goes through to the fuel filter, replace it with a GENUINE unit and make sure that the filter housing looks good.
  4. Look at all plastic/rubber fuel supply pipes and connections to and from the filter; they must be dry, there must be no signs of wetness. If they are damp, replace them.
  5. The High-pressure pump will probably have one to three electrical valves/sensors on it. Check that the electrical connections are all tight and look good. If you can remove the steel pipe from the pump to the rail, do this and check the fuel pressure exiting the pump, at cranking you should get between 200 and 300 bar. Remove the electrical plug on the volume /suction control valve and see if the pressure increases. Some pumps go into maximum supply pressure by disconnecting the electrical supply to the valve.
  6. .
  7. The next thing to check is the rail; they differ so check what you have on yours. Some have a pressure sensor, a relief valve and possibly a pressure regulating valve. The sensor tells the ECU what the pressure is in the rail. The relief valve returns fuel if the pressure gets too high in the rail and the regulating valve regulates the pressure in the rail.
  8. .
  9. The last area for a pressure loss is the injectors. Two things can cause a problem, either a nozzle is stuck open, and fuel is pouring into the cylinder, or the injectors are faulty allowing for fuel to pass through the injector and return to the filter or tank. This is normally called a back-leakage test.
  10. .
. Low Engine Compression Low engine compression will result in insufficient heat being generated to ignite the fuel and cause hard starting. This is more of a problem with older or high mileage vehicles. To find out the compression perform a cold engine compression test. Compression should be between 20 to 35 bars or 300 to 500 PSI. Anything below this will cause starting problems. Low Cranking Speed - Flat Battery If the engine turns over too slowly, the pump cannot generate enough fuel pressure to activate start of injection causing hard starting problems. This is usually seen more in the colder months especially if the battery is run down. Glow Plugs or Relay Faulty The engine relies on the glow plugs to generate heat to help with the combustion cycle. Some engines only use the glow plugs when cold but others will allow the glow plugs to work when the ECU (vehicle's computer) needs them to be on to help with combustion. Problems in this area will cause diesel engine starting problems, uneven running and white smoke when the engine is cold. Insufficient Fuel Supply This speaks for itself, not enough fuel in the tank or a problem with supply pipes being cracked or bent. The fuel tank breather can sometimes be blocked causing a vacuum in the tank which in turn draws the fuel back to the tank. Fuel Quality and Contamination Poor or contaminated fuel will reduce the life of your diesel injection equipment. Water robs the fuel of its lubrisity which will cause premature wear. Transfering fuel from drums also results in contaminated fuel, we are also seeing failures due to Adblue being put into the diesel. Air - Vacuum in Fuel Supply This is similar to "Insufficient fuel supply" (above) but dirty fuel filters or a faulty filter head assembly may also cause fuel supply issues and hard starting. Blocked Fuel Supply or Dirty Fuel Filters First thing to do when fault finding is to replace the fuel filter with and O.E. one. Also make sure that there are no blockages in the fuel supply lines. Faulty Diesel Injector(s) Probably the biggest result of injector failure is due to the injectors having excessive return flow or back leakage. This is due to worn parts which allow excessive fuel to go through the diesel injector and to return back to the tank or fuel system. This causes a drop in rail pressure (see "Low fuel pressure") which results in hard starting or not starting at all. Another problem resulting from worn parts is a delay in the start of injection which in turn results in rough running at low RPM or your diesel not starting. We are also seeing problems with the later Bosch Piezo injectors that are causing white smoke at idle. The vehicle builds up excessive white smoke at idle but then tends to clear on
acceleration. We have found that the nozzles dribble resulting in unburnt fuel.
For peace of mind send your injectors in for testing, ask us for a quote. Faulty High Pressure Pump If the pump is faulty there will be a "Low fuel pressure" problem. This problem arises if the pump "breaks up" internally causing swarf and iron filings to get into the fuel system. Normally this causes damage to the diesel injectors and unless the complete fuel system is attended to the problem will arise again. This is an expensive failure and no short cuts can be taken. Faulty Pressure Regulator or Sensor Most vehicles have a pressure regulator fitted on the high pressure pump and a sensor fitted on the rail. If either of these are faulty there will be running issues like hard starting, uneven tick over and the vehicle cutting out when the RPM is increased. Faulty Low Pressure Supply Pump Not all vehicles have a low pressure supply pump but if they do it can be found either in the tank or on the fuel pipe near the tank. If your low pressure pump is faulty, you may experience symptoms similar to those of a "Faulty high pressure pump". Cam and Crank Sensors Check that the sensors are not loose, cracked or damaged as they are not very expensive. If you have any doubts I would recommend replacing them. Electrical Wiring Harness As vehicles age the wiring harnesses become brittle and wires break causing very difficult faults to find. Check continuity and resistance on all supply wires. If in doubt give us a call on 01939 291155




Engine hard to start


An engine that is difficult to start probably has very similiar faults as one that does not start. Have a look at "Engine not starting" If in doubt give us a call on 01939 291155




Runs rough at low RPM


Low Fuel Pressure Have a look at "Engine, not starting." Low/ Uneven Engine Compression Low or uneven compression will result in poor combustion causing the engine to be unbalanced. To find out the compression perform a cold engine compression test or a cylinder leakage test. Compression should be between 20 to 35 bars or 300 to 500 PSI. Anything below this will cause starting/running problems. We have come across bent conrods, valves not seating and damaged cylinder head gaskets that will cause uneven running. Insufficient Fuel Supply Not enough fuel in the tank or a problem with supply pipes being cracked or bent. The fuel tank breather can sometimes be blocked causing a vacuum in the tank which in turn draws the fuel back to the tank. Air - Vacuum in Fuel Supply Similar to "Insufficient fuel supply" (above) but dirty fuel filters or a faulty filter head assembly may also cause fuel supply issues and running issues. Blocked Fuel Supply or Dirty Fuel Filters The first thing to do when fault-finding is to replace the fuel filter with and O.E. one. Also, make sure that there are no blockages in the fuel supply lines. Faulty Diesel Injector(s) Probably the two most significant results of injector failure are due to the injectors having excessive return flow or back leakage and delayed start of injection. Worn parts which allow excessive fuel to go through the diesel injector and to return to the tank or fuel system, causing a drop in rail pressure which results in hard starting or not starting at all. Another problem resulting from worn parts is a delay in the start of injection, which in turn results in rough running at low RPM or the engine not starting. We are also seeing problems with the later Bosch Piezo injectors that are causing white smoke at idle. The vehicle builds up excessive white smoke at idle but then tends to clear on acceleration. We have found that the nozzles dribble resulting in unburnt fuel. For peace of mind, send your injectors in for testing, ask us for a quote. Faulty Pressure Regulator or Sensor Most vehicles have a pressure regulator fitted on the high-pressure pump and a sensor installed on the rail. If either of these is defective, there will be running issues like hard starting, uneven tick over and the vehicle cutting out when increasing the RPM or load. Cam and Crank Sensors Check that the sensors are not loose, cracked or damaged. They are not very expensive to replace if in dought. EGR problems Now including water-cooled EGR valves leaking water into the engine. The idea of an EGR valve is that while the engine is at tick over, a valve opens and allows some of the exhaust gases to pass back into the nice clean air intake manifold. After a while, the gases containing dirty, sooty carbons start to cover and coat the intake area and valves causing the air to fuel ratio to become unbalanced, thus resulting in black smoke. This black smoke is then drawn back into the air intake via the EGR valve. A vicious cycle then starts, thus causing air intake problems resulting in uneven running. A new problem with modern EGR valves is that some of them are water-cooled, great idea but as they age, they become porous and start leaking coolant into the engine through the EGR valve. To check remove the EGR valve, block of the coolant outlet connection, connect compressed air into the coolant inlet, drop into a bucket of water and see if you have any air leaks. Injector Blow-By or Injector Seat Leaking Injector "blow-by" can be the cause of some of the following symptoms. Hard or difficult starting, Erratic or uneven tick over, Lumpy running, Smoke on acceleration, Black tar around the injectors and a chuffing sound from the engine when running. Injector "blow-by" occurs when the injector does not seal against the injector seat in the cylinder head. On some engine applications if this continues severe engine damage could result because the ECU will over compensate the fuelling, causing piston wash or over fuelling. Even if the injector is removed, cleaned, a new copper washer fitted and then replaced, it will not always rectify the problem. The only way to remedy the fault is to reface the injector seat in the head using a seat cutting tool. Injector Blow-By or Injector Seat Leaking (link to Instruction) If in doubt give us a call on 01939 291155




Lack of power


At the moment on common rail systems, we are finding more high-pressure pump failures that cause the vehicle to have a lack of power or go into "limp" mode on hard acceleration. The vehicle starts ok and drives fine on light acceleration but will cut out on full acceleration. Other things to check are: Low Fuel Pressure It is in this area that most fuel supply problems occur. The problem could either be inadequate fuel supply to the rail/injectors/pump or the rail/injectors are not holding the fuel within the system. The best way to diagnose this is to start from the tank and ensure that sufficient fuel is available to the pump. Some High-Pressure pumps can draw fuel while other vehicles have an in-tank or in-line supply pump. Insufficient Fuel Supply This speaks for itself, not enough fuel in the tank or a problem with supply pipes being cracked or bent. The fuel tank breather can sometimes be blocked causing a vacuum in the tank which in turn draws the fuel back to the tank. Fuel Quality and Contamination Poor or contaminated fuel will reduce the life of your diesel injection equipment. Water robs the fuel of its lubricity, which will cause premature wear. Transferring fuel from drums also results in contaminated fuel, and we also see failures due to the addition of Addblue in the diesel. Air - Vacuum in Fuel Supply Similar to "Insufficient fuel supply" (above) but dirty fuel filters or a faulty filter head assembly may also cause fuel supply issues and hard starting. Blocked Fuel Supply or Dirty Fuel Filters The first thing to do when fault-finding is to replace the fuel filter with and O.E. one. Also, make sure that there are no blockages in the fuel supply lines. Faulty Diesel Injector(s) Probably the most significant result of injector failure is due to the injectors having excessive return flow or back leakage. Due to worn parts which allow excessive fuel to go through the diesel injector and to return to the tank or fuel system. This causes a drop in rail pressure (see "Low fuel pressure") which can result in poor acceleration. Faulty High-Pressure Pump As mentioned earlier, a common fault for lack of power or cutting out on acceleration. Send your pump in for checking. Faulty Pressure Regulator or Sensor Most vehicles have a pressure regulator fitted on the high-pressure pump and a sensor installed on the rail. If either of these is defective, there will be running issues like hard starting, uneven tick over and the vehicle cutting out when increasing the RPM Faulty Low-Pressure Supply Pump Not all vehicles have a low-pressure supply pump but if they do it can be found either in the tank or on the fuel pipe near the tank. If your low-pressure pump is faulty, you may experience symptoms similar to those of a "Faulty high-pressure pump". Air intake restriction Due to a dirty air cleaner, blocked pipes or a stuck butterfly valve found on some vehicles. Also, a faulty air flow sensor on the air intake will cause problems running and excessive smoke. EGR Valves Problems now including water-cooled EGR valves leaking water into the engine. The idea of an EGR valve is that while the engine is at tick over, a valve opens and allows some of the exhaust gases to pass back into the nice clean air intake manifold. After a while, the gases containing dirty, sooty carbons start to cover and coat the intake area and valves causing the air to fuel ratio to become unbalanced thus resulting in black smoke from the exhaust. This black smoke is then drawn back into the air intake via the EGR valve. A vicious cycle then starts with the engine producing more smoke and sootier carbons entering the intake manifold, thus causing air intake problems resulting in uneven running. A new problem with modern EGR valves is that some of them are water-cooled, great idea but as they age, they become porous and start leaking coolant into the engine through the EGR valve. To check remove the valve, block of the coolant outlet connection, connect compressed air into the coolant inlet, drop into a bucket of water and see if you have any air leaks. If in doubt give us a call on 01939 291155




Diesel knock / pinking


Faulty Diesel Injector(s) A problem resulting from worn parts or sticky nozzles are a delay in the start of injection or incorrect pre-injection which in turn results in rough running, diesel knock or pinking. For peace of mind, send your injectors in for testing. Fuel Quality and Contamination Contaminated fuel will reduce the life of your diesel injection equipment. Water robs the fuel of its lubricity, which will cause premature wear. Transferring fuel from drums also results in contaminated fuel, and we also see failures due to the addition of AdBlue in diesel fuel. Blocked Fuel Supply or Dirty Fuel Filters The first thing to do when fault-finding is to replace the fuel filter with and O.E. one. Also, make sure that there are no blockages in the fuel supply lines. Faulty High-Pressure Pump If the pump is defective, there will be a "Low fuel pressure" problem. This problem arises if the pump "breaks up" internally causing swarf and iron filings to get into the fuel system. Usually, this causes damage to the diesel injectors, and unless the complete fuel system is drained and cleaned, the problem will arise again. Faulty Pressure Regulator or Sensor Most vehicles have a pressure regulator fitted on the high-pressure pump and a sensor installed on the rail. If either of these is defective, there will be running issues like hard starting, uneven tick over and the vehicle cutting out when increasing the RPM. Cam and Crank Sensors Check that the sensors are not loose, cracked or damaged as they are not very expensive. If you have any doubts I would recommend replacing them. Injector Blow-By or Injector Seat Leaking Injector "blow-by" can be the cause of some of the following symptoms. Hard or difficult starting, Erratic or uneven tick over, Lumpy running, Smoke on acceleration, Black tar around the injectors and a chuffing sound from the engine when running. Injector "blow-by" occurs when the injector does not seal against the injector seat in the cylinder head. On some engine applications if this continues severe engine damage could result because the ECU will over compensate the fuelling, causing piston wash or over fuelling. Even if the injector is removed, cleaned, a new copper washer fitted and then replaced, it will not always rectify the problem. The only way to remedy the fault is to reface the injector seat in the head using a seat cutting tool. Injector Blow-By or Injector Seat Leaking (link to Instruction) If in doubt give us a call on 01939 291155




CP4 Pump failure (Bosch System)


The application of Bosch CP4 high-pressure pumps to some engines are experiencing costly repairs due to failures resulting in the destruction of the injectors and the contaminating of the complete fuel system. . We recommend that should the pump display signs of swarf or metal filings: Remove the pump and injectors and send them to us for checking. Also, send us the injector pipes and rail for ultra-sonic cleaning. Remove and thoroughly clean all fuel supply and return pipes. Remove and thoroughly clean the fuel tank and fuel sender unit. Replace the in-tank fuel supply pump. Replace the fuel filter with an O.E. unit and clean the filter housing assembly. When replacing all the components flush everything out with clean diesel before connecting the injector pipes. Unfortunately, there are no short cuts and failing to do all of this at the same time, or only part of the process will result in injector/pump failure again. If in doubt give us a call on 01939 291155




VAG 1.6 lt. Pump and Injector failure. (Delphi System)


We are starting to see pump failures on the VAG 1.4 and 1.6 lt. Engines fitted with a Delphi DFP6.1E high-pressure pump. O.E. part number 04B 130 755H and Delphi part number 28477820. This problem causes the injectors to fail due to swarf contaminating the fuel system. Below are some pictures of the pilot valve in the injectors, you can see the particulate matter present on the valve pin.
The pump and injectors will need inspecting and possibly replacing also the complete fuel system, tank, rail and pipes will need to be removed and clinically cleaned.
. We recommend that should the pump display signs of swarf or metal filings: Remove the pump and injectors and send them to us for checking. Also, send us the injector pipes and rail for ultra-sonic cleaning. Remove and thoroughly clean all fuel supply and return pipes. Remove and thoroughly clean the fuel tank and fuel sender unit. Replace the in-tank fuel supply pump. Replace the fuel filter with an O.E. unit and clean the filter housing assembly. When replacing all the components flush everything out with clean diesel before connecting the injector pipes. Unfortunately, there are no short cuts and failing to do all of this at the same time, or only part of the process will result in injector/pump failure again. If in doubt give us a call on 01939 291155 .





Should you have an enquiry or wish to place an order with us please email us your enquiry, phone us or complete and submit the enquiry form.

SENDING UNITS TO US.

Should you wish to send units in for testing or repair, please box them up well and either send them in or contact us and we will arrange collection. Don't forget to place a note in the package with your contact details.

Telephone: +44 (0)1939 291155

 

Email: info@uniteddiesel.co.uk

 

Address:

Unit 35, Atcham Business Park

Atcham

Shrewsbury
Shropshire
SY4 4UG
UK

Would you like more information on how we can help you?

By clicking the "Submit" you agree that we can keep you updated with news, information and offers. 100% privacy guaranteed - Your information will not be shared.

CONTACT