Diesel FAQs


General Questions

Why does my vehicle produce lots of black smoke when it is under load (when going up hills or towing)?

There are many possible reasons for this, but they can be broken down into three basic categories:

  • Your vehicle is in need or is overdue for a service. Blocked air filter, incorrect valve clearances and other such easily remedied faults can often be the cause, and you are advised to get them attended to first before investigating either of the next two possibilities.
  • Worn diesel injectors.
  • Worn or faulty diesel pump.

Why does the light on my dash take a long time to turn off once I've started my engine?

The Glow Plug light can sometimes take a long time to go out by design. If it is staying on for an abnormally long time however, this could be an indication of damaged glow plugs or a faulty glow plug controller.

My vehicle suffers from hard starting - it cranks over for a long time before starting - why?

Faulty glow plugs or glow plug controller and overall engine wear are the two most common causes of hard starting. Glow plug issues are normally very easily diagnosed and repaired. A simple compression test will give a good indication of the condition of the engine and whether it requires any major work.

Why does my vehicle produce a large puff of black smoke when it starts in the morning?

All diesel engines will produce some smoke on first start, and some engines tend to produce more than others. It is entirely possible that this is normal behaviour. However this can also be a symptom of the problems mentioned above regarding hard starting.

My vehicle doesn't run as well as it used to and is using more fuel. Is there a common reason for this happening?

The usual cause of this is worn diesel injectors. However the simple regular servicing issues such as filters, valve clearance and so on can also be at fault, therefore it is best to address them before assuming the injectors are the cause.

Sometimes when I turn off the ignition key my engine keeps running - why?

This problem is typically caused by worn injectors that leak fuel and allow the engine to keep firing. This fault is most commonly seen on Nissan TD42 powered vehicles, but can also occur on other engines.

How bad does my smoking exhaust have to be to fail a Warrant of Fitness?

The rules regarding vehicle emissions in New Zealand are currently changing quite rapidly. At the present time there is a 'Visible Smoke Test' rule in effect, and the requirements for the test can be viewed at Land Transport NZ's website: HERE

How much will it cost to give my diesel a tune up, and what is involved?

Unfortunately there is no simple answer to this question, as the requirements will vary greatly depending on the particular vehicle, its age, and milage.

How often do I need to service my diesel injectors?

For indirect injection engines (traditional diesel engines) you are advised to service after 80-120,000kms. Direct injection engines typically do not require the injectors to be serviced unless a specific fault occurs.

Should I have my injectors serviced, or just buy new ones?

Servicing injectors returns them to effectively new condition, so there is no real gain to be made from buying new ones. The cost of servicing injectors is also typically about 20% of the cost of replacement.

Should I have my diesel pump serviced, or just buy a new one??

As with injectors, pump servicing represents about 20% of the cost versus buying new. Diesel pumps are also typically not available to be purchased new off the shelf.

If I have my vehicle serviced or repaired, what level of warranty cover do I receive to cover the work and parts?

All parts supplied by Alltech will be covered by their standard manufacturers warranty, which naturally varies with different manufacturers. Any work done by Alltech will be stood by without question.

My vehicle failed a warrant of fitness inspection due to a fuel leak. What needs to be done to fix it, and how much will it cost?

The simple answer is that there are many possible reasons for diesel leaks. Some may be as simple as a gasket replacement, some may require major servicing. You are advised to take the vehicle in to be assessed rather than rely on an inaccurate phone diagnosis.

Vehicle Specific Questions

I have a Mitsubishi 4WD with a 4M40 engine. Why does the engine tend to cut out when it is cold?

The diesel fuel pump will require servicing. Front fuel pump seals fail on these pumps, and the cutting out is a symptom of the pump having been drained of fuel.

I bought a Nissan Terrano and have noticed that other Terranos are much faster than mine. Does mine have a problem, or is there another reason?

There is not necessarily a problem with your vehicle. There are many different variants of Terrano, and they have quite different performance characteristics.

Are there any particular makes or models of 4WD that I would be best to purchase or avoid?

There are numerous models available in the New Zealand market, some of which are better than others. However the scope of this question is too large to be answered in a few sentences. If you are looking at purchasing a particular vehicle then feel free to contact us to discuss the possible pitfalls and arrange for a pre-purchase inspection.

Help! I've filled my diesel tank with petrol by accident. What do I do?

If you haven’t yet started the engine then don’t do so. Drain the fuel tank and refill it completely with diesel; no harm will have been done. If you have already run the engine for a short period then you will need to drain and replace the fuel and replace the fuel filter. If you have run the engine for an extended period of time then there may have been damage caused to the diesel pump; naturally this will require an inspection to establish the damage.