Tech Page

Attention! Fuel Filters MUST be changed!!

With all common rail engines, you must change the fuel filter every service. We hear of some dealers doing filters in Nissan’s every 50,000 Kms. This is our view only, but the fuel filter must be changed at least every 10,000 Kms. Otherwise you can expect to be replacing the entire fuel system at some point. Again, this is just our humble view, but you may even find a future owner may have a claim of liability if generally accepted servicing practices are not carried out.

Built in Safety systems

Some units have built in safety systems that can protect the engine. Some do not! DTP Systems units have three built in safety systems

1) The DTP unit will retard power at approx 1% per second if the throttle has been at 100% for more than the preset time in the software. Usually 1 Minute, more on a heavy commercial engine, less on a very High performance engine. This will stop the engine building up excessive heat.

2) The DTP Unit will retard power 1% per second if the engine or exhaust temperature rises to much. The unit can do this in two ways. Some units come with a connection to the exhaust temperature sensor or for truck and tractor units that connect to the computer, the temperature is picked up at the computer

3) The DTP unit can also sees the standard injection pulse. If the cars computer retards power (which all common rail engines will do) due to a temperature rise, the kw Systems unit will see the injection pulse change as a result and will retard the power gain by 1% per second back to factory power to protect the engine.

Failure to do this can cause damage to pistons, turbos and exhaust filters.

Diesel Particulate (DPF) Filters

Many engines are today fitted with DPF filters that filter the particles out of the exhaust gas. They are not like a catalytic converter, you cannot see through them. The tiny holes go half way and stop. The exhaust gas must pass through the wall of the filter and the particle remains behind on the wall. Once the unit gets blocked up every few hundred ks, the engine puts fuel into the exhaust and burns the filter clean.

You must be very careful if you car is fitted with a DPF filter. They are sensitive to a change in fueling. The cheap unit that just add fuel by increasing pressure will almost certainly have a negative affect on the DPF filter. We are very careful when using our Magnum chip on cars with a DPF. If we do not have vehicle specific software that really limits fuel in the lower rpm. We will not use the Magnum chip on a DPF equipped car. We will never use our bottom end unit on a DPF equipped car. These filters are thousands of dollars and cannot be removed as there are sensors that communicate their condition to the cars computer. If you remove it, the car will immediately go to emergency mode

DTP Systems have tuned thousands of cars with DPF filters and never had a problem ever. Not one car!

We can remove the dpf filter by changing the software in the computer. This is a very technical job and requires the removal of the cars computer and soldering connections to it to re flash the dpf portion. But beware!

If the car is a 2008 or newer model, the dpf must be installed if it had one from the factory to get a warrant, If its removed a new one will be thousands of dollars and you will need it to get a warrant of fitness

So here are a couple of very important points to recap

Firstly, the factory designs the combustion chamber shape in the piston, to work in conjunction with the diesel injection timing. For example the piston below may need the injection between top dead center (+0) and 6 degrees past top dead center (+6) and a different piston may need +1 to +8 (this will change with RPM). This is why we disagree with changing the injection timing by remapping or re chipping the computer. Unless each map or chip is adjusted for each engine specifically, then you have the ability to generate a lot of heat in the piston. The injector needs to spray the fuel perfectly into the piston cup.

Secondly, the factory turbo is designed to blow a lot of excess air through the engine to lower or dilute the exhaust emissions. The more spare air in the emission test, the lower the emission result. This is why we can fuel up an engine without the need to add extra boost. In most cases extra boost will create higher air temperatures and cause a loss in power.

Remapping the cars computer has the ability to change many things, remove safety limiters and change timing of the injection pulse which can make dangerously high pressures. Our view is this is an inferior method in anything except race engines.

A DTP Systems unit only does one thing. it add fuel at the end of the injection pulse. That’s it! And these guys have been in business since 1987, and have tuned over 50,000 vehicles, and worked pre DTP Systems developing transmissions and Turbo Diesel engines in Aachen Germany for Volkswagen So if anyone tells you that they know more, or you should do it another way. Check their credentials and compare!

Injector Rattle

We have done a lot of research into injector rattle that accrues in some Hilux, Navara and other common rail engines. The cause of this is commonly dirty fuel which builds up in the injector.

A common rail injector fires several times during each power stoke to supply the engine with fuel. There are a couple of pilot injections (small amounts of fuel injected to establish the combustion process) and then the full injection cycle to add the fuel for the power stroke.

The problem accrues when there is a buildup of very fine residue, sulfa, dirt etc in the injector which has incredibly fine tolerances.

When an electrical current is passed through solenoid or Piezo stack it lifts the needle off its seat. It’s this action that fails during the pilot injection when the injector becomes dirty. Once this happens you will hear the full ignition detonation of the fuel just as you can in yesteryear’s diesel engines, there is no warm up so to speak. This has an effect on power as well as fuel economy of the engine. The trick is to change fuel filters regularly or install an aftermarket 2-micron filter to take as much alien material out of the fuel as possible.

From our experience some injectors get affected more than others. It seems that the Denso units are more prone than Bosch and Delphi units. That’s just an observation and not based on a study. We don’t see many European vehicles that predominantly use the Bosch or Delphi injectors giving trouble in this way.

There is an article on Wikipedia that talks about this in relation to Toyota engines.

Sometimes when you install a Common rail performance chip to a noisy engine it will make the engine quieter, sometimes no change and sometimes it makes more noise. It all just depends on the actual vehicle.

A DTP Systems unit will make no change. If its noisy at the start, it will still be noisy with a DTP Systems unit installed, If it quiet, It will stay quiet.

Suction Control Valve

The Suction Control Valve is responsible for controlling fuel pressure in common rail engines. All common rail engines have them.

The problem is they get affected by the same dirt and contamination that gives the injectors a hard time. When the suction control valve gets dirty or worn (they also are made to incredibly fine tolerances) they can cause the fuel pressure to jump around or spike. It’s quite easy to see on our scanner when connected to a car while viewing “live Data” – you can see the fuel pressure bouncing around over several thousand KPA.

The problem accrues when the pressure jumps beyond the limit set in the computer by the manufacturer for a specific RPM. When this happens the car will go into limp mode requiring the engine to be turned off and back on to reset the valve.

Solution – well often the valve can be cleaned and re-installed and the problem is fixed, it’s a good idea to turn the valve 90 degrees when re-installing for an extra lease of life. Sometimes a simple relearn of the computer will do it with a scan tool. The dealers call this a pump relearn. The worst case scenario is that it will need to be replaced. There is no average to how long they last, some have been known to fail at 25,000 km and others last the life of the vehicle.