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There was a time when diesels were strictly for farm implements and slow old trucks that belched more black smoke than a bushfire. Not anymore however. As 4WDers, most of us have realised the benefits of running oil burners for decades now. They deliver their peak torque figures at low rpm, perfect for off-roading and towing, and tend to get much better fuel figures than a similarly sized petrol equivalent, making them the logical choice for long distance tourers.
On top of that, the last 10 years or so has seen some pretty massive gains in the world of oiler performance. On a fundamental level, they still function as they have since Rudolph Diesel first came up with the idea for an engine to run on peanut oil. They still compress fuel and air to the point where it ignites, sending the piston back down through the cylinder to turn the crank and provide motive power. Where they have undergone significant changes however is in their fuelling systems.
Traditionally, a mechanically driven fuel pump (off either the crank or cam) would send the fuel directly to each injector where it would be introduced to the cylinder, via a pre-combustion chamber on indirectly injected motors such as Toyota’s 1HZ or straight into it on direct injected motors like Nissan’s TD42, and the combustion cycle would be completed. While this system works fine, it does fall short somewhat when it comes to getting the most out of each squirt of fuel. Computer-controlled common rail injection systems fix that.
Not only is the fuel delivered to the injectors from a high-pres¬sure fuel rail rather from individual lines straight off the pump, but it is also controlled a lot more efficiently. Precise amounts are delivered at exactly the right moment, or moments, with some engines receiving up to five injections per stroke cycle to achieve maximum power, rate of burn, and economy.
However, like everything from the factory, these systems can be improved. There has a been a lot of research and development by the aftermarket into these new-fangled systems with several Aussie companies leading the way in terms of how to get the most out of your modern diesel.
The biggest (and arguably easiest) gains are to be had from plugging in a piggyback power module, commonly referred to as a chip. These essentially affect when and how much of the fuel is delivered to the cylinder, as well as changing the pressure at which it is introduced. This optimises the power production and can often result in a more complete burn, not only making your vehicle more responsive, but usually improves economy too!
Of course, there are plenty of other mods you can perform on your modern engine as well, let’s take a look at the options to help you decide on what to spend your hard-earned on.
Before we get too far into the ins and outs of modifying modern diesels, we should really take a second to compare them to their older tech siblings. Many people still prefer the comparative simplicity and reliability of traditional mechanical injection vehicles. They generally don’t need much in the way of electricals to run, making them supremely reliable out in the bush. Plus they won’t ever resort to limp-mode when a sensor fouls itself, mainly because limp-mode on a mechanically injected diesel is when the driver hurts his right foot and has to go easy on the loud pedal.
Then there are the associated expenses with fixing them when they break. Injectors for common rail direct injection (CRD) trucks are roughly twice the price of older pintle-style units found on mechanical injection 4WDs, and let’s not even mention the price disparity between fuel pumps! Think MQ Patrol versus brand new Range Rover.
With that said though, economy is far and away better with newer diesels, often getting around the 10L/100km mark on full size 4WDs. And getting more power out of them is a snap! If you’re looking to get big torque numbers out of an older diesel, you’ll probably need to look at working your injection pump, intake, exhaust, turbo upgrade and injectors.
With a modern diesel, you plug in a chip and you’re done. While they may not quite have the proven track record in reliability of older tech engines, they certainly do have the numbers on their side! As the technology becomes more mainstream and prices become more and more affordable, we’re fast running out of reasons not to like common rail injection. Better than ever economy, easily achieved power gains that are just as easily reversed and cleaner emissions than many petrol powered vehicles. On top of that it seems as though newer and better improvements are coming out with each new common rail 4WD model released.
There’ll always be a place here in the Modified 4WDs garage for old tech mechanical injection trucks, they’re simply too reliable to discount, but we’d be lying if we said that we weren’t seriously eyeballing a modern turbo-diesel. Throw in a locker or two, a mild lift and some proper tyres and you’d have a comfortable and capable truck that could just as easily tackle any track in Australia as well as the daily commute.
1 Common rail fuel systems were initially developed in Europe with Swiss and German scientists developing the theory into working prototypes. The first commercial common rail systems were released in the mid 1990s by Japanese automotive parts supplier Denso for use on heavy duty trucks. The injection pump feeds a shared fuel rail that holds the diesel at high pressure and is connected to the injectors. When the ECU tells the injectors to open, the fuel is delivered directly from the rail rather than the pump, which allows much more precise delivery and higher fuel pressures, meaning that more fuel is allowed in for the duration of the injector being open. More fuel equals more bang, it’s that simple
2 The biggest difference between common rail and mechanical injection is that the modern systems are controlled by an ECU. There are examples of computer-controlled pumps that do not incorporate a common fuel rail, however they are largely being replaced with CRD injection as time goes on. Another important point to realise about CRD systems is that due to the fuel being stored remotely in the rail, the injection pressure remains close to the same as the rail pressure, meaning that it remains steady throughout the injection duration producing what’s known as a square-wave injection rate. This allows the pressure, and therefore the amount, of fuel to be precisely metered, giving excellent control and economy
3 Traditionally diesel engines used mechanically driven pumps that delivered the fuel to each injector separately. While there is nothing inherently wrong with this style of pump, they do have a few limiting factors. The main issue is that they are driven directly from the engine and as such the pressure at which they can pump the fuel is dependent on engine speed; the higher the revs, the higher the pressure. This is true for the majority of pumps, indeed even common rail pumps function off the same principle, however without the fuel rail, which functions as a pressure accumulator, the pressure at the injector is tied directly to the pressure at the pump and the problem is more pronounced and can affect driveability more profoundly
4 Common rail pumps, while functioning at much higher pressures, actually have an easier (at least in terms of complexity) job to do. They are responsible for supplying the fuel rail with diesel and that’s about it. The ECU and injectors handle the actual delivery of the fuel to the combustion chamber. The higher pressure, often up around 30,000psi, serves to facilitate better atomisation of the fuel upon it being injected into the chamber, allowing a much more complete burn.
5 On common rail systems, the injectors are where most of the magic happens. They are operated via the ECU with piezoelectric or electronically controlled solenoids and allow for multiple injections of fuel per combustion cycle. Some newer systems, such as the D-4D HiLux for example, perform up to five injections per stroke.
Not only does this allow for the timing and quantity for the fuel to be precisely controlled, but it also allows for decreased engine vibration and ability for the engine to permit for variations such as decreased fuel quality and cold starts. Common rail systems all but do away with the need for glowing before starting too, generally needing less than a second to be ready for ignition
6 With the need for electronic control and the fact that CRD injectors deal with comparatively higher pressures, they are a lot more complex, and expensive to repair than traditional-type units. In fact, reliable repair of common rail injectors is still in its infancy stages as an industry.
While companies such as Denso are actively pursuing and establishing a comprehensive repair network, there is still some conjecture surrounding the reliability and expense of repairing rather than simply replacing faulty units.
With a common rebuild costing as much as 80% of a brand new replacement, it’s often not worthwhile paying for the repair. However, with more and more diesel specialists investing both time and capital in the process, it’s only a matter of time before it not only becomes reliable, but economical too
7 However, throwing a chip at your engine is not the only way to up the power stakes on your modern diesel engine. They still respond exceptionally well to the traditional performance mods like an exhaust (many chips are actually designed to be used in conjunction with an exhaust package), turbo and intercooler upgrades
8 So we’ve established that common rail injection is not only more powerful, but more economical and releases less emissions, albeit at the cost of losing that fantastic diesel simplicity. The other huge plus with CRD systems is the sheer ease of which you can attain significant power gains over stock.
Where you’d be adjusting and tweaking several different components on an older system, potentially costing you several thousand dollars, gaining a huge boost in power is as simple as plugging in an elec¬tronic module and calling it good. Or to put it another way, if you started the job at 8am on a Saturday morning, you’d have netted yourself a bunch more power, torque and economy well before most people would have climbed out of bed.
1 All factory ECUs come with pre-determined fuel and timing maps programmed into them by the manufacturer. While they generally come pretty close to the mark, they have to opt for a conservative tune to conform to each of the countries the vehicle is being sold in emissions regulations, available fuel quality, and ultimately, get their product out there with minimal cost.
Whatever the reason, there is plenty more to be had reliably from these engines, which comes from altering such variables as injector timing, rail pressure and even turbo boost levels depending on the module you opt to go with
2 Generally speaking, there are three different types of power up modules for diesels. The first type operates by affecting the pressure of the fuel that’s stored in the rail. They manipulate the fuel rail’s pressure sensor and works out the optimal engine load and curve figures. This then causes the factory ECU to recalculate the fuel volume and timing, and of course rail pressure.
Having an increased pressure in the rail means that for the length of time the injectors are open, more fuel is allowed to pass through into the combustion chamber, causing the power to rise accordingly. Because injector duration (the length of time they’re open for) is unaffected, reliability and engine characteristics are not changed.
However, it is vitally important that throttle input is monitored in conjunction with rail pressure. Having the pressure turned way up right across the rev range can be hazardous to your engine so be sure to check you’re getting a quality unit!
3 The second type of module gains more power by plugging directly into the injectors themselves and essentially keeping them open for longer, allowing more fuel to be injected into the cylinder. They manipulate the ECU’s signals to the injectors and recalculate several key algorithms to increase the available power.
Most of these units will need to be spliced into the factory wiring harness for a positive and negative power source. With that said, installation is still very much within the average home mechanic’s skill set
4 The last type of power modules are a little more complex, affecting both rail pressure and injector pulse. They’re more like complete tuning units and can also change the turbo’s boost pressure.
Many of these units will need to be hardwired into the factory wiring harness and are much more difficult to install than the simpler plug and play units. They also require dyno tuning to get the most out of them; however, a dyno tune with any power up addition to your truck can make a huge difference anyway and is never a bad idea.
5 So which style should you go for? It’s a bit of an ‘ask 10 people and get 10 different answers’ situation. Recommending one style or brand of chip over another would only ever be an opinion, not gospel. The best advice we can give you is to talk to your diesel specialist and work out which style will suit you.
Keep in mind that some will promise the world in their advertising brochure, but provide zero after sales service, whereas others might promise more power than you would think is possible, although it’s usually at the expense of long-term reliability. As with any mod, a couple of hours spent talking to the professionals on the phone and reading up on some real world experiences on our web-forum can literally save you big bucks
6 One of the huge advantages of a chip is the sheer ease of installation, with most examples being well and truly within the abilities of the vast majority of Modified 4WDs readers. Forget about dropping a bunch of cash to get your old mechanical pump and injectors tuned by an expert.
On your modern diesel it’s as easy as jumping online and punching in the credit card digits and your brand new power module is sent right to your door. Ten minutes to half an hour later (depending on which model you go for), you’re ready to blast up the side of those dunes, get better acceleration, and in many cases save money on the fuel bill too!
Some modules will actually pay for themselves within a couple of years of installation. There aren’t really too many mods you can say that about
7 Some of the chips that require the ECU wires be spliced and tapped into for the unit are not as recommended as DIY installs. While we’re aware that our readers tend to be handier on the tools than most, the real hurdle to overcome is the need for dyno tuning once installed.
Be sure to get some quotes for tuning before cutting into your loom, there’s nothing worse than wiring up your new power module only to find you can’t start your vehicle. Having a good tuner on your team is priceless! This can all add on quite a bit to the budget, so make sure you leave some coin aside to do the job properly.
1 While a power module should really be one of the first mods to look at for your modern diesel engine, it doesn’t mean that it’s the only thing to consider. All of the power upgrades for old-tech diesels still do the job for late model versions too.
Take exhausts for example. Even though most modern common rail engines often come with some sort of turbo and intercooler already included, manufacturers still seem hell-bent on bolting up pea-shooter exhaust pipes and mufflers that could make a Boeing 747 quieter than an electric powered vehicle.
Yes, we realise that vehicle makers are subject to some pretty ridiculous noise and emissions regulations and aren’t necessarily to blame, but the fact remains that throwing some decent pipework can make a big difference. Look at this muffler’s restriction. The gas enters from the top of the image and has to make its way through three separate chambers, usually full of packing, before it can escape. Great for noise reduction, lousy for power!
2 A tuned exhaust is actually considered part of some power module packages, with the chip being designed to deliver maximum power and efficiency in conjunction with a proper exhaust system.
Make sure you use a reputable retailer, and if you spend plenty of time on the beach or highly corrosive environments, be sure it’s built out of a material with good rust resistance properties such as stainless or aluminised steel
3 For turbo diesels, don’t worry so much about getting a replacement turbo manifold, the factory items are actually pretty good. Instead you should definitely look at getting a dump pipe off the back of the turbo that matches it’s outlet size and has better flow characteristics than the restrictive original item.
Also be careful of fitting too large a pipe diameter. Many people choose to go for a 3in or larger pipe when 2.75in is actually more beneficial. Finally, make sure you’re happy with your muffler choice. Having a loud obnoxious muffler may sound great for a couple of weeks, but when it’s droned in your ear for the last eight hours up the highway, your opinion can easily change. With those things in mind, remember to enjoy the power and economy you’ve gained!
4 Manufacturers often tend to buy parts in bulk to fit to their vehicles, and turbos are no different. What this can result in is turbos that are not ideally suited to the engine they’re bolted to. Upgrading your turbo to one that has been specifically selected and built to suit your purposes can net significant gains.
Swapping out an oiled journal bearing type turbo for a ball bearing unit will decrease the internal shaft’s friction and make the turbo spool up quicker and easier, gaining both power and reliability.
It’s worth noting that some common rail diesels are running fairly high boosts from the factory, with 15psi being achieved frequently. This doesn’t leave a lot of room to increase the boost pressure for more power, so do your homework before you start chasing power output that way
5 With these high boost pressures comes increased heat. The air is warmed up as it is compressed, meaning that on non-intercooled vehicles when it reaches the intake manifold, it’s hotter than it needs to be and the density of the air is low.
An intercooler passes this hot air through it, cooling it down so that it is cooler and denser when it’s introduced to the engine, which in turn means that more of it can be crammed in and a bigger and better bang is produced.
Simple eh? Factory intercoolers are generally pretty small however and when the engine is hot and under-bonnet temps are right up there, they can actually warm up the intake charge, robbing power
6 By upgrading your intercooler to a bigger, more efficient unit, you’re ensuring that your engine is always receiving as cool an air charge as possible, even if you’re ploughing through the desert sand on a 40-plus degree day.
Intercoolers can be top mounted over the engine or front mounted in front of the radiator behind the front grille. Both mounting locations have their good and bad points: top mounts are more susceptible to higher under-bonnet temps and front-mounts are more prone to frontal impacts, but if you’re chasing higher boost and want to get as much air packed into the intake as possible, an intercooler will be needed.
There’s not a production diesel engine on the planet that can’t be improved in some fashion. With the late model common rail injection systems, a great many issues that have traditionally kept people away from diesels have been addressed, and many of the things that have made people fans of diesels for years have been improved upon.
Better economy, torque, power and responsiveness are all massive drawcards for the modern 4WD owner. While some may argue that all of these improvements are at the expense of reliability and being able to fix it in the middle of the outback with a shifting wrench and a roll of gaffer tape, it’s hard to deny that these modern engines are kicking a hell of a lot of goals.
How you modify them largely depends on the duties you want your vehicle to perform. However you could do a lot worse than by starting off with a power module and exhaust and going from there. After all, if having a fully laden 4WD that can hold top gear up a steep hill, with enough left in it to easily break the speed limit (if desired), while getting diesel economy and clean emissions doesn’t bring a smug grin to your face, we don’t know what will.
Exhaust gas recirculation (EGR) and diesel particulate filters (DPF) are mechanisms that serve to reduce a diesel engine’s emissions. They are both legal requirements, which in some circles is perceived as a great shame, mainly because they’re not particularly great for your engine’s longevity or power production after a bit of use.
EGRs work by reintroducing some of your engine’s exhaust back into the combustion chamber. The idea is that the gas displaces some of the air in the fuel-air mixture and burns off the excess nitrogen oxide in your gas. While this works extremely well for the first couple thousand kilometres, eventually the carbon and soot deposits build up around the intake to the cylinder, essentially forcing your engine to breathe through a progressively restricted passage.
This can wreak all sorts of havoc on your engine’s reliability and power production and reliability. The EGRs are commonly open at idle and a little above, so if your vehicle sees a lot of stop-start driving, you may want to get it checked out sooner rather than later.
DPFs are mounted in your exhaust system and are designed to filter out the soot from your engine. Again, these work extremely well until you’ve done a few thousand kilometres and they’ve become choked with deposits and are severely restricting gas-flow and causing more bother than ants in your undies. But surely it can’t be too much to replace right? Wrong. Try around $4000 for a new unit!
Due to them being a legal requisite, you’re not allowed to simply block them off or bypass them altogether, and because we’re law abiding citizens we would never advocate such behaviour (can anyone else hear those crickets chirping?). However, they do highlight that CRD injection systems simply cost a lot more to service and maintain, which is worth factoring into your long-term budget for that truck you’re eyeing off in the dealer’s lot. With that said, it should be acknowledged that there are several Aussie companies working with CRD manufacturers to bring these servicing costs down significantly. Stay tuned!
