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Electronic Diesel
Tuning Devices

With the advent of electronic control of diesel injection systems, a plethora of tuning devices have been released on the market to tempt the Land Cruiser performance enthusiast. With these devices, promises of improved power and torque are often realized so no matter which of the readily available chips or computers is chosen, gains will be felt through the seat of the pants.

One could easily draw the conclusion that they are all essentially the same. After all, they simply alter the state of tune of the engine in order to improve performance. One may quote a power figure and the other a tad less. And to confuse the issue further, the one quoting less power may, in fact quote more torque than the first, And so it goes, leaving the consumer even more confused and eventually making a choice without being fully informed.

Toyota has made it very easy for anyone with a basic knowledge of electronics to modify the fuel injection characteristics and to create what is essentially an electronic version of the main set screw from a good old mechanical pump. Indeed, most of the chips available are just that - simple devices that alter the amount of fuel injected into the engine. Whilst performance is improved, they are very crude and do little more than "turn up the fuel" as the old timers would say.

At the other end of the range, there are complete computer systems that have independent control of the injection timing, the amount of fuel injected, a variety of compensation strategies for situations such as high heat etc and perform these functions at precisely controlled intervals throughout the engine's operating range and throttle range.

There is little sound technical information on all the devices available to the consumer, yet wrong information is in abundance. More often than not, the truth is in what is not said - yet there is a great deal to be said. Much of the wrong information comes from some of the "chip" industry itself, though unlikely that it is spread for malicious reasons. More likely it is through having little understanding of the important issues in tuning a modern Toyota diesel engine. You see, many of the diesel specialist who market these devices have only a finite understanding of their own products and are more confused regarding the capabilities of competitor products. So, it is unlikely that clear, concise and factual information will be made available to the consumer when the very people who deal with these products are themselves confused.

The above statements should not really be seen in a negative light or as condemnation of the diesel tuning industry. Electronic control of the injection system is relatively new and much of the emphasis on creating tuning chips has evolved from the diesel industry's experience with mechanical pumps where external adjustments are relatively course with bulk changes made to the entire fuel injection volume through the main set screw, the entire injection timing through the base timing position etc. On turbocharged diesel vehicles, adjustment through the boost compensator to meter fuel relative to turbocharger boost pressure. In other words, most diesel performance chips mimic these mechanical adjustments through electronic means.

Conversely, computer chips targeted for EFI petrol engines generally have independent control of fuel, ignition timing, boost pressure via an array of data points that combine engine rpm, throttle position and sometimes turbocharger boost pressure. This allows them to alter the EFI parameters at discrete engine RPM/throttle position combinations rather than a bulk change of, for example, a fixed percentage change to the injection volume regardless of engine RPM or throttle position.

Generally, the diesel computer aftermarket industry has a decade of catching up to do over those who have been developing computers for petrol engine vehicles. That said, there are sophisticated computers for diesel engines that not only employ these advanced features, but also add diesel specific features for advanced engine protection.

There are two equally important issues that one needs to consider. The computer or chip features and the actual numbers or data that is programmed into these chips and computers. No doubt, one can have the most advanced computer hardware, however if the programmed data is incorrect or far from optimum, then performance, durability, fuel economy and throttle response will suffer. To begin with, let's deal with the chip or computer hardware and features.

Chips and Computers - how do they go about improving performance?

There is nothing magical about altering the state of tune of a modern Toyota diesel engine. Given the optimum mass of fuel injected into the combustion chamber at the optimum time in the engine's compression cycle and you have the optimum engine power and torque. It really is that simple. The standard ECU has data points stored in its memory that determine the mass of fuel injected and the timing at which that occurs. These data points vary quite markedly depending upon the engine's RPM and throttle position.

At this point in time, all the readily available tuning chips and computers do not alter these stored values but instead take that value and offset it by an amount that is stored in the performance chip or computer. The benefit of this approach is that when the performance device is removed, the engine is returned back to standard control and tuning.

Basic Basic Basic universal fuel increase units....and cheap to manufacture..

The most simple devices attack the fuel side of the injection pump only. Some claim that timing is altered as the fuel volume alters, though this is a tad misleading because the way the pump injects fuel is to hold the injector open for a longer period of time - hence the timing is altered. But this can in no way be called independent timing control.

The most basic of these devices increase the amount of fuel by a fixed percentage across the RPM/throttle range. Some may offer the option of several different percentages via an adjustable potentiometer or jumper switches, but again it's a bulk change across all engine operating conditions. These devices are very cheap to produce and technically well within the realms of the basic electronics novice. In fact, the ease with which bulk fuel changes can be made has brought out  products from people with limited electronics experience who have no diesel expertise or at best, just own a diesel vehicle. At under $1,000, these products may seem attractive in price however when one considers that at most it is $25 of parts from the clearance bin of the local electronics shop, little or no R&D along with the very poor level of tuning expertise that has gone into the product, it is an item that no Toyota Land Cruiser owner would be associated with.

In addition, due to the increase in combustion particulates through bulk overfueling in either the Prado 1KZ-TE and Land Cruiser 1HD-FTE, engine oil contamination becomes a serious issue and will more often than not require oil and oil filter service interval of 2,500 km instead of the standard 5,000 km interval.

What the above product has done is to simply mimic the main set screw of a traditional Toyota mechanical injection pump and cause a fixed change in the amount of fuel injected regardless of engine RPM and engine load. 

1000 RPM 2000 RPM 3000 RPM 4000 RPM
All Throttle Positions + 15% + 15% + 15% + 15%


Basic Basic....Multi point fuel adjustment.

The ability to adjust the amount of fuel injected at a number of different parts of the RPM range is a major step forward from the bulk percentage adjustment offered by units above. Multi point units will allow a different percentage increase at low engine RPM for example from that at high engine RPM. The advantage with these units is that they begin to address some of the limitations programmed into the factory engine management systems.

Due to strict European emission requirements that do not apply here in Australia, Toyota purposely limits the amount of fuel at low engine RPM. This results in an engine that feels sluggish at low RPM but gets up and goes when the engine revs beyond 1800 - 2000 RPM. All owners of Prado 1KZ-TE and Land Cruiser 1HD-FTE will have experienced this and most probably mistaken it for turbo lag (which it isn't - more correctly it is fuel lag).

The percentage increase in fuel at low RPM can be greater than that at higher engine RPM whilst still maintaining excellent engine durability. For example, at low engine RPM, a 30% increase in fuel may be appropriate, though at high engine RPM, only 15% increase. Multi point fuel adjustment allows for this variation through the RPM range whilst the very basic bulk adjustment units would have to be limited to the 15% increase in order to maintain engine durability and forsake the additional improvement at low RPM. Interestingly, both units may have identical peak power and torque figures, however the more advanced multi point adjustment unit will deliver superior low RPM torque and response.

The table below is an example of various fuel adjustment points that may apply regardless of the throttle position.

1000 RPM 2000 RPM 3000 RPM 4000 RPM
All Throttle Positions + 30% + 20% + 15% + 10%


Desirable Fuel Mapping

Taking the above multi point fuel adjustment further, we now get close to the capabilities of a sophisticated fuel management system where one can program many fuel points across the combination of engine RPM and throttle position.

Below is a simple example showing individual adjustment points for fuel injected at different engine operating conditions.

1000 RPM 2000 RPM 3000 RPM 4000 RPM
20% Throttle + 10% + 10% + 15% + 15%
60% Throttle + 20% + 15% + 15% + 12%
100% Throttle + 30% + 20% + 15% + 10%

But all is not quite as clear cut as it may seem. A unit that allows discrete adjustments as shown above must have the capability to interpolate between points (or to use the correct terminology - load sites). Because the example above is fairly course, using large jumps between load sites, the unit must be able to ramp up or down between load sites. For example, the 100% throttle adjustment goes from 30% at 1000 RPM to 20% at 2000 RPM. Interpolation means that at 1500 RPM, the unit will automatically adjust to 25% - and so on. This provides smoother engine operation particularly when cruising at or close to an RPM point where a change in percentage rate adjustment is made.

Independent Injection Timing

The ability to have independent injection timing on the Toyota 1KZ-TE and 1HD-FTE is technically difficult to implement successfully. In fact, most manufacturers of performance chips ignore this very important aspect of engine tuning because it is so difficult - settling instead for performance improvements through overfueling alone.

The benefits of sophisticated injection timing control to the Toyota performance enthusiast however are significant - not only for improved engine performance, but more importantly for efficient engine operation (improve fuel economy) and engine durability (lowering peak combustion temperatures). 

In addition, without effective independent control of timing - particularly at low RPM - engine oil contamination from combustion particulates becomes a serious issue. By making minor timing adjustments on the Prado 1KZ-TE and Land Cruiser 1HD-FTE engines, oil contamination is minimised and there is no need to make any adjustments to the service schedule. On the other hand, a bulk fuel only device such as those mentioned above may require more frequent oil and oil filter changes - typically every 2,500 km.

It is very desirable to employ the same capability as we saw previously with the fuel map to adjust the injection timing at a number of points across the entire range of RPM and throttle position combinations. Again due to strict European emission requirements, the injection timing is purposely set to values that are not optimum for engine power and torque or indeed engine response - particularly at low engine RPM by the manufacturer.

The chart below shows a simplified map of injection timing adjustments at different engine operating conditions.

1000 RPM 2000 RPM 3000 RPM 4000 RPM
20% Throttle + 4 deg + 3 deg + 4 deg + 3 deg
60% Throttle + 3 deg + 1 deg + 3 deg + 3 deg
100% Throttle + 3 deg + 2 deg + 1 deg + 2 deg

In the case of turbocharged diesel engines, sophisticated injection timing maps can be used to dramatically improve the turbocharger response characteristics and effectively improve the range at which the turbocharger is performing at high efficiency - producing strong boost pressure.

Briefly, the energy contained in the exhaust gases drive the turbocharger. The higher the amount of exhaust gas energy, the higher potential for the turbocharger to convert that energy into useful work. Of particular interest is the point in the engine's RPM range where the turbocharger begins to produce strong boost pressure - typically around 1800 RPM.

By slightly retarding the injection timing at that point in the RPM range, additional exhaust gas energy is created, thus allowing the turbocharger to deliver boost pressure earlier. This effectively widens the range where the turbocharger is operating efficiently. The above is certainly valid at large throttle openings when overtaking, however at small throttle openings the opposite is required. To run retarded timing under cruise or light throttle applications results in inefficient engine operation and increased fuel consumption. It is important then to advance the injection timing under these cruise conditions.

A simplified example may be seen below.

1000 RPM 2000 RPM 3000 RPM 4000 RPM
20% Throttle + 4 deg + 3 deg + 4 deg + 3 deg
60% Throttle + 3 deg + 1 deg + 3 deg + 3 deg
100% Throttle + 2 deg - 2 deg
+2 deg
+ 2 deg + 2 deg

Following on from the above discussion regarding retarded injection timing (as shown at load site 100% throttle/2000 RPM) to improve turbocharger response, a tuning strategy that employs this feature ideally will also have the capability to treat this in a transient manner. In other words, use the retarded value only (shown in red) until the turbocharger has settled and is producing the desired boost pressure level. Then the computer could creep that negative timing adjustment up into positive values (shown in green) so that the engine will be operating at peak engine efficiency under steady state conditions. Circumstances where this is of use to the driver is when towing up a hill. You put your foot down, the turbocharger builds boost pressure quickly (transient tuning parameters) and as the engine settles into the task of pulling the load up the hill, the tuning computer changes the tuning parameters for steady state conditions.

In summary - regarding independent injection timing control, this is a technically difficult feature to implement and requires sophisticated hardware and software. The improvements in engine performance and throttle response can be dramatic as can the enhancements to engine durability when adjusted in conjunction with increased fuel injection volume.

Engine Durability

The whole idea of improving engine performance in a Prado or Land Cruiser really goes out the window if engine durability is significantly affected. Very few LCOOL members would consider a device that will break a 1KZ-TE or 1HD-FTE engine - regardless of the performance improvement. It is important that a good deal of development goes into ensuring that engine durability is not adversely affected - preferably enhanced.

To this end, the performance features such as independent injection timing control are important for enhanced durability, as are the numbers that are programmed into each chip or computer. However the more highly technically advanced units also employ a number of safety features in order to add further engine protection under sever operating conditions.

For example, if engine coolant temperature increases above a certain point, the standard engine management system will take some action to rectify the situation by making small adjustments to the fuel injection volume. If however an overfueling only chip such as that first described is installed, it will simply continue to supply 15% - 20% more fuel on top of the fuel volume that the standard computer is injecting. This will result in engine damage if allowed to continue because the standard ECU's safety program is not designed to cope with a large bulk increase in fuel. A more advanced unit however will continually read the engine coolant temperature and when above a certain point, make changes to the injected fuel volume in order to save the engine.

There may also be other items such as air temperature, boost pressure etc. that may be used for tuning compensation as well, though this makes wiring more complicated since more and more signal wires to and from the standard ECU must be spliced into if not utilising a plug in loom. Actually, this raises yet another issue that may not at first be seen as an engine durability feature. If a unit has a plug in adaptor that has access to all the signals entering and exiting the standard ECU, then the higher the chances that even more sophisticated engine protection strategies are in place.

In any case, from a chip or computer hardware point of view, those that have built-in safety features are by far preferable to those that do not.

Another aspect is the data that is stored inside the standard ECU. Most factory computer systems log and store operational data such as vehicle speed, throttle position, temperatures, boost pressure etc. This data often cannot be erased by traditional means such as removing power from the factory ECU. Hence if the logging of altered operating conditions is of concern, the devices which monitor and control the input of the ECU as well as the output should be of interest. These devices will often present data to the ECU that reflects normal operating conditions. There has been talk that the standard ECU may does not log this data, however those comments have been made by those who do not have the equipment to read it.

Programming, Numbers, Data - The stuff that goes into a computer

So far we have dealt with the chip or computer features that are used to improve the performance of a Prado or Land Cruiser. As has been indicated throughout, regardless of the features, if the data programmed (or in the case of simple overfuling devices, jumper or screw position) is not appropriate, then engine performance, engine durability, fuel economy or all will suffer.

Not unlike the issues faced mechanical injection pumps, simple overfueling devices face the same issues when it comes to adjustment. Put simply, it is a matter of how much risk the tuner or 'Cruiser owner is prepared to take. The greater the volume of fuel injected, the higher the risk. Since there is no other adjustment for timing or inbuilt safety, the improvement will be at best a compromise.

Typically, these devices will be set up on the road without extensive use of data logging equipment, gas analyser or chassis dyno. Hence with little knowledge of what is happening to the engine during the combustion of the greater volume of fuel over standard.

More sophisticated devices that have provision for independent timing adjustment and fuel adjustment through comprehensive maps are typically programmed using elaborate test and measurement equipment as well as on road testing. The complexity of these devices demand the right tuning equipment as well as tuners who have a deep knowledge of not only diesel engine operation, but the ability to properly comprehend exhaust gas analysis, oil analysis etc. and to understand how this data relates to fuel combustion and engine operation. Setting up of these devices cannot be performed successfully on road alone as it is impossible to have all the relevant equipment connected and operated under controlled conditions. These devices, once tuned, will typically be locked so that tampering or altering of the programmed values is prohibited. This is mainly due to the fact that those who wish to tamper will more often than not have no access to the relevant test and measurement equipment that is so important in achieving the optimum parameters.

Before or After the ECU

There are two schools of thought here. One is to place the tuning device between the ECU and the injector pump and the other is to place the tuning device before the ECU.

Technically, between the ECU and the injector pump is by far the easiest to implement because all it does is to take the signal from the ECU and alter it before sending on to the injector pump. This also requires very simple electronics and wide tolerances in terms of the quality of the electrical signal.

Unfortunately, when between the ECU and the injector pump, if the ECU tries to alter injection parameters under abnormal running conditions - such as high engine coolant temperature etc., the tuning device will continue to modify the signal for greater performance ignorant to the fact that the ECU is attempting to save the engine from damage.

On the other hand, devices that are placed before the ECU achieve a similar or better performance result, but with a good view of the data that flows to the ECU, they have the opportunity to complement the ECU when an abnormal condition occurs. This is generally a safer option if the vehicle is to be operated in severe conditions or when towing heavy loads.


As stated up front, with the advent of electronic control of diesel injection systems, a plethora of tuning devices have been released on the market to tempt the Prado and Land Cruiser performance enthusiast. Let's face it, a chip is a chip isn't it? 

On the face of it, all promise improved performance however as is plainly seen from all of the above, there is a huge leap in going from a simple overfueling device to a sophisticated plug in computer system with comprehensive fuel map, independent timing map as well as built in safety features.

The cost of these units on the other hand is not necessarily relative to their features or capabilities. For example, simple overfueling devices installed between the ECU and the injector pump can cost between $600 - $1300. It could be argued that, given that these devices are very simple and inexpensive to develop and manufacture, the retail price is geared more towards preying upon consumer ignorance rather than technical merit.

LCOOL members should now be in a position to better evaluate the variety of options for their Prado or Land Cruiser and to ask more relevant questions rather than relying simply upon quoted power and torque figures. In fact, these very figures which may have at first been the most significant criteria to the LCOOL member, are ultimately the least important, for all devices will deliver an improvement. The important criteria are those that are used to determine which devices deliver the best improvement in engine performance across the entire RPM range and throttle range, fuel economy and engine protection at a reasonable cost.



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