Diesel Kits

The diesel conversions have to be one of my favorite because of how simple they are and the immediate response you get from the addition of the CNG to the current system.

Things to know before we begin.

These are not a true “conversion” in the sense of the other conversions I have discussed in the fact that you are simply adding the fuel to the existing system and not replacing the fuel like a petrol/gasoline conversion. I like the term dual fuel or split fuel because it is a better reference on how the actual system performs or uses the compressed natural gas.

CNG – Compressed Natural Gas.

Pyrometer or EGT-  Exhaust  Temperature Gauge.

So how does this system operate?

These systems are exponentially simpler to install compared to the petrol/gasoline style conversions. All it is, is a low pressure gas line that is plumbed into you air intake before the turbo. This low pressure fuel line is fed natural gas from the regulator. The regulator receives the CNG from the high pressure tubing that is attached to the tank(s) that contain the compressed natural gas in quantity. The Regulator also has two coolant lines that are running in and out of the regulator to help maintain an operating temperature and prevent the regulator from freezing. It would likely freeze and be damaged as the CNG decompresses it looses temperature and the coolant helps to prevent the equipment from freezing and warms the natural gas to a burnable temperature before it enters the motor.

The newer systems that have just recently been released also include a step motor between the regulator and air intake on the low pressure gas line. This acts to regulate the flow throughout the RPM range. In order to maximize the efficiency and fuel savings the motor can handle a higher concentration of natural gas above idle and in the higher RPM range. However if you add to much at idle it begins to idle rough and back burn until the turbo and air begins to move in the middle end of the RPMs. To avoid the back burn and the rough idle and still have a higher concentration of natural gas in the system the step motor closes off the low pressure line as it approaches idle then reopens it as you accelerate. The settings that control the step motor are in the software (usually included in a good kit) and can be manipulated by you the user to increase your upper end concentration without affecting the idle. This is an awesome recent advancement in the kits and will save you money without affecting your low end performance. As always with these kits, use common sense in your setting so that you are not adding to much natural gas in the top end and damage the motor. At maximum i would only be running a 70% CNG 30% diesel mixture. On average a 50/50 split has been the most reasonable for application in the motors I’ve done. You can always increase and decrease that percentage depending on what type of driving you will be doing that day and it will only take a minute to adjust.

There is no mixer required for this system and all is needed is to securely add a low pressure fuel supply prior to the turbo. The fuel supply is managed by dialing the regulator up or down depending on the performance of the motor. The natural gas is actually pulled from the regulator as the turbo winds up and the vacuum increases. So more natural gas is added when you have more boost from the turbo at higher RPMs and less natural gas is added at lower RPM if any at all at idle. Ideally you want to add approximately 50-70% CNG and respectively 50-30% diesel. I have found that in my installations if I add much more that those figures it is adding too much near the idle and it causes it to be rough on the low end or until you begin to accelerate and it smooths out.

Some of the wiring needed for this type of a system are the following.

RPM Signal -  This wire communicates with the CNG controller to let it know when the truck is actually running. If you can’t find this on your diesel you can use the crank shaft position sensor or any other signal that is only on when the truck is actually running an not simply when the key is on the on position.

Ignition Wire – Provides power to the system. It provides power to actuate the solenoid on the regulator and gives lights to fuel gauge on the dashboard changeover switch.

Permanent Hot – This is a for memory storage on the controller if the kit you use has this capacity.

TPS -  Throttle position sensor. This is used for kits with more advanced settings to dump more CNG at the higher RPMS. Not on all kits.

Step Motor - Wires to the CNG ECU for low pressure gas regulation to the motor at different RPMs/throttle position.

Ground - Provides the ground for the system.

Pressure Gauge – These wires communicate the actual remaining pressure left in you high pressure cylinders to your change over switch for a fuel gauge.

Pyrometer Gauge or EGT – Exhaust Gauge Temperature sensor. Not all kits have one of these included. If your kit doesn’t have one then purchase an aftermarket one so you can monitor the exhaust temp during your driving conditions.

Pros and Cons


  • Adding CNG to the fuel can help off set and reduce the amount you spend in fuel. You will be purchasing two separate fuels but you will burn it more efficiently and save money from better fuel economy.
  • Increased horse power. The CNG helps to atomize the diesel and when the diesel begins to burn it ignites and allows for a more complete burn of the fuel in your cylinder. This decreases the amount of fuel you need for the RPM you want to maintain and because of the efficient burn increases the overall horse power output. I don’t have numbers to quote but it can be significant compared to a stock truck. Add it to a truck that is chipped and its eye opening.
  • Because you are more efficiently burning the fuel it is cleaner in your cylinders and cleaner for your exhaust. It will also save you money by increasing your mileage between oil changes and increasing the life of your motor.


  • Kit and fuel cylinders or tanks can be expensive. At least an upfront cost that will take some miles to recover.
  • If you do not monitor your exhaust temp and you HOT ROD your diesel everywhere you can cause damage to your motor from the heat. Just as if it were chipped, or if you add this to an already chipped motor you are increasing the burn temperature and too hot for too long is not good for the motor.
  • Lose bed space because of the tank size.

Overall these kits are awesome. I have installed several without a problem and they are still running strong without any issues. I do not mean to steer anyone away because it burns hotter. Yes it burns hotter but as long as you monitor the vehicles exhaust temperature and know the respective limits for temperature you won’t have any issues. You can even turn down the CNG output during towing to ensure you still get a more efficient burn but at the same time you aren’t approaching the temperature limits on your motor. I have seen chipped Duramaxs get up to 56 miles per gallon and i’m not partial to any diesel. The most recent Cumins i installed wasn’t chipped and saw an increase in fuel economy up to 36 mpg average highway miles per gallon and 30 around town. That is amazing!. I have only done these conversions on the light duty trucks and have yet to put a kit on a smaller diesel like the VW or Mercedes  but I am anxiously waiting to see how well it performs.

These kits are incredibly simple and i’d suggest purchasing them as a kit so you have what you need. Most kits I have seen don’t have a Pyrometer and i would highly recommend getting one installed if you decide to have a CNG kit added to your vehicle. Here are some pics of a most recent truck I installed a kit on. It was a 1998 power stroke and it runs like a dream and is now getting 28 average miles per gallon city driving and 35 average miles per gallon on the highway. He isn’t out to drag race and he drives average (not slow but not pedal to the metal either). Hope you enjoy and I will try to add some videos of the operation soon.