CNG Conversion Kit: Basic Installation
*NOTICE: This is for EDUCATIONAL purposes only. We highly recommend you get an experienced ASE Certified mechanic who knows about CNG. Before any install you should be very familiar with the common regulations such as “NFPA 52” (the fire code) pertaining to CNG conversions.
The Below Is For Aspirated and Sequential Bi-fuel CNG Kits… If you don’t know what those are, then you can learn about them here.
You must make sure you have a good CNG conversion kit. For a complete list of parts you can view the PDF of the SkyCNG kits and make sure you’re comparing apples to apples. Even if you do not buy the SkyCNG kit, you can still put us up against the other guy. Get very familiar with these components and know what they do.
STEP 1: Make sure you have a good 3600psi CNG cylinder (tank) with a Pressure Relief Device (PRD) and shut-off valve (manual or remote). The cylinder and PRD are not included in the SkyCNG CNG conversion kit.
You’ll also need some good steel straps/brackets for the CNG cylinder mount. They are required by fire code law NFPA 52 Section 6.
STEP 2: Come up with a plan before you start bolting things on. If you know what the components of the CNG conversion kit do, then you will be able to plan your install and locate the best place for each part and hose. You’ll be installing things under the hood, on your dash, and underneath the vehicle. Are you planning to install the cylinder inside your vehicle, like the trunk? Then NFPA 52 (fire code) rules say you must make the pipe joints/components air tight and create a vent for the PRD (usually vented through the floor). Click the “regulations” link at the top of this article to learn about NFPA 52.
STEP 3: Where will the CNG filler receptacle go? This is the place you “pump” the CNG into. I have seen it next to the gas cap, in the truck bed, under the hood, and in the grill of your car. There are NFPA rules for this as well. (NFPA 52 Section 6 covers all this)
STEP 4: Try to keep the high pressure hose line away from the exhaust pipes and system. NFPA says you must have maximum “practical” clearance. This CNG line includes the regulator and could also inclue a filter (if desired). Find a place for these. The CNG filter will go between the cylinder and the regulator. The shut-off valve will go pretty much next to the cylinder. This will help you isolate the CNG in an emergency.
STEP 5: SkyCNG CNG conversion kits include a 20ft length of 6mm steel high pressure fuel line. This is rated up to 3600psi. Make sure this CNG fuel line can be securely fastened under the vehicle and is resistant to road vibration and debris. Cover it with rubber fuel hose if you go through metal or on sharp corners. Keep away from the exhaust. Make sure you leave slack for installing components. Put the pressure gauge (manometer) inline with the T set (with SkyCNG conversion kits).
STEP 6: Install the regulator. You can get steel straps at any hardware store. Make sure it’s fastened nice and tight so the high pressure CNG fuel line doesn’t move around. Make sure it is positioned so the outgoing low pressure CNG is pointing towards the car engine. Keep in mind that the coolant lines will run into this regulator as well. These will tap into the heater hoses on your vehicle usually with a “T”-hose joint. Put one of the lines between the heater control valve and the engine.
STEP 8: FOR MIXER aka “Venturi” aspirated CNG conversion kits- Install the mixer into the intake inlet hose as near to the throttle body as you can. The inner circumference of the mixer should be half the throttle plate circumference (C= 3.14 x diameter). It’s OK if your kit bolts directly on to the throttle body inlet. Secure the mixer with no gaps or spaces inside the intake hose. The stepper motor control valve goes in the low pressure CNG line between the regulator and the mixer. Make sure its positioned so moisture will not get inside the motor itself.
STEP 9: BACK TO SEQUENTIAL: The scariest part is when you drill, tap, and install the metal nozzles into your intake manifold. If your manifold is plastic then its easier and you may not even have to remove it.
Put the nozzles as near the original gasoline injectors as you can. Fasten them as tight as you can with “LocTight” or some compound. Your SkyCNG conversion kit will come with hoses you can cut to length from the injectors to the nozzles. Use a firm clamp on both ends of the connection. Put the “injector rail” as near to the nozzles as you can. You can get pretty creative when installing the injectors by using brackets and joint pieces you can buy from the hardware store.
STEP 10: Use the SkyCNG wiring diagram, the included wires, the USB-to-serial computer cable, MAP sensor, and your vehicle’s OBDII system to plug into the ECU (the Electronic Control Unit aka computer). The RPM wire should be connected to the negative engine coil. SkyCNG OBDII kits do not require tampering with oxygen circuits or sensors (O2 sensors). The ECU communicates with your car computer to make sure everything is proper. The SkyCNG kits comes with diagrams to do this properly. Put the ECU in a protected and dry place under the hood or where convenient.
STEP 11: CNG controller/ fuel gauge- Try to find an existing hole through the engine firewall and then mount the guage where convenient on the dash. This connects to your CNG conversion kit ECU.
STEP 12: Calibration- Use the SkyCNG serial cable to connect your latop to the OBDII as noted in the wiring diagram. Follow the steps to fine tuning your new CNG conversion kit! You may need to update the calibration from time to time if you notice changes in performance or you get lots of miles on your car.