First I like to say that in no way, shape or form was the existing emission systems modified. No Lambda emulator to fool the oxygen sensors, no oxygen sensor wiring was cut, no timing advance processor was wired. In fact the only wiring modifications that were made was a tap for engine RPM and the gasoline fuel injector wires were spliced. That is it.

Second I would like to say that the Technocarb SVIS kit is phenomenal . It runs right out of the box. When I finished the conversion and started the Trailblazer for the first time, it started right up on gasoline. When the engine temperature reached about 170-180°, the vehicle switched right over to CNG automatically. I then took it for a ride and the power curve characteristics seemed unchanged from gasoline. Truly amazing.

The Real Story

Well the program director (wife) decided she did not want to drive a bi-fuel Cavalier anymore and wanted an SUV. After looking at some used SUV's we decided on a 2008 Chevy Trailblazer. It had low miles, a large cargo bay, a full steel frame and most important my wife liked it. If it was not for removing the intake manifold, the Trailblazer conversion would have been a really fun project. Below is my documented adventure from start to finish. It should help you get an idea what a CNG conversion is really like. Enjoy!

You already know most of the background information from the main page and above introduction, so I will not bore you with more dribble. Over the years I have collected many CNG parts off Ebay to repair my Cavaliers. Tanks and cradles, nozzles, fittings etc. With such a surplus, I figured someday they could be used in some kind of future conversion. So a lot of what you see here are used parts. With that, the first order of business was to get a conversion kit. I meet a guy named Dennis, he has a cool YouTube Video showing the operation of his CNG rig. We got to talking and he ended up getting me a kit from Technocarb. I feel the best features of a Technocarb SVIS (Sequential Vapor Infection System) is that it will run right out of the box and it is computer tunable via a USB cable. Here is the contents of the kitspread out on my assembly table. The next order of business was to design and fabricate the tank cradle and cradle mount. It just so happens that I had 2 CNG tanks, cradles and miscellaneous parts for a Cavalier, stowed away from an Ebay purchase 9 months ago. So now I need to cut the straps out of the two cradles in preparation for the mount design. Once the two strap assemblies were ready, it was time to do some preliminary fit up in the Trailblazer cargo bay. This will determine how much modification, if any, is needed. Once the fit up and design work is complete, it is off to fabricating the main tank support and attaching the tank straps. The design work was done with AutoCAD Mechanical Design software. It is truly sweet to be able to design to scale and transfer that design into a perfectly fitting assembly. Once the fabrication was complete, it was time to paint the main supportand add the rubber isolation strips. The main tank support was then installed in the Trailblazer cargo bay. During the main support install, I had to fabricate some underfloor support plates which are needed per NFPA 52. With the CNG tanks installed, I needed to replace the Chevy style HPL (High Pressure Lock-off) with a Ford style one. That is where I found the dreaded left handed thread. After I got the HPL issue out of the way, my attention turned to routing the CNG tank supply pipe, electrical tank connection and installing the vent booting. Moving on, my next task was installing the fill nozzle on the rear frame. Once the fill nozzle was installed I began to route the CNG supply line. At this point I decided to take a look under the hood and begin some planning of components there. I chose to install the injector nozzles first. This entails removing the intake manifold and what a job that was. With the intake manifold finished, I turned my attention to installing the CNG regulator. The regulator placement was important in that multiple connections needed to be made and working clearance was a high priority. It also needed a special bracket made to position it correctly. Once the regulator was mounted, I had to fabricate and install a shield to protect the regulator from water and debris flying off the radiator fan blade. I then moved on to installing the shutoff valve and plumbing the final leg of the CNG supply line to the regulator. At this point it was time to turn my attention to installing the heater lines that warm the CNG regulator. It took some time and fooling around to splice into the heater core. Limited space and funky hose connectors complicated the effort. Well I could see the end was near for fabricating speciality brackets and mounting hardware, however I still needed to mount the manifold vacumn/injector pressure sensor which found a home in a nook between the battery and drivers side headlight. There was also enough room to fit the fuel gauge interface module next to it. The last component that needed mounting was the Technocarb ECM. The placement was critical as there are locational requirements beyond the ease of routing wire. With all the components mounted it was time to route the miscellaneous vacumn and pressure lines from the intake manifold to the pressure regulator and injector pressure sensor.

With all the components now mounted, it is time to dig into wiring everything up. This was probably the most stressful part of the job. After a phone conversation with Technocarb support we ironed out all the problems. With all the wiring issues resolved I began to figure out a wiring plan and started wiring the FGIM (Fuel Gauge Interface Module). From there it was time to establish the hot and ground wiring along with HPL (High Pressure Lockoff) wiring. With the power distribution wiring out of the way, I set my sights on wiring the rail injector plugs and connecting them to the rail injectors. With the rail injector wiring out of the way I turned my attention to an ugly little job, that required wiring a pickup wire to obtain engine RPM. I am now down to 2 wiring tasks left to do. I chose next to wire the fuel level gauge which mounts in the drivers compartment. Well, I have been putting off the last wiring task to the bitter end. Procrastinating the whole way, it was time to splice and wire the fuel injectors. With the wiring complete the last item on the list is to add information stickers to complete the job.

Well you probably think this post is done, oh no there is another chapter to come. I will post it soon.