How do I switch my CNG on? 1994 Chevrolet c15000 (IMPCO conversion)

[ninjabluedog]

I just bought a 1994 Chevrolet c15000 from a guy who said that he got it from a military auction. It is supposed to be bifuel, but I can’t figure out how to get it to switch to CNG. I am new to the CNG scene and don’t know much about it.

After filling up the tank I was hoping it would automatically switch over to CNG, but that was not the case. It has an IMPCO conversion kit in it and the control board didn’t seem to be plugged in. I plugged the wires that looked like they belong to it into it, but still no luck. The only non OEM switch I can see in the cab is an orange button that looks like it should light up. It doesn’t seem to do anything when I push it though.

Any suggestions would be appreciated.

[BruceEB]

Re: How do I switch my CNG on? 1994 Chevrolet c15000 (IMPCO conversion)

Make sure there is not a fuel shut off valve located on drivers side on the frame.

[ninjabluedog]

Re: How do I switch my CNG on? 1994 Chevrolet c15000 (IMPCO conversion)

Hi BruceEB,

Thanks for your suggestion. There is a valve on the side of the frame and I have tried turning it on and off, but with no positive results. I found an IMPCO manual training manual at http://www.impco-beru.nl/IMPCO%20Training%20Manual.pdf and according to what I read in the manual there are 7 components to the fuel system:

Fuel storage cylinder & valve --> ¼ turn valve --> pressure gauge & multi – turn vavle --> high pressure regulator (HPR) --> fuel lockoff --> pressure regulator --> fuel air mixer

I believe the valve you are referring to is what the manual described as the “¼ turn valve.”

The manual says (p.47) that the “multi –turn valve” is located in the engine compartment and provides a place to shut off the flow of CNG for when the servicing the fuel system. I think this valve may be shut off, but I am not sure where it is or how to turn it back on if it is off--any suggestions?

[ninjabluedog]

Re: How do I switch my CNG on? 1994 Chevrolet c15000 (IMPCO conversion)

I took the truck to a mechanic at Semi-Service in Salt Lake City, and they told me that my computer was bad and recommended I get a new one. I contacted IMPCO (the maker of the conversion kit) and they said that the part hasn’t been produced for a long time and it would be very difficult to get a hold of (he also mentioned that it was very very rare for that part to break, so I wonder if I got a correct diagnostic) and recommended that I try and replace the system with something more current that is serviceable.

So I am wondering if any one out there knows of a place I can get a hold of that part, or if any one knows where I can get some replacement equipment that will work with my truck?

The part I am looking for is a black box with wires sticking out of it that has the word
IMPCO written in large letters across the top of it. It is roughly 8 X 3 X 1 inches and has two numbers part numbers on the bar code label. One above a bar code reading "AC8-16910" and the other below the bar code reading "TAG9410A-0126"

If no one can help me on this I guess I will be trying to sell the truck after this.