Switch to Gas before using the CNG

[UtahValley]

I have a 2000 Chev with an IMPCO factory install. I initially had to replace the internal switch to indicate when it was running gasoline or CNG. Now that this is working I am seeing that the CNG switches to gasoline after the gage is only down to 3/4 full. If I fill-up with CNG (couple of gallons) then it will go back to CNG for a time until the pressure drops - but far from empty then again back to gasoline. I am getting tired of visiting the station for 2 - 3 gallons of CNG. What's wrong?

[CNGfamily]

Re: Switch to Gas before using the CNG

Now that this is working I am seeing that the CNG switches to gasoline after the gage is only down to 3/4 full. If I fill-up with CNG (couple of gallons) then it will go back to CNG for a time until the pressure drops - but far from empty then again back to gasoline. I am getting tired of visiting the station for 2 - 3 gallons of CNG. What's wrong?

This sounds just slightly different than problem than I had, but it may be worth checking into... the pressure transducer on mine went out (5V, three terminal device showed electrically "open") During the time it was going flakey before totally not working, I had similar operation where it would run and show full for only the top bit of fuel pressure. It wasn't very long before it stopped working even with a full tank. In the diagnosis phase, and until the part came in, I used a potentiometer in place of the transducer to fake out the system to tell it I had CNG (in conjunction with keeping tabs on the analog pressure gauge under the hood)

[Lancer Automotive Group]

Re: Switch to Gas before using the CNG

Sounds like a transducer problem, it messures the pressure in the tank.

[UtahValley]

Re: Switch to Gas before using the CNG

So what is the cost for a transducer? Is it a DIY job or do I need to take it to a shop? Where do I locate one? Many thanks for your timely response. This is on a Chev Truck 2500.

[CNGfamily]

Re: Switch to Gas before using the CNG

So what is the cost for a transducer? Is it a DIY job or do I need to take it to a shop? Where do I locate one? Many thanks for your timely response. This is on a Chev Truck 2500.

If it was like mine, I couldn't purchase it directly from the manufacturer. It didn't matter that I work with high pressure systems in spacecraft and understand the do's and don'ts for high pressure systems, I'm technically not a certified CNG shop and couldn't get the part by myself.

You'll save yourself some time by getting the PN info and have the shop order it, but I wouldn't recommend DIY.

[UtahValley]

Re: Switch to Gas before using the CNG

Thanks - Any tips about where the transducer is located or since I need to take it to the shop - should I just let them take care of those details?

[Lancer Automotive Group]

Re: Switch to Gas before using the CNG

I would let the shop handle it but I am a little bias.