Gas gauge no longer shows fuel in the tank

[sponge]

I have a full CNG tank, but the truck refuses to use it. Someone said it might be a broken transducer sensor or something like that. Is this something I can fix from home? Is this under the truck's hood, or something close to the storage tank in the bed? If easily to install, where can I buy the needed part?

Thanks!

[siai47]

Re: Gas gauge no longer shows fuel in the tank

What year and model is your truck? Is it a GM factory or aftermarket installation? It makes a difference. Could be a tank pressure transducer. Failure of the transducer, wiring, or it's power supply would give a improper fuel gauge reading and make the ECU think there is no cng in the tank. Yes, it can be checked at home with a voltmeter .

[CNGfamily]

Re: Gas gauge no longer shows fuel in the tank

I've had a high pressure transducer fail in the past... like everything else CNG be prepared for an expensive part in this case cannot even be sold directly to you (I've worked with high pressure systems in spacecraft for years and couldn't buy direct). Like siai47 says, you can do the troubleshooting yourself to isolate the problem.
If you find it to be a failed transducer, there are workarounds. For a time before I had the part replaced, I faked the system into working by using a potentiometer in place of the electrical connection to the transducer (so the system thought there was fuel no matter what the state of the tank). Good luck!

[sponge]

Re: Gas gauge no longer shows fuel in the tank

It's a 1998 Chevy Cheyenne pickup. This was a government fleet vehicle, so I'm almost certain it is a factory installation. Does anyone have a digital photo of this transducer? This would be helpful so I know where to look.

If I can't order one of these high pressure things, then I assume I need to have a specialty shop order it for me? Any tips on this little adventure will be greatly appreciated.

Thanks

[siai47]

Re: Gas gauge no longer shows fuel in the tank

The FPS (fuel pressure sensor) is located on the fuel tank. Remove the tank cover and locate the thingy with all the wires and hoses going to it. The FPS is a silver gizmo about 3/4" in diameter and a couple of inches long. It is located on the bottom of the high pressure lockoff valve (the thingy). There is a connector on the FPS with three wires going to it. The connector also has 3 pins in it marked A, B and C. The wire going to pin A should be dark blue, B orange and C gray. Using a voltmeter, with the connector disconnected from the FPS, and the ignition key on, check for 5 VDC at pin B (orange) 1 VDC at pin C (gray). Then switch to ohms and check for ground continuity on pin A. (be carefull not to short out any of the pins during this check ). If this doesn't check out, you have a wiring problem. If it does, re-connect the connector to the FPS. With the key on, and a full tank of fuel, poke the gray wire with a test probe. You should read somewhere between 3.75 and 4.10 VDC if the FPS is working correctly. If it is reading 1 volt or less, the sensor is bad. The sensor, I believe, is common throughout the CNG Chevrolet line. Any year Pickup, G-van or Cavalier sensor should interchange with the one you are using. If you need more help post again .

[sponge]

Re: Gas gauge no longer shows fuel in the tank

Thank you, I will try to look into this during the weekend.