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Not Getting Full Tank Capacity on refueling

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  • Harpoon
    replied
    Re: Not Getting Full Tank Capacity on refueling

    Just FYI. I had a problem on my Cavi where I wouldn't get full fills. I was checking the pressure at the pump and I was getting 3200PSI but I would only see half tank in the car. And my car would switch over to gasoline when the needle got down to the normal under red line spot. I was only getting 105miles on full fills instead of 150miles. I was only getting 3.5gal vs 5gal.

    Defect was:
    The Fuel Pressure Sensor (FPS)
    The FPS is a special designed transducer GM had specifically made that was a 0-4000PSI 0-5VDC output. You can get the FPS from GM but it was >$500. I found and purchased a pressure transducer that was 0-5000PSI 0-5VDC for $100.

    I never installed the new transducer due to my GM one auto corrected. It was reading wrong for over a month. Then when I went to Moab for a weekend I filled in Price and got 4000psi The sensor didn't correct but it did hit 3/4 tank rather than half. Then on the way home I got a second 4000psi in springville. And the sensor immediately corrected.

    My theory:
    A) The heat from the 4000psi fills re-adhered the bridge in the transducer to the glass.

    If you determine your FPS is bad then let me know I still own the 0-5000PSI I purchased for $100.

    Leave a comment:


  • krnorth
    replied
    Re: Not Getting Full Tank Capacity on refueling

    I almost always get around 5.2 and up, even in the summer time when it's 100 degrees out. if I ever get less than 5 I am disappointed.

    Of course, I pretty much run my tank down to 50psi or so. It was a matter of disconnecting the fuel gage, and now I can drive farther. The most mileage I have ever pumped on one tank was 167 miles, not bad I'd say.

    I usually average around 140 or so, the tank is small, but it's cheap, and cheap makes me happy!

    Leave a comment:


  • CNG MOTORS
    replied
    Re: Not Getting Full Tank Capacity on refueling

    Zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz............. .........:0)

    Leave a comment:


  • Highmarker
    replied
    Re: Not Getting Full Tank Capacity on refueling

    Let me put this to bed.

    The Cavalier does state the tank is a 6.2 GGE tank. However that is the tank capacity if the tank were completely empty and then filled with CNG to 3600 psi at 70°F. When a Cavalier switches over from CNG to gasoline, there is approx. 300 - 400 psi still in the tank. When you fill your Cavalier, temperature effects natural gas more than you think. You will get more CNG in your tank in the winter than in the summer (assuming pressure is the same). The most I have ever gotten was 6.002 GGEs in October of 2007. My average fill up (assuming pressure is the same) is about 5.1 - 5.2 GGEs. In the summer, I am lucky to get 4.8 GGEs.

    Leave a comment:


  • krnorth
    replied
    Re: Not Getting Full Tank Capacity on refueling

    I have an 00' Cavalier, and a 99' Cavalier. We were told from MANY numerous sources even from GM that the Cavalier comes with a 6GGE tank. I could further do some research on this.

    However, the 00' which I drive around I am able to completely run it out of CNG and I am able to fill up anywhere from 5GGE up to 6GGE, the most I have ever let the tank accept is 6.008GGE. This was at Springville pumps in Utah. They usually have around 3600PSI. I have also filled at stations which register 3000 PSI and have filled up with 5.8GGE before. But I would certainly wonder the accuracy of these PSI gages....

    Leave a comment:


  • freedml
    replied
    Re: Not Getting Full Tank Capacity on refueling

    Don't think I've ever gotten more than 4.5 from a fast fill, but I only fast fill on vacation.

    Leave a comment:


  • CNG MOTORS
    replied
    Re: Not Getting Full Tank Capacity on refueling

    I have sold huindreds of cavaliers and filled up just as many and never have I gotten anywhere near 6 gallons from empty. Curious about you 6 gallon cavalier guys. The cav gets roughly 30 mpg at 6.2 gallons are you getting a 186 mile range on NG?. At 5 gallons i get 135-150 miles on cavs. Empty it and fill back up and I still get only 5 gge.

    So I am wondering several things. Are the pumps you are filling from inaccurate or are they over-preassurizing you? 4000+ psi?

    BTW. Honda says 8 gge also but I only get 6 gge's into it. 2005 and older, duno about 06 and newer

    Leave a comment:


  • freedml
    replied
    Re: Not Getting Full Tank Capacity on refueling

    Maybe it's switching with a lot of CNG left in the tank.

    Leave a comment:


  • midijeep
    replied
    Re: Not Getting Full Tank Capacity on refueling

    I have fueled several times now and looked at the gauge on the fuel pumps. The more the pressure on the fule pump the more I got in the tank. I am going to try Questar tomorrow. I hear they have more pressure at their fuel pumps.

    Leave a comment:


  • midijeep
    replied
    Re: Not Getting Full Tank Capacity on refueling

    Originally posted by CNG MOTORS View Post
    I assume this is a factory CNG cav. If so I read no mention of an aux tank. So it you actually have trunk space as little as it is you only have one tank and it's 5 gge at 3600 psi not 6.2. I don't think they make 1.2 gge tanks even.

    So assuming you have just the stock 5 gge tank, I agree with the others low station pressure is to blame. Unless you already had fuel in the tank and you have another issue with the CNG system could be another reason
    Its a 6.2 @3600 psi, manual and on the tank itself says so.

    Leave a comment:


  • midijeep
    replied
    Re: Not Getting Full Tank Capacity on refueling

    Originally posted by freedml View Post
    Was the needle inside the car reading Empty on CNG when you started (or switched to gasoline) and Full on CNG when you finished?
    Switched over to gasoline

    Leave a comment:


  • CNG Utah
    replied
    Re: Not Getting Full Tank Capacity on refueling

    Just so you know. There is a gauge on the side of the pumps. Look at it before filling and you'll get a good idea of the pressure at the pump. You can also watch it raise and stop while you're filling. You'll notice that you very rarely see a reading of 3600 psi in Utah, although it does happen occasionally.

    On a side note, we sometimes get over 5 gge in Cavaliers and on one occasion got just over 7gge although that might have been a fluke of the temperature and an extra pressurized pump.

    This document shows the CNG capacity of a 2001 Cavalier as 6.2 gge.

    Leave a comment:


  • CNG MOTORS
    replied
    Re: Not Getting Full Tank Capacity on refueling

    I assume this is a factory CNG cav. If so I read no mention of an aux tank. So it you actually have trunk space as little as it is you only have one tank and it's 5 gge at 3600 psi not 6.2. I don't think they make 1.2 gge tanks even.

    So assuming you have just the stock 5 gge tank, I agree with the others low station pressure is to blame. Unless you already had fuel in the tank and you have another issue with the CNG system could be another reason

    Leave a comment:


  • freedml
    replied
    Re: Not Getting Full Tank Capacity on refueling

    Was the needle inside the car reading Empty on CNG when you started (or switched to gasoline) and Full on CNG when you finished?

    Leave a comment:


  • Devo
    replied
    Re: Not Getting Full Tank Capacity on refueling

    Probably just low pressure at the pump (maybe a big vehicle came through before you). I've filled at that station a few times and didn't always get full pressure.

    Leave a comment:

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