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2015 CNG Impala with problems

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  • #16
    Thanks siai47

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    • #17
      Mine is in the shop now for Fuel Mode Unavailable with 40 or 50 miles to go. Also, having banging and whistling when tank is on the full side. Are any of these issues consistent with the problem you're experiencing.

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      • #18
        How long have you been driving your Impala and have you had any other previous issues with the CNG system. Please keep us updated on the outcome.

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        • #19
          The dealership is trying to tell me this is normal. I've put 32k on it so far, it's not normal! The pressure regulator was replaced a while back, which caused a small leak. It took several months to get the part.

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          • #20
            Curious as to what the regulator Mfg being used, did you happen to see the replacement unit.

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            • #21
              I hear the "whistle" sound after a complete fill up. As soon as you apply throttle at light loads you hear it. However, it seems to go away in a couple of miles. It's done it since it is new. There is a note in the supplement about sounds you might hear when operating on CNG so I wouldn't worry too much about it. As to fuel switching to "fuel unavailable" with 40 to 50 miles to go, how does this happen? Are you driving on CNG and all of a sudden the fuel switches while showing many miles left on the range display? Or, did you stop with a low fuel level and when you restarted you got the warning? The reason I asked (and I am just throwing this out there) is the Chevrolet Cavalier did this same thing on a low fuel restart. In the Cavalier, the car would use CNG down to about 200 PSI of pressure in the tank before automatically switching to CNG. However, if you were below 500 PSI in the tank and stopped the car and turned off the engine, it would not restart on CNG. I am pretty sure this buffer was designed to eliminate the car from transitioning back and forth on fuel as the tank neared empty. I'll agree that with 40 to 50 miles to go, the lockout of CNG operation is a little (a lot) steep. Maybe you could determine on a longer trip if the transition occurs at a lower point, longer range, if the car is being driven at the time. In the Cavalier, the transition was strictly pressure related with no temperature compensation in the fuel level calculation. I would be nice to know what pressure this is happening at, not fuel level if in fact the system reacts to low fuel like the Cavalier did.

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              • #22
                I get the whistling it seems to be consistent with what you described, but what about the banging? Yes, the Fuel Mode Unavailable is definitely while driving and the CNG just turns itself off and can only be turned backed on by shutting off the car. If you press the CNG button on the dash, it brings back the Fuel Mode Unavailable message on the information screen. If you fill the tank, you can continue running on CNG. Unfortunately there is no visible CNG pressure gauge on the vehicle, so mile to go (MTG), is the most accurate way to measure verses the standard fuel gauge on the dash that displays whichever fuel your currently running on. The low fuel restart happens somewhere in the 10-15 MTG range and CNG low at 20 MTG.

                So, I picked it up Saturday morning and it happened again today on my way to work (45 MTG). So I went right back to the dealership and didn't shut the car off this time. I spoke with the shop foreman, who happened to be a CNG owner and he agreed that this isn't normal. More to follow, thanks for the help.

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                • #23
                  Either I am missing something or mine may eventually have a problem:
                  NO whistle sound after a full refueling (or any time), under any engine loading.

                  As for your CNG fuel level reading/transition point, maybe the ambient temp sensor and/or tank pressure sensor is off on accuracy.
                  Maybe the ECM needs re-flashing. If still under warranty, suggest that be done.
                  '13 Chev Silverado 2500 Ext Cab Factory Bi-Fuel
                  '08 Green Tea Metallic GX
                  FMQ-2-36 Fueler

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                  • #24
                    Something isn't right and it is not connected to the thoughts I gave you. The telling thing is you state the fuel switches to gasoline and then the fuel mode unavailable message comes on. Then you can shut off the engine and restart it and run again on CNG without refueling. If I read that correctly it seems like some other sensor is giving you problems. Possibly one of the temperature sensors--there is one the prevents CNG operation on a cold engine for example. When the problem exists, the dealer should be able to scan the vehicle and see the sensor data to determine if everything is there to allow CNG operation. As cnguser said, a ECM re-flash might be in order. My Impala had a corrupt calibration (flash) that caused all kinds of trouble. Also the dealer should be able to install a data recorder that will freeze frame the data at the point the car switches over to gasoline to help isolate the problem.

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                    • #25
                      Well, I think I have just been hit by a regulator problem on my 2015 Impala. Over the past several months I have been noticing the "whistling" sound I heard at low throttle openings was getting louder. I traced the sound to the pressure regulator located in the engine compartment. The last time I filled at a commercial station (quick fill) upon starting the engine, several loud "bangs" came from the rear of the car and then stopped. The car ran normally on CNG after that. Having owned several Cavaliers, I knew the sound of the 250 PSI safety valve operating and this sounded just like it. When I got home I time filled the car to 3600 PSI. The following morning, I got in the car and noticed the SES light on and the car was in gasoline mode. I could not be switched to CNG. My code reader could not erase the code but identified it as P01A9 which is fuel rail overpressure. Looking on the internet, I found a post in 2015 by a mechanic referencing the DTC and said that there was a problem with sticking regulators, GM was aware of it and was working on a fix and a re-call. Well it is now 2018 and I have never seen a fix or a re-call for this problem. I sure hope it is the rear regulator as only that regulator is shown as an available service part. The front regulator is no longer available and I remember when it was it was extremely expensive to purchase. My fear is the failing rear regulator might have damaged the front regulator. Anyway, the lucky dealer gets the car tomorrow and I will get the usual deer in the headlights look from the service writer.

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                      • #26
                        I bought a new Impala a few months back and have no issue so far. I can't make out the manufacturer of the regulator, but the Blackstone is of similar appearance's. Anybody to this day have update on the model of the hp reg used on the Impala.

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                        • #27
                          It was in fact the regulator sticking. The car had code P125D (small leak) in addition to the P01A9 (fuel rail overpressure) code. Tech ordered replacement regulator, installed and all OK. BTW--the "whistle" is also gone.

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                          • #28
                            The regulator is manufactured by Rotarex.
                            https://rotarex.com/applications/automotive

                            My understanding is GM should have ample stock of replacements now.

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                            • #29
                              Originally posted by John Mitton View Post
                              The regulator is manufactured by Rotarex.
                              https://rotarex.com/applications/automotive

                              My understanding is GM should have ample stock of replacements now.
                              John, Is there a generic version of that regulator available thru a third party, or is it a GM only OEM special component ?

                              Is the regulator over or under $ 1k at GM list parts price ?

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                              • #30
                                There is no indication on the part as to who made it. It is complex as it is marked as being able to accept pressures up to 350 Bar. The outlet pressure is adjustable from 0 to 9 Bar. There is a lock off valve solenoid on the top of the regulator. It has water heating pipes on it. There is a two pin connector on the solenoid and a three pin connector going into the regulator. I believe that the output pressure is adjustable by a PWM signal sent by the ECU. The reason I think this is that the test to determine if the regulator is sticking, you command the pressure through its entire range and make sure it is responding to the commanded pressure within two seconds. If it doesn't do that (and the one I my car didn't) then the regulator is defective. The list price is around $600. The good guy price is around $400. There is a good supply of these regulators in the Lansing, Mi. warehouse.

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