Cavalier Gas Gauge

[midijeep]

I have a 2001 chevy cavalier. The problem exists for the gas gauge when reading cng. The needle tends to move around slowly (I have no alternator or battery problems). I will fill it up with cng, the needle points to full, then about 5 minutes later it has moved to half full, then 5 minutes later move to 3/4 full, etc... It doesn't matter if the tank is full or not. Any Ideas?

[freedml]

Re: Cavalier Gas Gauge

Does it keep going down to empty, or does it stop at 3/4 full?

[siai47]

Re: Cavalier Gas Gauge

Another question--After filling with CNG does the car run the expected distance (120-140 miles) before changing back to gasoline regardless of what the fuel gauge says? If it changes over at less then the expected miles, does it ever go back to CNG operation after shutting it off and restarting? The reason I ask is that there are two sensors that determine what the fuel level gauge indicates. They are a temperature and a pressure sensor. The gauge reading is determined by a combination of both sensors. However, changeover to gasoline is only determined by tank pressure. If the car runs normally (other then the fuel gauge reading) most likely it is getting bad information from the temperature sensor. If the car is changing to gasoline early (or changing back to CNG) it is getting bad information from the pressure sensor. The problem could be sensor related or a bad connection between the sensors and the AF ECU. There is also (I believe) a relay that controls what input the fuel gauge sees which could also be faulty. If there are no other problems with the car, it might be easiest to live with the problem. You can check the connectors and wires to be sure everything is OK. If there is a connector problem it would be most likely around the AF ECU located behind the drivers side headlight. The ECU and the four relays located next to it are in a location that is likely to have corrosion. There are also connectors located at the firewall just above the area where you would rest your left foot inside the car and a final set of connectors located at the tank in the trunk.

[midijeep]

Re: Cavalier Gas Gauge

Does it keep going down to empty, or does it stop at 3/4 full?

It eventually keeps going down. I'm trying to remember if the gauge stops between 1/2 and 1/4 full. I think it stops at that position. I am going to take a 170 mile trip in the next few days. I will know for sure if the gauge stops at a certain position. Let me get back on this one.

[midijeep]

Re: Cavalier Gas Gauge

I travel ~ 80 miles a day before filling the cng tank back up. I haven't let the car run completely out of cng for about a month now. So, it seems the car is doing what it should. It doesn't switch back and forth between cng and gasoline while running with cng in the tank. I should mention that last week I had to change the alternator because it became intermittent in charging the battery (gas gauge was moving all over the place, warning lights on dashboard would come on -ABS,battery, etc...) to the point where the car would completely die. After replacing the alternator I had the battery and alternator checked out, test indicated both were good. I'll check the things you mentioned to see if they are the problem. I will post what I find. Thanks!!

Another question--After filling with CNG does the car run the expected distance (120-140 miles) before changing back to gasoline regardless of what the fuel gauge says? If it changes over at less then the expected miles, does it ever go back to CNG operation after shutting it off and restarting? The reason I ask is that there are two sensors that determine what the fuel level gauge indicates. They are a temperature and a pressure sensor. The gauge reading is determined by a combination of both sensors. However, changeover to gasoline is only determined by tank pressure. If the car runs normally (other then the fuel gauge reading) most likely it is getting bad information from the temperature sensor. If the car is changing to gasoline early (or changing back to CNG) it is getting bad information from the pressure sensor. The problem could be sensor related or a bad connection between the sensors and the AF ECU. There is also (I believe) a relay that controls what input the fuel gauge sees which could also be faulty. If there are no other problems with the car, it might be easiest to live with the problem. You can check the connectors and wires to be sure everything is OK. If there is a connector problem it would be most likely around the AF ECU located behind the drivers side headlight. The ECU and the four relays located next to it are in a location that is likely to have corrosion. There are also connectors located at the firewall just above the area where you would rest your left foot inside the car and a final set of connectors located at the tank in the trunk.