Fuel Gauge and On Board Computer

1984 E30 I think my low fuel light is out. Is there a way to get all of the indicator lamps in the dash to light or do I have to get to the wires on the fuel sender under the rear seat? Also, the RANGE on my on board computer is acting funny. Does anyone know if that is also tied to the fuel sender unit?

I do believe one of the inputs the OBC uses is the sender in the tank.
Looks like a trip under the back seat.

Does the warning light come on during the start cycle like the other lights on the dash?

Bob in Lake Havasu

On my previous 318iS, the low fuel light never came on when cycling the key. I thought the light was gone, so I went to the pump in time. Until that one day I couldn't reach a pump in time, or so I thought, and the light came on, bright, it hurt my eyes.

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Bob in Everett
Does the warning light come on during the start cycle like the other lights on the dash?

On my cars, 1987 325e and 1988is, neither of them show the low fuel lamp when the key is cycled. But I know they both work (I've seen them!).

I'm not sure what Michiel is talking about but I'm sure Peter is right about the OBC taking readings from the sending unit.

Rick

I meant I had never seen it until I ran so long that te low fuel light came on. I thought it was broken as I had never seen it when starting the car.

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Michiel 318iS
I meant I had never seen it until I ran so long that te low fuel light came on. I thought it was broken as I had never seen it when starting the car.

Right, I've seen the same thing.

OTOH, I seldom refuel before the "low fuel" light is on, thats the way I use to keep track of mileage.

Fix your odo then ;-)

The E46 puts on the low fuel light at a DTE of 150-170 km, way to soon. Don't want to run it past DTE 50 km though, especially at summer times, those common rails heat up the fuel a lot and when there's little left in the tank... Don't want it to fail before I've got 400.000 on the clock...

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Michiel 318iS
Don't want to run it past DTE 50 km though, especially at summer times, those common rails heat up the fuel a lot and when there's little left in the tank...

Also, the in-tank pump gets hot when it's not sitting in fuel. Constantly running the tank low is gonna shorten its lifespan.

Hot pump inside of a fuel tank...........what could possibly go wrong?

The fuel vapor is heavier than air so it is not a flammable mixture.

Bob in Lake Havasu

The pump in my E46 is under the driver seat, so fuel level doesn't have an impact on pump temp, except for warmer fuel when nearing the empty mark.

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Bob in Everett
The fuel vapor is heavier than air so it is not a flammable mixture.

Fuel vapour by itself is not flammable but there is also air inside the fuel tank. No matter the air is on top of or under the fuel vapour; a spark woould ignite it

Just sayin'............................................. The official cause of TWA 800 blowing up after take off was________________. And JP4 is not nearly as easy to ignite as gas is. In fact, it is pretty hard to get going.



Edited 1 time(s). Last edit at 07/30/2013 03:30PM by alanrw.

There is a new movie out about TWA 800 that might lead to a different conclusion. Gasoline vapor is heavier than air and the tank is full of gasoline vapor that is not a flammable mixture. Jet fuel is not very volatile so the tanks are vented with fresh air to a level below the flammabilty point.

Just saying...

Bob in Lake Havasu

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Bob in Everett
There is a new movie out about TWA 800 that might lead to a different conclusion. Gasoline vapor is heavier than air and the tank is full of gasoline vapor that is not a flammable mixture. Jet fuel is not very volatile so the tanks are vented with fresh air to a level below the flammabilty point.

Just saying...

Sorry; it is impossible to keep air out of the gas tank. Each time you fill up there is a fresh influx of air. Sure the fuel pushes most of it out(along with the fuel vapours) but enough is left inside for an igniteable mixture.

Most gas pumps these days have a vapor return feature on the nozzle. The vapor from the tank is exchanged into the gas station storage tank as the car fills. Likewise when the tanker truck comes to fill the station tanks, it captures the vapor from the tank and puts it into the truck as the fuel empties into the station tank.

There is some air but the fuel air mixture in the gas tank is too rich to burn as there is not enough oxygen in it. Fuel vapor will flow downhill in a no wind condition outdoors and follow a storm drain. There have been some "interesting" incidents related to this phenomena.

Bob in Lake Havasu

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Bob in Everett
Most gas pumps these days have a vapor return feature on the nozzle. The vapor from the tank is exchanged into the gas station storage tank as the car fills. Likewise when the tanker truck comes to fill the station tanks, it captures the vapor from the tank and puts it into the truck as the fuel empties into the station tank.

There is some air but the fuel air mixture in the gas tank is too rich to burn as there is not enough oxygen in it. Fuel vapor will flow downhill in a no wind condition outdoors and follow a storm drain. There have been some "interesting" incidents related to this phenomena.

I remember those pump nozzles from my days in SoCal.
Unfortunately, the nozzles we have here are not sophisticated; they just pump the fuel into the filler tube. If you are standing in the wrong place while filling up you can get a snoot full of vapour fumes

We had a fuel truck accident and spill a few years ago in a suburban area where only a small amount of the contents of the truck spilled and leaked into the storm sewer system. Several neighbourhoods were evacuated. Fortunately when the explosion did happen all that occured was about a dozen manhole covers were blown a hunfred feet or more into the air; causing minor damage to whatever they landed on

As for the amount of air in the gas rank; not everyone fills their tanks. Young poor students often run the tank below 1/4 full and can only afford to put a few dollars of fuel in at a time. That most certainly would leave a nice combustible mix.