OBC Upgrade Info/Question

[GoldenEagleFan]

I want to thank everyone who contributes on this board.

Due to the search engine I was able to find out I need a new trim piece/bracket for the heatercontrols/radio/obc (Ebay for $1.00) found an OBC ending in 055 (Ebay, $37.00) and was able to switch out the clock/temp unit and plug in the OBC. No power, found another link and spliced line 17 into 9 (A hint for anyone doing the conversion, on the connector in very small letters on each side of the connector the pinout is labled with a 1, 13 on one side and 14, 26 on the other so it is easy to find the correct pinout, my wife's sewing needles for her machine made great pinout measure tools for my cheap voltmeter). After fixing this the OBC lit up.

Was disappointed at first as I had no display on the dash, even though it appeared the car had the correct stalk (little arrows pointing in/out with an picture of an unfolded book on top of them). Found another link and realized my car was prewired for a cell phone, found the correct connector under the rear section of the center console (yellow connector with three wires, spliced the two outside multi-color ones together) and viola, display on the dash.

Now the question. I have unlocked the OBC and can see how much fuel I have (in liters) and can then check my average gas mileage. However, when I do the math I consistently calculate less range than the OBC range display show. For example, tonight coming home from work I was getting 10.0 L/100 KM, 79.8 liters of fuel. I should get 798 km for the range, But the OBC says 867 km. What gives? I can't find a correction for this and am wondering how this could be if the fuel left and average mileage are used. Just as a check I compared the range in miles predicted and my average mileage and got a fuel in the tank calculated of 23.4 gallons. Since the tank is only 21.4 how is this possible???


Any insight?????


1994 525i, built in March of 1994, US model. Manual transmission.

[Interceptor]

Now the question. I have unlocked the OBC and can see how much fuel I have (in liters) and can then check my average gas mileage. However, when I do the math I consistently calculate less range than the OBC range display show. For example, tonight coming home from work I was getting 10.0 L/100 KM, 79.8 liters of fuel. I should get 798 km for the range, But the OBC says 867 km. What gives? I can't find a correction for this and am wondering how this could be if the fuel left and average mileage are used. Just as a check I compared the range in miles predicted and my average mileage and got a fuel in the tank calculated of 23.4 gallons. Since the tank is only 21.4 how is this possible???

The reserve is not taken in consideration when calculating range in the OBC.

[GoldenEagleFan]

I'm confused. If the reserve isn't taken into acount, why does the OBC predict more range than if I take the tank volume from the OBC and multiply it times the OBC predicted gas mileage?

[Interceptor]

I'm confused. If the reserve isn't taken into acount, why does the OBC predict more range than if I take the tank volume from the OBC and multiply it times the OBC predicted gas mileage?
Because tank volume in the OBC has reserve in it :)

You also have to take into consideration compensation mechanisms inside the OBC and a large time constant for the tank volume prediction.

[brick8]

I am in the process of replacing the simple version OBC that came with my 1992 525it (temp and digital clock) with a full-version OBC that I purchased from fleabay. Anyhow, despite the seller's promise that the unit was fully-functional, the OBC arrived with three burned out bulbs. Fortunately, I had some spares left over from an Audi cluster repair that I did last summer. I put the new bulbs in, cut out the old frame back using my trusty dremel and hooked up the new OBC. The OBC backlight for the keys went on (the lowest of the three bulbs) but I got no illumination on the OBC display itself. I tried swapping the bulbs around but got the same result. Does this mean I bought a dead OBC or is this a sign that I need to start splicing wires? Thought I would ask first to avoid damaging something (been there done that).



I want to thank everyone who contributes on this board.

Due to the search engine I was able to find out I need a new trim piece/bracket for the heatercontrols/radio/obc (Ebay for $1.00) found an OBC ending in 055 (Ebay, $37.00) and was able to switch out the clock/temp unit and plug in the OBC. No power, found another link and spliced line 17 into 9 (A hint for anyone doing the conversion, on the connector in very small letters on each side of the connector the pinout is labled with a 1, 13 on one side and 14, 26 on the other so it is easy to find the correct pinout, my wife's sewing needles for her machine made great pinout measure tools for my cheap voltmeter). After fixing this the OBC lit up.

Was disappointed at first as I had no display on the dash, even though it appeared the car had the correct stalk (little arrows pointing in/out with an picture of an unfolded book on top of them). Found another link and realized my car was prewired for a cell phone, found the correct connector under the rear section of the center console (yellow connector with three wires, spliced the two outside multi-color ones together) and viola, display on the dash.

Now the question. I have unlocked the OBC and can see how much fuel I have (in liters) and can then check my average gas mileage. However, when I do the math I consistently calculate less range than the OBC range display show. For example, tonight coming home from work I was getting 10.0 L/100 KM, 79.8 liters of fuel. I should get 798 km for the range, But the OBC says 867 km. What gives? I can't find a correction for this and am wondering how this could be if the fuel left and average mileage are used. Just as a check I compared the range in miles predicted and my average mileage and got a fuel in the tank calculated of 23.4 gallons. Since the tank is only 21.4 how is this possible???


Any insight?????


1994 525i, built in March of 1994, US model. Manual transmission.