Fuel guage values. Lapuwali?, Here we go again..... Options

[Dr Evil]

So I am in the process of putting my VDO fuel gauge in. I decided to call NH speedo, and PA speedo again to see what they had to say for values. I did this because last time I called them they told me 10-180 ohm empty-full. This was disputed by lapuwali (IIRC) when he said it was 0-90 ohm and I believed that he had tried it. I believed what he had to say, but was confused by the info that I had gotten from the "pros". Well, when I called today I got even wackier numbers. NH speedo told me that I needed a gauge that went from 67-1.8 ohms empty to full. WTF! PA speedo told me that thier tech had gone home for the day and they couldn't tell me anything. Both places offered to calibrate the new gauge for me for as little as $65. One guy said that all they would have to do is insert a POT to change the values.....I don't think so. If the full value is now the low one and the empty the high, you cant change them by using a POT. So basically I am back where I started: No real clue.

Lapuwalli, did you get it to work with a 0-90 ohm? Anyone else? I am trying to add to the information so someone can sift throught hte confusion later on.

[lapuwali]

QUOTE (Dr Evil @ Feb 28 2005, 11:19 PM)

James, But wait there's more! I was looking for a 90-0 gauge and found that they are more rare (at least from the sources that I shop from). There are plenty of 0-90 ones though. The first number listed is the empty, right? Howcome when you placed a 100 ohm resistor in series with the gauge it did not read empty? 100 is close to 90, are they that sensitive?

The "no connection" (infinite resistance) point on the gauge has the needle resting between the light and R, which is pretty empty in my book. 100 ohms gave the same reading. I didn't have any resistors handy from 70-ish ohms to 100 ohms, and 70 put it at roughly 1/8th, and 100 was dead empty, so it's a safe bet "R" is 80-90 ohms. I also didn't have enough resistors to make one up below 10 ohms. Full could be 1-30 ohms for all I know.

You're right on the flip for the GM sender. 0 is empty on the GM unit, and 90 is full, which is backwards from the 914 setup. My mistake. I were wrong again...Egauges does have a 90-0 fuel gauge which is even adjustable, though it appears to have been discontinued.

You shouldn't need to "rig" a switch for when the tank is empty. The stock 914 sender has one already. That's what makes the low-fuel light work. The float connects a pair of contacts at the bottom of its travel and grounds one of the terminals on the sender. I'm ONLY using the low-fuel light now. I have no gauge as there's a 911 oil pressure gauge where the fuel level gauge goes.

Obviously, one wants to calibrate against the sender, not the gauge. I only have one sender, and it's sitting in a tank of fuel right now, so I'm not going to pull it out to test it. Just pulling it out and measuring the "empty" resistance should be enough. IMHO, the gauge doesn't need to be all that accurate at the full end, just the empty end.