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.

I do remember not saying 0-90 ohm, which is a commonly available ohm range (I think it's old GM and some British). It's some wacky, nobody-else-uses-it value like 0-30, or 30-0 (full to empty). I can't remember now, and my car is outside in the cold and dark. I also seem to remember it's exactly the same for early 911s.

Other people have gotten other values, and claimed that other gauges have worked.

This isn't hard to measure, and it's even easier to determine what the gauge itself wants. If you have an ohmmeter now, just buy $5 worth of resistors and multi-strand from Radio Shack. Use some resistors in the 3-5ohm range as "0", and use other resistors in series or parallel to get "30" or "90" or 67.5, or whatever (series resistors mean more resistance, parallel resistors mean less resistance). Hook up the gauge to a car battery and hook the resistors to the sender terminal and the negative post of the battery. See what the gauge does with different resistance values.

You can quickly determine if "0" (it's never really 0, but just really low) is full or empty by just hooking the gauge sender terminal to ground on the car itself, ignition on. If it pegs full, "0" is full. If it pegs empty, "0" is empty.

I've got the bits here, including a couple of 914 fuel gauges. Give me an hour or so...

Thanks James,
I know of the stuff that you spoke of as I have over 15years of experience in electrical/electronics/avionics. It is sad that I have to go this route to find out something like this. I wonder if they are missinforming me on purpose. It is time to check my stuff. A 0-90 would be easy to draw down. 10-180 would be pretty easy, too. PITA. I think that I got 0-30 when I measured my sender a while ago. I'll have to see.
Thanks again for you help.

OK, I have THREE (count 'em) spare 914 fuel gauges on the shelf (how did this happen?). I used my benchtop 12v (13.6v) power supply and a handful of mixed resistors I had lying around.

0 is full. Short the gauge terminal to ground and it pegs full. A 100 ohm resistor (99.2, really) didn't deflect the needle from "no connection". A pair of 100ohm resistors in parallel (49 ohm measured) put the needle at a tad above 1/4 tank. So, empty is somewhere between 50 and 100ohms. A 100ohm and a 300ohm resistor in parallel (about 70ohms measured) put the needle at about halfway between 1/4 and R. So, it looks like 0-90 (full to empty) is indeed the range for these gauges.

I were wrong... (I think I first heard this from Dave Darling though, so it's really his fault )

Fortunately, this is a REALLY common ohm range, used on scads of GM vehicles, and VDO makes a 0-90 gauge in all of their styles, as do Autometer, et al. Works for me, considering my 914 currently has a 911 oil temp/pressure gauge, and I've been relying on using the oil pressure light in that gauge as the low-fuel light. I think I even HAVE a VDO 0-90 fuel gauge in my parts bin...

You rock James! Thanks for saving me the time. I have too much stuff on my bench right now and would not have been able to run these tests until my engine was in the car. Thanks again!

I'll be picking up mine in the morning 10-73 range.
I'll report results, of course.

KT

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?

I think that I am gonna test the many gauges that I have here with a power supply, a potentiometer, and an ohmmeter in parellel with the pot. This should give me some finer numbers to work with as well. Maybe I can do this at work during lunch?

Trekkor,
You are using the TI VW one? 73-10, empty to full?

It might be easier to just rig a switch or a tranzistor to the gauge to trigger when the tank reaches a certain level. I can always get another sender that works with more things.

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.

FWIW, I measured about 10 ohms when the tank was full to the filler neck (actually I think it was 12 ohms), and about 35 ohms when the tank was empty enough that the light was on. That's the sender in my car's tank; could be I have an odd one.

...Or that I wrote the numbers down wrong, or screwed up the measurement somehow...

--DD

Installed the 301 020D VDO fuel guage.
10-73 ohm unit.

with full tank the needle points to full. Who knew?

I'll let the fuel level run way down and report back with my findings.

Had to wrap the gauge in black electric tape a few times to make it fit snug in the center console.

KT

QUOTE (trekkor @ Mar 1 2005, 05:45 PM)

Installed the 301 020D VDO fuel guage. 10-73 ohm unit. with full tank the needle points to full. Who knew? I'll let the fuel level run way down and report back with my findings. Had to wrap the gauge in black electric tape a few times to make it fit snug in the center console. KT

they make adapter rings

buy a 904 gauge

KT,
Is your gauge a 2 1/16" or a 2"?

2 1/16" they call it.

QUOTE

they make adapter rings

I did...

KT

Trekkor,
Hows it working? I am close to needing the gauge, but need to make sure what will work, of course.

I tried to test mine, but the values were inconclusive

QUOTE

Hows it working?

Great! When I topped off the tank it said full now, it's creeping toward 3/4.

I won't add any fuel until it get's close to empty or I run out of gas

I spent more time hounding my FLAPS for the guage than doing the actual install.

KT

I let the needle creep down to just below 1/4 tank.

Topped it off. ( I got scared )
It took 11 gals. Whats the capacity on our tanks, 15ish?
Seems accurate to me, it's pegged at full again.

I win!

KT

QUOTE (trekkor @ Mar 12 2005, 03:48 PM)

I let the needle creep down to just below 1/4 tank. Topped it off. ( I got scared ) It took 11 gals. Whats the capacity on our tanks, 15ish? Seems accurate to me, it's pegged at full again. I win! KT

I finally bothered to look it up, and the 301 020 gauge is for VW, which should come as a complete shock to everyone...

Thenks KT! I will be ordering mine correctly now. James, thank you too.