fuel gauge problem

When I installed the gas tank in my car I put in a new sending unit. When I hooked it to the gas gauge it only registers from the full mark and above. In other words, when the needle gets down to F the tank is about empty. The car has CMC Vintage gauges. The sender is a VDO unit. Anybody run into this before?

You may need to adjust the sender float travel range to suit the tank; e.g., float about 1.5" from the bottom should read empty which will give you a little reserve. All the way up it should read near the full mark.
(Message Edited 10/12/2003 9:31:06 AM)

Mine too, when I fill up it's OK as it goes down to about 3/4 it stays on the guage but under 3/4 it starts to bounce Up and Down. I have trained myself that when it stops bouncing, it's GAS TIME!

Thanks for the replies. I tried adjusting (bending) the float arm. All that seemed to do is keep the needle around the F mark which is like empty for the gauge. Is there something that can be done with the gauge itself?

Martin: You can also find more info by doing a Forum Search for
"Fuel Gauge". There a many posts that may help you.

BD

The gauge and the sending unit need to have the same impedence range. If the ranges don't match, the gauge will not work properly. I'd guess that is your problem.

Mike C., if you have the stock Brazilian replica fuel/temp gauge you can have the gauge matched to the sender. I ran into this with my new car - most builders use the stock VW tank sender but the Brazilian gauge's impedance doesn't match. You can send your gauge to Palo Alto Speedometer or North Hollywood Speedometer and have them change the coil to match your sender.

Mike, I think the bouncing needle at low fuel level is caused by the fuel sloshing around in the tank, causing the float to raise and fall quickly. Eddie

Does anyone know the specifics of the change to match the impedance. I would rather do it myself than send it in.

Another Mike C.

It entails opening the sender unit, and removing some of the copper coil, until the impedence matches the impedence of the gauge. I didn't have the juevos to attempt it so I took both sender and gauge into palo Alto speedometer. $210 later (AAAUUUGHHHH!!!) they work like a charm. sorry , I don't have specifics, there is a blurb under knowledge on this site, and I would bet GB would know exactly how hany wraps of the coil to remove.

Gclarke

I haven't got a clue...

My company uses sending units and gauges so we have access to all kinds of them from a company called Isspro. www.isspro.com. A sending unit is usually less than $100.00. Sounds like a better way to go than over $200 for a recal. I'm guessing it would take a bunch of emails, but we could figure out what you need and I could get it drop shipped to you.

It might help to find a mid 60s Ford gas gauge they had a small adjustible module you could remove and use it had VW type conections to boot.
It might help reduce the impedance, it even had a adjusting screw you raise and lower the needle a little.

Ron, do you think Isspro has a sending unit that could be installed in a VW tank?

They sell fuel senders in roughly two types, float arm actuated and internal float. The internal float senders don't bounce around nearly as much as the float arm ones. That means the needle doesn't bounce around as much either. They have lengths from 6" to 23" in float arm units, and 6" to 36" in internal. Standard SAE 5 bolt mounting. Resistance curves available are:
240-33 ohm (stock)
0-90 ohm (special order)
78-10 ohm (special order)
10-180 ohm (special order)
The 10-180 is listed as Euro, and VDO compatible.
I'm not sure of the shape of the VW tank, and how close to the bottom you could get with an internal unit, but that would be the best way to go.

Ron,
Who is they?

Sorry about that. Further up this thread I listed 'they' as ISSPRO. www.isspro.com.

Thanks. I'll give Isspro a try and let you know how it works.

Mike, kudos; sounds like you have found an easy band-aid for everyone that has the repro fuel gauge; the full reading is acedemic anyway you just need to know for sure when to start looking for a gas station...

Mike, how did you make the measurement on the gauge. I have a multimeter but I ain't too good with it yet. Also, where will you wire in the resistor, just in the wire that goes to the gauge?

Great Job Mike ,a ohm meter and resistor's from Radio Shack should be easy enough to find.

I measured the resistance of the sending unit by removing it and putting a digital ohm meter across the + and the cover that is to be grounded.

While this was out, I temporarily wired a variable pot in it's place (0-500 Ohm). I turned the key on and worked the pot until I got the empty reading and then turned the key off and measured the resistance across the pot. I did the same at full.

All I did was go to Radio Shack and I bought some 33 Ohm and 47 Ohm resistors (1/2 watt) because that is what they had.

I hooked a jumper with the resistor between the + terminal (the isolated one) on the sendor (with a spade terminal) and then a lug terminal for the ground screw at the sendor. I put heat shrink over the resistor.

I hooked it up last night and got a reading in the range of the gauge. Now, I have a center mounted filler, and the location of my sendor does not allow full range of movement (I think). I will need to calibrate this by playing with the sendor bend to the float, or by changing resistor values all the while with a known level in the tank. I am thinking I might just buy a pot of a narrower range and wire that in lieu of the fixed resistor so I can calibrate simply.

This could work....

I'll really get a laugh from you guys on this but I have been seriously thinking of using a wooden 12 inch rule as my fail safe tank checker outer! Why not, thats what the tank trucks use when filling up service station gas storage tanks. Old technology rules!

Early VW's and Porsches came with a stick to measure the fuel level before they were fitted with gas gauges.

My old 1969 Mooney airplane had a cork float with stick that rode up and down in a graduated tube in the header tank in front of the cockpit. No mistaking your fuel situation with that.

Mike

Thanks for not laughing at me and in a way acknowledging my retro guage.

Mike, beautiful up here today. Going to be coming up this way soon? Remember to give me a call when you do, if the weather looks OK I can
zip over to the Applegate, Bruce

Yelp I still have the stick ,I used on my Dune buggy. I often wondered who made it because it had that factory look.

Its a shame they didn,t set the gauges up to use a pre 66 bug mechical cable gauge.

It was grude, but it worked fine

Oh yes they leaked and they smelled. and no smokers allowed to ride

Okay, I took some measurements last night - my stock VW sender is definitely 10 Ohm at full indication and 74 Ohm at empty. I put a pot on the VDO Porsche reproduction fuel gauge and the gauge wants 4 Ohm full and about 30 Ohm empty.

Putting a resistor of about 50 Ohm across the sender should give me a range of 8 Ohm to about 30 Ohm which will give me a range of about 3/4 full to empty with more accuracy on the empty (which is where I need it). Of course I will have to switch the + and - on the gauge (or bend the sending unit the opposite direction) to get the gauge to indicate properly.

This should be a fairly easy and low cost fix for people (like me) who don't want to send their gauge in.

Mike

Bruce,

I am trying to plan a trip to the Applegate around Thanksgiving...I hear it has been just perfect up there...I am sure you are enjoying your car!

Mike

Okay, last night I calibrated my tank on the low side - because of my center mounted filler, my sender is offset from the usual location and doesn't travel to the deepest part of the tank. This is a spyder also, and the tank seems to be angled more than stock. There is a bit of unusable gas left when the level reaches the bottom of the exit strainer.

I get 50 Ohms at the sender when near empty. I put two 33 Ohnm resistors in series and this resulted in a reading of just about empty on my gauge. I will see what it reads when I fill it up.

I will post a picture of the installation when it is done.

Mike