79 Fuel Gauge & miles per gallon question

[79bugman]

my question has to do with a 1600 DP 79 super that has a carb

carb = solex SVA which means single vacuum advance only. It is not an SVDA or a DVDA.

fuel = regular unleaded. 89 octane

timing = 7.5 BTDC

vibrator, sending unit, speedo, fuel guage ETC...everything that has to do with fuel = BRAND NEW. I purchased them a few years ago, but car has not been running that great so there are not that many miles on theses parts to assume they are bad.

car runs like a gem, so I am not going to mess with anything in the engine compartment! (Please no suggestions about the carp/engine setup since it took me way too long to figure it out and get it correct.)

my issue = fuel guage reads just a bit over 1/2 & the tank is FULL and my Odomoter sometimes does not work (issue for another thread)

I NEED MY FUEL GUAGE TO BE AS CLOSE TO 100% ACCURATE AS POSSIBLE.

I have read multiple threads over the past 2 days and need some help since I just filled the gas tank to the very top = EXCATALLY 11 gallons & I really dont want to drain the tank and then refill multiple times testing the sending unit.

I am going to drive it this weekend and want to know how many miles I should expect to get on a FULL tank I will mainly be on flat roads crusing around 45-55MPH.

I have completed the following 2 speedy jims tests "TESTING THE GAUGE"
Pull the wire off the sender. The gauge should go to EMPTY. = YES THIS IS CORRECT
Take the sender wire and ground it (Ground it to chassis, not the tank). The gauge should go to FULL. = YES THIS IS CORRECT
If it passes both these tests, the gauge is good and any problems are in the sender. = OKAY, NOW I KNOW MY SENDING UNIT HAS AN ISSUE.

what are some easy tests to run on sending unit (without pulling tank)

i read taking off the 4 bolts/washers that hold the tank to the car and clean up to bare metal could help the ground.

any ideas?

thanks

[kangaboy]

Simplest way to adjust the gauge is to remove the sending unit and bend the float arm. It may not be going all the way up or all the way down because its hitting the top of the tank, and not able to go through its whole sweep.
I have a ground wire running from one of the sending unit screws (the ones that secure the unit to the gas tank) to a good ground, just to improve the ground of the sending unit.
Remove the sending unit and you can test how the gauge will act with the ignition on (not running). I bet you will find that the float wouldn't be able to show a full tank due to it hitting the top of the tank before it can complete its whole sweep. Prolly need to bend the float arm down. That's just how the aftermarket unit is right now.

EDIT: With no idea what mileage you are currently getting, I would go with a super conservative number...say 20mpg? So I would safely say you could get 220 miles on a tank. With this said, drive around with a 1 gallon tank of spare fuel, just incase.
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-74 Standard - "CaliBug" 2084T, MS3X w/FI and Crank Fire
-76 Westy - "Gandalf"
-18 GTI SE

[busman78]

Does the current gauge function normally after the fuel drops below the halfway mark?

Attach a ground wire to the metal cap (sender) if no change then pull the sender, any other test require it out.

[Q-Dog]

I would also start with getting a good ground to the sending unit to see if that fixes it. But, You cannot assume that "brand new" parts are good. There are plenty of reports of bad parts right out of the box.
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Brian

'69 Dune Buggy
'69 Beetle Convertible
'70 Beetle

[AlmostHeavenWV_VW]

[sjbartnik]

Yeah your comment that the sending unit is NEW is kind of a red flag as I'm not sure good quality new sending units are available.

Additionally it's possible you have the wrong sending unit (maybe for a standard vs. a super, not sure if they are different).

However it also could simply be a ground issue in that the tank is not making a good ground connection to the body.

Test this theory by running a jumper wire from the tank to a good ground and see if this improves the accuracy of your fuel gauge reading, then report back.
_________________
1965 Volkswagen 1500 Variant S
2000 Kawasaki W650

[VW_Jimbo]

Went through this exact issue four months ago. Ended up running a ground wire from the headlight ground screw (clean that up and use some dielectric grease). Then, I removed the sending unit. Figured out the arm position of full and empty, while in the tank. Took precise measurements and removed sender. Made a jig to hold the sending unit and then with it connected to the car, key on, bent the arms to give me full when full and empty when empty. Lifted it to what I thought Reservoir should be, about a gallon, and made sure the arm measured about a gallon. Rechecked full and empty - all good. Reinstalled into the car. Drained the tank (only had a couple gallons in it at the time). Gauge read first white line or empty. Put 1 gallon in the tank, it was at the white line past the R. Filled it up, it was full. Put it all back together and have never thought about it again!
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Jimbo

There is never enough time to do it right the first time, but all the time necessary the second time!

[sawed off]

I recieved new sending unit a while back and it wouldnt work at all. I ended up removing one of the nylon washers between one of the monting screws and it worked. grounding issue.

[79bugman]

Thanks for all reply’s.

I’m going to “try” to do tests tonight.

Sjbartnik, I used a jumper wire hooked directly to battery hooked to the ground wire from sending unit (I had taken the ground wire off the sending unit and hooked the other side of jumper directly to ground) = Guage still read 1/2 full.

Vw Jimbo, I will try a new ground hooking it from sending unit to headlight ground and will report back with result.

I am also going to clean all 4 bolts and holders that hold tank in place down to bare metal. I will report back with these results also.

Again, want to eliminate all possible tests prior to taking tank out. It has 11 gallons in it and I have nothing to empty it in.

I’m hoping it is just a ground issue

Thanks again.

[79bugman]

Also, I don’t know if guage is correctly working after 1/2 way mark. I have run out of gas before and did not look at guage to see where it was.

I have the right sending unit for SB. It has 2 floats and no screws holding it in. It twists on and there is a rubber washer/seal between the sending unit and the tank.

[79bugman]

well, I was able to perform the following tests and I dont think I got any further than before the following tests...

1. I hooked a brand new wire with spade connector to the sending unit ground side and grounded it to a know good dround in the trunk area (headlight ground)

turned key to ON and and guage still reads about 1/2 or just a little over 1/2 full if I tap the glass on the speedo.

I then placed the original ground wire back on sending unit and did the following test...

2. I cleaned all 3 (for some reason I only had 3 holding my tank in & not 4 like there should be) holders down to bare metal using a grinder as well as cleaning the area on the trunk and chassy to bare metal. the bolts/screws that hold the metal pieces were in pretty good shape, so I did not have to clean them.

turned key to ON and and guage still reads about 1/2 or just a little over 1/2 full if I tap the glass on the speedo.

3. I then disconnected the original ground wire and used the brand new wire with spade connector to the sending unit ground side and grounded it to a know good dround in the trunk area (headlight ground)

turned key to ON and and guage still reads about 1/2 or just a little over 1/2 full if I tap the glass on the speedo.

4. I again tried the following test.... using the original ground hooked to sending unit, I disconnected the positive side on the sending unit and grounded it to the battery using a jummper.

turned key to ON and and guage went past 1/1 (full)

so based on all of the above, I think my guage, vibrator and all the other things behind the speedo and working properly and there is an issue with sending unit. I think I have eliminated possibility of a ground issue.

i am going to drive it this weekend and see how many miles I get to a full tank. I am going to run her until she is out of gas. I just hope my odomoter continues to work or I'm totaly screwed.

once the trailer picks me up (I dont want to drive around with gas in car since the interior is in 100% better than new, perfect condition and if I spill gas on the carpet, I may just die) & gets me home, I will take out sending unit and try to adjust arms based on the amout of gas I put in tank.

this is exhausting!

thanks all for all the ideas and tests. I will report back over the weekend.

[cletus_zuber]

[VW_Jimbo]

[volksworld]

fwiw last summer had 2 dansk senders that didnt read correctly....an unknown brand of mexican sender from rock auto cured the problem....never had these issues when real VDO's were available

[glutamodo]

[VW_Jimbo]

[79bugman]

so I took her out today and drove a total of 220 miles excataly.

drained the remaining gas in tank and there was 1.75 gallos remaining (give or take a few drops of gas here/there)

that means I was getting approx 23.78 miles to gallon which I think is pretty good.

I noticed a "gas smell" when driving. i guess the tank was about 1/2 full when I noticed it. it was especially strong when turning both left and right.

I'm thinking that obviously the gas is sloshing more.

i posted pics of how I have everything hooked up and want to see if anybody has any suggestions before I take it apart to work on sending unit.

any suggestions are welcome!!!!!

[garyloos]

Something else you might check.

When I installed my new dual float sender in my 1972 super I had the same problem until I notice that there were baffles in my tank. When I put sender in tank my float was hanging up on a baffle and would only would go to 1/2 full even when I had the tank full. I repositioned the sender a couple of times until it read full.
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Gary Loos

1972 Super Convertible

[79bugman]

thanks for reply.

got tank out and here are some pics below.

question .... should I clean up the area on the tank under where the sending unit goes to "bare metal" to make sure I have a good ground?

right now, it has black paint under the seding unit (
first picture)