Hi All,

I sprung for one of the new Quanta fuel senders. It reads way too low, so that even when it is topped out ( Full tank position), it reads only 3/4 full. When it is half full, it only reads just above E. How do I calibrate these two pieces so that they read more or less correct? I thought of just bending the sensing arm, but that will not fix the problem when it is full.

Thoughts?

Greg

Greg:
You can not calibrate your sender unit to the gauge. It is nothing else than a variable resistor or rheostat that will increase resistance when tank is empty -float down to bottom of tank- letting a low voltage reach the gauge giving you a low reading, "E/", and will decrease resistance when tank is full -float at top of tank- allowing a higher voltage to reach the gauge giving you a higher reading, "\F".
You need to verify resistance of your new sender unit when "empty" and "full" to see if it matches Mopar's specs. The typical Mopar sender should read about 60 to 75 ohms when "empty" and about 5.0 to 8.0 when "full".
See the following link for more information on gauges. You may catch a couple of things you may be overseeing now.
http://auto.howstuffworks.com/framed.ht ... .html#faq1

_________________
Rafa

Hecho en México

Hi Rafa,

Thanks for the response. I saw your thread where you had to deal with some of the same issues.

Here is where I am at: The resistance is a little higher than it should be, at about 12 ohms when it is full. So, I see a couple of options.

1. Adjust the rheostat, to lower the resistance. This, I don't know how to do yet, but there might be a way. Layson's offers calibration services for their guages and senders.

2. Use a different voltage regulator ( I converted to a 7805). Perhaps, I could use a 7806, and that extra volt might be all I need.

3. Send the sender back. This kinda stinks, because I am not getting very far along, plus I solderd a grounding lug on the sender, so I might have some explaining to do.

Thoughts? What did you end up doing?

Greg

STOP!!! Let me do a little calculating. I may be able to come up with a way to correct things with just a visit to a Radio Shack. I'll get back to you in this string.

Roger

1.-I guess one way to "move" those 12 ohms to, say 8 for "full", would be to bend the sender's arm for the float to hit top of the tank "later" allowing the brush inside the case to go closer to the end of the resistor wire, but this will also alter your "empty" gauge reading for the float may not hit the bottom now.
What is your ohm reading at "empty"?

2.- Your 7805 conversion is probably the reason for your 3/4 reading when full. In my opinion 5 VDC is not enough for a correct reading. I tried 7808 but with this IC the needle went way beyond the "F" mark and was difficult to bring it below the "E/" mark.
Was not able to find a 7806 which I think would have given me the correct readings, but who knows?

3.-Ended up installing a brand new analogue IVR. Ha! after so may hours of soldering and testing, etc.

The following is a link on recalibrating gauges.

http://www.moparts.com/Tech/Archive/elec/8.html

Based on this link when checking the 7808 IC I played a lot with the total travel of the needle and was able to obtain fairly reasonable readings at both ends of "E/" and "\F", but I thouhgt that the bimetal strip at the gauge might not withstand the 8 VDC for a long time. No scientific facts for this, just a gut feeling something might burn...

I did it because i have 4 JY clusters for F bodies and should a gauge broke it would be ok if it served its purpose. Sure enough I'm down to three gauges.

Be careful if you want to recalibrate your gauge, if you don´t have a spare and break this one you will be worse than what you are now.

But hey!, let's wait for GTS225 he may come up with something great.

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Rafa

Hecho en México

How much did that Quanta unit cost? If it was advertised to fit for your application I don't think you should have to deal with recalibrating. When I bought my sending unit (not sure where, maybe year one?) it worked fine and didn't have to fuss with it.

If the coil of wire that makes up the variable resistor on the sending unit is exposed, then you can shift it in either direction so it will suit your gauge. Or, you can bend the little arm that touches it (not the whole thing, just the part that touches the wire).

By the way, what was wrong with your original one? If it just stoped working and theres no physical damage, the resistive wire may just be gunked up or the float ball may of developed a leak and sank. If you search this forum for "ford float" you will find the ford part # that is a direct match.

Hi all,

The Sending unit was about $100. It is a new, 3/8 inch pickup style. ( I oversized it, because eventually, I want to go the Silver State Classic with this car, and I will need to support some big fuel requirements)

There were a few problems with my original. Not just gunked up, but it didn't read at all, and the float was eaten up. I tried just a new float, but that didn't do the trick. The resistor part was shot as well.

I think that I know where Roger (GTS225) is going with his approach. Roger, if you are thinking about the variable voltage regulator, I am very interested. Maybe we can work together to come up with a design that others here could use.

Rafa, the 7806s are not too hard to find. Here is a link:

http://www.kelvin.com/Merchant2/merchan ... e=ELPCICVR

and
http://www.digikey.com/scripts/dksearch ... 46&Site=US

If I go this direction, I could just buy a few, and send you one, Rafa. Let me know if you are interested.

Thanks,
Greg

Call up quanta and see what they say first....

For $10-20 you can probably get one at a Pick-n-pull and keep exchanging untill you find one that works.

Remember, that if you mess with the voltage regulator in the dash, you will also be messing with temp gauge as well because temp and gas gauge both use the same regulator.

OK....here we go. First, I'm a college-trained electrician, and my classes included computing resistance values in a parallel circuit, which means I can also figure out how to get a specific resistance in an "unbalanced" resistive circuit.

What we have in the fuel sender circuit is a simple resistive circuit, where the guage is the load, the sender is the controlling device, and the voltage regulator is the power supply. (Kinda like a simple light dimmer) Approximately 5Vdc comes out of the supply and ties into one point on the fuel guage, but also goes out, (by wire), to one side of the sender, out the other side of the sender, and back through a seperate wire to the other point on the guage, right?

So...what we need to figure out is just exactly how much resistance we need to "correct" the (unchangable) amount of resistance we already have in the sender.

Now...in a parallel circuit, we need to invert the known value, and start plugging in different (inverted) values, the re-invert the sum. (I'll try to text out the formula; Ra (inverted)+Rb(inverted)=Rx(inverted).

I've already done the desk work, but I wanted to type out this explanation in case I did make an error, and somebody can point it out before any damage is done.

So, if you go to a local electronics shop and get a resistor from the "chart" below, this should correct your sender/guage combo to read properly. I suggest at least a 1/4 watt, maybe 1/2 watt to play it safe. What you'll need to do is connect your chosen resistor ACROSS the terminals on the back of the fuel guage. This will give a parallel circuit of lower resistive value, thus fooling the guage into thinking that your sender is of a lower value.

Your sender= 12 ohms (at full, and we need 6-8 ohms)
Add----------- 12 ohms=6 ohms
13 ohms=6.24 ohms
14 ohms=6.46 ohms
15 ohms=6.67 ohms
16 ohms=6.86 ohms
17 ohms=7.04 ohms
18 ohms=7.23 ohms
19 ohms=7.34 ohms
20 ohms=7.5 ohms
21 ohms=7.64 ohms
22 ohms=7.79 ohms

As one can see, one could tailor the value to whatever one needs, in order to get the guage reading correctly.

WARNING: I am presuming the circuit is a closed, resistive circuit only. I strongly recommend you check out the electrical schematic for your vehicle, paying particular attention to the fuel guage circuit. (Sorry, I don't happen to have a schematic available to check.)

OK...THE REST OF YOU....SHOOT ME DOWN IF I'M WRONG. DON'T LET ME BURN UP THIS GUY'S DASH!!!

Roger

That would take care of one end, but it would adversely affect the high end. So it would correct the empty reading, but throw off the full reading (or the other way around, can't remember on the sending unit if low resistance = full tank or = empty tank)

I don't have a degree in electricity , but I do know that the 5v supply goes to one side of the gauge and the other side of the gauge is grounded through the variable resistance sender. The gauge "reads" the impedance of the sender, like an ohmmeter. What I have found to be a common problem is that the sender itself is not properly grounded. It relies on the little metal barbed strip that clips onto the sender pipe and the fuel line, providing a ground through the line itself (theoretically). In reality, it is a poor connection at best, totally missing or broken at worst . The tank is usually insulated by rust and the tar mat, so it doesn't ground well either. A quick test would be to check resistance between the body of the sender and the car frame. Any resistance you find is being added to the sender's resistance and making your gauge drop. I have fixed many fuel gauges on old Mopars by adding a proper ground connection from the sender to the frame.

Pierre....you could be right.....but. Do me a little favor....go back to the first post in this string and re-read it. The way it's worded, I interpreted it to mean that the guage was reading consistently, but low for both tank conditions. (Read 3/4 with a full tank, and almost E at 1/2 tank.)

If you disagree, though, do speak up. That's what this forum is for....to try to iron out kinks before they cause damage.

I say again, though. Somebody please check out a schematic and confirm my suspicions about the guage/sender circuit. I'm confidant in my calculations, but I am missing a touch of confirming information.

Roger

Half Full reads at about the E... So your mod Roger would move the needle towards the F (from its current state) by 1/2 a span of needle travel. So, since I'm assuming the system is linear, when in the full position, it would read 1/4 span past the F when the tank is full (Because it was at 3/4 before, and we added 1/2 span needle travel to it).

I could be wrong, the variable resistance in the sender isn't necessarily linear over various levels in its travel.

OK!.....I'm following your thought processes now. You're correct....if the sender is linear. He may have to end up choosing a "happy medium", or just go with an accurate empty reading.

Roger

If you go with an accurate empty reading, and when full, the gauge will peg. If too much juice is flowin through the gauge when pegged for too long it could overheat the coil in the gauge and, well, poof.

Even if the sender wasn't linear you may have unexpected results. First off, switch back to the stock regulator and see if anything changes. I have a feeling this may be the culprit because the original style regulator can accomodate slight changes in sender resistances due to its design while still producing proper output to make the gauge read right.

Then the next best thing to do is get an extra cluster, pull out the sender, and experiment with everything outside on a table to make sure all is stable before permanently mounting everything in the car. That way you can perfect your calibration as well.