Lpg sender setup

[Lpg08]

Hi i have a toyota lanecruiser with twin tanks and connected by a hydrostatic t.

At the moment only one tank has a sender and the king lpg injection system gauge only starts on half tank when its full tank and stays half until one tank is used uo then starts to function normal until the tank goes empty.

Its a standard 0-90ohm sender.

I want the guage to read full when full tank does this mean i have to put another sender on the other tank?

If so how do i wire it in? Just tap into the other sender wiring?

Or can i get it to read proeprly with just the one sender? I have tried other settings in the king ecu and it comes up with all bars on the guage but dosnt move at all even when empty.

Regards

[LPGC]

It may seem you could wire 2 x senders in series (or parallel) and set up the gauge to show full at close to 0 Ohms resistance, empty at close to 180 Ohms (or 45 Ohms) resistance...

But in practice it wouldn't work so well, not as simple as that, it might work or it might be even less accurate than only having the one sender - at least with a sender on only one tank you might have a decent idea of how much gas is left in that one tank even if tells you nothing about the other tank.

Could fit 2 x senders and fit a switch to flick between reading one tank and reading the other, but again this might not work so well because it's usually best to calibrate the ECU versus tank sender readings... the ECU can only be calibrated for one sender. If both your tanks are the same design/capacity/etc and both senders are the same spec it may be an advantage toward good results but I'd still expect to calibrate both tank gauges differently in software if the 2 tanks were on separate installs.

Could fit 2 x senders and use a separate gauge for each, but most of the discrete gauges don't feature/allow calibration.

Could get really involved and set up a circuit (or even some sort of little microcontroller system / Arduinio with A/D convertor and D/A converter) to allow calibrating each sender individually, or to add up total fuel remaining and output a relevant voltage signal to the ECU.

[Brian_H]

It might be worth checking your sender actually works - You already know its a 90 ohm type, its possible to operate the sender by removing it fron the tank and using a screwdriver on the back to move the pointer around, and monitor the resistance or voltage your seeing on the software, or by using a multimeter.

It may be that its emptying one tank before the other, which complicates what Simon's already said above as well.

Posting your settings might give an idea if you can improve on it with a single sender - it showing half to start with on a full tank suggests the sender might not be working as well as it did originally, or it isn't setup/calibrated correctly. The settings you currently have might help to identify that?

[disco stu]

Can you set individual voltages for tank level on that ecu? Just wondering if doing what LPGC said with both senders in series (or parallel) and then using another resistor to make voltage divider (of appropriate resistance for appropriate voltage to ecu). Then set the voltages in ECU for each level. Just a possible addition to his suggestion

[hitman2]

I just reset my trip meter on every fill up and know I get about 380km between tank fulls.

Level transmitter has always been somewhat erratic.

[LPGC]

I was presuming it does empty one tank before the other - If both tanks empty at the same rate and fill at the same rate 2 senders would always point to the same level in which case might as well just have 1 sender

One aspect that complicates accuracy of readings if 2 senders are wired in series or parallel is that the step changes in voltage readings for different levels are not even (there might be a bigger step change in voltage between say 1/2 a tankful and 3/4 of a tankful than there is between 1/4 of a tankful and 1/2 a tankful). They're not even because the electronics are not set up to be linear, the sender doesn't use it's full 0>90 Ohm range (or movement range) between empty tank and full tank and because the float is on the end of an arm that follows the path of an arc as it rises and falls on liquid gas in the tank.

These are the standard settings for KME Nevo using a 90Ohm sender (which isn't to say they are anything like correct for most real world situations)..
Empty <0.41v step change from 0v 0.4v
between 1/5th full and 2/5th full >0.41v>0.92v Step change 0.51v
between 2/5th full and 3/5th full >0.92v<1.2v Step change 0.28v
between 3/5th full and 4/5th full >1.2v<1.41v Step change 0.21v
over 4/5th full >1.41v. If the trend above continues (but there isn't really much to suggest it will) a full tank might give voltage reading of around 1.6v (another step change of 0.19v) or perhaps due to 'arc' the step change will increase a bit back up to something like the 0.51v step between empty and 1/5th.

The difference in step changes (the none linearity of step changes) implies that if we just average the readings from 2 senders (as in wire in series or parallel) we can end up with a not very proportionate output when both tanks are part full.. but at least it should show empty when both senders send empty voltage and show full when both senders show full voltage. If we wanted to make it more proportionate for middling tank levels we'd have to use some electronics.

In the ECU the tank sender is often connected to a 5v reference via a 100Ohm resistor so the sender forms half of a 2 resistor voltage divider circuit (the sender is one of the resistors). The AD convertor is connected to the voltage divider, so the AD convertor might see 2.36v if the sender is at 90Ohms and 0V if the sender is at 0Ohms. The standard level gauge settings above imply that the designers of the ECU anticipated a voltage reading above 1.41v for a tank above 4/5ths full... The 1.41v equates to a resistance of only around 40Ohms, the 1.6v equates to a resistance of only around 47Ohms... on a single hole tank the sender will never be at 90Ohms because it will never be rotated it's full extent because full to empty tank doesn't rotate the sender it's full extent. This is why if a sender goes open circuit the gauge on the dash will often show full tank, because with no pull down resistor (no sender connected) the AD convertor may see close to the full 5V (probably closer to 4.5v with Nevo because there's more to the voltage divider circuit than just the 100Ohm resistor).

[Brian_H]

I was presuming it does empty one tank before the other - If both tanks empty at the same rate and fill at the same rate 2 senders would always point to the same level in which case might as well just have 1 sender

So probabbly the first thing to look at is the gauge on the tank to see where its actually pointing to at various points of use, as that should tell if its emptying 1 tank or the other or both?

Rest of your reply is quite interesting - I've never been able to get the Galaxy to show a sensible reading on the gauge as it only ever gets to around 1.5v dropping to 0.02v, even though the sender shows the expected resistance between 0 and 90 ohms when tested with a meter at the wiring on the front end. Main problem is it doesn't seem too consistant and can vary by around .5v on the same level, which with such a narrow band makes calibrating it rather more difficult!

[LPGC]

Yeh if you test the sender when removed from the car with a meter you can turn it to the full extent so see the full range of resistance between 0 and 90 Ohms but the tank valve won't turn it to the full extent, especially on a 0deg tank.

Can be problematic getting gauges to show correct reading anyway - The liquid gas is only half as dense as water so the weight of the float and float arm will mean it will have to displace a lot of the float volume before it will rise from the bottom of the tank (the float will be on the bottom of the tank until there's a fair depth of gas in the tank). Then there's the play in the mechanism that turns the up down motion of the float into turning motion for the sender - on e.g. Tomasetto tank valves this mechanism is basically just a pin on the pivot end of the float arm that rides between 2 pins on the turning mechanism (plenty play because of the clearance between the 2 pins, plus the design means a small movement of the arm will see a different amount of turn on the turning bit depending on how high the float is i.e. the equivalent of different gearing at different float heights), then there's only a magnetic connection between the turning mechanism and the sender. I find 0 degree multivalves for full toroidal tanks to be the worst for gauge accuracy, this may be due to the comparatively long length of the float arm (more weight for the float), the less overall movement of the turning bit of the mechanism and the position of the pivot point

Difficult to get 0deg valves to show a reading away from empty when the tank might be 1/4 full, maybe even 1/3 full or more... So although lights on a switch might be designed to show 5 levels such as below 20%, 20% to 40%, 40% to 60%, 60% to 80%, above 80%... if we can't distinguish between empty and 1/3rd of a tank (33%) might as well try to set lights to come on to show below 33%, 33% to 50%, 50% to 67%, 67% to 84%, above 84%.

[disco stu]

Just having a think further about this. If the 2 senders were put in series, wouldn't just doubling the resistance on the line from lpg ecu put the voltages back to the same as if there was 1 sender? Assuming it's 100ohm, putting another 100 ohm resistor in. I'm not sure what the set up is on these wiring wise, but it appears that resistor on the stock set up would be between ecu and earth, and then on tank you have one side of sender going to earth and the other side is signal back to ecu

[CNG]

I've used Spiyda's fuel-gauge wizard for lumpy stuff like this. I've got a 0-5V sender displaying to a 60s Land-rover 130 Ohm petrol gauge. Allows v.accurate calibration too.
And you won't pull that trick off easily any other way.

Has a 'orrible name but that might just be me.... Takes just about any output from any sender and calibrates to any flavour of gauge. Bit dear for what it is, and aims at the classic market more than modern voltage derived senders, but can be configured to do voltage too, if you ask....

Get it to switch to your petrol gauge when running gas as I've done. Gets rid the shonky LPG switch fuel display and is easier to read, and because you'll calibrate until it's crack-on, more accurate. Gauges and senders are never linear, and don't match at the best of times. The Wizard translates levels to account for this.


https://spiyda.com/fuel-gauge-wizard-mk3.html