Yanmar 6BY Fuel Gauge Issue

The fuel gauge on my Yanmar 6BY260 has decided to only read full.
I've tested the sender (0-180 ohm) and the cable. I've also tried the usual grounding tests, where possible...
The situation is complicated by the fact that the 6BY uses NMEA 2000 protocol, so the sender runs back to the engine, before going back up as part of the NMEA bus and there is a 6 pin plug that plugs into the back of the gauge.

Any suggestions as to how to test whether the gauge is ok?
Having tested the sender etc, my inclination is to think that the gauge is faulty, but I'd obviously prefer to test it prior to buying a new one of possible...

 

Hi Will,

I am inclined to believe that you have somewhere a bad contact along the line. If I understood you correctly, as soon you switch the mains on, the meter jumps to full? But forgive me, I don't have much knowledge on petrol/gas engines/tanks, but if it jumps to full, I believe you have the circuit disturbed with a bad contact.
Bert

 

Double check the sensor with an Ohmmeter.... The sensor is most likely analogue like a masthead unit...it doesnt talk NMEA. The signal is convert to NMEA in the microchip Volvo brain

If you are confident that the sensor works then the fault must be downstream.


Ive got no idea how the electronic brain works with the NMEA.

Ive got a simple Raymarine speed log compass instrument system . Every now again for no reason, its display seizes up and the boat is stuck doing 7 knots in 20 meters of water forever and ever. The only way to bring it back to life is to turn off the power supply for a minute or so..then re energize. Presto, it works again

Perhaps disconnect the power supply, then energize... and see

 

Thanks guys...
Bert - yes it may be possible that it is a bad connection somewhere - though I've checked &/or re-made all the joints along the system - at least as far as to where it joins the main Yanmar wiring loom. Like you, I don't have much experience with NMEA stuff. If I knew the codes, I could plug a laptop into it and see if the gauge is getting the correct message through, but it may just be simpler to change over the gauge and see if that works....

Michael... yep tried that...the sender was my 1st point of call, but it spans the 0 - 180 ohms correctly.

I might try plugging one of the other gauges in - oil pressure or something...see if that gets a reading...obviously it won't be correct, but it might at least tell me if there's a signal coming through....

 

Will, the sender is an analogue device, so to get the signal on the NMEA 2000 bus it must be converted to digital somewhere, probably a bus controller near the engine. The gauge must then convert the digital signal back to analogue; I can hardly imagine Yanmar has taken that road.

The NMEA signals can be made visible on a laptop if you connect the RS-232 port to it, but what you see is not meaningful, just an endless row of characters transmitted at a speed of 250 kbits/second. There is software that can handle the data stream by filtering out all but one address header, but it is not for free. The NMEA even wants money for a hard copy of their structures and protocols.

 

I agree with you. Normally the analogue sender is part of an analogue bridge circuit and then, if one contact or wire contact is bad, the meter jumps to full
blast. Will, a photo with some hand sketches may help.

Your suggestion of elimination by using another device (provided it has the same parameters) is indeed the best. It will tell you all.
Bert

 

Yes - the standard system just has a little multi-function digital display within the tacho. I specified 'analogue' gauges for temp, oil pressure, fuel etc as well

I think the gauges themselves are OEM units from Teleflex, but I'm not sure...there's no branding on them. Any conversion back to analogue occurs within the gauge itself - the NMEA bus plugs directly into the back of it. (see pic below)

As I said...its my suspicion that the gauge is the problem, having checked all the non-yanmar wiring and the sender...but its only my suspicion....

 

Oops...forgot the pic....

 

That is definitely not NMEA 2000. The connectors should have 5 pins, round with a key in the 6th position. Wires are blue and white for the bus signals, red/black is power and the signal return is bare.

Is there a short adapter cable between the gauge and the NMEA bus ?

 

I think the smaller analogue gauges are 'slaves' to the larger multi-function Tacho....
http://us.yanmar.com/products/marine-engines/powerboats/can-bus-systems/nmea-2000-can-bus-system/

 

What if you had two tanks and two sending units ?

Somehow the NMEA brain would have to identify tank 1 and tank 2 input signal

Perhaps in your NMEA menu has a configuration that allows you to notify the Yanmar Brain of fuel source or sensor type ?

 

Hi Will,

If I had to design a system, I would do it as follow.

1) assuming I have 14 different units to display.
2) I have a 4 wire CAN system, either wireless or hardwired.
3) I have thus 16 possibilities with a 4 wire system of which I would not use 0000 and 1111
4) My main microprocessor would give a 4 bit code out on the CAN line and the device which has this code, will then transmit the digital analogue information on the CAN busbar. However 16 is not a good method to accurately transmit analogue information in digital format. Thus I would use 2 extra wires, a sixth wire and transmit the analogue signal over the sixth and the minus.
5) The analogue signal will be derived from a bridge circuit in the via "CAN connected" device like per example a windspeed sensor.
6) thus, if a connection in the sensor bridge is broken on the minus side, automatically I will transmit full analogue voltage to the main processor.
7) should a connection be broken on the + side of the bridge, the main panel will show zero.

But I have designed such system in 64 bit mode. i.e. 4 x 8 bit for my horse timers and in my case I could transmit the analogue information in digital form to the main microprocessor. I don't need an analogue line.

Your photo shows 6 points, thus 6 wires, which let me think that you are right and that the actual sensor is packed up (or has a connection cut).

Bert

 

Michael, thread no 12 explains it. tank 1 will have a different code like, "0110" then that of the tank no 2 which could have "0010" .
Bert

 

The CAN bus looks more like a very slow USB concept with one signal return added because of the longer distances and the higher current transitions on power ground that might otherwise cause data errors. Speed is 250 kbps for NMEA-2000.

There is only one controller on the bus, it sends a string containing an address, type of operation and a data field. The nodes listen to the transmission and if the address is valid for a node it sends an ACK string with or without a data field.
A node can have several addresses, I/O ports and analogue circuits, usually 8 or 16.
The controller has a table of all valid addresses and their capabilities, so it will not send a DATA_RQ to a display or a DSP_DATA to a pressure sensor.

In the case of Will's stubborn tank gauge, there are only 2 options: the controller sends a wrong signal to the port address, or (more likely) the gauge is defective.
As I wrote in post #9, the gauge is no NMEA device. The 6 pins are probably signal input + and -, light + and - , low level warning light + and -. There is an Italian manufacturer who offers amber and blue backlighting, all with separate pins.

If there is no proper documentation, a digital multimeter can supply all answers.

 

Sorry for that, I expressed myself a little clumsy. I was more looking at what happens in the units themselves, after the serial transmission via the Can bus or radio transmission. I use 868 Mhz small radio-modules which I program in assembler language from the microchip. The photo, I thought, could be only the front-end and not the part after the can bus integrated circuit. I am probably wrong.
In anyway, my conclusion is that the problem lies between the microchip (or similar device ) and the actual sensor. One broken connection will give you a full reading as off the tank is full.
Bert