mikuni heater sensor

[epic]

My Mikuni x40 has just stopped working, i have counted the flash code being one, (ignition flailed) cleaned the optical sensor but was not dirty before i buy a new one is there a way of testing the sensor. your help please

[nicknorman]

One flash means it failed to light up after 3 attempts. 2 flashes means the flame sensor is detected as being failed prior to it starting.

 

So in your case, it may or may not be the flame sensor but in fact is probably something else. You need to completely remove the power from the Mikuni to reset it (eg 30 A fuse out, or battery master switch off for a few seconds) and then try to start it whilst listening to what is going on. You should get water pump starting, the air motor starting. If you can check the current flowing you can tell if the glowplug is taking power (>20A assuming a 12v system), then the fuel pump should start ticking, then you should hear the fuel light up (bit of a roar) then the air motor and fuel pump should go to their max speed, shortly after that the glowplug switches off and you will hear a jump in the air motor speed.

 

That is what it should do. Let us know how far it gets and then we can help.

[epic]

Thanks for your help, i removed the main fuse for ten mins.Turned it on again,the water pump ok ,air motor ok fuel pump clicking and a roar from the exhaust blowing only warm, not hot as before then shuts down the flashing led is consistant

[nicknorman]

Does it just go through that startup sequence once, or does it try again after a bit of a purge?

 

Reaching the limit of my knowledge here (because the only time I had a problem with it lighting but then shutting down the flame sensor just needed a clean) but perhaps a clue is that you say the exhaust is cooler than expected. Silly question but do you have plenty of fuel? Presuming there is a dedicated fuel filter for the Mikuni, is this clean? It would be worth removing the glowplug and the fuel entry boss / gauze inside to check for excess carbon / soot since this is quick and easy to do. When was it last serviced /decoked?

Edited January 3, 2014 by nicknorman

[epic]

Hi

 

The unit was stripped and de-coked only a few months ago and has worked fine until last week. It seems to attempt to start 3 times then shuts down with a constant flashing of the led light and my manual says one flash - clean optic flame sensor which was spotless. So i dont think it could be coked up so soon, so was thinking is there a way to test the sensor.The fuel comes from the main fuel tank so plenty of fuel and the fuel pump clicking away starts to heat up but does not get mad hot like before. then shuts down. I have checked the tiny filter in the fuel pump and was clean when the unit was stripped down,

[nicknorman]

It could be the flame sensor but seems a little unlikely since the system checks the continuity of the flame sensor prior to startup - so it won't for example be open circuit (wiring disconnected) - you would get 2 flashes and no attempt to light up if it was detected as being faulty. But yes it could be working, but out of its normal spec. It is a phototransistor, that means its conductivity changes in the presence or absence of light. You might be able to remove it and check it with the diode check setting of a multimeter - you should see the indication changing if you shine a torch directly onto the sensor vs blocking all light from the sensor with your finger. But that will only indicate it is vaguely working and not necessarily within its normal spec. A phototransistor is polarity sensitive so you may need to try the meter both ways round.

 

Of course a cheap way to check the sensor would be to substitute it with a known working one from a mate's boat, if you have such a mate willing to let you mess with his Mikuni!

 

But if you are sure the heater is getting less hot at the same point as it used to get hotter - ie before the fuel pump and air motor go to full speed (which is when the light-up is detected by the flame sensor) then it must be something other than the flame sensor and lack of fuel is the obvious one.

[epic]

Thanks for your time i will remove the fuel filter from the pump just in case it has got blocked. Thinking about it, it was running for about an hour last week when it shut down for the first time so maybe it is a fuel fault but i was thinking if there was a shortage of fuel the pump would not click or bring on the led 6 flashes

[nicknorman]

The fuel pump will still click in the absence of fuel (for a while, until the system shuts down) and the 6 flashes means something electrical wrong with the pump (eg open or short circuit) and in any case, since it seems to light, there must be some fuel getting through but maybe just not enough.

[steve hayes]

Be careful the LED flashes are a best guesstimate the control module is not that bright. I've been fooled in the past with the flash codes

[nb Innisfree]

Maybe a faulty water thermostat? Our MX60 has two on the top, one is 70c the other is a higher overheat one which has to be pushed manually to reset. Could be the lower one which puts heater into shutdown cycle?

[nicknorman]

Maybe a faulty water thermostat? Our MX60 has two on the top, one is 70c the other is a higher overheat one which has to be pushed manually to reset. Could be the lower one which puts heater into shutdown cycle?

But if it was, wouldn't it just shut down without any failure lights?

[nb Innisfree]

But if it was, wouldn't it just shut down without any failure lights?

Dunno, if it actuated early it would put the heater through a normal shutdown sequence and as someone has said the diagnostic lights sometimes lie.

[Doorman]

Hi

 

The unit was stripped and de-coked only a few months ago and has worked fine until last week.

 

Hi Epic,

 

As your unit was stripped and de-coked recently, was it removed from the boat? I repositioned our MX40 heater and when reconnecting the main electrical feed snap connector, I mustn't have pressed the two connectors together properly, causing a resistance through poor contact. This resulted in a voltage drop whenever the unit cycled on start-up and maximum current was required for the glow plug. The symptoms I experienced were identical to yours. Try checking that all connections are secure and fuses are positioned correctly in their holders. Once I discovered the problem the heater worked fine.

 

Just a thought!

 

Mike

[epic]

thanks for your help, i did remove the unit from the boat to de coke it, but when refitted it ran ok until last week. I have been working in side the engine bay and may have of disturbed something well worth a second look. But if there was a fault to the heater plug wiring would the led be flashing (7) pulses.

My led is flashing (1) ignition failure.

 

It is nice when people take the time to try and help others, you don't feel like you are on your own with problems

[nb Innisfree]

thanks for your help, i did remove the unit from the boat to de coke it, but when refitted it ran ok until last week. I have been working in side the engine bay and may have of disturbed something well worth a second look. But if there was a fault to the heater plug wiring would the led be flashing (7) pulses.

My led is flashing (1) ignition failure.

 

It is nice when people take the time to try and help others, you don't feel like you are on your own with problems

I believe a heater plug fault is detected by an open circuit, a bad connection resulting in a voltage drop probably wouldn't be detected.

 

Edited for clumsy typing.

Edited January 4, 2014 by nb Innisfree

[Biggles]

My MX60 when I had it in suffered from 2 irritating faults. The first one was and never happened again was the tiny gauze filter in the fuel pump body getting blocked.

 

The other was the top heat sensor which has a solid wire coming out which fractured causing intermittent running. I think I soldered that up to make it work.

 

The only other time it played up was when it needed a decoke which is routine maintenance.

 

I have a Hurricane now and much less in the bank!

[Doorman]

But if there was a fault to the heater plug wiring would the led be flashing (7) pulses.

 

My led is flashing (1) ignition failure.

 

 

Exactly the same led indication that I experienced. As the main connector was only partially made and insufficient current was flowing to the glow plug, there wasn't enough heat being produced to ignite the atomised fuel around the gauze, resulting in ignition failure. Once the fault was diagnosed and corrected, the heater functioned without any further problems.

 

 

I believe a heater plug fault is detected by an open circuit, a bad connection resulting in a voltage drop probably wouldn't be detected.

 

As explained, it wasn't a heater plug fault but ignition fault that was being indicated. An ignition fault can manifest itself from various causes such as an air lock in the fuel feed, air motor intake restriction or as in my particular case, poor electrical connection causing a voltage drop.

Edited January 5, 2014 by Doorman

[nicknorman]

However in the OP's case he is reporting that he can hear the fuel igniting.

[Doorman]

However in the OP's case he is reporting that he can hear the fuel igniting.

So could I Nick, but only for a very short period until the air motor ramped up the flow then the heater would proceed to its 'shut down' cycle. The OP's symptoms bear an uncanny resemblance to my own.

[nicknorman]

Oh I see, that's interesting - so presumably the increased air flow was cooling the barely-hot-enough glow plug and thus the fuel cooled below its flash point. So a clue to the OP if his heater shuts down at the time the air motor ramps up. That means flame has been detected, but then goes out. I got the impression his start cycle wasn't getting that far but he does not specifically say either way.

[smileypete]

Maybe try with a squeaky clean fuel filter and fresh can of white, level with the heater.

 

Also check the voltage at the heater terminals and glo plug while firing up, better still run directly off off a freshly charged bat via fuse.

 

Oh I see, that's interesting - so presumably the increased air flow was cooling the barely-hot-enough glow plug and thus the fuel cooled below its flash point. So a clue to the OP if his heater shuts down at the time the air motor ramps up. That means flame has been detected, but then goes out. I got the impression his start cycle wasn't getting that far but he does not specifically say either way.

 

Often there's install issues that mean the heater works marginally and problems may manifest later, the heaters themselves get a lot of blame for these, though their internal fuseholders sometimes have a lot to answer for.

 

Fault diagnosis is often a game of finding and proving what *isn't* the problem.

 

cheers, Pete.

~smpt~

Edited January 5, 2014 by smileypete

[epic]

thanks chaps

 

when i go back next week i will check and clean the fuel pump filter, check fuses and connectors and check the glow plug and then wack it with a big stick

[nicknorman]

If that fails, (and check the fuel filer between tank and Mikuni presuming there is one) and having tried a bigger stick, then a new flame sensor is not too bad at around £30

[Doorman]

Oh I see, that's interesting - so presumably the increased air flow was cooling the barely-hot-enough glow plug and thus the fuel cooled below its flash point. So a clue to the OP if his heater shuts down at the time the air motor ramps up. That means flame has been detected, but then goes out.

That's exactly how I read it. The problem is compounded as the heater calls for optimum air motor speed and in doing so, reduces the available current to the glow plug further.

[epic]

I can borrow a amp clamp to see what the heater plug is drawing. There are two wires on the heater plug if i do one at a time what amount of amps would you expect to read