One in a million electrical faults

At some time, we must all of heard about a vehicle electrical fault that appears to be a "One in a million fault" the sort of fault which garages/dealers are unable to find and fully cure. In many cases they only manage to temporary cure and the fault returns. During my time I have undertaken a few such faults and thus far managed to fully diagnose them, maybe more luck than judgement to say the least. Some members who are very electrically minded may find my recent such event quite interesting especially when I explain the cause of the fault.

A motorcyclist had a charging problem with his motorcycle, the alternator (3 phase, delta windings, permanent magnet type) was undercharging but this was not a straightforward fault.

The motorcycle had been taken to several dealers for rectification of the fault, a new alternator stator, regulator/rectifier unit and motorcycle wiring harness had been fitted by these dealers and the owner was told that the fault was cured upon collecting the motorcycle on each occasion, but each time a few days later the battery would run down yet again.

The owner was recomended to bring the motorcycle to myself for diagnoses of the fault. Under the circumstances I felt sorry for the owner and took the job on with no charge, i.e. parts only if used. Symptoms of the fault were as follows; At tickover, the alternator was balancing the electrical loadings with the headlight on and still showing a 3 amp charge. When the engine speed was increased the charging rate decreased (opposite to what should normally happen) and when the engine reaches 3000 RPM the alternators output totally terminates even though there is still a heavy electrical demand at this time.

I must admit, this one had me pulling my hair out but I applied one of my old time theories; "If there is a fault, there must be a cause, as there is a cause, it must be curable" in other words, in my book, there is no such thing as cannot be done or rectified.

After a long detailed investigation I found that the motorcycles electronic ignition unit (often reffered to as a CDI unit) was at fault. One could say; what has the motorcycles' electronic ignition unit got to do with the alternators output and regulation?

Well this is what was happening; The motorcycles' electronic ignition unit was functioning correctly as in allowing the engine to run and function correctly even electronically advancing and retarding the ignition between; 10° BTDC and 40° BTDC at 3000 RPM, but something had gone wrong electronically inside said unit and it was emitting electrical pulses into the motorcycles wiring harness which was effecting the alternators' electronically controlled regulator/rectifier unit causing it to totally shut down when the motorcycles engine was fully advanced at 3000 RMP.

An interesting one to say the least

Colin 

After "At some time...", my eyes start glazing.  Hope its not made into a film Colin

"The Art of Taxidermy springs to mind"

At some time, we must all of heard about a vehicle electrical fault that appears to be a "One in a million fault" the sort of fault which garages/dealers are unable to find and fully cure. In many cases they only manage to temporary cure and the fault returns. During my time I have undertaken a few such faults and thus far managed to fully diagnose them, maybe more luck than judgement to say the least. Some members who are very electrically minded may find my recent such event quite interesting especially when I explain the cause of the fault.

A motorcyclist had a charging problem with his motorcycle, the alternator (3 phase, delta windings, permanent magnet type) was undercharging but this was not a straightforward fault.

The motorcycle had been taken to several dealers for rectification of the fault, a new alternator stator, regulator/rectifier unit and motorcycle wiring harness had been fitted by these dealers and the owner was told that the fault was cured upon collecting the motorcycle on each occasion, but each time a few days later the battery would run down yet again.

The owner was recomended to bring the motorcycle to myself for diagnoses of the fault. Under the circumstances I felt sorry for the owner and took the job on with no charge, i.e. parts only if used. Symptoms of the fault were as follows; At tickover, the alternator was balancing the electrical loadings with the headlight on and still showing a 3 amp charge. When the engine speed was increased the charging rate decreased (opposite to what should normally happen) and when the engine reaches 3000 RPM the alternators output totally terminates even though there is still a heavy electrical demand at this time.

I must admit, this one had me pulling my hair out but I applied one of my old time theories; "If there is a fault, there must be a cause, as there is a cause, it must be curable" in other words, in my book, there is no such thing as cannot be done or rectified.

After a long detailed investigation I found that the motorcycles electronic ignition unit (often reffered to as a CDI unit) was at fault. One could say; what has the motorcycles' electronic ignition unit got to do with the alternators output and regulation?

Well this is what was happening; The motorcycles' electronic ignition unit was functioning correctly as in allowing the engine to run and function correctly even electronically advancing and retarding the ignition between; 10° BTDC and 40° BTDC at 3000 RPM, but something had gone wrong electronically inside said unit and it was emitting electrical pulses into the motorcycles wiring harness which was effecting the alternators' electronically controlled regulator/rectifier unit causing it to totally shut down when the motorcycles engine was fully advanced at 3000 RMP.

An interesting one to say the least

Colin 

After "At some time...", my eyes start glazing.  Hope its not made into a film Colin

"The Art of Taxidermy springs to mind"

Wow just read that post  . I love your comment "Cannot be done or rectified . reminds me of my early days when my mentor said "Theres no such word as Cant " stuck with me ever since . As to spotting that fault as the CDI unit take my hat off to that one . On a more simper fault as that one but in reverse . A 760 vovlo battery empty , and charging I think ,if I remember at 16 volts (Machine sensed alternator ) new battery and alternator fitted in warranty still charging at 16 volts ,Doh !!!!       by chance, disconected a temp sensor that was fitted under the battery, charging rectified . Think they stopped fitting them after that and I think they (Volvo ) issued a technical buletin about it ,I did feel a bit smug about that one . I'll look forward to reading more of your post in the future . And Ignore the others when you write a long explanation . Best regards Martin

Blimey Richard!  A CB175? That's going back a bit. I used to have it's poor relation ie  CD175, but that was about 35 yrs ago ;-)

I had a new one back in the early '70's, rebuilt this US imported one (started life as a CL175) a couple of winters ago.

DeJaVu  My First bike was also a CD 175 Arrived in a box in bits on my 16th birthday with a single note from Dad  Well this was what you asked for!!!

Someone thinking the way i do if there is a fault intermittent or not there must be a cause, i used to lecture in automotive diagnostics and found the biggest error most techs made was trying to cure the symptom without first identifying the cause. That and not looking at all the info available before making a diagnosis unlike yourself

And dont worry about the spelling mine's the same If only someone knew how to fix it??

In my Job as worshop controller to save time i used to go ut with the custmoer and first get the exact details of what there fault ,read compaint ,was . And listen to them .As you said an intermiment fault is there its just intermitent  It is easier when you know the car you can make calculated guess to look in one direction

 First job over I could then give really specific areas or details of the fault to the mechanic or make the desicion to give it our diagnostic mechanic  ,in them days before they became called technicians . without a waffled story

. MY good mate , still moans at me when he tells me a complex fault and I reply ...... "What"..... so let me get this straight ..... its doing such and such ! he then says " Dont you listen "  ...... 

Water off a ducks back as thery say !

Blimey Richard!  A CB175? That's going back a bit. I used to have it's poor relation ie  CD175, but that was about 35 yrs ago ;-)

I had a new one back in the early '70's, rebuilt this US imported one (started life as a CL175) a couple of winters ago.

DeJaVu  My First bike was also a CD 175 Arrived in a box in bits on my 16th birthday with a single note from Dad  Well this was what you asked for!!!

Blimey !!!!!!!!!!!!! my first bike was a CB72

My first bike was a Royal Enfield 'Prince' 150 cc. It was a bit like the Francis Barnet but a posher tank. Well, I thought so.

Many moons ago when i was in the road transport section at work i had a lighting fault on an artic tractor unit.All was ok until we tried the brake lights and then it was like strobe lighting all over the vehicle.After a coupe of hours the fault was traced to a brake light bulb.The bulb was a stop/tail bulb and the stop element had broken and fallen across the side light element joining both circuits together which causes all sorts of problems.

v9

Yes Peter, I can understand how such a fault like that can happen from a bulb filiment fault. It's one of the first things I check these days after checking fuses of corse. Earlier within this discussion with regard the said caravans fault, I mentioned  there was a possibility it could be something simple like a shorting bulb filiment. In the gentlemans case it appeared to be something entirely different.

Colin

Sorry, cocked up, it was not earlier within this discussion, it was said caravan in the discussion titled "Marker lights failed both sides" 

Said discussion is within the Caravan discussions section.

Colin

Many moons ago when i was in the road transport section at work i had a lighting fault on an artic tractor unit.All was ok until we tried the brake lights and then it was like strobe lighting all over the vehicle.After a coupe of hours the fault was traced to a brake light bulb.The bulb was a stop/tail bulb and the stop element had broken and fallen across the side light element joining both circuits together which causes all sorts of problems.

v9

Those symtons were common when a customer put a single filament 21w bulb in stop/tail socket .