Stihl Long reach hedge trimmer - Fault diagnosis

[Andy Collins]

I think the ignition module has failed, it has compression, fuel is getting through, changed spark plug, checked carb is working ok and so on. Yesterday it became erratic would cut out for no apparent reason, put it down, pick it up, pull it over and it would fire up again for a while, then die. Repeat over and over, then at the end of the day it ran fine for nearly a tankfull, then cut out again, only this time it wouldnt re-start. left it last nght, tired it again this morning and it wasnt interested in firing at all. Repeated all the basic checks, and gave up. Not firing at all. With all the plastics in place its tricky to get a decent earth where you can see the spark on the plug, if it is sparking at all that is. Any tips on things to check so I will know if the ignition module is definitely at fault, is there a way to test it directly?

[High Scale]

It may be the HT lead leaking Andy, I have a normal Stihl trimmer and it acted the same as your long reach, it was earthing the charge for the spark, the only way it keeps running is to put the HT lead only slightly on the plug, if you fit it on properly it cuts out.

Edited January 14, 2011 by High Scale

[Pat Ferrett]

:idea:put the swith to the on position, Pull the HT lead off, lick your baby finger, put it in the cap so it touches the metal ring and pull the engine over, you'll know then if its got a spark:011: sorry mate ignore that I've been at the Haribo and they make me hyper

[Jonesie]

Remove the covers and take the earth lead of the coil, check the HT lead over if all OK take a small amount of fuel and put it down the plug hole. This has now eliminated everything and it should fire, if it doesn't then it's probably the coil. If it does try running it without the earth wire off, if it runs fine you have a broken lead or switch somewhere.

Remember to take a screwdriver with you to pop off the plug lead to stop it, or it might make your hair stand on end.

[Andy Collins]

Thanks, hopefully i'll have more patience tomorrow, nothing worse than trying to get on with a job and something goes all unreliable on you. With 500metres of hedging, top and both sides my tolerance level was wearing a little thin:001_rolleyes:.

[WoodED]

I think the ignition module has failed, it has compression, fuel is getting through, changed spark plug, checked carb is working ok and so on. Yesterday it became erratic would cut out for no apparent reason, put it down, pick it up, pull it over and it would fire up again for a while, then die. Repeat over and over, then at the end of the day it ran fine for nearly a tankfull, then cut out again, only this time it wouldnt re-start. left it last nght, tired it again this morning and it wasnt interested in firing at all. Repeated all the basic checks, and gave up. Not firing at all. With all the plastics in place its tricky to get a decent earth where you can see the spark on the plug, if it is sparking at all that is. Any tips on things to check so I will know if the ignition module is definitely at fault, is there a way to test it directly?

 

i had a similar problem with an fs85, it would run for abit then die and would not start until it was cold again,, it was the ignition coil, hope this helps

[Treeworld]

I had the same problem on a km85, the problem was in the ht lead where it meets the spring bit which fits onto the spark plug. The metal piece bites into the ht lead and this had come loose. My solution was to buy the coil and ht lead as this only comes as one piece!! bad design as it was only a few pennies fault that needed a £40 part. Sounds you have exactly the same problem, hope this helps.

[Jonesie]

I had the same problem on a km85, the problem was in the ht lead where it meets the spring bit which fits onto the spark plug. The metal piece bites into the ht lead and this had come loose. My solution was to buy the coil and ht lead as this only comes as one piece!! bad design as it was only a few pennies fault that needed a £40 part. Sounds you have exactly the same problem, hope this helps.

 

Just so you know next time we sell one that will clip on the end of the ht lead for about £4.00.

[Andy Collins]

Ok, update time. Just stripped off the cover, checked it over, fired it up and it ran lovely, stopped/started everytime on request. Replaced top cover, splutter and died. Take off top cover, wiggle HT with engine running....fine. Replace cover again... nothing. Repeat above a couple of times with same results. Hmmm.

Then I spot it. The Problem. Where the little black earth lead comes off the coil to return to the switchgear, its rubbed against metal and shorted out. With the cover off of course this wasnt happening, but press the cover down and it effectively acts as a on/off switch. Temporary solution, wiggle wire away from metalwork, wrap in insulation tape, replace cover.... test..... WOO-HOO

Thanks for help

[tractorboy1]

Ok, update time. Just stripped off the cover, checked it over, fired it up and it ran lovely, stopped/started everytime on request. Replaced top cover, splutter and died. Take off top cover, wiggle HT with engine running....fine. Replace cover again... nothing. Repeat above a couple of times with same results. Hmmm.

Then I spot it. The Problem. Where the little black earth lead comes off the coil to return to the switchgear, its rubbed against metal and shorted out. With the cover off of course this wasnt happening, but press the cover down and it effectively acts as a on/off switch. Temporary solution, wiggle wire away from metalwork, wrap in insulation tape, replace cover.... test..... WOO-HOO

Thanks for help

 

Wrapping in insulation tape is a preeminent solution in my book