Dodgy ignition coil??

[NJA]

I've got a little Stihl kombi unit that suddenly cut in use.  I presumed fuel so filled it up, but noticed still probably ¼ of a tank in there.  It then wouldnt start.

Checked spark, nothing doing. 

Put new spark plug on, still nothing

 

Put a tester on the spark plug lead, shows a spark when earthed to the machine, but not when connected to a spark plug.

 

Even with a plug i took off a working saw or a new plug (had been in workshop for 5years but still in box)

Maybe all 3 plugs are mysteriously duff but Im beginning to doubt it?

Disconnecting on/off switch doesnt make any difference so can't be that

 

Could it be that the ignition coil has gone a bit dodgy, works when tested on its own but not when connected to a plug?  Almost as if the resistance of the plug is too much?

 

Just want to check I'm not doing something stupid before ordering a new coil.

 

Thanks

[Mark_Skyland]

If you remove all the wires going to the coil and you're sure that the HT lead isn't shorting out and you have no spark at the plug then its usually the coil that needs replacing. 

 

[spudulike]

Double check the coil to flywheel gap and if you can unscrew the HT lead ( some you can), then unscrew it, check the continuity, clean it and refit it.

It is also worth checking the continuity between the HT cap and earth. You should get a reading of sorts, possibly 20k ohms, but it will show the cap and lead are OK before purchasing a coil.

I had a 461 once that had a corroded HT line and this check saved purchasing a new coil.

[NJA]

11 hours ago, Mark_Skyland said:

If you remove all the wires going to the coil and you're sure that the HT lead isn't shorting out and you have no spark at the plug then its usually the coil that needs replacing. 

 

Thanks Mark, I only pulled one off will do the other.  Good point ref HT lead but I'm sure its not. Thanks for confirmation, new coil it is I think.  Just seemed strange the coil was working until a plug is connected.

[NJA]

10 hours ago, spudulike said:

Double check the coil to flywheel gap and if you can unscrew the HT lead ( some you can), then unscrew it, check the continuity, clean it and refit it.

It is also worth checking the continuity between the HT cap and earth. You should get a reading of sorts, possibly 20k ohms, but it will show the cap and lead are OK before purchasing a coil.

I had a 461 once that had a corroded HT line and this check saved purchasing a new coil.

Thanks @spudulike, I'll double check the gap to check its hasn't moved.  Don't think the HT lead does unscrew on this one.

[woody paul]

I ve had new plugs that were broken, when I have problems with stuff always use plug from other machine to, know it's good. 

Had a problem with a Husqvarna saw last year, would start and tick over but splutter at full revs, tried different plug carb clean, then change ignition module for one on other saw and fixed it. 

Years ago working for someone he had saw that wouldn't go, was quite new so I took it back to dealer as I was passing, they point bank stood there and said couldn't be ignition module, but I was 99% sure so pulled plug cap off and put finger in cap and pulled starter. And I didn't get a shock but dealer did. 

[Tree monkey 1682]

Ive a stihl br400 blower, 24 years old past few years its been running a bit like a knob, started ran, but not to full revs .

Local  garage re tuned her and got it almost right ..one day it wouldn't fire, swopped plugs got one hell of a belt off it , then it went back in again and the coils fked , they can spark enough but not enough to fire ,

Answers a new coil but im not paying £180 plus labour for it