Failing coil symptoms

[Bendy toy]

My bike starts easily and runs fine when cold but when hot it ticks over with the sound of a a single cylinder. Recently, the RHS started to really missfire and fuel consumption went ballistic. The RHS plugs and O2 sensor were totally sooted up. The LHS were normal colour.

I replaced all four spark plugs and the RHS O2 sensor. Fuel consumption is now a lot better but still not quite back where it was. The plugs are now all the same colour.

I dont have a GS-911 but suspect the main coil is failing when it gets hot. It tests out OK with a meter but other than just swapping it out, how can I confirm if which coil is failing.

 

[ianran]

My bike starts easily and runs fine when cold but when hot it ticks over with the sound of a a single cylinder. Recently, the RHS started to really missfire and fuel consumption went ballistic. The RHS plugs and O2 sensor were totally sooted up. The LHS were normal colour.

I replaced all four spark plugs and the RHS O2 sensor. Fuel consumption is now a lot better but still not quite back where it was. The plugs are now all the same colour.

I dont have a GS-911 but suspect the main coil is failing when it gets hot. It tests out OK with a meter but other than just swapping it out, how can I confirm if which coil is failing.

If you unplug the leads to each spark plug in turn, if it doesn't run any worse then that will likely be the failing one. Just be careful, I did have a connector that plugs into the end of the stick coil fail which gave intermittent running. If its a 1200 they don't have "one coil" they have stick coils in each of the plug leads.

 

[KSMITH]

fairly easy to do

plug the coil out with the 3 pin electrical plug still connected.

plug in an old spark plug into the coil and lay it onto the top of the engine.

start the engine and with a cloth or a heavy rubber or rubber glove , pick the coil up carefully at the back and hold it no more than 5 cm away from the cylinder ( not the tappet cover) and note what the spark is like.

if you are getting a nice blue viscious spark jumping onto the engine then the coil is good

if you are getting a yellow weak spark - you would have to hold it very close to the engine maybe even touch the spark plug end electrode to the engine to get a spark then you have a failing coil and replace it with a new one.

you can do the same test with all of them and see what you get

I had more or less the same issues and it turned out to be a weak spark on one onf the main coils causing all kinds of havoc- i got a new coil and problem solved- i have different bike compared to what it was like before.

 

[Bendy toy]

Next time its fully hot I'll give it a try.

 

[KSMITH]

you can do it from cold engine doesnt matter on the engines temperature

 

[Steptoe]

Simple test.

Unplug the connectors that attach to the coil sticks each side on the bottom coil/spark plug. Go for a ride running on just the top two plugs. Does it ride ok ?

If so reconnect the connectors into bottom coils and disconnect the top connectors on each side. Then go for a ride running on just the bottom plugs.

If you suspect they're breaking down under load that's the perfect way to test them. If one or two are that bad you may even have trouble starting the bike and getting ti to run.

Coil faults don't show up on a GS911 diagnostic unit.

 

[Bendy toy]

Ive come down to Oxford again today. It began all fine but it's now running like a bag of spanners and the exhaust is again getting smoky. Its probably the RHS main coil as that side was sooty last time. I'll do the coil disconnections tomorrow and drop into North Oxford for a new coil(s).

Does anyone know if there is a generic stick coil that will fit?

 

[KSMITH]

i wish there was a generic one!

i searched and searched the internet nothing, but they are now made in china and have the words PULSE on them and no longer the BMW name or logo.

there probabably is one- just someone needs to come across it and tell all of us.

one thing i did figure out is the front telelever ball joint rubber boot is the same one as used on the rack ends of the BMWE90 car and there are LOADS of them around at the scrappers ect-

make sure your plugs are gapped correctly as these bikes appear to be very sensitive to the size of the gaps-

 

[Steptoe]

Does anyone know if there is a generic stick coil that will fit?

None.

We had a long thread going a couple of years ago trying to source another option with all sorts of things being checked, nothing came up.

But there is good news, after bmw trying three or four different manufacturers the most recent of the coils seem to be far better, with no short term failures.
Fingers crossed they've cracked it.

 

[Bendy toy]

I pulled the coil connection on the RHS and bike sounded just as rough. I pulled the coil out and immediately smelled burnt insulation.

One new coil from North Oxford and it certainly sounded better and the mpg went to over 50mpg. But less than 10 miles it was dropping again.

I'm now back to 38mpg and running on one cylinder at low revs. :-(

Could the old coil have killed the new lambda?

 

[Bendy toy]

Does anybody know if the unburnt fuel from a failing coil can kill the lambda sensor?

The old burnt coil is replaced but it's running rich again

 

[KSMITH]

Not sure , but it would appear that the o2 sensors are very robust?

any one else have any other ideas?

try disconnecting the battery and leave it off for bit reconnect and take it for a ride again and try it

 

[Bendy toy]

Swapped coils left to right and the problem persists so coil probably not the cause. The said the LHS coil (probably the original) as a slight hot insulation smell, so could be failing when hot. If it not for the high cost I would just fit a replacement.

However, disconnecting both O2 sensors gave me 55mpg for a while and the engine felt punchy. I tried one sensor disconnected then the other and the fuel consumption increased again though not too much. But now its heading below 40mpg again with O2 sensors connected or not.

Pulling the main spark plugs, it's always the RHS which is a darker colour. The LHS is amazingly clean. So could this be an injector problem RHS rich or LHS weak? I'll start a new thread.

 

[KSMITH]

these coils on these bikes can be very decieving

check them in the manner as I described, comparing all of them to each other ( uppers and lowers)

you should get a nice fat blue spark and not a small weak yellow one

the 02 sensors do pack up , but not easily, i would confirm the coils first, clean the plugs up, then note which coil is fitted where, ride the bike, pull your plugs and check and make a note of the condition

with good coils you should have good colour on the plugs- the lowers do tend to be a bit black.

it is important that you know that all your coils are indeed good.

clean the plugs up again and then pull the 02 sensors, swap them , ride the bike and see if there are changes.

if there are changes to the 02 sensor, ie the same side goes bad then either it is an injector leaking, air leak on that side.

take a small amount of petrol and a small brush and brush the intake tubes near the cylinder head while the engine is running and note of any changes to the idle- if no change then no air leak

ps do this with a cold engine as obviuosly hot exposed engine parts and petrol are a dangerous mix.

O2 sensors are fairly easy to come by in your part of the world, unlike us here no body even knows what they are- i can appreciate that they are a bit pricey, but worth a try.

my GS had all sorts of issues and i went through all sorts of nonsense with it to get it sorted- it turned out to be 1 stick coil messing me around with a weak spark! replaced it and it was a different bike.

 

[Bendy toy]

Latest tests.

Main coils swapped Left to right. The RHS has a dirty plug regardless of which coil is fitted. But the RHS plug is now just dirty, rather than sooty black which it was when the problem began.

Plugs swapped left to right, still the RHS which is dirty. (ok they are now both a bit dirty but RHS looks worse when pulled out after a short run and full temperature.

Lambda O2 sensors disconnected - trip screen showed 55mpg.

Connected LHS O2 sensor leaving RHS disconnected. mpg now shows 46-47.

Connected RHS O2 sensor with LHS disconnected. mpg now shows 46-47

Connected both O2 sensors and mpg dropped to around 38 mpg

Disconnected both and mpg went back to mid 40s, but not back to 55 as it was.

Each time the trip was reset.

RHS plug is always dirty compared to left.

I have not had chance to swap O2 sensors left to right, but from the above findings I suspect it wont change much. Not yet tried the plug to metal test because pretty much everything is painted. I need to get some wire to earth the plug body while I watch the spark.

The plugs are new but Ive not yet tried a brand new one to replace the dirty one.

Ive also pulled both injectors. The spray pattern when cold looks the same. Ive not had chance to run the bike and repeat with a hot engine, but my rough and ready eyeball calibrator says they look the same. TBH if one was injecting below par (making the other over inject) I think there might be some sign on the cold test.

Valve clearances are ok so no reason to believe compression has gone down on the RHS. I may need to get a compression tester, but for the short stints when it runs well, the bike feels very punchy.

 

[KSMITH]

dont go on your figures as per the obc

they are known to be HIGHLY inaccurate on short runs

also you need to do a good 20 mile run to get a decent result on the plug condition.

it is important that you know that all your coils are good first.
once you know they are ok, go onto the next item which would be the O2 sensors

 

[Pukmeister]

My money is on a faulty Lambda probe. If plugs go blacker on one cyl, swap Lambdas and test ride/recheck. If blackness swaps with the lambda swap its QED.

A GS911 can plot lambda trace for sawtooth curve, and will also tell if Lambda internal heater has failed.

Other things like propylene or silicone dissolved in fuel will kill a lambda sensor quickly.

 

[Steptoe]

these coils on these bikes can be very decieving

check them in the manner as I described, comparing all of them to each other ( uppers and lowers)

you should get a nice fat blue spark and not a small weak yellow one

.

Your way of testing isn't accurate.
The coils can break down under load
i.e. work perfectly in your test but when having to produce a spark under compression in a hot engine can be intermittant or breakdown. .

The only way to be sure is to test them how i stated.

 

[Bendy toy]

Thanks for all the ideas.

Failing coils will often seem fine when cold and play up when normal running temperature expands the windings. (Ive had that happen on a car). I've swapped the main coils around and the problem persists on the RHS. Its looking like the O2 sensor, but running with only The LHS sensor connected also had a bad effect on the trip fuel figures.

Agreed, the trip mpg isnt accurate, but it was reset every time and should be adequate for a rough idea of better or worse consumption. It went from from over 50mpg no O2 connected to 45mpg with LHS or RHS connected and then 35mpg with both connected. That much of a change cant simply be an accuracy issue. That's the question mark - why would running either one give a similar middling consumption figure when running both soots up the RHS?

Next job is to swap the O2 sensors left to right and see if the dirty spark plug swaps sides.

Fuel contamination would kill both sensors at the same time, but the LHS has always been clean and it's always had Shell posh petrol.

By the way it always runs nicely on cold start then goes rough when warmed up.

 

[Bendy toy]

It seems like I have it sussed. All the following tests were on the M6 and M40 stopping at services or otherwise leaving the M-way to make changes.

With the O2 sensors swapped over the one which was on the RHS now causes the LHS to run rich. MPG is mid 30s. The dodgy sensor also rattles.
Why didnt I do this check first time out.

Disconnect both sensors and the bike runs fine for a while showing well over 50mpg and its punchy to use so the fuel mixture must be pretty good. However, after a few miles the mpg falls to the low 40s mpg. I kept resetting the display to get a better spot reading.

Plug in the good O2 sensor and leave the other one out and bike runs initially at over 50mpg but this drops to upper 40s after a few miles. I guess its the ECU adapting again.
The bike also feels rougher. Who knows why, maybe the spark timing is independent and gets retarded on the non sensor side.

Both spark plugs are good colour though maybe a bit dirty on the rim.

New O2 sensor is on order from North Oxford.