Diagnosed Coil and/or related issue...a few questions.

Johnny Canuck · Jun 5, 2016

My 1999 ST1100 has 119,000KMs on the clock and has only had the odd minor hic-up since purchasing 3 years ago @ 104,000KMs. Anything I've needed to know I've found the solution for or have been guided by the experts from this site. Having said that, the bike has been pretty much issue free for me.

Returning home from work on Monday last week I stopped in to a store. They have a rough driveway/parking lot and when I hit a minor bump the engine immediately started running rough, and actually stalled out just as I came to a stop.

Hoping this was simply a temporary issue and would go away upon start up....well...not quite! The engine was running quite roughly...I thought I was only running on 3 cylinders. Got home just 3KM away driving very slowly.

Couldn't work on the bike until today. Stripped off the tupperware, I started up the engine (still running rough) and felt all four exhaust pipes heating up. Hot enough that you couldn't touch any of them. Then I remembered I had received a portable laser temperature reader last Christmas...got it out and took a reading on each exhaust pipe. Interesting...on the left side the two pipe temperatures were in the 260- 275 Celsius range. On the right side both were at approx 75 Celsius. Humm? Took off the air cleaner, started the bike (still rough running) and placed my hand over the two stacks providing air to the left cylinders and the bike stalled out. Restarted the bike (still running rough) and covered the stacks for the right cylinders showed no difference the bike was still running roughly. Pulled the plug wires/caps on the right cylinders and again, no difference - the engine was still running roughly. Pulling the left cylinder plug wires/caps resulted in the engine stopping.

Since I can smell unburned fuel, I'll assume the right cylinder carbs are working fine, but just there's no spark. Seems to me like this is a coil related issue affecting the right cylinder bank.

So, what procedure is recommended next? BTW, I'm not even certain how to get my hands on those coils...they appear tucked away in a difficult to reach place. Any assistance or information on just how to get to those coils or any other tests I can conduct on the coil itself would be helpful...and/or other suggestions are certainly welcomed.

Uncle Phil · Jun 5, 2016

Do the old 'ground out' the spark plug wire first to make sure it's not the plugs. Screwdriver up in the plug wire and ground out plug wire (unless you have a spark plug wire tester). I have had plugs fail completely. It's nice to do in the 'dark' so you can really see the spark if there is one.

skidlid1300 · Jun 5, 2016

Yep simple things first - see if there's spark in them thar plugs!!

kiltman · Jun 5, 2016

Even if there's spark switch them from side to side and see if the problem is reversed. If it is then try a new set of plugs.

SMSW · Jun 5, 2016

You can pull the spark plug boot, plug in a new or cleaned old plug and lay it on the metal of the bike (the side of the plug must be grounded) crank the bike over and watch for a spark at the gap on the end of the plug. I find this a bit safer than sticking the screwdriver into the plug wire and holding the screwdriver against the bike. One time I moved the screw driver (broke the ground) and I served as the path for the high voltage to ground. OUCH!

Jim Van · Jun 5, 2016

Sounds like a fun problem to troubleshoot. Sounds like you have a bad connection that was induced by the "shock" of the bump you rode over. My bet is in the primary circuit.

You can swap the plugs side to side. I bet the right side will still be bad ( the plugs will be OK ).

You can pull both right plugs and take an Ohm reading between the two right spark plug caps to check the secondary circuit. I forget the spec, but I think it's around 16K Ohms. There are little 5K Ohm resistors in each cap, plus the secondary resistance of the coils. You can compare readings from both sides. It only takes a few minutes to do that.

If the secondary is OK, then move on to the primary circuit. Gotta get at the coils for this. You can swap the coils to see if the problem goes to the left side , or you can Ohm out the primary circuits and see how they compare.

Another possibility would be the connector between the ignition module and the coils, or at the ignition module. I'm betting on this being the cause of your problem. You could have some corrosion in that connector like a recent poster had. I think he mentioned something about "the big connector in front of the steering head". I'm out of town and don't have my Service Manual with me, BTW. Another possibility is a broken wire inside the insulation at the small connector to the coil.

So, you will need a meter and schematic to troubleshoot this problem. John O. has posted colored schematics, BTW.

Have fun, let us know what you find to be the cause of the problem.

mcthorogood · Jun 5, 2016

Jim Van said:
John O. has posted colored schematics, BTW.

Wiring schematics.

TerryS · Jun 6, 2016

Jim Van said:
Sounds like a fun problem to troubleshoot. Sounds like you have a bad connection that was induced by the "shock" of the bump you rode over. My bet is in the primary circuit.

You can swap the plugs side to side. I bet the right side will still be bad ( the plugs will be OK ).

You can pull both right plugs and take an Ohm reading between the two right spark plug caps to check the secondary circuit. I forget the spec, but I think it's around 16K Ohms. There are little 5K Ohm resistors in each cap, plus the secondary resistance of the coils. You can compare readings from both sides. It only takes a few minutes to do that.

If the secondary is OK, then move on to the primary circuit. Gotta get at the coils for this. You can swap the coils to see if the problem goes to the left side , or you can Ohm out the primary circuits and see how they compare.

Another possibility would be the connector between the ignition module and the coils, or at the ignition module. I'm betting on this being the cause of your problem. You could have some corrosion in that connector like a recent poster had. I think he mentioned something about "the big connector in front of the steering head". I'm out of town and don't have my Service Manual with me, BTW. Another possibility is a broken wire inside the insulation at the small connector to the coil.

So, you will need a meter and schematic to troubleshoot this problem. John O. has posted colored schematics, BTW.

Have fun, let us know what you find to be the cause of the problem.

I had corrosion in the big red connector behind the steering head, but that affected both coils. I'd be looking at the small connector on the left side of the bike that feeds power to the individual coils, and if not that, the connector on the ICM. Then you have spade terminals on the coils themselves. If you remove the airbox, you can access a gold coloured bracket behind the steering head and remove the connectors and if needed the coils .

Al st1100 · Jun 6, 2016

I have my wife hold the screwdriver if she stabs me with it there is good spark....only works one time

Uncle Phil · Jun 6, 2016

SMSW said:
One time I moved the screw driver (broke the ground) and I served as the path for the high voltage to ground. OUCH!

Betcha you didn't do that but once ...

Uncle Phil · Jun 6, 2016

Al st1100 said:
I have my wife hold the screwdriver if she stabs me with it there is good spark....only works one time

Then do you get a new wife for the next test? ;-)

ST1100Y · Jun 6, 2016

TerryS said:
I had corrosion in the big red connector behind the steering head, but that affected both coils.

+1...
The symptoms described by the OP would indicate a loose coil feed (check the crimp connectors there), or other intermittent connection in that line; so checking that region is a good start.

BTW will downpipe temp not give a true indication, as there bypass-tubes right underneath the flanges (behind the heat-shields).

Al st1100 · Jun 6, 2016

Uncle Phil said:
Then do you get a new wife for the next test? ;-)

I plead the 5th

The Cheese · Jun 6, 2016

I'd start with new spark plugs just to be safe. Although it doesn't sound like it would fix the issue, couldn't hurt, and ya get new plugs. The coils are very hard to get to, much less change. Check all connections on the coils themselves and the other end of thier sub harness. Plug and unplug em. Wiggle em around. Should be on the left side of them near a large harness if I recall correctly. I changed my coils while trying to fix a intermittent issue not long after I bought my bike. Pain in the neck! Get ya a spark tester. It goes between the spark plug and the coil lead. Clear window so you can see a spark when you start it.

I have a known good set I can send you. Bought on eBay and tested on my bike. Was replaced for my original set when I found my faulty part. The side stand switch.

Johnny Canuck · Jun 7, 2016

Good advise everyone! My work schedule is preventing me from getting back to work on the bike, but I'm hoping for an hour tomorrow evening. Will certainly do the spark test and/or change over the plugs...I've got some spare plugs...the ones currently in are the colder plug and have about 15K on them. Will also hope for a connection issue as opposed to a coil issue. Time will tell. More later. Thanks!

TerryS · Jun 7, 2016

You can do some basic coil/plug lead testing with a multimeter, and you only need to access the connector on the left side under the grey service cover to do the coils, and then the ends of the plug leads. Page 18-6 onwards in the service manual.

Johnny Canuck · Jun 15, 2016

OK...problem solved. It was corrosion in the pin connectors located below the ignition switch and behind/underneath the flexible rubber protector. I can only come to this conclusion as I had gone through all the other connectors including the spade connectors on the 'right side' coil. Nothing I did was able to produce a spark in the right cylinder bank. Everything was testing "correct" with the multi-meter.

I had read somewhere that someone else had struggled with this problem and eventually discovered corrosion in the red connector...so now I was trying to remove the red connector and boy was it stubborn. Lots of tugging and twisting went on for a few minutes and by doing so I must have "reconnected" the corroded pins. Not being able to actually remove the connector top at this time I actually switched gears mid-stream and simply decided to try the right cylinder bank spark plug test...looking for a spark. Man, was I surprised to see a spark! Put the plugs back in and she started like a champ firing on all 4 cylinders.

So, then back to the red connector (and the three others located there) to really get to the bottom of this and separate all and have a look inside. Eventually I did get the connectors separated and inside each were signs of light corrosion and dust. I simply used some wet sandpaper and "filed" the connector pins as best I could. Lots of electronic cleaner was squirted in (alcohol based or carbon tet...not sure). Reconnected and again, perfect firing on all cylinders.

As my plugs had gone 20K, I elected to change them out for new ones. Just finished putting all the tupperware back on and .... and as nature rewards such efforts, I was graced with the liquid sunshine. So, no ride tonight, but, as they say, tomorrow is another day!

Thanks for all the suggestions, I truly appreciate everyone's input.

ST1100Y · Jun 16, 2016

Johnny Canuck said:
...I did get the connectors separated and inside each were signs of light corrosion and dust...

Yep, often neglected due their out of sight location...
I'd suggest checking/servicing them at least every 1~2 years.
One wouldn't believe where water can end up when washing the bike or riding in bad weather... spray and dew get just everywhere...

SteveST1300 · Jun 16, 2016

I would also check the grounding of the coil maybe its a bit loose?

Diagnosed Coil and/or related issue...a few questions.

Blacksheep Tribal Member

The Cheese