2005 S4R Dropping a Cylinder

[2KLuder]

First some background. I've put about 7000 worry free miles on my S4R with no issues. I've kept up regular maintenance, valves adjusted, belts changed, fresh oil and filter every season. I replaced the plugs when I first got the bike with Iridiums. I'm pretty mechanically inclined, don't mind getting my hands dirty to solve a problem. A week ago I filled up at my normal station and rode to work. No problems at all getting on the high way and riding to work. But when I got to the parking lot, i started feeling a lot of hesitation at low RPM and random surging. I'm definitely dropping a cylinder intermittently. I parked the bike and did a quick visual check and didn't see anything wrong. After the day was over the bike fired right up and showed no signs of what i'd heard and felt previously. The next day i rode to work again and the same issue cropped up when I got to work. I did several hard pulls on the way and everything seemed fine. Until once again I got to the parking lot where i felt the same rough idle and surging. This time the problem started immediately after I got off work and when i got to my neighborhood it was worse. Definitely running on one cylinder it but it would intermittently pick up both and surge.

After some searching I decided to replace both the fuel filter and coil packs, but soon after start up I could hear the same issue at idle. It looks like my horizontal cylinder is running a little lean. Any ideas? Fuel injector maybe? Still seems to run just fine when I give it gas, but i cant hold anything at low rpm. I just put a fresh set of tires on the bike so I'm dying here. Thanks


Update, I just drained the tank and replaced with fresh gas since my problem started after a fill up. No change...started ok and sat down to a nice idle, thought I had it. But soon i could hear a cylinder dropping in and out.

Also I don't know if it matters but i'm not getting any check engine lights.

Update 2. On the off chance there is some moisture in my tank I ran a bottle of HEET thinking maybe there is some water stuck at my injector not allowing fuel to flow freely. Once again, when cold the bike started and idled just fine, but as the temp cam up to operating the cylinder started cutting again. Anyone have any ideas why this could be effected by heat? I'm a pretty decent mechanic and i'm stumped. I'll try to check the injectors tomorrow but i dont have much confidence as they fail so rarely.

Update 3. After letting the bike set overnight I fired it up this morning. Ran perfectly, smooth idle....right up until it got to around 140-150. Then the exact same symptoms. Whatever it is must be temperature dependant. I pulled both fuel injectors and did my best to clean them out. Still showing lean on the horizontal cylinder no matter what combo of plug or coil i switch. But i'm still not sure if that means its the problem. I'm running the factory termi exhaust with no other mods so i'd expect to run a little lean.

[2KLuder]

Cleaned the injectors. No change, still dropping the horiz cylinder intermittently. I'm lost.

[Speeddog]

Cleaned the injectors. No change, still dropping the horiz cylinder intermittently. I'm lost.

Try swapping the wiring to the injectors, .see if the problem follows the wires, shifting to the vertical.

I had a similar problem on My S4 a long time ago, turned out the ignition channel for the horizontal in the ECU was giving up.

[2KLuder]

swapped the actual injectors but no change. I dont think i can swap the harnesses to the injectors because then they'd fire at the wrong time. I ordered a timing light so I can use the inductive circuit to check both the ignition wiring and injection wiring to see what's dropping out.

[Speeddog]

The injectors would indeed fire at a 'wrong' time, but it's still useful to aid in locating the perpetrator.

[2KLuder]

Swapped plugs to some new Champions and it runs perfectly. I'm about three rides deep with abosolutely no signs of the hesitation reappearing. I'm stunned in the end it was plugs, the old ones looked fine and I could get both to show a nice blue spark. Oh well, for now i'm just glad I didnt go to the dealer.

[S21FOLGORE]

I replaced the plugs when I first got the bike with Iridiums.

Somehow, I missed this part.

You may be surprised, but, Iridium or Platinum spark plugs will give you WORSE performance than conventional (stock Champion) plugs in your Ducati.

Iridium plugs are not some sort of magic plugs. They don't give you any performance gain, but longer service life.
(That's what they were originally invented for.)
Some people report on online forum saying that switching to the Iridium plugs made throttle response better/ felt more power / run smoother  , it' because they are comparing brand new plugs to old, worn out plugs they just replaced.

[2KLuder]

I actually really noticed this yesterday...I thought something was wrong BECAUSE my bike was running so differently, and in almost every way better. When I bought the bike, I thought the premium plugs were the iridiums, so I was trying to go above and beyond when I replaced them. I've really never ridden it with anything else until now. I'm officially converted. I'll just add it to my regular service from now on.

[koko64]

I also recently went back to regular plugs in my Ducatis. Down here each Iridium plug costs 20 bucks more.  I use NGK or Champion or Ducati branded which can be either. I guess I'll change them every 6000-10,000 miles. Do you have a recommendation on mileage?. In cars with difficult to access plugs I use Iridium plugs.

[Howie]

The basic problem with iridium plugs in some engines is they kinda work too good.  Faster spark kernel at lower voltage at the same gap and can cause misfire due to a lower spark temperature.  Open the gap and modify the ignition system for sufficient spark at high RPM under heavy load, now you have something. 

[koko64]

Absolutely. I think the effort  is worth it if someone else is paying for it.

[Duck-Stew]

I also recently went back to regular plugs in my Ducatis. Down here each Iridium plug costs 20 bucks more.  I use NGK or Champion or Ducati branded which can be either. I guess I'll change them every 6000-10,000 miles. Do you have a recommendation on mileage?. In cars with difficult to access plugs I use Iridium plugs.

Our local shop (my shop actually  ) uses regular NGK's religiously.  I've never bought the hype on the iridiums.  I actually prefer to get into my bike every-so-often as it lets me look for things about to go bad...

[koko64]

In my M900 I ran Iridiums at 0.9 -1 mm gap supported by strong coils, leads and carefully tuned adjustable ignition.  They worked well, but something has changed recently. I feel our local fuel issues are interacting badly with them excacerbating low rpm problems.

They are useful regarding modern family cars. I put them in our cars and forget about 'em.

[GreasySnipe]

just wondering if you have ohmed out your ignition pick ups at the flywheel. These indeed could be temperature affected and cause the problems you are experiencing.

[Duck-Stew]

just wondering if you have ohmed out your ignition pick ups at the flywheel. These indeed could be temperature affected and cause the problems you are experiencing.

Although the above advice is practical and important, it only applies to the carbureted Monsters.  The EFI bikes run a single engine position sensor for both EFI and ignition.  It's on the left side cover, accessible from the outside and quite robust.