Suzuki rough idle now only one cylinder firing

Subject: SUZUKI DF-40 ROUGH IDLE NOW 1 CYLINDER
Engine: 2005 Suzuki DF-40, 4-stroke electronic fuel injection, less than 200 hours. Fuel/water separator changed in 2010, quality gas storage additives used.
Problem Description: The Last year or two engine started to idle rough (700-800rpm) but was OK above about 1200 rpm, and boat performance of 5800 rpm, 26.3 mph ran like new. Before winterizing, pulled plugs and #1 had some black stain/carbon residue on center post ceramic (plugs #2, #3 looked good). Then I ran boat thru one 8 gal tank of gas with strong mix of fuel injector additive. Monthly during winter ran engine on muffs 10-15 minutes, idle still rough. First time out engine started and ran at high idle for about 5 minutes. Within 1 minute of leaving dock engine started missing and quit. Very difficult to restart, sounded as if only one cylinder firing, then with restart, returned to dock.
Troubleshooting on muffs: (summary of numerous actions)
· Cleaned all three plugs (#1 some hard carbon residue, #2,#3 looked OK, grayish ceramic)
· Rough idle at low rpm, better at 1200 rpm but at max idle throttle engine rpm cycled up/dn (surging) between about 2600rpm and 3000 rpm.
· Reduced idle power level and engine “dropped” into running OK mode about 2300 rpm
· Ran engine per above conditions for 1.5 hours, running ok except periodically ( 10 min or so) there was an occasional miss. (NOTE: Last year running at full power there was an occasional miss which I just assumed was some “junk in the gas” going thru.
· Then reduced idle speed and engine idle rough (bit worse than before), and at low idle speed engine stopped. Was very difficult to restart (just like first time this year on the water described above), multiple misfiring and finally with engine running only on one cylinder (#3).
· Fuel injectors look like NEW, plugs mostly like before.
· Outside of engine with plugs connected to ignition circuitry and grounded, all plugs were firing while using engine starter and with battery charger connected. It did seem that the first few rpm firings were brighter than the later rpm firings in this short duration test. Occasionally some “sparks” seemed brighter.
· Focusing on #1 and #2 cylinders, first interchanged injectors #1 and #2, then restored and interchanged #1 and #2 ignition circuits/plugs> No Change/Difference in results. This was when cylinders #2 and #3 were working in early tests.
· When rough idle (only one cylinder missing) it is always #1 and disconnecting electrical feed to ignition coil makes no difference, leading me to conclude that #1 is not combusting at all.
· It appears that #3 cylinder works OK (most all of the time) thru all of this testing.

Would appreciate any help or suggestions, especially troubleshooting to locate actual problem component(s). With the price of parts I can’t afford to randomly buy new parts hoping they will solve the problem.

I really hate to say this but, you may have a cracked piston. It happened a lot in the 2005 DF-50, alot. To the point that in '06-'08the powerheads were hard to get from Suzuki because they just could'nt keep up with the demand. I was working for a Suzuki dealer at the time and had to wait for several months for powerheads meanwhile blown DF-50 and similar models just kept stacking up, all 2005 models. Suzkuki said it was bad gas and things like that at first but it quickly became apparent that they had a bad batch of pistons. Even if they never would admit it. You should do some more diagnostic testing like compression and try swaping up all the coils, I guess you already tried the injectors. You might go ahead and clean the injectors. You can't always tell it they are clean by inspection, the contamination could be inside. I have cleaned then before with Powertune by Quicksilver. Soak the tips in Powertune and occasionally shoot some inside each injector. After about 30-45min blow them out, blow compressed air through them oposite fuel flow. Sounds Red-Neck I know but I'm a field repair tech and I've done it many times with success. Suzukis are very picky about plugs when one gets colored it may not fire just becuase it is fouled, even if it looks good. I can't tell you how many times I've come across Suzukis that ran rough or would'nt even start and all they needed was new plugs, NGK only-always. I have factory manuals if you need specific information for more in depth diagnostic testing. Oh yea, If you have a cracked piston you should also find abnormality in the oil like too much oil or excessive oil in the air box from the crank case breather. You seem like a smart guy, you're on the right track, I'm sure you'll figure it out. Hope it's simple, Good Luck.

yep, they also had bad powerhead gaskets

First thank you for the detailed reply, and excuse the delay in my reply as I had to make a trip out of town and wanted to reply after I tried some of your suggestions. Lots of good info, what I decided to do is to : completely replace all filters inthe fuel system: HP, LP and vst HP pump filter(looked good). ALso soaked injectors for two days in star tron and momentraily acitvated with 12v and resoaked. DId not think of compressed air blow out. Although plugs looked fairly good to me, I decided to replace all with new(should have done this at the start). Also cleaned out engine idle air screw adjust (set idle rpm) to recommended, was a bit low)and squirted cleaner in IAC-inlet air control valve. Reassembled and engine runs almost like new. Still a bit rough(slight) at idle so may resoak injectors and do a compressed air blow. THe really good news is I think my pistons are OK. (that was a scary thought). Pee tube stopped squirting so now am replacing the water pump; found about 1/2 in of one impeller blade end missing so will now have to find out where it went.
Thanks again for your helpful suggestions

Sounds like you've covered it all. You seem to know your way around this engine. One more thing you might check is the valve adjustment. It should be checked at 20 hrs. and then every 100 hrs. As the valve and seat wear from smacking into each other the valves eventually begin to leak. These engines are very much effected by inproper valve clearence as they produce very high compression. If you have never checked them now might be a good time. Also, for good measure, reset the warning system via the key switch excercise. I'm assuming that you have a manual, if not I have some and can give you detailed information if needed.

The key switch exercise:
If you have never done this before if may take a few tries. Keep in mind that the whole thing runs on a rythm of one whole second intervals and the rythm is most important.
Here goes,
1. Turn the key to the "on" position. The eng. will beep. When the beep stops (or within 1 sec.) pull the safety lanyard off.
2. Wait one second and pull the kill switch out and hold it for 1 sec. and release it.
3. Repeat step 2 two more times for a total of three 1 sec. pulls with one sec. between each pull.
4. On the 3rd pull hold the button out until you hear a long beep. This usually takes 2-3 sec.
If you don't hear the long beep while holding the button out on the third pull the reset did'nt take. Try it again and don't hurry, remember one whole second of pull and one whole second between pulls (hold the third pull until you hear the beep). This will reset your warning system in the event of a "code" of if for some reason a you get a warning. We often do this when there is a check engine light or a code that claims a faulty sensor or abnormal reading. If the warning of condition returns after being erased it is legitimate, ususally it goes away and was merely a side effect of a poor electrical connection or corroded batt. terminal.
This may not fix your problem but it's good to know and you really should try to perfect your technique at this exercise. If you suspect an ignition problem first inspect your electrical system from the batt. all the way through. You have a DC ignition system and a poor connection or ground could make for some crazy symptoms. Make sure there is no corroded of loose connections ANYWHERE including your fuses. Most of the sensors on this engine are for the most part problem free and suprizingly reliable, save for three parts. Crank Position sensor (CKP), Manifold Absolute Pressure sensor (MAP), and possibly the Throttle Position sesor. Have a good look at these items if you identify them. That's what I might be doing right now. I know this is begining to sound like "shotgun" tactics but somewhere in there you just might find it. Too bad this engine isn't in front of me, we could really put our heads together, then we might both be frustrated. Good luck again. I'm sure you're getting closer.

Greg
Suzuki certified since 2001, all models
Tohatsu certified since 2003, all models
Yamaha 5 star certified since 2005

Thanks for the continuing helpful suggestions. I did not think to reset the warning system and the detailed instructions are helpful and reinforce the manual (which I purchased on recommendation). You all give me more credit than I merit, and your input on valve clearance and head gaskets is a bit worrysome. I have never checked valve clearance on an engine. I do remember a similar check called out for my twin 150 HP Yamaha's (since sold the boat as it was too big for me to mussle by myself) but talking to a trusted mechanic and his experience was they had yet to find an engine that needed adjusting after 20 hours, I decided to pass on that action.
Well for my SUzuki, this is something I will have to think about and study the manual, meantime the engine is running great.