Suzuki DF140 lacks power - one cylinder down?

[ianyoung77]

I have a 2003 DF140 with about 220hours. I bought it just after the 200hr service but it does not seem to have full power - quite sluggish but eventually gets near full revs. Mate said it could be down a cylinder so I thought why not change the plugs.
During the change I found cylinder 3 plug was like new where the others were somewhat blackened. I assume the plugs were changed at the service so it looks like cylinder 3 is not working. Changed the plugs but no improvement.
I then tried running without the plug leads and sure enough disconnecting plug 3 made no difference. I thought it may be the fuel injectors so I swapped 2&3 injectors but the issue still seems on plug 3.
Since the motor uses a coil pack shouldn't removing plug 3 stop cylinder 2 anyway? If this is the case does this suggest the coil pack is down on plug 3? I checked the impedance from 2 to 3 and it was 25kohms which is in spec
Any ideas on what to test next?

 

[99yam40]

need to be testing ignition and the fuel system as service manual calls for.
I do not have a motor or a manual like that so not much help

 

[ianyoung77]

OK, so when I disconnected plug 3 it made no difference and when I disconnected plug 2 it ran rough. When I put plug 2 into cylinder 3 it ran ok. To me this seems to indicate the coil/lead is not working on plug 3. I'll get a new unit and see how it goes

 

[tommarvin]

Before you spend any money, test the coil/lead with a DVMeter, or have somebody do it for you, Diagnose the problem correctly, before you start throwing money at it.
I would get a service manual and parts catalog, to diagnose problems. Test all the ignition electrical you can test.

 

[flyingscott]

Go to the auto parts store get a $10 spark tester set it for and set it for 7/16" it should jump the gap. Then buy a factory manual to help you diagnose it.

 

[tommarvin]

If your motor has a computer on it,borrow a laptop, buy the software and cable and diagnose the problems and lot all maintance.

 

[Melbournite]

Have you checked the HT lead and spark plug boot on cylinder 3 using a multi-meter to see if there's a break in the wire somewhere? Have similar issue on Yamaha 70 HP and found the spark plug boot on 2 cylinders had a break in them.

 

[ianyoung77]

Thanks Melbournite,
As I mentioned I tested the impedance from lead 2 to lead 3 and it was 25kohm - as per the manual - what other check is there? The only checks in the manual seem to be coil resistances and ignition timing both of which are ok.

Thanks also to flyingscott, Unfortunately supercheap only have these testers on line now so I have ordered and I will see what happens. It is a race between the tester and the new coil.

Thanks also tommarvin, The test lead is about $150 so will see how the other tests go and if I can't get it going then I will buy one and see what it tells me. I suspect the lead 3 side of the HV winding has failed to earth and it would be interesting to see what the test program would say

 

[ianyoung77]

OK, the coil has arrived before the tester. So I put in on the boat for the only true test. BOOM hole shot and WOT.

Thanks for all the comments. This can be marked as fixed

 

[ianyoung77]

I ended up taking the old coil to work and testing with an insulation tester. From plug 3 it went down at about 400V and from plug 2 at about 1400V which lines up with the coil insulation failing at the plug 3 end. I would assume a spark plug coil should pass up to about 20kV.

 

[99yam40]

Thanks for the update, it is good to see people posting what caused their problem and what fixed it

 

[ianyoung77]

No worries. I figure if the spark can jump 10mm then the insulation should be at least 10kV, probably more like 20. The question is how do you know what gap to set on the spark tester?

 

[99yam40]

Do not know about a Suzuli, but yamaha calls for 7/16" in service manuals
1/2" should work

But if you get shocked by touching plug wire while motor is running, it is leaking voltage

 

[tommarvin]

If you have EFI there is diagnostic software on e-bay, to diagnose problems and log maintance it's about 70 bucks, borrow a laptop or tablet the cable is included
CDI electronics.com explains the troubleshooting steps perfectly for every part, fill in your year,make , hp, and part,start with the plug wires, coil test,then power pack,trigger, stator

www.boatinfo.no/lib/library.html the best free service manuals.