#4 cylinder no spark - Help!

[fmcandrew]

Electrical gurus...

My '95 Max has just decided to stop firing on #4. Other 3 fire fine, but #4 not getting spark. Tried new plugs - nothing...Plug is wet with gas, but not fouled...I have COPS so I switched the harness & COP from a running cylinder to #4 - still no fire. Believe it has good compression but don't have a compession tester. Motor only has 10K on it

What could be causing this? It's like the COP isnt getting the juice to spark. I have a programable Vboost controller, but can't see how this would cause an issue.

Somebody make my day so I can salvage what's left of the riding season...

Thanks,

Frank

 

[tugla]

Do you have the old coils....maybe try tat and see. I assume wires to cop are ok...

Could be the carb also. If you rev it up does that pipe start to get warm?

 

[Fire-medic]

Well, I suggest 'old-school': make-sure the COP & plug are well-grounded, and turn the bike over to see what kind of spark you are getting, compared to another normally-firing cyl. A compression tester will tell you if the cyl is sealing correctly, and a leak-down tester will show if it's the rings, the intake side or the exhaust side, from the sound of the escaping air. HFT has acceptable stuff you can use, probably not as-well-made or durable, but good-enough. Someone recently posted that the HFT compression tester was on-sale for ~$20.
http://www.harborfreight.com/8-piece-automotive-compression-test-kit-69885.html

http://www.harborfreight.com/quick-connect-compression-tester-95187.html

http://www.harborfreight.com/cylinder-leak-down-tester-94190.html

Choose one of the first two, and the third, ~$60 total.

Do you have anyone you can switch CDI's with?

 

[fmcandrew]

Carbs are all freshly rebuilt and bike was running 100% with good plug color. Started up next morning and cylinder will not fire regardless of rpm. I'm thinking cdi...only because plug is wet (getting gas) and harness with cop worked fine on other cylinder. Read posts that cdi can impact 1 cylinder...could it be cdi and should i consider a dyna 3000?

 

[fmcandrew]

Fire medic, i have a tester, just not the right adapter for the plug hole. I'll use the "old school" thumb test to ballpark a ring issue ( suggested by Steve). When i pull the new plug it has zero signs of cumbustion...no intermitent fire in that cylinder. Bike is kept indoors and has never seen rain in the 3 years ive owned it. I have an omes tester, but im no electritian and wouldnt know how to test the cdi or just the connector.

Old coils are gone as ive been running cops for 2 seasons without issue...the cop kit was from Gannon and are VERY well made...plus i tested another harness/cop on a running cylinder...motor has less then 10k and i do not ride hard. It still runs good on 3, but obviously much better on 4

 

[Fastatv]

Fire medic, i have a tester, just not the right adapter for the plug hole. I'll use the "old school" thumb test to ballpark a ring issue ( suggested by Steve). When i pull the new plug it has zero signs of cumbustion...no intermitent fire in that cylinder. Bike is kept indoors and has never seen rain in the 3 years ive owned it. I have an omes tester, but im no electritian and wouldnt know how to test the cdi or just the connector.

Old coils are gone as ive been running cops for 2 seasons without issue...the cop kit was from Gannon and are VERY well made...plus i tested another harness/cop on a running cylinder...motor has less then 10k and i do not ride hard. It still runs good on 3, but obviously much better on 4

So, you have proven that the COPS are good, move around and fired on another cylinder, but COPS from another cylinder won't fire on # 4. So, COPS assumed good. What other wiring is associated with #4? When you unplug the COPS, where does the other end of the wiring terminate....? The CDI? You might inspect the wiring, and grounds as someone else has mentioned. In regards to CDI testing, using your OHM meter...not sure. Vmax may be different than other things I have worked on but the many bikes and ATVs that I have worked on did not have any reliable tests in which to prove the CDI bad.....it was more like proving everything else was good.....then replace the CDI. Again, the VMAX CDI may have a means of reliable testing. I'll give it more thought and try to help in some way if I can. Rick

 

[alorio1]

I have read that if you have a bad channel in your CDI, connect the plug wire to a spark plug out of the engine. Ground the suspected or non firing plug to the motor and cycle the ignition switch on and off. If the plug fires when ignition is turned to the off position that channel of your CDI box is bad. I have never had a bad CDI to try this method on and do not know if this information is true, but it is worth a try.

 

[fmcandrew]

I appreciate the comments, but it sounds like this issue is not common and there is no real way to determine if I now have a bad cdi. I'll clean the connections as suggested, if no luck I'll be looking or a cdi...thoughts on best aftermarket cdi? Steve suggested an Ingnatech from Dingy...I have no experience in these matters...

 

[fmcandrew]

I have an update, just installed a new Dyna 3000 and presto, #4 is once again on fire! Just as an FYI, looks like all new Dyna 3000's are software configurable, mine has no dip switches, just a small USB port for custom configuration. For $230 shipped, plug & play and software configurable, I think it was a pretty good deal. Will give a ride impression when I get chance.

Thanks for the help,

Frank

 

[Fire-medic]

Given the age of most of our rides. it pays to have a spare set of carbs & a CDI on hand for trouble-shooting. Here is one more example of that. If the bike gives you trouble, switch-out 1 or the other based on symptoms, and get back on the road.

 

[fmcandrew]

This was most certainly an odd one...Sean said it best in another post and basically said he's seen the cdi do just about everything. I took a gamble buying a new one, but it was a calculated risk given the suddeness of the symptom and the other work i'd recently done. Just thought if that thing failed it would shut all the cylinders down. Actually, i shouldn't complain...it got me home on 3 cylinders and spared me the misery of being stranded...

 

[Fire-medic]

This was most certainly an odd one...Sean said it best in another post and basically said he's seen the cdi do just about everything. I took a gamble buying a new one, but it was a calculated risk given the suddeness of the symptom and the other work i'd recently done. Just thought if that thing failed it would shut all the cylinders down. Actually, i shouldn't complain...it got me home on 3 cylinders and spared me the misery of being stranded...

Glad you found it. Swap it back-in and see if alorio 1's method holds true:

... if you have a bad channel in your CDI, connect the plug wire to a spark plug out of the engine. Ground the suspected or non firing plug to the motor and cycle the ignition switch on and off. If the plug fires when ignition is turned to the off position that channel of your CDI box is bad. I have never had a bad CDI to try this method on and do not know if this information is true, but it is worth a try.