engine dropping onto 1 cylinder

discussions specific to the 906 Paso
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yosemite
Posts: 8
Joined: Sat Apr 28, 2018 9:31 pm
model: 750 Paso
year: 1990
Location: Ireland

engine dropping onto 1 cylinder

Post by yosemite »

Hi
since i put the 906 on the road its been dropping on to 1 cylinder, and after a few seconds it will pick up and run on both of course it always happens just before I go into a bend and picks up halfway round, makes life interesing. tried to check which cylinder was dropping out but as it only occurs for a few seconds at a time it is virtually impossible. At the moment I am waiting for new plugs caps and ht leads to rule out the easiest potential scource of problems.
As it is probable that plugs and ht leads wont cure the problem,i think if it was either the misfire would last longer, then I will need to understand the ignition circuit better.
first, can someone explain how 1 pickup manages to give sparks to both coils, does it run a wasted spark.
second, what should the primary resistance of the coils be, according to manual should be 0.34ohms, but read on here that people are using coils of resistance of 3.5 or 5 ohms
and finally (for now) has anyone used the alternative digiplex fitted to theLancia Thema 16V or Fiat Croma 1600
Yosemite
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JWilliam
Posts: 328
Joined: Wed Oct 06, 2004 12:00 am
model: 906 Paso
year: 1989
Location: Nottingham, UK

Re: engine dropping onto 1 cylinder

Post by JWilliam »

I replaced the ignition coils with ones from an Aprilia twin, 5 ohms resistance. I did this after running the Paso at the racetrack and picking up a misfire; due to over-driving the Digiplex. Your cutting out does sound like an electrical problem.
angelix
Posts: 338
Joined: Thu Nov 29, 2007 2:38 am
model: 907 I.E.
year: 1990
Location: UK

Re: engine dropping onto 1 cylinder

Post by angelix »

The digiplex can be replaced with the IGNITECH, i am not sure if it will be plug and play , but in kn ow it is feasable and the Digiplex Flywheel will allow a much better mapping than the Kokusan Flywheel (limited to 32degrees) to teh point that you could even fuit a MAP sensor and mimic the digiplex Mapping.

It soumds you have a sort of contact , I woul go through every connector related to the ignition, tighten the contacts with a small scredrivers, then lubricate the connectors and refit , most likely is just a connector getting loose a little bit overtime.
Tamburinifan
paso grand pooh-bah
Posts: 1501
Joined: Thu Jun 21, 2007 12:00 am
model: 907 I.E.
year: 1991
Location: Gothenburg, SWEDEN

Re: engine dropping onto 1 cylinder

Post by Tamburinifan »

Gert

907 I.E. -91
M900 -97
MTS 1100s -07
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paso750
paso grand pooh-bah
Posts: 5505
Joined: Sun Jul 18, 2004 12:00 am
model: 750 Paso
year: 1987
Location: southern Germany

Re: engine dropping onto 1 cylinder

Post by paso750 »

About 0,35-0,4 ohms is the correct resistance for coils being used on a Digiplex ignition.
My practical experience has always been that fuel injected bikes use low resistant coils and carbed ones have ignition coils with 3-5 ohms. That seems to be so in most cases but the 906 is an exception.
Theoretically one can say that the coils' resistance has no effect on the power of the spark it generates. After all every coil is connected to 12V and gets a ground signal as trigger. In practice it's more complicated than that as the coil resistance is matched to the ignition system. I had some ideas which effect using coils with a different resistance could have but figured I'd verify by asking someone who would know. This is the reply from Dynatek's technical support.

The short answer is yes, coil resistance is generally matched to the ignition system requirements. Depending on how the coil dwell, how long the coil is charged for any given ignition controller can use anywhere from 0.5 ohm to 5 ohm coils. Ignitions like points and the Dyna S that have no dwell control typically use 3-5 ohm coils depending on the application while, as you noted some more modern EFI systems use 0.5 to 1 ohm coils. While you may use an higher resistance coil, say a 5 ohm in a 3 ohm application you will see lower spark output because the coil cannot fully recharge during the crankshaft cycle. The good news is this will typically not cause any harm to the ignition system. If you reverse these values though like in the case of your Ducati and use the 0.4 ohm coil in a 3 ohm system the coil will typically overheat in a very short period of time and short out usually causing catastrophic ignition failure. The bottom line here is always follow the manufacturers recommendations for coil values for use in a given system. If we can be of any future assistance please feel free to contact us anytime.

Regards,

Technical Support
Stepaso
Posts: 14
Joined: Sun Dec 29, 2019 11:30 pm
model: 750 Paso
year: 1988
Location: New Zealand

Re: engine dropping onto 1 cylinder

Post by Stepaso »

My 750 Ltd did that although the last time it went on 1 cylinder it stayed on one cylinder and I had a 20klm very slow gentle ride home. It turned out to be one of the pickups which I replaced and off she went again happy as. My thoughts from your explain would be a loose wire somewhere, so follow back from the spark plug, contact clean everything you can and wriggle every wire you can, (while the engine is running) try to get it to fail again.
My advice is to do this slowly and methodically set the idle up a bit so the motor is burbling along at about 1500 revs and keep wriggling until the sound changes..

Good luck
yosemite
Posts: 8
Joined: Sat Apr 28, 2018 9:31 pm
model: 750 Paso
year: 1990
Location: Ireland

Re: engine dropping onto 1 cylinder

Post by yosemite »

Hi
fault has now become permanent.
so far checked pickup (only 1), coils by swapping , coil wiring by swapping(unplug from digiplex connector and swap over) , power supply to digiplex and coils replaced/ modified with relay as per wiring mod in FAQ . Ht leads plug caps plugs. none made any difference. When wiring to coils and ht was swapped rear coil fired front cylinder
In the absence of anything else to check have decided the digiplex is at fault so ordered an Ignitech unit to replace digiplex,will fit that when I get back in a couple of weeks, have to ride the zzr had hoped the Paso would be ready.
Wil have to ask Ignitech if the low impedance coils will be ok or if they will need to be changed.
Thanks for all your suggestions will post updates when I have any but for now waiting for parts
yosemite
Posts: 8
Joined: Sat Apr 28, 2018 9:31 pm
model: 750 Paso
year: 1990
Location: Ireland

Re: engine dropping onto 1 cylinder

Post by yosemite »

Hi
fitted the new ignitech unit, fastened stray wiring out of way fitted tank, cranked bike over and ......nowt
turned fuel on and let prime, bike fired up and ran well, fitted rest of fairing went for a quick ride, (was meant to be a reasonably paced test ride but you know how it is) and apart from lumpy tickover as carb needs setting up properly everything running well, in fact very well indeed.can recommend the Ignitech unit both on service from there staff and quality/ performance of there unit. :D
Yosemite
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