Doubled-up Sparks

[NickNZ]

From previous enquiries, most issues are now sorted with "V-twin" dual inputs from 1 cam tooth setup, V3.78 code, firing two LS2 coils. That is, I now have fuel and engine tries to start. But it keeps spitting back when it seems it might start.

Full investigations show that cranking with plugs out, sparks happen at each plug in turn as the cam tooth passes each sensor, spot on timing. But with plugs in, both plugs fire as the tooth passes each sensor - in other words, it behaves as if the outputs are tied, which they are not. I have run these tests with injectors connected and disconnected (in case it is an interference thing) and this makes no difference.

So, what is different between plugs out and plugs in? Obviously cranking speed is a little higher with plugs out, is less uneven, also the MAP reading is barely a ripple. The rpm numbers, plugs in and out, seem sensible, i.e. no doubling or halving. Sure has me scratching my head. All I can think of is that for some reason the code is tieing the ignition outputs together when the plugs are in due to some difference in cranking conditions, but how? Has this been seen before? Even if it was to do with uneven tach pulses due to cranking under duress, and the need to set up some kind of input masks/filters/, it seems very clever that it would choose to fire both ignition channels spot on the correct timing. Mind you, I am using 'trigger rise' for cranking timing, but why fire both outputs at once?

All suggestions gratefully received!

Nick

[24c]

Just a quick thought, the cranking speed in your set up isn't anywhere near the actual cranking speed with the plugs out, is it?

Anyway your test with the plugs in explains why it spits back.

[NickNZ]

Thanks for getting in touch. Yep, no mystery about the spit-backs! Have already had to rebuild the starter, that was last week, it is making noises like I probably need to do it again this weekend ... Will be testing with no fuel until I get this ignition issue sorted!

Cranking rpm with and without plugs in is well below cranking limit, which I have set to 450 at the moment, but I will test with it set to some higher and lower values. I thought my mind was playing tricks on this one, but it really is firing both output channels when under compression, I have checked a number of times. I think my setup is basically OK. I haven't played with the default input mask/filter settings, but I feel that if this was the problem I would be missing sparks instead of getting freebie extra ones. Or could it be that the irregular cranking characteristics of this lumpy motor are causing resets which are firing the outputs, but I thought in that case I would see a vertical green line in the datalog?

Will generate a couple of logs tomorrow, one with plugs in and one without, and post them in case something leaps out. Apart from starter clutch rollers, that is!

Thanks

Nick

[grippo]

I tried your msq on the bench and both fuel and spark are one for one with the respective VR sensor inputs, that is, the plugs do not fire simultaneously, which agrees with your results when no plugs are in. This was at 300 rpm. What I then did was lower the crank speed input from 450 to 250, which immediately took it out of cranking mode and I believe it threw in a little more advance, but again there was no simultaneous plug firings. But I agree you should record a brief cranking with plugs in and out in case anything pops up.

The only time there is simultaneous sparking is when in wasted spark mode without dual spark coils. But this doesn't happen in your dual tach configuration. The only other way would be if the 2 sensors had no angle separation. I have seen a lot of problems, but mostly its not getting spark on a channel, not getting too many. I don't remember ever seeing a case like yours, especially being correlated with whether the plugs were physically in or not. But do make sure the spark wires are separated as far as possible from each other and from the VR inputs.

[NickNZ]

Hi Mr Grippo - looks like i'm being a bit of a pain! But I have just come back in from the Lavertory and have established the following:

1. Plugs in, fires both plugs at every tach event
2. Plugs out, grounded at base of barrels, correct firing
3. Spare set of plugs put in plug holes, originals left grounded as above, correct firing!
4. As 3 above but moved connected plugs to top of head, close to spare plugs, corrrect firing!

So it has nowt to do with cranking speed/compression and nowt to do with the lie of the HT leads. I am using non-resistor plugs as I always do, but with 5kOhm resistor plug caps. But I wonder if the additional circuit resistance due to plugs just sitting on the engine is enough to stop this weird happening, so I will get some resistor plugs and try again tomorrow, still with the 5k caps. I do not understand what this has to do with this issue (I could understand it causing dirty/erroneous signals, perhaps) but I will let you know either way. Might ride over to tell you ...

Cheers

Nick

[NickNZ]

Now with resistor plugs and new Bosch Super Sport inductive leads, good sparks cranking with no fuel but timing goes erratic when engine is actually trying to fire with fuel on. Need to order some bearings for the starter before going any further - this is a weak point of these motors, unfortunately. Then will maybe try to figure out input signal masking, filters, etc.