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 Post subject: Re: Twin-spark misfires under boost - ECU power?
PostPosted: Thu Jul 12, 2018 9:19 am 
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Joined: Tue Aug 02, 2011 12:08 pm
Posts: 2901
Location: Norn Iron
ECU Model: No ECU
I agree it is not an ecu issue...but I would assume very few are using a pair of 4 tower wasted spark coils...in twin spark mode.

It does introduce a new variable....perhaps more so as both are inductive.


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 Post subject: Re: Twin-spark misfires under boost - ECU power?
PostPosted: Thu Jul 12, 2018 12:51 pm 
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Joined: Tue Aug 02, 2011 2:05 am
Posts: 33
Location: The Netherlands
ECU Model: S60 Pro
Firmware Version: 63
stevieturbo wrote:
How close are the 2 plugs together ?


Image

Its a pretty wide 98mm bore, so relative to other cars, save for the 3,6 ltr aircooled Porsches (which run 100mm), its a big bore and plugs are not that close I think.

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'74 VW Beetle turbo S60pro


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 Post subject: Re: Twin-spark misfires under boost - ECU power?
PostPosted: Thu Jul 12, 2018 4:02 pm 
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Location: Norn Iron
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That is cool...is it a common thing ?


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 Post subject: Re: Twin-spark misfires under boost - ECU power?
PostPosted: Fri Jul 13, 2018 3:38 am 
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Joined: Tue Aug 02, 2011 2:05 am
Posts: 33
Location: The Netherlands
ECU Model: S60 Pro
Firmware Version: 63
stevieturbo wrote:
That is cool...is it a common thing ?

Nope, its a set of billet alu heads, small batch.
I'am not the only one running these, but pretty sure I am the only one using them in a boosted application ;)

The problem isn't there for others with these twin-spark heads and dual coils either, but thet are N/A. Its the boost that blows it out at that moment. On the dyno that was very clear: boost came in and the misfires started. Same on the road.

Hopefully coming week I can run some more tests and reduce off-set untill the problem re-appears or untill I find another possible cause.

I'll also try to upgrade the wiring a bit. All little things help and as I am now at only 0,65 bar boost, upping boost a lot more could have the problem reappear again.

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'74 VW Beetle turbo S60pro


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 Post subject: Re: Twin-spark misfires under boost - ECU power?
PostPosted: Fri Jul 13, 2018 4:40 am 
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Joined: Tue Aug 02, 2011 12:08 pm
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Location: Norn Iron
ECU Model: No ECU
Altering the offset almost proves it isnt a wiring/ecu problem as such.

And 0.65bar boost is very low by any reckoning for even a low powered coil so whilst it may only be apparent to you then....it doesnt mean there isnt also the same problem off boost.

A scope for coil current and secondary outputs might reveal something as to which pair is not firing correctly.


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 Post subject: Re: Twin-spark misfires under boost - ECU power?
PostPosted: Sat Jul 14, 2018 4:20 am 
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Joined: Thu Jul 28, 2011 4:10 am
Posts: 855
ECU Model: S100 Pro
Could it possibly be the sudden rise (from 2 flame fronts) of cylinder pressure causing massive detonation? So just a tiny offset might cure it, I think only a dyno could tell you the best plug to fire first. Perhaps one of those det detection kits. Never used one personally. Perhaps try and find out the strategy of something like the Alfa twin spark?


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 Post subject: Re: Twin-spark misfires under boost - ECU power?
PostPosted: Sat Jul 14, 2018 8:36 am 
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Location: Norn Iron
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I've never seen detonation of any kind exhibit what is being described..

But certainly some det cans and listening if you can would be easy to do.

Or so would pulling a lot more timing ?

Although given spark duration and burn time....an offset of say even 1deg would really have to be negligible really ?

I've just never seen too much timing make an engine behave like that. Too little....too rich or spark issues.

Too much timing usually just blows shit up lol


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 Post subject: Re: Twin-spark misfires under boost - ECU power?
PostPosted: Sat Jul 14, 2018 10:09 am 
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Joined: Thu Jul 28, 2011 4:10 am
Posts: 855
ECU Model: S100 Pro
Just thinking out loud really.
I checked out the Alfa and they would appear to be fired simultaneously.


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 Post subject: Re: Twin-spark misfires under boost - ECU power?
PostPosted: Mon Jul 16, 2018 3:04 am 
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Joined: Tue Aug 02, 2011 2:05 am
Posts: 33
Location: The Netherlands
ECU Model: S60 Pro
Firmware Version: 63
Thanks so much for the thinking out loud guys, that really helps me and my thinking process a lot too!

Yesterday I renewed and upgraded one coil-pack with thicker wiring (the kind that _just_ fits into the DTA socket :) ) and a new coil-pack socket. The other one already had the tick wires.
From the succesfull run last time I had some good fuel corrections from the now also properly working closed loop and there seemed to be a lot of averagely -8% corrections in fuel (too rich) to be made.
Sunday eveneing was a great quiet moment for some further testing and I had reduced off-set to just 1 degree for testing purposes. I know its not scientific to adjust two variables at once, but time is scarce and accelerating on a public road like this is not something I wan't to do too much.

With a less rich mixture, the new wiring and just 1 degree off-set, she was flying again and again no ignition problems whatsoever!

Not sure what the main cause was after all (could be too rich after all perhaps?), but it is fixed now fortunately!

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'74 VW Beetle turbo S60pro


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 Post subject: Re: Twin-spark misfires under boost - ECU power?
PostPosted: Mon Jul 16, 2018 2:50 pm 
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Joined: Tue Aug 02, 2011 12:08 pm
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Location: Norn Iron
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certainly too much fuel can cause the symptoms you describe....falling flat on face and refusing to rev

Now time to try 0 offset again !! Or 0.00000001 ? lol


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