High boost misfire VEMS and LS coils

[V6quattro]

I got the full set from marc. So I don't know what make they are. That how much trust I have put on him

I think that they are LS2 coils from General-motors. First i just wanted to order 5 new ls2 coils as they are plug and play but original GM coils ware really expensive at the dealer.

So i ordered the AEM coil which i heard really good things about. Thees coils are made for big 2-stroke compressor outboard engines so they need to spark good and really fast as a 2 stoke needs a good spark every revolution.

So when operating at low dwell they are just chilling when creating sparks for 200hp per cilinder at a 4 stroke engine

I use those coils, but the "dumb" version driven by Vems IGBT. Really nice

[V6quattro]

Replaced everything today. New loom / coils and plug wires.

Still not good

I changed coil 1 with the weak spark to coil 2 and coil 2 to 1. But now it still had a weak spark on coil 1. So now the problem is not the coils but the VEMS ore wiring i think.

All ready tried a other ignition output but still a weak spark on 1
Also checked the wiring. All fine.

I think a will measure the dwell time with a scope to see if vems just gives a low dwell time on coil 1. But not today

[V6quattro]

I just get this on the VEMS forum :


There has been an issue with manually triggering the coils and its effective dwell, this issue has been corrected 2 okt 2013 (released around 1.2.18 firmware). If you are running any firmware version lower than this, this bug is indeed present.

However since it is only active during manual engagement of spark test (not during normal running conditions), it should not impact running engine performance.

Best regards, Dave

Im running firmware 1.2.11 so i will just take the car on the road later this week to test it.

Some photo's off the finished ignition system.

[quattrostyle]

Looking very nice!

Does that mean you got something to sell now?

[V6quattro]

Looking very nice!

Does that mean you got something to sell now?

Yes i have

I will test my car this week and if everything is okay i will contact you.

[A80Avant]

Resurrecting this thread as I seem to have issues with my stroker. High compression and missing ponies. As I mentioned in the past I always had charge time set to 2.5ms and map to 20.

Now since I had been getting misfires with 3 different types of spark plugs, all gapped to 0.6 (bosch double platinum, bosch original rs2 and BKR8EIX) i dug up this thread and contacted Marc as well.

So i was instructed to increace the charge time to 3ms.

I tried the following:
Charge time 3
Map: 5
Still misfiring

Charge time 3
Map10
Still misfiring

Charge time 3
Map 20
No misfires and according to the log, the car regained 50whp which i had lost!

According to a link above I notice that the ls2 coils are able to go to 5ms charge time. Is that correct? If so, how does the slope on the map setting on vems affects the way they operate?

Should I be increasing the charge time @13.2v more whilst keeping the Map scale below 5?

[A80Avant]

The way i understand the map scale, is that it can add +0.4ms max at a slope depending on number you give it, ie if 20, it gives the +0.4 by 150kpa.

So in essence isn't it better for the coil to have a reduced charge charge at 13.2v and have the slope set to 20 for the added boost that may be required?
if the ls2 can run up to 5.5ms then theoretically its better for them not to be constantly at 5ms and map set to 1 so that they remain cooler.

Right?

[k.alle]

First off, I have no idea on how VEMS is handling the dwell or how to tune that.

But isn't the basic principle that you add dwell until your misfires are gone on low load / idle and then ramp up from there when boosting?
If you have 5.5ms to play with you have a lot of headroom if the RPM allows.

To my understanding you want more dwell at lower voltage so I would rather add dwell at 13.2V compared to 14v.

I'm sorry if this is not at all what you are asking as I don't quite understand the ramping/slope terms etc used regarding VEMS.

[Error404]

Use the MAP dwell overlay since from what you describe you only need more dwell with the increased cylinder pressure at higher MAP.

[A80Avant]

more on this..

looking at my logs, even from 2019 and the 2.2l engine, i seem to have the ECU see 12v at high boost/revs. So in other words i get a drop in voltage during a high boost run to the limit.
Obviously this hurts the coils as the ECU is trying to compensate.
In addition, the ECU is adding up to 40% dwell at a given slope which means i saw 7.5ms on a recent run in order to alleviate misfires AND produce a better spark! Perhaps it could be better with a bit less, but i need to do more checks.

It appears that i need to check that my alternator and battery are working properly, but given that i have had this even on my previous engine and battery has been changed in the meantime, while the alternator is the same, its very likely that the 25y.old cable tree is not able to sustain the power required to supply the coils.
SO...
i may have a relay with a separate harness fitted to supply the coils and maintain a better voltage during those situations. (thanks Marc for the input!)
Also the 514A coils i am using apparently are able to hold 8ms peak and seem to be optimal at around 6ms according to Marc.

more testing follows....

By the way, it was very interesting to see using my VDR file and dyno, that i could lose up to 50whp on a run, without misfires and things improved after the ignition was tweaked. So you may get a poor spark and performance simply from that. I hope i wont have to invest on something more. Never realised that the stroker could give you a stroke whilst trying to get it as optimal as possible!!haha