Megasquirt Support Forum (MSEXTRA)

Hi guys,


I found some useful information about the overdwell problem with the ls2 truckcoils d585, which I wanna to share.
I couldn't post a link, therefore I printed it as a pdf.

As a conclusion the coil fires by itself, when the primary current goes over about 8,5 amps, which leads to uncontrollable more ignition advance.
So really pay attention that your dwell time is set correct!

Origin of the info is http://forums.rennlist.com/

Regards Julian

Good information, thanks for posting.

I just started using these coils. How do I tell if Im getting premature firing like stated? my setting are the same as in the manual but in that forum they say the megamanual is wrong about the coils. right now my dwell times are at 3.0ms at 14v and goes to 3.3ms at 13.8v.
What is too much dwell at 13-14v on these. This has really got me concerned now since I was getting knock earlier while my Ign Adv. was setting pretty low, Im thinking it was sparking earlier probably.

does anyone have any recommended settings for these coils eg cranking dwell, nominal dwell, spark duration and a dwell battery correction table i can try, they seem to get good press on one place then bad on the next.

This is a facrory dwell table for an LQ9, If you stick with these walues you should be safe.

Tommy

I have updated the MS3 and general manual sections to say 4.0ms and added the warning. If you find anywhere in the manual I've missed please post here and I'll update it.

James

Is there there any MAX or MIN amount of dwell these coils can see before burning out and stop working? also how do you diagnose coils like these to tell if there still good or bad?

Thanks for posting this, i had backed mine down 4ms based on a tip from another member because i was dealing with ignition advance at increasing rpm.

jsmcortina wrote:I have updated the MS3 and general manual sections to say 4.0ms and added the warning. If you find anywhere in the manual I've missed please post here and I'll update it.

James

James,
if the person in charge of the regular Mega manual needs to make any changes ..... http://www.megamanual.com/seq/coils.htm it indicates the 5.5, not sure if the same stuff applies or not but it was the link i stumbled across when i first googled it at the time i started messing with it, even as an extra user. Just an observation.

JAM wrote:Thanks for posting this, i had backed mine down 4ms based on a tip from another member because i was dealing with ignition advance at increasing rpm.

jsmcortina wrote:I have updated the MS3 and general manual sections to say 4.0ms and added the warning. If you find anywhere in the manual I've missed please post here and I'll update it.

James

James,
if the person in charge of the regular Mega manual needs to make any changes ..... http://www.megamanual.com/seq/coils.htm it indicates the 5.5, not sure if the same stuff applies or not but it was the link i stumbled across when i first googled it at the time i started messing with it, even as an extra user. Just an observation.

No one here has any control over the content of the megamanual. So the only way to have this seen by the editor of the megamanual is to post on the msefi forum. But if the information comes from here, it is likely to be ignored.

Jean

I kind of figured, I guess they can do their own learning, just thought it may be helpful to them as well

One other observation ( I dont mean to nit pick) but in the dialog window shown on the msextra link it does show 5.5 (example screen shoot at bottom of page) http://www.msextra.com/doc/ms3/ls1.html

in the text it shows 4.0 so i only mention as an item to hopefully save someone an error by only looking at dialog box. or not....

EDIT: By the way, is .7ms max spark duration a standard number for the coil or ??? if not can anybody point me to additional info on this?

I verified solid ignition timing up to 6ms base dwell with this battery voltage correction table, derived off of the oem GM dwell table. My testing shows that the default battery voltage correction table is too aggressive.

Id like to reask the spark duration question. Headed to the dyno Wed. i thought i read in the manual its near 2ms for the truck coils.

Spark duration only comes into play when there's not enough time to allow the full spark and discharge time periods. This mostly applies to a single coil on V8s or more.
i.e. at 6000rpm each engine cycle (720 deg) takes 20ms. Eight cylinders fire per cycle, so time available = 20 / 8 = 2.5ms. The code maintains a balance between time to charge and time to fire the coil.

Now, in a true coil-on-plug install you have the full 20ms to charge and fire, so the spark duration value does not come into play.

Even with say 4ms dwell and 1ms spark duration, you would need to be turning 24000rpm before the available time equals the required time.

James

jsmcortina wrote:Spark duration only comes into play when there's not enough time to allow the full spark and discharge time periods

Thanks for the clarification on the spark duration James. So it looks the spark duration value would rarely come into play on a COP setup as there should always be plenty of available time for dwell and duration? is it correct to say that your actual spark duration is however long it takes the coil to discharge assuming the time is available?

That's it, although the effect on the spark when the dwell period starts up again while the coil is still discharging is a little fuzzy to me.

Slight OT - The desperately short dwell times James alluded to are why CDI became so popular prior to COP designs; when it takes more time than the coil has to charge, your spark suffers as revs increase, limiting power. When you replace this with an ignition system that charges in less than 2 ms and fires in a small fraction of 1 ms, your effective and attainable redline is now limited by the engine structure and breathing capacity, not the spark.

Thanks for the additional info. I have wondered the same about when the coil cannot discharge complete before it must recharge....


Just out of curiosity how would the ecu/code deal with this if (in the case that James outlined with COP) if the dwell was set to 4ms and for some reason the user put a large value in the spark duration such as 20 ?

It isn't only the truck coils, they can actually deal with a tad more dwell than the "normal" LS2 coils.

I ran into this awhile back, had some very intermittent single cycle glitches, chopping the dwell down to 3.7 and using the GM dwell/volt table dealt with that. (basically use GMs default values)

To answer an earlier question:
LS2 coils are "self protecting".
The downside is that when they "self protect", they will fire when they NEED to, not as directed.

If you use the GM "stock" values for dwell and the voltage table, no issues.

Question about the d585 coils:
This is the PN for "Yukon coils", but are there any other coils that physically look the same (same connector, heat sink etc) as these but may have a different part number and be internally different?

JAM wrote:Question about the d585 coils:
This is the PN for "Yukon coils", but are there any other coils that physically look the same (same connector, heat sink etc) as these but may have a different part number and be internally different?

There are several companies that make clones of it and sell them with the same part number. They aren't all the same inside.

BTW apparently there are people who "boosted" these coils with up to 6+ms without any spark scatter issues. I made a search on the web and not all people get the mentioned problem. It seems this could be related pretty much on production place, date or sequence. The coils I have (stripped down from Chevy Tahoe) have e 19005218 number stamped on the metal bracket and C19M142312 on the plastic body near the connector. I haven't tested them yet though. The more important question is do we really need so much (5+) ms dwell with these coils? In Mr.Bowlings video http://www.youtube.com/watch?v=C1WH0OExQyA at about the 14th minute he increases the dwell up to nine ms and concludes that there is not much of improvement when dwell is more than 5ms.