Dwell for LS2 D514A Coils

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sedd
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Dwell for LS2 D514A Coils

Post by sedd »

I believe I had my dwell for the LS2 D514A coils set to high. I had 6 for cranking and 5.5 for running. From other posts I see that 4.0 for cranking and 3.5 for running is recommended. Could I get some feedback on my current settings of 4 cranking and 3.5 running?

The reason for changing this is a high speed miss or stumble. That occurs around 5500 rpm.
1970 Chevelle, 540 big block, AFR heads, headers, mild cam
MS3 release 1.4.0, sequential fuel, LS2 coil per plug
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Dennis930
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Re: Dwell for LS2 D514A Coils

Post by Dennis930 »

I use 12 of these coils for twin plug installation. 4.0ms is recommended for running. 5ms is OK for cranking because you are at a lower voltage. This is what I use with no issues at 6500 RPM's and I am running 17 psi boost. Are you using resistor plugs? what gap? You could try closing the plug gap some to see if it helps.
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sedd
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Re: Dwell for LS2 D514A Coils

Post by sedd »

Champion RC12YC. It has been a very long time since I gapped them. What would you recommend for the gap? I took some pictures on them a while back. due to file size limitations I have only shown number one cylinder plug. Most of them looked similar.
1970 Chevelle, 540 big block, AFR heads, headers, mild cam
MS3 release 1.4.0, sequential fuel, LS2 coil per plug
Tuner Studio MS V3.0.05
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Re: Dwell for LS2 D514A Coils

Post by Peter Florance »

I'd want to see a log of this problem.
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Re: Dwell for LS2 D514A Coils

Post by ducman82 »

i had the same issues with my D585 LS truck coils. had to lower my Dwell as well from 4.5 to 2.3 to get that "stumble" past redline. cranking it 6, works fine.
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Re: Dwell for LS2 D514A Coils

Post by nathaninwa »

Keep it under under 4 and run the proper gap. I'm running the d585 coil, 33 psi, .032 gap on an irridium plug. I use the dwell table and cruise at 2.5 and anything above about 150kpa get 3.5. I have zero breakup to 8200rpm
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sedd
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Re: Dwell for LS2 D514A Coils

Post by sedd »

I have tried to find the stumble on the logs but I can't find it. I plan to run more logs once the weather gets better and keep them shorter so I can better analyze. the log I took is huge and I can't send that due to size. I will try to cut out a section and send that once I figure out how to do that again.

Are those who posted recommending I go with 2.5 for the dwell versus 3.5. Is there much to gain from the extra dwell time? I have looked for data on how long it takes for the coil to be saturated and have not found that. Is around 2.5 adequate, and any longer than 2.5 doesn't add any benefit?
1970 Chevelle, 540 big block, AFR heads, headers, mild cam
MS3 release 1.4.0, sequential fuel, LS2 coil per plug
Tuner Studio MS V3.0.05
sedd
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Re: Dwell for LS2 D514A Coils

Post by sedd »

nathaninwa
Could you share more info on the plugs you use?

I went with plugs recommended by AFR for my heads. They appear to be pretty inexpensive and not very high tech. Copper or something similar? I have assumed that more expensive plugs with the special iridium or platinum or ??? tips as used in modern auto might be better? Of course the next question is what plug gap to use with those. I have also assumed the more expensive plugs can accept and use bigger gaps that are possible with the higher output coils?

I am naturally aspirated and am hoping for recommendations for that. 10.2 comp ratio.
1970 Chevelle, 540 big block, AFR heads, headers, mild cam
MS3 release 1.4.0, sequential fuel, LS2 coil per plug
Tuner Studio MS V3.0.05
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Re: Dwell for LS2 D514A Coils

Post by nathaninwa »

I'd run it up when the power comes on, but back it off when your just cruising. I've had breakup before under boost that got worse and worse as the days went on. I'm running coil on plug and the small springs between the coil and plug were just inadequate. I've seen it happen with spark plug wires too
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sedd
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Re: Dwell for LS2 D514A Coils

Post by sedd »

partial log and the msq in place at the time of the stumble.
1970 Chevelle, 540 big block, AFR heads, headers, mild cam
MS3 release 1.4.0, sequential fuel, LS2 coil per plug
Tuner Studio MS V3.0.05
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Re: Dwell for LS2 D514A Coils

Post by Peter Florance »

sedd wrote:partial log and the msq in place at the time of the stumble.
The car seems a little lean for a motor with mild cam. Maybe lean misfire.

Try this tune and see if it runs better (save your current then open this one).
This is with WOT targets around 12.8; if it works, you can start leaning it out.


I tried to upload just the table and it was rejected by forum software as possible attack vector???
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sedd
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Re: Dwell for LS2 D514A Coils

Post by sedd »

I took the car out tonight for some quick runs. It didn't stumble like before.

I used autotune and the last set of higher rpm runs were much better. I had over 10% increase in VE in many cells, some almost 20%. Since I had tried to run higher AFR settings earlier and had the stumble, I have to assume the coil dwell settings made the difference.

I had my rev limit set low to help protect the engine in case the dwell didn't work out. I need to analyze the logs I did get to see if I actually hit the rev limit. It appears to have sharp AFR changes between normal AFR readings? I am not certain.........

The logs were not very satisfactory as I was using the automatic log system and my settings resulted in really short logs.

I have adjusted the AFR settings to higher levels at wide open map. I have set the REV limit at a bit higher now. I will post again once I get better logs.
1970 Chevelle, 540 big block, AFR heads, headers, mild cam
MS3 release 1.4.0, sequential fuel, LS2 coil per plug
Tuner Studio MS V3.0.05
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Re: Dwell for LS2 D514A Coils

Post by Mario »

Be careful with the D585 coils. If they are given to much dwell they will auto fire as seen here. I have verified this in my car.
5ms Dwell Vs. Output.jpg
I also plotted it up to max output
LS Truck.jpg
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sedd
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Re: Dwell for LS2 D514A Coils

Post by sedd »

Very interesting. Can you describe more on the top screen shot that shows the early fire. I can't figure that one out.

On the lower screen shot, does it indicate that 4 ms dwell is still ok? I see that the curve doesn't flatten out until around 5ms.

any info on my D514A coils? Can we assume they are very similar?
1970 Chevelle, 540 big block, AFR heads, headers, mild cam
MS3 release 1.4.0, sequential fuel, LS2 coil per plug
Tuner Studio MS V3.0.05
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Re: Dwell for LS2 D514A Coils

Post by Mario »

The yellow line represents the dwell, and it is charging the coil while high. The purple is the coil firing. And it sits so before the ECU goes low, or when the coil should fire.

You can run them at 4ms, I wouldn't run them past 4.5ms to prevent an advanced spark event. This could be very bad at high load. Setup your over dwell protection to prevent it.
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sedd
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Re: Dwell for LS2 D514A Coils

Post by sedd »

So the time difference is between where the yellow line drops and the purple one rises? How much time is this in ms?

I decided to raise the dwell to 3.7 and left the spark duration at 1.0.

I took out my Champion RC12YC plugs and changed to Bosch Iridium 9652. The Champion plugs looked good, light tan color on most of them.
1970 Chevelle, 540 big block, AFR heads, headers, mild cam
MS3 release 1.4.0, sequential fuel, LS2 coil per plug
Tuner Studio MS V3.0.05
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Re: Dwell for LS2 D514A Coils

Post by Mario »

The yellow dwell could have charged to 10ms, the coil will still automatically discharge when it hits just over 4.5ms
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Re: Dwell for LS2 D514A Coils

Post by jalai »

This curve is measured at LS2 coil (D514A ??).
Red line = primary current @ 14 V.
No self discharge, but current is limited about 10 A.
Image

And three different "Truck" coil (14V).
Dwell = 8ms
Image

sedd wrote:So the time difference is between where the yellow line drops and the purple one rises?
Difference is between where the purple line drops and the yellow line drops.
But, coil "automatic" discharge is not time depends, it is a current limit. Lower voltage > longer Dwell is possible.
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Re: Dwell for LS2 D514A Coils

Post by Mario »

My findings where at 14v for a OEM D585 coil. I didn't try higher or lower voltage in this particular test since I wasn't calibrating for voltage compensation. It just goes to show how different these coils react I would say. Always good to test them before installing.
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Lokiel
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Re: Dwell for LS2 D514A Coils

Post by Lokiel »

I've been trying to find some actual values for the MS Dwell Battery Correction table for these coils.

gross_polluter at http://forums.tbforums.com/showthread.php?t=254712 states:
"The dwell time for an LS2 coil at 13 volts is 3.15ms, taken directly from an LS2 ecu.

Your dwell battery correction table should look like this (again, values taken directly from an LS2 ecu):
6.0v 193%
8.0v 182%
10.0v 141%
12.0v 113%
14.0v 89%
16.0v 75%"


The Megasquirt MegaManual at http://www.megamanual.com/seq/coils.htm mentions the following (Nominal Dwell at 14v):
Maximum Dwell: 4.5 ms
Maximum Spark Duration: 2.0 ms
Net Voltage Dwell Compensation
8.0 Volts 2.4 ms
10.0 Volts 0.9 ms
12.0 Volts 0.0 ms
14.0 Volts -0.5 ms
16.0 Volts -0.9 ms


I created the attached spreadsheet in OpenOffice Calc with both these tables for comparison. The grey cells are the numbers from the data above. The yellow cells are calculated fields. The Green cell allows the table to be re-calculated with the specified Nominal Dwell value.

If you set the MegaManual Nominal Dwell time to 3.5ms (as recommended now in the MegaManual) in the spreadsheet (highlighted in green), the two tables are very close (ie. the "Calc Dwell(ms)" values are VERY close).

Am I over-thinking this too much?

Should I just plug in gross_polluter's numbers, my calculated values, or has someone else got a more accurate table for these coils?
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