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Old 04-21-2015, 03:12 PM   #1
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Default Misfire above 7,300 under boost?

'99 miata, MS3 PRO, IGN1A race coils, BKR6's gapped at factory 0.9mm/.035", 10.5:1 comp, 19-20 PSI boost, Full sequential fuel/spark, 4.5ms of dwell on coils, running 18 degrees of advance when it misfires. Injector duty cycle/afrs are steady when this happens.

Right around 7,300 it just falls on its face for about 1/4 of a second, then it takes back off and climbs again.

Any ideas? I'm thinking try gapping the plugs down perhaps? I thought this ignition system could fire a .035 gap in boost but maybe not?
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Old 04-21-2015, 03:51 PM   #2
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Is this a recently built MS3 Pro?
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Old 04-21-2015, 04:56 PM   #3
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No sir I bought this one about 2 months or so after they were released. Just now getting it installed and the car running.

I made a small discovery though, when the engine cut out, the datalog shows my fans were switching from Low to High, and the log shows that shortly after the misfire, the battery voltage drops to about 12.3V. Thus I'm thinking the fans might be pulling the voltage down too much, and it may have infact dipped much lower with the inrush current and the MS3 just isn't showing this. Will test this later by disabling the fans and see if the problem goes away.
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Old 04-21-2015, 05:30 PM   #4
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misfire or rev limiter/boost control?
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Old 04-21-2015, 05:33 PM   #5
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Good point actually. Both are set higher, but maybe they are kicking in too soon? I'll turn them off and test that too.

Also went ahead and ordered a new alternator since with the fans, WI, bigger fuel pump, etc, I seem to be over the factory 65A alternators capability. Found a 140A NB alternator on Amazon for 205 shipped.
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Old 04-21-2015, 05:54 PM   #6
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Post the tune?
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Old 04-21-2015, 11:22 PM   #7
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I suspect insufficient power and/or ground wiring.

-How EXACTLY do you have the coils grounded?
-What wire gauges are you using for power and grounds? How long are runs? Did you add condensers?
-Scope primary voltage at the coils under load.

We (literally) use these coils on ProMods, 250hp+ per cylinder, and all sorts of nasty boost and meth.
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Old 04-22-2015, 12:34 AM   #8
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It was the fans causing the voltage drop. I turned the Fan High pin off and problem disapeared, voltage is staying up around 14.2-14.1 all the time, misfire gone.

These coils are beast, I don't doubt them. I'll be putting them to the real test when I try to run a 10% Water/Fuel ratio tomorrow!

Regarding wiring, I followed the directions more or less. Used 16 gauge wires for the Power and GND, all 4 wires come together to a 10 gauge. Both 10 guage GNDs to cylinder head, less than 10" of wire as coil packs are on top of valve cover. Power is a 10 Gauge wire going to a 40A relay with 10 gauge wires and a 30A fuse, power for relay directly from alternator. Sensor Gnd to sensor Gnd.

Ben, question, what Dwell/Spark gap do you recommend I run with these coils? I'll be around 25-30 PSI boost, running 93 Octane with 100% pure water injection (no meth) at a 10% Water/Fuel ratio in boost. I'm currently running .035" and 4.5ms dwell.

Last edited by patsmx5; 04-22-2015 at 12:48 AM.
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Old 04-22-2015, 12:50 AM   #9
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Also Ben, when is MS3 PRO going to allow me to set Dwell by RPM? So I can run 3 ms dwell at lower revs and 6+ at high RPM where more is better?
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Old 04-22-2015, 09:40 AM   #10
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how about just tune your battery voltage coil dwell corrections?

a lot of people turn OFF the alternator at high rpms, not increase the load.
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Old 04-22-2015, 10:14 AM   #11
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Would you have time to even have 6ms of dwell at 6000+rpm?
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Old 04-22-2015, 10:19 AM   #12
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Quote:
Originally Posted by patsmx5 View Post
It was the fans causing the voltage drop. I turned the Fan High pin off and problem disapeared, voltage is staying up around 14.2-14.1 all the time, misfire gone.

These coils are beast, I don't doubt them. I'll be putting them to the real test when I try to run a 10% Water/Fuel ratio tomorrow!

Regarding wiring, I followed the directions more or less. Used 16 gauge wires for the Power and GND, all 4 wires come together to a 10 gauge. Both 10 guage GNDs to cylinder head, less than 10" of wire as coil packs are on top of valve cover. Power is a 10 Gauge wire going to a 40A relay with 10 gauge wires and a 30A fuse, power for relay directly from alternator. Sensor Gnd to sensor Gnd.

Ben, question, what Dwell/Spark gap do you recommend I run with these coils? I'll be around 25-30 PSI boost, running 93 Octane with 100% pure water injection (no meth) at a 10% Water/Fuel ratio in boost. I'm currently running .035" and 4.5ms dwell.
Did you measure 14V at the coils under load, or are you going by your battery voltage? These are not the same thing. A single 10gauge run isn't going to cut it for these coils. You need condensers, too, especially if coming off the alternator.

I'm surprised your 30A fuse has held up.

Dwell vs load has been in firmware for at least a year.
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Old 04-22-2015, 11:06 AM   #13
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Quote:
Originally Posted by patsmx5 View Post
Also Ben, when is MS3 PRO going to allow me to set Dwell by RPM? So I can run 3 ms dwell at lower revs and 6+ at high RPM where more is better?
Update to 1.3.4 firmware, and you'll have this.
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Old 04-22-2015, 01:27 PM   #14
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Quote:
Originally Posted by Ben View Post
Did you measure 14V at the coils under load, or are you going by your battery voltage? These are not the same thing. A single 10gauge run isn't going to cut it for these coils. You need condensers, too, especially if coming off the alternator.

I'm surprised your 30A fuse has held up.

Dwell vs load has been in firmware for at least a year.
Ben,

How should I wire them up? I couldn't put anything bigger than a 16 gauge wire on the pins. I guess after that I could immediately switch to a larger wire. Basically what do you recommend? What condenser?

I have not measured voltage going to the coils.

Check this out:

Im running 14V system voltage and 4.5ms dwell, so that puts peak current at ~7A, but Average current during the charge at ~3.5A/coil.

It looks like i should go to a 40A fuse immediately. And it appears I could probably run ~5ms dwell with the 40A fuse no problem maybe 5.5.

Also I found the dwell table!
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Misfire above 7,300 under boost?-488987d1360012486-aem-ign-1a-mercury-marine-ignition-coil-info-install-ign-1a-vs-voltage.jpg  
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Old 04-22-2015, 01:28 PM   #15
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Quote:
Originally Posted by richyvrlimited View Post
Would you have time to even have 6ms of dwell at 6000+rpm?
Yes
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Old 04-22-2015, 01:29 PM   #16
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Quote:
Originally Posted by Braineack View Post
how about just tune your battery voltage coil dwell corrections?

a lot of people turn OFF the alternator at high rpms, not increase the load.
Because the MS is lagging the voltage measurement by about 1/4 of a second, thus the 1/4 second hesitation! Once the ECU saw the voltage drop the dwell correction worked and the car took off.
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