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Discussion Starter · #21 ·
Voltage drop tests, test the entire power circuit. It's not specific to the coil. I would recommend watching some YouTube videos to get an understanding of it. If you have a ground issue, the spark has a hard time completing the circuit which could be where your problem is coming from. There are so many people who run stock ignition without a CDI which is why I'm suspecting something else.
I wouldn't know where to start as I've been through this car thoroughly front to back. The car has 53k original miles with no rust whatsoever. Everything works that's electronic. The car ran perfectly before adding boost. There were no ignition problems.
I would think that poor grounds would affect the Megasquirt as well. I have all of my gauges grounded to clean sheet metal at the tranny hump. That shows a good ground plane.
I'll test voltage at the coil plug tomorrow.
 

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Showing a good ground with no load means nothing. It's when there is a load on the system it matters. 53k miles but it's still 25+ years old. I've seen plenty of voltage drop issues over the years. Low mileage or high mileage makes no difference. All it takes is one bad connection, one corroded wire, one poorly contacting wire to cause issues. It's your call but it's a free test. Why not check? You have nothing to lose.

Oh yeah. My car when i got it had been through multiple people all having odd issues with it never running right for years. It was a voltage drop issue that was the cause of all the problems.
 

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If you need help understanding a voltage drop test. I am more than happy to take it to PM's if you need a thorough explination. Electrical is probably my strongest skill set. I've been doing electrical work and troubleshooting for 20+ years for multiple performance shops and random people over the years.
 

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Cylinder pressure is what makes the spark harder to jump the gap. More boost for example, more cylinder pressure. More air into the cylinders, more cylinder pressure.

The mark on the strap is the timing. If the burn mark is by the threads, you have to much timing. I like to tune where the mark is at the turn on the strap. The only way to see the spark plug reading is to do a pull and shut it down, than read a plug.

I ran ar3923's for around 9-10 years with no issues on e85 and 15psi with good flowing parts making 900hp. Never had an issue with the plugs (crane cdi igntion).

IMO it's a good idea to put a stronger ignition system on the car when boosted. I'm not sure if you have another issue going on or not. Those plugs are to cold imo.

Also a richer mixture is harder to ignite. 10s for a/f are pretty rich for that boost level.

I attacked a picture of a plug from one of my event dyno pull pulls. E85 making 1068whp. I kept the tune very safe.
 

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I’m still running a 15 year old 6 series MSD box.
 
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Discussion Starter · #28 ·
If you need help understanding a voltage drop test. I am more than happy to take it to PM's if you need a thorough explination. Electrical is probably my strongest skill set. I've been doing electrical work and troubleshooting for 20+ years for multiple performance shops and random people over the years.
PM'd you. Thanks!
 

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I still have a Mallory Hyfire IV that I didn't use, plus the coil, I went with a Jacob's ignition system for a Fox Mustang. That worked well for the stock NA, and had an anti-theft which was cool.
 

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Discussion Starter · #32 ·
I’m still running a 15 year old 6 series MSD box.
That's just the thing. The older boxes seem to be fine. The problems seem to be with the new Chinese made boxes.
 

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That's just the thing. The older boxes seem to be fine. The problems seem to be with the new Chinese made boxes.
True. MSD has outsourced their products which has resulted in poor life expectancy and in general poor quality. I do have a 6al2 in my car from about 10 years ago for the 2 step feature but its not plugged in and I just use the stock ignition plug until i take it to the track. It was also dyno'd without the CDI plugged in. I have the OEM and MSD coil plugs at the coil so I just unplug one and plug the other in. 99% of the time my car uses the stock ignition with no CDI. I also replied to your PM (y)
 
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It seems that everyone can get away with the factory ignition except me. I have one cap and rotor from Rockauto and another new cap and rotor from Autozone. Neither one makes a difference. I tried a tfi and coil from Oreillys. No dice. I tried 3 different sets of wires. 4 sets of plugs at various gaps. Here's the rub...
My tune was rich up top and I leaned it out to 11.5. When the tune was rich; I got no breakup at WOT but the idle sucked. After I leaned it out at WOT; the breakup was back. I could feel the added power after leaning it out. 2nd gear traction was noticeably worse. More power. More power; more cylinder pressure. Make sense?
That’s odd that it broke up when you tried to lean it out to 11.5, which really is really about where it should be.

In my friend’s old 91 I tuned we ran 20lbs+ on a msd tfi coil and no cdi box and everything was fine. It used to break up, but we changed valve springs (was an old set of performer heads) and the pos blaster 2 cylindrical coil, that someone thought was a good idea, and it was good after that.

Send me a log of it making 14psi, I’d like to take a look.
 
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Discussion Starter · #35 ·
That’s odd that it broke up when you tried to lean it out to 11.5, which really is really about where it should be.

In my friend’s old 91 I tuned we ran 20lbs+ on a msd tfi coil and no cdi box and everything was fine. It used to break up, but we changed valve springs (was an old set of performer heads) and the pos blaster 2 cylindrical coil, that someone thought was a good idea, and it was good after that.

Send me a log of it making 14psi, I’d like to take a look.
Let me dig up a log and I'll send it. Thanks!
 

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On the dyno I ran 14psl, no problems. It's fully spooled by 3500 on the dyno, .023 gap, ngk plugs, taylor 10mm wires, accel coil, older msd cap standard motor products rotor. What cap and rotor are you using? The new MSD stuff is very often problematic.

Msd 6al or 6al2 are probably ther most commonly used cdi boxes but i try not to recommend anything from "My Spark Dissapeared", their quality has gone down hill.
or Might Suddenly Die.
 

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Had a msd 6a box back in the 80s. JUNK

Bought a Crane HI6 box with matching coil 32 years ago. Still going strong today. 7200rpm and 30lbs of boost. Never a hiccup.
Ive heard the Crane Hi6 boxes were pretty good. I just have never used one.
 

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All I can say is, my car came with MSD cap, rotor, coil, and 6al box. It runs a little smoother every time I replaced each component with OEM and got rid of the box.
 

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Have you reduced (adjusted) your maximum boost to see if the miss still occurs at those RPM's?
If it still happens at reduced boost levels you can rule out the spark getting blown out at those low spark plug gaps.
 
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