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Discussion Starter #1
Ok my brother has a 496 BBC in race has been fighting a ignition pop. Changed magnetic pickup on crank trigger with .050 gap, wheel in going right direction, rotor is in phase, checked grounds, changed plugs, cranked car in pitch dark to see if anything was arcing on plug wires and nothing. Fuel bowls at 3/4 full.
We are using a MSD 7 AL-2 igniting box with msd blaster 2 coil with coil on firewall. From one weekend to another it started this popping. It cranks up fine and sounds good but at higher rpms it starts intermitting and then shifts and will sound ok for just a moment and go back to popping. Any idea what it could be. Could the chip modules be causing this? Going to be risky on next test session and take all rev chips out and see what it does. The box is fairly new as of last year as well as the coil. This shit is pissing me off.
 

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Discussion Starter #3
Check ALL your grounds. Narrow your plug gap up. Box usually either works, or it don’t. Take all your chips out. Good thought.
It seems like the chip sometimes when you change them it acts funny. Wanted to see if anyone has had these issues like this before with chips interfering with each other.
 

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DamCoonass
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It seems like the chip sometimes when you change them it acts funny. Wanted to see if anyone has had these issues like this before with chips interfering with each other.
Anytime there is an apparent ignition problem I take the chips out & disconnect the tach.
 

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I’ve been taught, to watch the tach, and it will damn sure show up on the tach, when it misses. But I’ve had those same problems, and unhooked the tach, and found nothing. I miss the old cable drive tachs . Always accurate, and no worries.
 

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Discussion Starter #8
I’ve been taught, to watch the tach, and it will damn sure show up on the tach, when it misses. But I’ve had those same problems, and unhooked the tach, and found nothing. I miss the old cable drive tachs . Always accurate, and no worries.
I will definitely give it a try. Going to order new one anyway. The one I have is really old. It’s a autometer Autoguage tach. It’s probably 10 years old. Not sure how the tach output is wires inside ignition box If it somehow jumps straight to coil through the box or not. Going to pull the rpm chips out and see what that does too. My rpm activated switch is wired into tach output on ignition box to get rpm reading. Wondering if that could cause anything.
 

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Blaster coils are for 6AL boxes,not 7AL. Try .040" crank trigger clearance, not .050". Just put in different chips 200 RPM higher if you are nervous about no chips. And yes, just disconnect tach and make a run without it.
 

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Discussion Starter #11
Blaster coils are for 6AL boxes,not 7AL. Try .040" crank trigger clearance, not .050". Just put in different chips 200 RPM higher if you are nervous about no chips. And yes, just disconnect tach and make a run without it.
I have a spare hvc II coil for my top sportsman car I’ll throw it on there. I’m going mid week testing so I’ll try all of the above. I want to get away from the chips and wire a power grid module into his 7al. My grid system is spot on with shift points and rev limits.
 

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May be a stupid question and I’ll try it but what would unhooking tach do?
Over the years I've seen a tach do everything from making a vehicle not run (shorted out inside, signal wire touching metal) on a whim, to missing/popping just like you mention (signal wire too close to other wires, wire blowing around under mph increase touching down, demand on ignition goes up... spark jumps to ground/firewall, ect).

Get your signal wire unplugged from the MSD or wherever you have the source. Just my Thoughts, Lorne
 

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Discussion Starter #14
Over the years I've seen a tach do everything from making a vehicle not run (shorted out inside, signal wire touching metal) on a whim, to missing/popping just like you mention (signal wire too close to other wires, wire blowing around under mph increase touching down, demand on ignition goes up... spark jumps to ground/firewall, ect).

Get your signal wire unplugged from the MSD or wherever you have the source. Just my Thoughts, Lorne
I ordered new tach, plug wires, and ordered MSD diagnostic tester. So I’m hoping to find the problem soon. The tach is at least 10 years old so it could be it. My luck it isn’t but I’m willing to try it. Has anyone used the diagnostic tester. May need a few tips too on how to diagnose it with the 89981 tester.
 

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Discussion Starter #15
My MSD rpm activated switch is hooked right up to where the signal wire is to run the tach. Could the rpm activated switch cause this too?
 

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Anyone you know have a MSD tester?

I had one. Haven’t seen it in years. But, lots of things came up missing in the last 20 years. I’ll look when I’m in the shop. Bought if for obvious reasons. Then, all it turned out to be was a bad ground.
 

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You sure its ignition related. Sounds like it may be a broken valve spring. Seems like if it was ignition related it would be doing it all the time and not just at high RPM. Just a thought.
 

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I would also look for a voltage drop on the feed to the box with respect to the ground and also between a good 12v source and the ground. Use a DVM with a record and min max feature
 
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