CDI boxes

[madmike]

Casper love'em, eats them like there going out of style
I've had at least 6 or 7 boxes take a shit. all diff. MSD 6al, ate two of them, sent them in to MSD both had diff. issues , mallory's work the longest, got a couple years out of a brand new Mallory 6al box, then I had a hankering to try a 2step so i hooked up a MSD 7 box worked great for about 200 miles, had to 'Walk' home today ,bug was running great today, acted like I just reached up and shut it off yesterday it started to miss ,spit & backfire slightly ,then pick up and run so so,, always missing ,, ran fine when cooled down again,, swapped coils twice, I was about 40 miles from home, but it ran good enuff to get me home MSD dizzy was bought new years ago boxes were all rubber mounted too., Any guesses?????, I'm going to slap in my last Mallory box or an 009 I have to pick up my grandson from skool tomorrow

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'Black Ice'Drag Buggy 'Turbo'
Rail Buggy 1915 turbo
76 Drag/Street bug 2180cc 'Turbo' 11:85 @113 mph"If I go any faster I'll burn up the Hamster" ,gets 28 mpg. also 10/09/22 11.90 @115 mph
"If I'm ever on Life Support,UNPLUG Me, Then Plug me back In see if that Works"

[67rustavenger]

Have you thought abut trying a different brand of CDI?

Maybe a Crane Hi6N will last a little longer than the MSD/Mallory units you have been killing with reckless abandon!

Or reach out to Jon Miller and see if he can build something a little more sturdy than what you were running.
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I have learned over the years.
Cheap parts are gonna disappoint you.
Buy Once, Cry Once!

There's never enough time to do it right the first time. But there's always enough time to do it thrice.
GFY's Xevin and VW_Jimbo!

[madmike]

was thinking about it but i like the features,like a 2 step
_________________
'Black Ice'Drag Buggy 'Turbo'
Rail Buggy 1915 turbo
76 Drag/Street bug 2180cc 'Turbo' 11:85 @113 mph"If I go any faster I'll burn up the Hamster" ,gets 28 mpg. also 10/09/22 11.90 @115 mph
"If I'm ever on Life Support,UNPLUG Me, Then Plug me back In see if that Works"

[jpaull]

Hey Mike, if your able to kill a MSD 7al within 2 years. The problem is not the box

[[email protected]]

I would create some new, and over redundant grounds. Also check for anywhere the spark from the coil could be arcing to ground. They don’t like odd voltage spikes. Maybe try using the ignition wire to trip a relay to turn the box on.

I’ve known numerous people that have killed MSD boxes by doing a quick weld somewhere on the car with the electrical system fully hooked up.

I’ve seen poor/nonexistent engine grounds arc through throw out bearings.

[stevemariott]

Mike,

I don't have the CDI knowledge that others do, but I made sure to ground my old Mallory Hyfire 6a directly to the battery per the instructions - no issues here. Double check your grounding.
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1963 Manx copy
1968 Bus

[mikedjames]

As they say.. if you are killing so many CDI boxes the problem lies outside the boxes...

Voltage regulator issues causing high voltages and or voltage spikes on DC feed.
Earthing layout causing voltage spikes on DC feed ?

I mess a lot with electronics around the engine and I have found fitting an 18 volt Transient Voltage Suppressor diode across the DC feed to electronics in the engine bay gets rid of a lot of problems.. these are like grown up Zener diodes.. the 600 size can dump 600 watts of power for a short time, about 2 watts average.
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Ancient vehicles and vessels

1974 VW T2 : Devon Eurovette camper with 1641 DP T1 engine, Progressive carb, full flow oil cooler, EDIS crank timed ignition.
Engine 1: 40k miles (rocker shaft clip fell off), Engine 2: 30k miles (rebuild, dropped valve). Engine 3: a JK Preservation Parts "new" engine, aluminium case: 26k miles: new top end.
Gearbox rebuild 2021 by Bears.

1979 Westerly GK24 24 foot racer/cruiser yacht Forethought of Gosport.
1973 wooden Pacer sailing dinghy

[dunk]

Adding to what the above has to say... regardless of box manufacturer, they will want a smooth input..i.e. no surges in the supply...

Maybe try a smoothing capacitor, or "noise filter" as I believe msd call it... most of the cdi box companies have offered one... or just use a capacitor of a relevant spec..

I have a generic capacitor on mine... have used crane and msd boxes through it... no problems as of yet....

https://www.erareplicas.com/427man/wiring/msd-install.htm

The above is worth a read..

[Fred Winterburn]

Heat is another electronics killer. Do you have it mounted in a cool enough location? Fred

[madmike]

Hey Jeff, 7 box, try 200 miles not 2 years
Fred, I mount them in the Back seat area , see Photo above,,I'll recheck all grounds today :wink
No welding on the bug,, all wire's installed properly,,,checked a thousand times
_________________
'Black Ice'Drag Buggy 'Turbo'
Rail Buggy 1915 turbo
76 Drag/Street bug 2180cc 'Turbo' 11:85 @113 mph"If I go any faster I'll burn up the Hamster" ,gets 28 mpg. also 10/09/22 11.90 @115 mph
"If I'm ever on Life Support,UNPLUG Me, Then Plug me back In see if that Works"

[Fred Winterburn]

Probably voltage spikes then as mentioned already. However most CDIs have built in filtering. Yet another possibility are misfires due to too wide a plug gap that could stress the discharge capacitor or whatever switching means is being used, IE SCR for example. It could also stress the power supply depending on the design. That's not as likely a scenario though and you would likely notice the misfires if they are frequent enough to damage the unit. Fred

[Fred Winterburn]

Perhaps your coil is leading to the short life spans? Some CDI coils aren't much better than dead shorts on the output which will stress components within the CDI. A slightly tamer coil might be all it takes if that is the issue. Fred

[Clatter]

Could a janky VW ignition switch kill a CDI?

Ignition switches on these old cars can be intermittent on a good day..

There’s also the big black wire that usually feeds the coil a.k.a. “Old crispy”.
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Bus Motor Build

What’s That Noise?!?

[madmike]

I have a 'switch panel' no stock vw ignition switch
Thinking about pulling that Alternator,because, well just Because
Fred I've tried 2 different coils
_________________
'Black Ice'Drag Buggy 'Turbo'
Rail Buggy 1915 turbo
76 Drag/Street bug 2180cc 'Turbo' 11:85 @113 mph"If I go any faster I'll burn up the Hamster" ,gets 28 mpg. also 10/09/22 11.90 @115 mph
"If I'm ever on Life Support,UNPLUG Me, Then Plug me back In see if that Works"

[chrisflstf]

Failing alternators can put out over 18vdc

[Erik G]

I'm with the above on the grounds

I'd think you would fry batteries if it was alternator over current

[Alstrup]

I´m with Fred on the ground. But it is not just the box that needs good ground. The engine/transmission needs good ground too. Both rust, paint and sloppy ground wires can be the reason to not sufficient ground.
When using especially powerfull CDI´s i always add a second ground between trans and chassis.
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https://www.thesamba.com/vw/forum/viewtopic.php?t=435993

[Fred Winterburn]

That wasn't my suggestion but it certainly is something to check. Without a good ground for the case, high voltage might try to sneak back via a more delicate part of the circuit. Fred

[VdanielW]

I'm running the summit racing cdi box in my daily driver and seems to be doing good. My fitech unit handles rev limiter and 2 step if I wanted to hook it up.
Don't you have a mallory hyfire VI?

[74 Thing]

Where are your grounds?

Do they ground to the body or the floorpan or both?

I would ground them to the battery or the panel that the battery is grounded to (eg floor pan). I know the body is supposed to be grounded to the floor pan through the body mounting bolts but there is corrosion there so I ran a separate ground wire on mine from the body to the battery floor pan grounding point.