Checking CD box?

[Neal Boysen]

I've had some coil issues recently and now I'm concerned about the CD box in my 71 T. It is the original CD box, is there a way to check it? Do they wear out? Do they just quit working (like the silver replacement coil did to me recently)?

Any advice or help is appreciated!

[kwm]

What is the issue/symptoms and yes of course they go out at some point doesn't everything. I repalced mine with a MSD set up.

[pwd72s]

Warren Hall has posted extensively on this subject. Do a search under CDI unit, also (hope I remember this correctly) early_s_man. These units can be rebuilt...our host sells rebuilds, and they work well. Two camps here...original vs. MSD. Both systems work well, so I'm not going to take sides other than to say I prefer to use original in my '72S....Perhaps Warren will note this and provide links? Hope so.

[kwm]

My MSD system brand new was like 1/6 the cost of a rebuilt and about 1/10 the cost of new Bosch stuff. Plus I later sold the Bosch box for MORE than I paid for the MSD set up (in my case my Bosch box was still working just fine it turns out it was my rev limiter up behind my guages that was bad) and the MSD set up runs better, pushes a hotter plug that burns more gas than the Bosch unit could ever push and I swear it revs faster so yhea I am sold on the MSD but then my car is just a daily driver so I want what works best, gets me home rain, snow, sleet, etc...

[Early_S_Man]

Neal,

Yes, the CDI unit can be checked on a bench for proper operation ... and if NTF [no trouble found] that means one or more connections in the wiring harness need to be cleaned and treated with silicone grease to eliminate future corrosion problems!

Here are some threads with Bosch publications and additional info on component testing, theory of operation, etc. pertaining to the CDI system:

1. History of Bosch CDI ... toubleshooting info, parts list changes, and schematics ...

2. Perma-tune CD or Bosch CD?

3. BOSCH CDI discrete components troubleshooting

4. Ignition Troubleshooting??????

No, the old Bosch CDI units DO NOT 'wear out' in any sort of fashion!!! Components such as capacitors, Zener diodes, transistors, SCRs fail, yes, but can be replaced with reasonable ease. What it takes to troubleshoot a CDI unit is knowledge of discrete logic circuitry, and test equipment usage.

The most likely failure scenario for a CDI unit is a bad connection due to corrosion, loose connector, etc.

[skinnerd]

Try plugging it into your buddy's car that has the same box.
If it works in his car, it should work in yours as well.
I know it's dumb....but that's how I determined that my CD box was working.

[alwaysflat6s]

Great responses! One simple thing.. if it won't start is to stick your head in the engine compartment with the ignition on and see if you hear the very high pitched noise from your CD box. That works every time.... until you lose your ability to hear that stuff.. but by then most people are driving reasonalbe old man cars.... Note I said most.
JR

[pwd72s]

Originally posted by alwaysflat6s
Great responses! One simple thing.. if it won't start is to stick your head in the engine compartment with the ignition on and see if you hear the very high pitched noise from your CD box. That works every time.... until you lose your ability to hear that stuff.. but by then most people are driving reasonalbe old man cars.... Note I said most.
JR

Be careful here...I represent that remark!

[Neal Boysen]

Thanks for the responses! Warren I will check out your links, thanks. One thing I want to make clear is my CD box has not failed, but my coil did.
I was just worried about the CD box since it now 36 years old and I don't want to be stranded by the side of the road again.

[pwd72s]

Originally posted by Neal Boysen
Thanks for the responses! Warren I will check out your links, thanks. One thing I want to make clear is my CD box has not failed, but my coil did.
I was just worried about the CD box since it now 36 years old and I don't want to be stranded by the side of the road again.

So, buy a "core" from a wrecked-em yard, have it rebuilt, if needed, then carry a spare. By the way, the silver Bosch coils made in Brazil are not specifically too good. Warren has posted on those as well.

[KNS]

So if the silver Bosch coils aren't as good (and they aren't because mine started leaking goop a few months after I purchased it) what is a good alternative?

BTW, I recently had my CD box quit working even though it still made the high-pitched whine...

[pwd72s]

MSD blaster coil vs. Bosch coil

[Early_S_Man]

Kurt,

The whine only means that about one-third of the internal circuitry of a Bosch CDI is still working -- the DC-to-DC inverter. The trigger circuit or SCR switching section could have faults, or a loose/dirty Faston connector could have prevented the trigger circuit from getting a good signal!

A good, used black Bosch 0.221.121.001 or 0.221.121.006 CDI coil ... or an MSD High-Vibration epoxy-filled coil from Pelican. Used coils show up on eBay now and then ... that is where I got my spare for $45.

[Gunter]

Wonder why people don't carry spares.
Get a used spare CDI module and coil, swap it out to ensure it works.
Spares give you a good feeling on the road! Especially when you get stuck on a back-road in Hicksville.

I even carry a new spare fuel pump along with a bunch of other small stuff.
VISA, Radar Detector, CDI Module, Coil, Rotor, Cap, Fuel Pump, Fan Belt, Tools...............Don't leave home without them!