67 Eldorado - Never trust a vacuum modulator

[67_Eldo]

The transmission warranty work inches forward on my 1967 Eldorado.

It turns out that the vacuum modulator, which was new two years ago, failed. Repairing that will also eliminate the traces of ATF that were being sucked into my Quadrajet, eliminating (the last?) potential cause of an imperceptibly lumpy idle.

If anyone tells you that your vacuum modulator is too new to fail, point them to this cautionary tale.

A weird side problem: The 10-amp fuse running to the brand-new Pertronix coil and Ignitor (I) system blew while the mechanic was moving my car around. He's heard lots of Pertronix failure stories (as has everyone else, apparently), but blowing a 10-amp fuse is something to think about. We put in another fuse and the car started up just fine, telling me that the Pertronix unit is still working. A mystery!

BTW, I've got all the correct Pertronix tweaks covered: a new Flamethrower coil with the recommended resistance, a fat new wire (not the original resistor wire) running out to feed the system the full amount of fresh juice, and clean connections everywhere else. I installed this stuff in March 2019, I think.

[Caddy Wizard]

Vacuum modulator uses a rubber diaphragm, I would imagine.  If the thing was a NOS unit, the diaphragm could have been quite old and the rubber fairly fragile.  It could easily fail shortly after being put into service.  This sort of thing happens all the time with NOS vacuum advance units for the distributor.


As for the fuse, in the 50s the ignition wire is not fused.  10A is plenty of power for the Pertronix unit, but might be at the limit for an ignition coil.  I would not be surprised to find that the fuse blows again.

[bcroe]

It turns out that the vacuum modulator, which was new two years ago, failed. Repairing that will also eliminate the traces of ATF that were being sucked into my Quadrajet, eliminating (the last?) potential cause of an imperceptibly lumpy idle.

The replacements are a completely different construction than
the original, my bet is the original would not have failed.  I try
to stick with the originals, but they do not adjust as easily. 
Bruce Roe

[67_Eldo]

As far as the modulator design goes, I'm sure they're using the new (cheap) design. Although the guys doing the work have a few old cars sitting around their shop, I'm sure they're making no attempt to remain true to the original designs in the repairs they do. :-)

On the Pertronix problem, I've been looking into more Ignitor I (the version I have) details. I knew vaguely that you can't leave the ignition on for a long time without the engine running with an Ignitor I (pouring straight DC through the ever-heating-up coil). But I didn't realize that Pertronix counts 30 seconds as a "long time." I'll bet somebody shut down the engine but left the key on and, very shortly, popped the 10-amp fuse I stuck inline to protect the system.

With a 1.5-ohm Flamethrower coil and 13.8 volts, the current draw while the engine is running should peak out at a little over 9 amps, so that's where my 10-amp figure came from. Thank goodness the inline fuse holder for the Pertronix system is tied up in that huge run of wires coming off the back of my temporary instrument panel. Easy to get to, down by your right foot! The mechanic was, at first, terrified and then impressed. :-)

[TJ Hopland]

Are you sure that the Pertronix can stay on?   That seems like a pretty big design flaw if it does.  They have to be doing the dwell control with some electronic timing so they would almost have to go out of their way to make it stay on.  I would also presume that the module is doing the current limiting which is why they don't want the resistor in the feed.  If there was a chance it was going to stay on you would want that resistor so you don't instantly fry the coil if it stuck on.     Also there are what 4 different versions available for the more popular applications now, maybe the original has this possible flaw?

[67_Eldo]

I'm using the first version of the Pertronix, Ignitor I. It is just a simple points replacement. The dwell is fixed. And yes, not being able to leave it on when the engine isn't running is a big bug. :-)

The Ignitor II adjusts dwell on the fly, apparently eliminates the leaving-the-ignition-on-when-the-engine-isn't-running problem, and is generally more sophisticated.

The newest version -- Ignitor III -- adds a rev limiter, multiple sparks, and more.

When I looked over their choices, I picked the Ignitor I because I'm not a hot rodder trying to find yet another way to improve my quarter-mile times. Since I installed it, it has been working great. But I do keep in mind that key-on, engine-off limitation.

In fact, that limit is one reason I've been building my "shadow" electrical system. The original electrical system remains in place, unaltered, while the "shadow" system allows me to add a stereo and other goodies that didn't exist in 1967.

For current limiting, it appears that they count on the resistance of the coil. This means that they expect you to buy the Flamethrower coil that matches your Ignitor version. Pertronix sells coils with 3 ohms, 1.5 ohms, and super-low ohms resistance to line up with the Ignitor I, II, and III systems. I have the 1.5-ohm coil which they recommend for eight-cylinder Ignitor I oldies.

With the electrical stuff I've added, I have never left the ignition on when the motor isn't running because I don't have to. But anybody who isn't me wouldn't know that. It would be easy for someone to leave the key on thinking that they need it for accessory power. POOF, the Ignitor I and Flamethower would melt down ... if I hadn't installed a fuse.

So now I'm thinking that I should either 1) install an Ignitor II and never think about the position of the ignition key again, or 2) carry even more spare 10- and 15-amp fuses than I already do. :-)

[TJ Hopland]

Have you considered running something like an MSD6 box off the points?   Seems like it may be a good fit for you with the parallel electrical system concept.   You could also design and build it with some sort of connector that would allow you to unplug the 'box' and install a jumper that would restore it to a conventional points system. 

The MSD6 and similar boxes just use the points for a signal so they are not arching/wearing the points like a conventional system would.   Unlike other points driven electronic systems they do seem to have enough load to keep the contacts clean but still reducing the load on the original system.   They also allow you to leave the condenser in place as well as the resistor.  You can even set a factory dwell.   Some of the points electronics kits you can't have the condenser in place or use a typical dwell settings so going back as a limp mode is more complex.

These style of boxes typically have a + and - constant power feed direct from battery so that makes things easy because you are not adding loads to original wires.   You also don't need to screw around with relays and finding a on when cranking and run circuit or any junk like that that can sometimes be difficult.    There is then the key on wire which you can tie to the original coil + wires.   Again they don't care if there is a resistor in there or not, they are just using it as a sense wire to know when the key is on.   There is a single wire to the points which is a sense wire, no real load.   There is a tach terminal for if you have some sort of tachometer.   You can't hook to the coil anymore because the multi spark and higher voltage will screw up the reading and maybe damage the meter.    Last wire are the 2 wires that lead to the coil.   I think similar to most of the electronic conversions they recommend their brand super coil but they do seem to work with stock coils. 

I have a few of these setups and it really helps with starting and idle.  I have not noticed a major difference in performance in the cars I have done it on but in my boat the 'off the line' is much stronger.   Only real word of warning if you do one or mess with one of these is make darn sure the key is off before you mess with anything near the secondary side of the ignition system,  these thing bite hard.   You really jump and risk secondary (pun intended) damage to yourself like banging your elbow into the broom stick that is holding up the hood.   

[67_Eldo]

I had forgotten about MSD. You're right, they do lessen the load on original ignition systems.

25 years ago, I put an MSD system on my 1969 TR6 and it worked well.

Once I get my Eldo back, I'll be able to assess the damage done by the mechanic. :-) (He put in his own jumper wires and coil to move the car before I showed up to tell him where my Pertronix fuse was located.) If my Flamethrower coil and Ignitor I don't look healthy anymore, I might move to the MSD solution.

But the Pertronix setup is so simple and tidy that I'd hate to bail on it without evidence.

[TJ Hopland]

Flamethrower may be an appropriate name if there has been wire jumping going on.   Ever seen one of those traditional round coils blow?  Its pretty impressive and if its one of the oil filled ones you could be in for an extra flamie mess.

[Big Fins]

I installed the FlameThrower II system on my '59 and never looked back. You just have to be sure the resistance wire is eliminated and a full 12V is going to the coil to garner the advantages of the system. I also increased the plug gap from .030 to .045, but stayed with the same heat range and depth of the electrode. In other words, stayed with the factory plugs.

[fishnjim]

Electrical trouble shooting sez; never re-energize a circuit til you find the cause of the fault or show it has been eliminated.   Not a common trait, using good practices, but will save some fires, damage, etc.
Sounds like your mechanic needs a tune-up...