first published Mar 2012, revisions on-going (mostly when the spirit moves me!)
Insulator on the Distributor
The Vintage Volvo “IGN SWitch”, (and key killer)
Review of Ignition System and Troubleshooting Notes
Ignition System Troubleshooting
“Wifes Startomat” [HUH?]
Discussion of Ballast Resistor in the Standard Ignition Primary Circuit
Consideration of SwEm Start Pushbutton
Link to separate
Ignition from Scratch
Insulator on the Distributor Throughbolt (Pointsbolt of the Two-Part Points Distributor): 3 Mar 2012
The OE insulator keeping the points-spring of the common two-part points from contacting the Distributor housing are essentially of heavy paperboard reminiscent of matchbook material. This paperboard deteriorates over the years (paperboard harvested from a matchbook has even been suggested as a replacement). I would use this only in a pinch…it’s not really the best thing if one wants a long-term replacement…I don’t know about the original paperboard, but that from an inexpensive matchbook cover is surely porous, so will hold moisture, which can promote a breakdown under the high voltages it is exposed to (not ignition high, but still higher than 12V! Reference Ignition primary voltage waveform below: FIGURE 2. Blue). It is a good idea to replace the insulators after fifty or so years of faithful service with the Right Stuff (those darned Volvos and their Bosch components just don’t last!). Here are my thoughts on replacement.
First, a list of what I perceive to be the requirements for this material: Non-conductive (to medium voltage) flat stock, 0.010” to 0.020” thickness, pliable, stable to 250 Deg. F, oil contact compatible.
Teflon is another material which was suggested. It will certainly stand up to the heat and voltage, and would certainly last, but it is not physically stable in that it is subject to cold-flowing when under pressure of the hardware stack of that Pointsbolt (and more so when at an elevated temperature). Sandwiched between the various components on the bolt, under high compression, it will flow, probably resulting in the bolt becoming ever looser…so I would recommend against it.
A resin fiberboard (common trade name: Fish Paper) intended for home and industrial electrical duties, is beefy enough to stand up to the compression forces it would be subjected to in the Distributor application, but thin enough to be easily able to form into the curve of the inside of the housing is available. This material would fit the bill very well.
I have found yet another option…thin fiberglass reinforced epoxy circuit board material. I also consider this material to be just about ideal: Nonporous, high-temp and high-voltage qualified, yet still thin like to original to be follow the curve of the inside of the distributor housing …and probably able to last forever too! This is what all my Distributors have! I cut this into the shape of the original, punch a hole through it, and install it in place of the original…voila!
Points Bolt Insulator of G10 (fiberglass reinforced epoxy board) and an original (curved) for reference.
Anyone sending a SASE to the PO Box address on the SwEm Kits page will get one of these babies by return mail!
Related info while working on Pointsbolt: It’s crucial to get the hardware stack of the Pointsbolt right!
The shoulder washers on either side of the distributor housing serve an important purpose. They should be installed with the shoulders facing each other and dropping into the through-hole in the housing, thereby centering the bolt in that hole. But if the shoulders of the washers are worn (as they very well may be after many disassemblies and reassemblies), the washers may not center the bolt correctly. Failure to notice this and correct for it during assembly can result in shorting (including intermittently) of the bolt to the distributor housing, leading to intermittent or total Ignition failure…not so good!....I recall a pesky Ignition failure thread on the Brickboard forum not long ago where this turned out to be the root cause.My solution which permanently addresses this condition is to not only be acutely aware of the Pointsbolt centering during the reassembly process, but to guarantee it! I do this with an insulated “centering sleeve”, made from a short section of the circular insulator of a 14-16ga.(Blue) crimp, slipped it over the Pointsbolt (between the shoulder washers). The sleeve takes up the room between the OD of the bolt and ID of the through-hole to guarantee a good centering of the bolt… it’s a little thing, but it’s called sweating the details…but that’s how I roll, and intend to keep rolling…no Ignition Failure Allowed!
The Vintage Volvo “IGN SWitch”, (and key killer). 3 Mar 2012
The vintage Volvo “IGN SWitch”, (and key killer) is a complex assembly! It consists of the (replaceable) Lock Cylinder (the mechanical part one inserts the key into) whose tailpiece fits into a slot of the contact-base, and turns the Electrical Switch behind it. The wire powering the Ignition Coil positive is completely encased and connected by the Armored Cable (of fame and lore) to the Ignition Coil. Since there is no access to this electrical node, there is simply no way to “Hot-Wire” a so equipped vintage Volvo.
Like any Lock, the Lock Cylinder should be lubricated and as free as possible to turn with the IGN Key so that it does not contribute any significant friction or counterforce to the turning of the Key (the gorilla return spring in the Start position does enough of that already!). I use and recommend Tri-Flow for this.
In the Volvoniacs (German) Vintage Volvo Forum, I have also seen the advice of saturating the Lock Cylinder of your Ignition Switch with a sprayed-in lube whose name I won’t mention, but which rimes with “I gotta pee (40)” and which even comes in a spraycan in the Swedish colors, until it runs out the bottom…this advice and technique has about as much value as finding a nickel…it may feel pretty good, but has little value beyond that. This is because this technique only lubricates the mechanical Lock Cylinder front part of the Ignition Switch Assembly (and only short-term temporarily at that), and that is OK I suppose, but it does not address the major contributor of counter-torque against the turning of the key into the Start Position … because, the actual electrical part of the switch is a separate, semi-sealed part behind it, which would not be getting any of the material sprayed into the Lock Cylinder anyway, and that is where the Gorilla Spring is located which the Ign Key must be turned against! Finally …lubricating a spring will never change its spring constant, so lubing the spring would not decrease the counter-torque it applies!
Bottom Line: Short of replacing the Gorilla Spring (that would be incredibly involved and prohibitively difficult, believe me!), the only real solution strategy is changing the rules and "cheating"…installing a Start Switch Upgrade and not even using the Start Position after that! Tricky huh?
If you are interested in disassembly of these components, look at this series of videos: http://www.youtube.com/watch?v=vStZoVUQIWk&list=UUWjGjlKYRCG8tLhuMIUHziA&index=3&feature=plcp
..the video poster uses non-standard terminology, and he rather breezes over the Gorilla Return Spring (I wonder if he even realizes what it is), but one can see good detail of the Ignition Switch, a quality constructed component.
Link to detailed analysis of the root-cause of Key Breakage: Ignition Switch Key Breakage Tech Article
Review of Ignition System and Troubleshooting Notes: 7 07 R. Kwas
The manner in which the high voltage is generated in a Kettering LINK TO WIKI (conventional) spark IGN system takes advantage of some special characteristics of electronics and inductors...specifically, the high voltage spike generated by a collapsing magnetic field, and the voltage step-up action as a function of turns-ratio of a transformer. Combining these two effects yields some very high voltages which are capable of jumping across the air-gaps of sparkplugs to perform the slight magic of igniting an explosive mixture there.
What is crucial to remember is that the important part (IGN spark) occurs at the moment of points opening. It occurs due to the magnetic discharge (of coil primary), but that shouldn't take away from the importance of what is happening during the time the points are closed...namely to complete the primary circuit and allow current to flow from the power source and charge the coil primary in the first place! If either doesn't happen, no spark will result, period!
Further, the IGN switch / Armored cable/ IGN coil Assembly of fame and lore on our vehicles is a wonderful thing...it makes stealing so equipped vehicles quite difficult (Good!), because the Coil primary + connection just isn't available for "hot wiring" by a thief...unfortunately, it also makes troubleshooting IGN system failures by the rightful owner, or his duly appointed mechanic, by checking voltage on that node, a bit more tricky for the same reason...but this shouldn’t be a problem for the owner/mechanic who has the IGN key and understands what is happening...read on!
When points (or the switching transistor of your groovy electronic ignition module) are closed during operation, Ignition Coil current flows in the primary winding, building up (relatively slowly due to primary inductance), and thereby storing electrical charge magnetically. When (and exactly when!) points open, this current path is broken, the resulting reverse inductive spike, caused by the instantaneous discharge of the primary circuit inductance, in addition to a voltage step-up transformation to the secondary winding, results in a very high voltage being generated by the secondary winding. Both conditions are necessary for correct function of the Ignition system. Points must therefore cycle in order for the Ignition system to charge and discharge. Any failure condition which interferes with either of the two conditions will prevent the system from generating the desired high voltage.
FIGURE 1. Kettering Ignition System Primary voltage and current waveforms. Timing: X= Points close, Voltage across points (Blue) drops to zero, primary current (Red) begins rising at a limited rate peaking out at some impedance limited maximum level. O= Points open, voltage across points spikes up, primary current drops to zero. Graphic Source: See pic.
FIGURE 2. Kettering Ignition System Primary and Secondary Voltage and waveforms. Timing: T1= Points open, voltage across points spikes up(Blue), as does secondary voltage (Red). T2= Some ringing occurs as stored energy is used up and exhausted. Graphic Source: Shown (marked-up by author)
Ignition System Troubleshooting:
If no spark occurs at the spark plug wires when the points open, several things could be wrong. Among them, (listed somewhat in order of occurrence in my experience)...
1. “Non-Opening Points Condition”. The connection to battery negative (chassis) may not be opening to break primary current...sure, the points themselves may be opening mechanically, but if the (early production) distributor through-bolt and its stack of hardware has become uncentered and is making contact to the distributor housing (this was indeed the root cause of a failed IGN system on a recent Brickboard posting: LINK to Thread: http://www.brickboard.com/RWD/volvo/1340687/120-130/122_wont_start.html ); or the (by now, also pretty vintage, insulation paper* on that bolt looking similar to the Declaration if Independence in terms of color and crustiness) between points-spring and dist housing has become dislodged or deteriorated to the point that it is not insulating that critical connection from a connection with chassis either*, the points are not opening electrically, and your IGN system, and your engine, are dead in the water, caused by what can be called a “non-opening points condition”). A hint of this condition is when coil gets quite warm with IGN ON during troubleshooting. This occurs due to the continuous and uninterrupted primary current.
* (Send a SASE to the SwEm PO Box, and I’ll send you a free aerospace rated replacement made of G10 glass reinforced epoxy circuit board, guaranteed to outlast your car AND you!).
A shorted Condensor can also cause this condition, but this condition is quite rare.
2. No High Voltage at Spark Plugs: If no spark is reaching the spark plugs, it doesn’t necessarily mean that the high voltage is not being generated...its just that the high-voltage generated in the IGN system has a real preference for jumping to the nearest and easiest chassis point available to it...if this happens to be elsewhere from the spark plugs [Safety Notice: This includes the mechanic!], you can be quite certain that the high voltage, although being generated, will never make it to the plugs to make the all-important jump across the gap. That is why it's always advisable to check for the high-voltage at the coil output wire first. Do this by disconnecting the middle high voltage wire from Dist cap and laying it on a convenient chassis point (like the valve cover), with a slight spark-gap at which the output spark of the Coil can be observed (no touchy!). Have an assistant turn ON the IGNition and then activate the starter to turn over the engine as you watch for IGN sparks at the test gap (or do it yourself by turning ON IGN with key and activating Starter with a remote Starter or even more slick: The SwEm Service Switch under the hood). Having verified that the Points and Coil are making the high voltage, one can now move on to check the distribution process for which this assembly in named...”divide and conquer” is THE preferred technique for finding IGN problems!
3. Distribution Problem: Once it has been determined that high voltage is being indeed generated, the routing and distribution needs to be checked. As the high voltage comes in on the center connector of the Cap, it gets connected by a spring loaded carbon brush, to the Rotor. As this rotor turns, it lines up with terminals of the individual wires running off to the sparkplugs (the rotational position of the Distributor assembly is strategically aligned to point to the appropriated spark-plug at the right time. See: Timing). One thing that may come as somewhat of a surprise to casual mechanics is that in addition to the high voltage jumping the gap at the sparkplug, where it is supposed to(!), it must also jump the small(er) gap between Rotor and fixed contact in the Cap, where the wires running off to each cylinder's sparkplug terminate...no big deal except that the carbon dust from that Rotor contact brush, combined with some early morning moisture may someday, if not periodically cleaned, present an easier path to chassis for that high voltage...then it becomes a big deal! Dirt (particularly carbon dust) and moisture are the enemies of a properly working high voltage system!
4. High-Voltage Breakdown / Leakage Problems: If it has been determined that the high-voltage is being generated, but a problem lies in the general distribution process to all cylinders, or an individual cylinder which is not firing (continuous misfire), or (an even trickier) an intermittent misfire needs to be located, that gets a bit more complicated. High-voltage leaks (sparks across an air-gap, or more commonly, creepage along a surface) occurring external to components like cap of plug connectors are often able to be spotted when checking under low light conditions...internal breakdowns are trickier still but can often be located by substitution methods (swapping cables, plugs etc.). Again, dirt and contamination on Cap, Rotor, or Wires can lead to a voltage breakdown in a location other than Spark-plug gap. Keeping all of these components clean is a good practice. A cleaning once a year with high order solvent which leaves nothing behind like carb or brake cleaner or or even in the kitchen sink with a common surface cleaner (i.e. Fantastik or Windex) is a very good idea as a preventative service! Dry components well before reinstalling!
Last. IGN Switch / Armored Cable / IGN Coil Assemblies Failure: The very last thing on my personal list, would be a failure of the IGN switch or coil. While not impossible, failures of these are thankfully rare on the quality Bosch assembly. The typical failure mode is an internal breakdown to the high-voltage generated in the secondary of the IGN coil, and most uncommon I would have to say, a failure of the IGN switch to supply power to the + node of the coil-primary coil (both of these conditions would be found in the tests outlined in Step 2.). I just wonder how many IGN switch / armored cable/ IGN coil assemblies have been wrongly condemned because of the troubleshooter's inability to deal with them to correctly locate and remedy the true problem...furthermore, I offer a hot-fudge sundae and to cover shipping (within continental US only!) to anyone who will send me a failed assembly for a post(alleged)mortem inspection!
Additional Troubleshooting of overall IGN system failures:
Steady State Test: Connect a
voltmeter between the points terminal (either at Dist or at Coil) and vehicle
chassis. Turn IGN ON with key. Either battery voltage or 0V will be measured
(depending on where distributor and points-lobe happened to stop when engine was
last turned OFF. If points are open, battery voltage should be read, if points
are closed, 0V should be read). A low wattage 12V Test Light can be simply used
instead of a multimeter which may not survive the medium voltage pulse when
points are opened (Reference: FIGURE
1)...this is certainly less that the high voltage pulse generated by
the secondary, but why take a chance with a meter!
* I have personally sent an expensive Fluke brand Digital MultiMeter (DMM) to the electronic happy hunting ground by connecting it to the points terminal to measure that voltage…apparently the primary spike occurring at the instant of points opening (see: FIGURE 2) was enough to permanently whack the DMM input circuit!
Dynamic Test: Connect a dwell-meter to the same points node, and crank the engine over with starter. The meter should show between 40 and 50degrees of dwell.
Tachometer Function and Troubleshooting:
...more when I think of it...R
Huh?...don’t complain to me about
the name!…I didn’t christen this device (with a grammatically incorrect name
even…no apostrophe! Because I doubt they meant it in plural)…I just calls ‘em
like I sees ‘em…see Pix! …and it seems to me that if this is indeed a valid
product, it might just help the “old man” start the engine too!
Robby Ross of the European Volvoniacs Forum ran across an example of the device at an automotive fleamarket a while ago and it apparently peaked his interest...this simple and novel device from the 60’s peaked my interest too…this calls for some more investigation!
The device consists of cylindrical aluminum housing with a momentary pushbutton. Two wires exit the housing. Upon disassembly, here is what Robby found: A switch and relay! The Wifes Startomat was to be wired from the points node to ground and the push-button activated during starting attempts. A 6V rating is printed on the side of the can under the unique name. The question is: How can this possibly do anything to help starting?
Update: Robby has been kind enough to supply me with the model shown and another version of this device...watch this space for results of my evaluations!
FIGURE 3A, 3B. “Wifes Startomat”. Disassembled.
Picture credits: Robby Ross
Background: For Starting, ignition designers on both sides of the Atlantic saw the advantage realized by Load-Shedding, and American designers used an additional Ballast Resistor / Ignition Voltage Boosting strategy also (perhaps because of the big V8s which they typically needed to start).
Analysis of the Wifes Startomat Circuit: Given that the Europeans didn’t always use the Ballast Resistor / Ignition Voltage Boosting strategy which increases spark energy, designers of the "Wifes Startomat" decided to exploit another route…a Multiple Spark Strategy… as an additional aid to starting.
Wifes Startomat Circuit (from the: Neat Idea Department): The clever designers of the circuit recognized the fact that one and only one discharge of the Ignition coil primary, accompanied by a single high voltage spark occurred per opening of the points. This is a valid weakness at cranking RPMs because that one spark is only one attempt (and opportunity) to ignite the mixture. If this single attempt is unsuccessful…tough luck!...there’s no second chance on that cylinder, and the starter motor will need to continue to crank to the next cylinder’s firing point and give that cylinder a chance. It’s a one-shot, one bullet approach…
FIGURE 4. “Wifes Startomat” circuit.
Upon closer inspection of the Wifes Startomat, details are revealed. A simple relay wired to self-vibrate (similar to in a common horn), is added in parallel with the points, and optionally energized only during Starting Attempts, when the associated manual momentary pushbutton is pressed. The strategy and function is cute and almost brilliant in its simplicity: Used only during cranking (which are the slowest engine RPMs) and active while the mechanical points are open, the additional electric relay buzzes away making and breaking the primary coil circuit many times at a rapid rate. The electrical action as it would be at the points would at elevated RPMs…the ignition coil primary doesn’t know the difference and it is certainly capable of operating at that rate, so the result is a series of multiple sparks at starting revs, yet still under the timing control of the normal points…it’s an early, non-electronic, Multiple Spark, machine-gun approach…
Viewed from the standpoint of electrical timing, this is no different from the view of the Ignition Coil than what it does at high RPMs…put out many sparks at a fast rate under timing control of the distributor…what is different in this special arrangement is that it puts out those multiple sparks and they are routed to only ONE cylinder because the distributor rotor has not moved very much…it is in-fact still directing the sparks to the same cylinder! It’s so simple and effective, it’s quite ingenious…and, proving that a good idea never goes out of style, high-tech modern “Capacitive Discharge” or “Shower-of-Sparks” ignition systems use a very similar strategy to this day!
Timing: Reviewing the OE system, as shown in the following graphic, the one spark (Red) gets one chance per cylinder per (distributor) revolution. This is not very exciting…and also maybe not very effective at starting if everything is not just right… With Wife’s Startomat circuit in place, one can see the multitude of additional sparks (Green) after that, with each one that occurs being another chance to ignite the mixture, to make a power stroke.
It can also be seen in the timing graphic, that at dead-slow cranking RPMs, the primary Charging Time (Pink) is only a very small part of the beginning of the Points Closed Condition (PCC), (approximately 4mS Reference: FIGURE 1. Kettering Ignition System Primary voltage and current waveforms.), after that, the primary is fully charged, and it is essentially just waiting around for the rest of the PCC for the instant to discharge (Blue)…so it can also be seen that sufficient charging can easily occur, and repeatedly, under the much faster relay control. This is the fact that the Wife’s Startomat exploits to generate the Helper Sparks.
It should also be clear from the timing relationship shown, that since the Helper Circuit is only activated during the Points Open Condition (POC) and because of the 1 to 2 rotational relationship of the Distributor to the Crankshaft, that the Helper Sparks are limited to the first half of each cylinder’s Power stroke. This is actually good also because an (unignited) mixture would be being decompressed after that point anyway (actually any time after TDC), and therefore even less likely to be ignitable…and we wouldn’t even want it to be ignited too late, and still be burning when the exhaust valve was opening for the exhaust stroke.
FIGURE 5. Distributor and Crankshaft Timing Diagram, showing relative timing of Distributor and Crankshaft as well as Ignition Coil charging timing with single OE single Ignition Spark and with Helper Sparks. (40 degree dwell angle is shown.)
This is a conceptual graphic showing relative action and timing only…don’t hold me to the number of green sparks…!
Circuit Critical Review…Considering Downsides: The astute reader might have questions about the function of this device or reservations about connecting a foreign device to his Ignition System, so it must first be carefully considered. The reader may also observe that only the first spark would be normally and correctly timed and that the subsequent sparks would all be somewhat late…this is absolutely true (see Figure 5. Distributor and Crankshaft Timing Diagram)…but ignition by one of the many “late sparks” is still possible, and also just as effective, and this is certainly better than no ignition by the single spark of the original system.
Also, it should be apparent, with the circuit as shown, that the additional sparks are occurring during the entire Points Open Condition (POC), and that the rotor will also continue to turn…this means that the possibility of High Voltage being routed to the wrong cylinder or “Cross-Firing” to the next cylinder (which will be on the Compression Stroke at that time, meaning there may be an ignitable mixture present) must be considered. It would not be good if the rotor was so far along that it directed the spark to that next cylinder…I don’t believe the rotor will have moved enough to allow this to happen and also the mixture in the next cylinder will not be compressed sufficiently to be ignitable…but I need to study this completely...including all possible effects of the mechanical/vacuum advance systems.
More Tests are Required: I will study this possibility of cross-firing to the next cylinder some more, and run some tests to assure myself that no significant possibility of cross-firing exists…worse-comes-to-worse, a (time or number of cycles) limiting circuit might need to be added, which cuts of the circuit action after only several cycles and doesn’t allow it to free-run for the entire POC.
Incorporating the "Wife’s Startomat" Circuit into a Vintage Volvo: If you have a Volvo vehicle which is tough to start, I first recommend you perform a full tune-up and make sure everything of the Ignition and Starting Systems is right and adjusted well. Generally, that will rectify a hard starting condition…but if you have done this, and have fresh fuel in the tank, and have your Choke adjusted to work well, but are still having starting difficulties in the dead of winter, and are at your wit’s end, this might just be the ticket…I’m dying to try out the “Wifes Startomat”…!
Conclusions: …watch this space for a report on the results!
Related Links: Volvoniacs Forum Thread (…being able to read German will help!): http://volvoniacs.oldtimer-info.de/showmessages.afp?xid=943093 "http://volvoniacs.oldtimer-info.de/showmessages.afp?xid=943093"
Discussion of Ballast Resistor in the Standard Ignition Primary Circuit:
This subject comes up repeatedly, particularly when someone is considering replacing their Ignition Switch/Armored Cable/ Ignition Coil Assembly with separate, “better” components… Installing a new Ignition Coil typically requires the installation of a separate “Ballast Resistor”. This discussion is intended to help the reader understand what a “Ballast Resistor” is anyway…what it does, and why the vintage Volvo Ignition System doesn’t even have, or need one…
Function of the Ballast Resistor in an Ignition System: The Ballast Resistor is a carefully designed resistance in series with the Ignition Coil primary circuit. Its electrical function is to drop a part of the voltage supplying the Ignition Coil primary precisely in the same manner a carefully designed Dropping Resistor (used when performing a 6-12V changeover on a vehicle) drops some (specifically, half) of the 12V power, leaving the other half to be supplied to the original 6V rated components.
In the Ignition System, the Ballast Resistor does this in order to allow the coil to work at a reduced operating point, which produces less heat than if it were to be supplied by the full 12V. The astute reader might ask: If they wanted to “allow the Ignition Coil to work at a reduced operating point which produces less heat”, couldn’t they just have designed the coil with a higher impedance in the first place? Answer: They certainly could have, but this does not take into account the other very important condition which the Coil and Ignition System must satisfy under: Starting!
Since Starting is a pretty important phase in the operation of an engine, and its success is quite important, it gets some special treatment in order to help assure its success. Two tricks are used. One is Battery Load-shedding. Fact is that before the engine is started, ALL electrical power comes from one place: The Battery. Another reality is that batteries are not always brand new, nor are they always fully charged, nor are they always at their best operating temperature…all factors which reduce their output (and the chance for starting success)…so any reasonable thing that can be done to improve the chance of starting is not such a bad idea…
Load-shedding is as simple as removing all non-essential loads from the Battery during starting attempts. One certainly doesn’t need the Wipers, Blower, Brake Lights, Horns, AMP, OIL Indicators, Blinkers or Brake Lights to be taking Battery power during a staring attempt (…notice that Headlights are conspicuously absent from this list because they are typically not routed through Ignition Switch, and therefore not under its control…but it would certainly be a good idea to have those OFF while starting as well!).
In many vehicular systems
including the Volvo system, load-shedding is mechanically implemented in
the Ignition Switch (refer to: FIGURE 6.), the reader should notice that power
is disconnected from ignition power terminal 54, in the momentary Start Position
4. In this manner, all non-essential loads are disconnected from power, such
that the battery is in its least loaded state and therefore able to
supply the absolute maximum voltage and power for the starting attempt.
Load-shedding, additional: Load-shedding is considered to be such a good idea, that it is still employed in modern vehicles…even Headlight control has been added, because this is such a major load…try it!...see what happens when you try to start a modern vehicle with a bunch of non-essential loads powered…
Load-shedding is also the reason power OR’ing (not to be confused with an O’Ring made of rubber!) is required when installing an electronic Ignition module in a vintage Volvo. Refer to: FIGURE 6. It is not enough to simply power the ignition module from the Ignition Power Terminal 54…this terminal doesn’t have power during cranking because of load-shedding!!
…but load-shedding is not the only trick…another simple trick is used to help starting: Ignition Voltage Boosting.
Ignition Voltage Boosting is a matter of “turning up the volume” ( er... voltage) so to speak, at which the Ignition System is operated during Starting attempts. This results in a higher energy, hotter spark which will hopefully increase the chance of the desired result.
Implementation of the Ignition Voltage Boosting is where the Ballast Resistor comes in. During Starting, “they burn the candle twice as bright, for half as long”…by taking this voltage dropping element out of the circuit during starting attempts (Position 4), the primary gets a voltage boost. After the (hopefully successful) attempt, the Ballast Resistor is placed back in series with the Ignition Primary circuit, as the Ignition Switch is returned (by a spring) to the Ignition ON position (3), supplying a lower voltage and once again operating the coil at a reduced voltage level during its continuous (albeit pulsed) operation while the engine is running…(the candle is back to its normal intensity).
FIGURE 6. Standard (non-Volvo) Ignition System with Ballast Resistor, Start Position of Ignition Switch makes a connection to bypass Ballast Resistor and apply full power directly to Ignition Coil Primary to provide temporary Ignition Voltage Boosting. Electronic Ignition Module is powered in Positions 3 and 4 by diode OR’ing.
Designers of the Vintage Volvo Ignition System (Robert Bosch) designed the Primary Coil Impedance (the complex parameter which limits the coil current and ultimately how much energy it stores), not to require a Ballast Resistor / Ignition Voltage Boosting system. The system works fine with a full 12V applied for the entire time while engine is running...but the coil does require the continuous pulsing of a running engine to stay within safe operating temperatures. The reader may (or should) be aware that if the Ignition of our vintage Volvos is ever left ON for an extended time without the engine running (during which time Ignition Coil current would be continuously being pulsed by the Make/Break action of the Points), the Ignition Coil will get quite toasty.
Overheated Ignition Coil: If the points happen to be closed, allowing a continuous primary current flow, when the Ignition is ON but engine is not running, the coil may even be damaged from overheating if left in this condition for a long time. Therefore, leave Key in the Ignition ON position (3) with engine not running for limited time only during troubleshooting or special situations…a few minutes maximum is good general rule…when in doubt, check temperature of Ignition Coil: Warm to the touch is OK...if Hot, it could use a rest! If it is necessary to have Ignition Power ON for a prolonged time for any reason without engine running, one could simply assure no primary current was flowing by disconnecting the points wire (or assuring open points by turning engine manually while watching points contacts or even by simply placing an insulator between the contacts). …it’s simple when you understand what is happening!
Review of Starting with respect to Ignition and Electrical Systems:
Starting: (Charging System is Off-Line, Battery is supplying ALL power):
1. Load-shed all unnecessary Ignition powered Loads during starting attempts, to give maximum voltage for Starting Attempt.
2. Power Ignition System and operate Primary Circuit at boosted voltage to give maximum spark voltages for Starting Attempt (essentially shorting across Ballast Resistor. This is not applicable to vintage Volvos).3. Energize Solenoid to initiate Starter Motor cranking.
FIGURE 7 shows how these functions are performed within the Ignition Switch in the Volvo application.
FIGURE 7. Ignition Switch Internals. Detail of the Volvo Ignition Switch,
including internal connections in the various key positions. Switch position are labeled as they are
for consistency with Ignition Switch information of owners manual.
Consideration of SwEm Start Pushbutton: Whereas the Position 4 of the Ignition Switch supplies power to Terminal 50 in the original unmodified factory system to energize the Solenoid and Starter, this position is also known for it’s heavy (Gorilla) return spring, which after it pushes the poor key back X-thousands of times, eventually (and always) fatigues and breaks the poor key (“…those darned Volvos just don’t last…!”). See also: http://www.sw-em.com/ignition_switch_key_breakage_tech_article.htm
With the SwEm Pushbutton Upgrade, switch Position 4 is no longer used, so broken keys are pretty much a thing of the past. The pushbutton removes the momentary switching function to an external switch, so the reader should see that once the key is no longer turned to Position 4 where the Switch performs the load-shedding. Load-shedding must now be performed manually by the driver.
Also, if an electronic Ignition Module is to be fitted, normally, in order to assure power in both key positions 3 and 4, the diode OR’ring function must be included as shown in FIGURE 8. If however an electronic Ignition Module is fitted and the vehicle has a SwEm Start Pushbutton, an OR’ring cable is not necessary because the Ignition Switch will never be turned to the Load-shedding Position 4. See also: http://www.sw-em.com/123Ignition_in_a_Volvo_with_Armored_Cable.htm
FIGURE 8. Vintage Volvo Ignition Switch with Diode OR’ing connections.
Note: In the interest of "doing the most with the least", this can also be functionally accomplished with just a single diode. See: http://www.sw-em.com/Volvo%20Ignition%20from%20Scratch.htm#Modifications
External material attributed. Otherwise, these articles are Copyright © 2010-17 Ronald Kwas. The terms Volvo and Bosch are used for reference only. I have no affiliation with either company other than to try to keep the vintage products of both working for me, and to help and encourage other enthusiasts do the same. The information presented here comes from factory or my own wiring diagrams and is strictly my own experience and opinion, and can be used or not, or ridiculed and laughed at, at the readers discretion. As with any recipe, your results may vary, and you are, and will always be, in charge of your own knuckles!
You are welcome to use the information here in good health, and for your own non-commercial purposes, but if you reprint or otherwise republish this article, you must give credit to the author or link back to the SwEm site as the source. If you don’t, you’re just a lazy, scum sucking plagiarist, and the Boston Globe wants you! As always, if you can supply corrections, or additional objective information or experience, I will always consider it, and consider working it into future revisions of these article...along with likely the odd metaphor and maybe wise-a** comment, as they come to me...