Volvo Ignition from Scratch
12/01 R. Kwas, Revisions On-Going
Static Timing a B18/20
Detailed Centrifugal Advance Servicing.
Vintage Volvo Ignition system and the Armored Cable.
Troubleshooting the Vintage Volvo IGNition System.
Understanding the Failure of a Diode ORing Cable used with Electronic Ignition Module
Troubleshooting the Vintage Volvo IGNition System
Waveforms of the Kettering IGNition System
Quick Ignition Troubleshooting Info
Ignition Additional (separate page)
So you've been lucky enough to get a great deal on that vintage Volvo...the way you tell it that is, (not your wife or even maybe your friends)...because there's just a slight problem...the Ignition System is kind of apart...more like an Ignition System do-it-yourself-kit really. This page, in addition to just about any of the available shop manuals, should help you get that Ignition System back together and working, and allow you to keep some, if not all of your hair!
Reassembling a B18/20 Ignition System in Disassembled or Unknown Condition including Static Timing:
For reference: Firing order for B18/20 motors is 1-3-4-2, cylinder closest to radiator is NO.1, a quality beer smells and tastes good even at room temperature and, distributor rotation is counter-clockwise (CCW).
Note: The procedures following have been prepared with the utmost care, are however strictly guides, to be used in conjunction with normal cautious shop practice. I cannot be responsible for your actions. Work safely!
Checking Distributor Installation and Setting Motor to Ignition Point:
1. With ignition OFF and no gear selected. Use a wrench at crankshaft nut holding pulley on front of motor, to turn motor, in normal running direction, to desired timing (16 degrees BTC is a good start), as seen by looking at timing marks on crankpulley and timing cover pointer on front of motor. BOTH valves for NO.1 cylinder should be up and closed (visible by looking into removed oil filler cap hole). If valves are not up and closed, rotate engine one more rotation in normal running direction, to timing marks, when this condition is achieved (reminder, this is a 4 stroke - Otto cycle motor, where TDC of cylinder No. 1 occurs once for every TWO times the timing marks come around on the pulley). Leave engine at this ignition point for rest of this procedure.
Note: If distributor is not installed, continue with Step No. 2., if distributor is installed proceed to Step 3.
2. Verify angle of drive slot position in distributor drive pinion as approximately 300 degrees when looking from distributor side of engine (see Pic 1). If repositioning is necessary, lift pinion to remove, turn appropriately, and reinstall pinion to achieve correct position (it will be necessary to turn motor to engage drive pinion with cam, so Step No.1 must be repeated). Install distributor, which has been checked over and has had points gap set at .016" (turn rotor to turn shaft until engaging pinion drive slot), then lock distributor holding collar to engine block.
3. Remove distributor cap. Determine to which plug wire the distributor rotor points when cap is in place. Starting with this wire, verify and/or correct wiring of firing order as 1-3-4-2.
Pic 1. Distributor drive pinion at ignition point
around 16 degrees BTDC (No. 1).
4. Assemble rest of the distributor and ignition system and proceed to Static Timing.
Static Timing a B18/20:
This procedure is to be performed AFTER: engine has been set to ignition point, distributor drive pinion and distributor have been correctly installed, cylinder No. 1 ignition wire has been determined, all ignition wires have been installed in the correct firing order, setting the points gap to .016", checking for free Centrifugal Advance, smooth return, and lubing CA mechanism with a few drops of engine oil (felt pad located in shaft center under distributor rotor).
1. With all ignition components in place and assembled, set motor to ignition point (see preceding procedure), remove plug wire from Cylinder No1. spark plug, and lay onto valve cover with a gap to cover so that a spark will be visible when it occurs.
2. Turn ignition ON with key.
3. Loosen timing adjustment locking nut on distributor collar.
4. Turn distributor housing CCW about 45 degrees to assure points are closed, and it is therefore positioned BEFORE ignition point (point at which lobe on distributor shaft opens ignition points and causes high voltage spark). Note: This procedure can still be used, even if ignition has been upgraded with electronics which eliminate the points, and replaces them with a Hall-effect, or an Optical sensor.
5. With ignition rotor, cap, wires in place, slowly turn housing CW (simulating a normal CCW distributor shaft rotation) until spark occurs at test gap. Repeat steps 4 and 5 as many times as is required to get a feeling for when the spark occurs, and to be able to IMMEDIATELY STOP turning the housing after the spark does occur.
6. Turn ignition power OFF with key, lock timing adjustment by snugging timing adjustment locking nut on distributor collar, restore No. 1 plug wire to No. 1 cylinder, assure ALL IS SAFE and engine is clear to run.
7. Ignition system is now timed and presuming all else is in order (fuel), engine can be started and run. After applying choke, handbrake, placing gearbox in neutral, engine may be started using ignition key and (preferred) Start push button (or better yet, Service Switch under hood!).
8. It may be necessary to reset the idle after timing. This should be done after choke has been disengaged, engine has come to normal operating temperature as indicated by thermostat opening (as can be seen on temperature gauge).
Note: I have used this this Static Timing method for years, and found it to be absolutely fine, and perfectly adequate for the B18/20 engines...after timing in this manner and checking with a timing light (NOT mine - I don't own one!...what for?), I have found that my adjustments, performed according to these procedures, have put the timing within one degree of the 16 degrees specified...can't argue with that!...plus, since minimal tools are required, this procedure can be performed - if necessary - on the side of the road, although the garage or driveway, with a well stocked fridge not too far away is clearly preferred! Cheers!
Automatic Adjustment of the Spark Timing
General: In addition to the fixed distributor timing adjustment, the precise timing of the spark during engine running is further influenced by the Centrifugal Advance, a mechanical system controlled by rotational speed (RPM) of the distributor itself, and also a Vacuum Advance/Retard (if installed, year and model dependent). Both of these systems function by further varying position of the top of distributor (where lobeshaft control the points), from the bottom of the distributor (mainshaft is driven by the camshaft). In the case of the vacuum system, it is possible to generally verify its operation by disconnecting vacuum tube at distributor, connecting a test vacuum tube, providing some test suction, while watching for movement at movable points plate (any leaking-down or outright failure to operate is a sign of a jammed points plate or damaged diaphragm). Here's a cute little animated graphic which I couldn't help stealing from a very informative automotive site: [http://www.kfz-tech.de]
Vacuum dependent timing adjustment in action.
It can be seen that the Vacuum diaphragm action changes position of the plate on which Points are mounted CCW, and away from the lobes.
Given shaft rotation is also CCW, this would make it an animation of a Vacuum Retard configuration.
Vacuum Advance Configuration. Note position change of Vacuum mechanism, and that it now rotates Points toward the lobes.
Vacuum Retard vs. Vacuum Advance? PLACEHOLDER for comparo...bottom line is Retard is performance killing and for weenies, but I will try to locate and add a link Phil Singher's excellent explanation which doesn't need anything from me to be added!
Centrifugal Advance In the case of the centrifugal system, it is a bit more subtle...centrifugal weights below the points plate, their rpm dependent force working against springs vary the relative position of the stacked concentric shafts of the distributor. Clearly, it is not possible to accurately check this action when motor is not running, but by turning an installed rotor, CW about 20 degrees, one can get a pretty good general idea of the state of the CA mechanism. A smooth action against the springs should be felt, returning to the non-advanced position when released (any step or binding, or non-smooth action is a sign of problems which can cause erratic engine surging while driving). I have seen wear of the centrifugal weight assembly (on a number of different distributors), which resulted in the centrifugal weights not moving smoothly, but this will take another specific section to cover. See: Detailed CA Servicing. The springs are arranged for a rising rate action, that is, initially one light spring acts against the turning force, and approaching the end of the travel, another stronger spring. In this manner, the springs set the shape of the advance curve.
Theoretical Advance Curve
Detailed CA Servicing.
The info presented here is in addition to distributor tune-up information found in just about any decent shop manual. The intent here is not to copy what they already cover (and every vintage Volvo owner should have at least one as a reference...preferably slightly soiled by oily hands... to show use, but also that a certain amount of respect was showed to the book!), but to augment their basic coverage with more detailed handling of what can occur due to high mileage, or what I call "excessive maintenance", etc.
Indication that there may be a problem with the CA mechanism. Poor Starting. High idle when it was previously fine (but otherwise decent running) is possibly a sign that the CA mechanism may be bound up, and not returning to the non-advanced position. Surging of engine can also result if advance occurs not smoothly but in steps...
Checking the CA mechanism is simple! Remove Dist cap, rotor should be against the CW stop and not be able to be turned further in that direction. If it is possible to turn it CW, it means it's time for a CA mech inspection. On the other hand, it should be possible to turn the rotor in a CCW direction for about 20 degrees, against an increasing return spring force. The movement should be smooth and return fully to the unadvanced position. If distributor is not installed on engine, distributor mainshaft must be held in place before the same checks cam be performed.
Bosch xxx078 distributor with Vacuum Retard. The plate on which the once-piece points assembly mounts is also movable by vacuum, in this manner, vacuum also adjusts the timing. This distributor has the vacuum diaphragm pulling the plate CCW, therefore it is arranged for vacuum retard. Some models were set up as vacuum advance distributors. CA mechanism is under the points plate.
View of the CA mechanism of an xxx003 distributor, once points plate has been removed. Note the differing springs, and that one end of the heavier spring has an extended end-loop, which allows the loop to slide, and not contribute any return force until the higher revs are reached. To check action, use a small screwdriver placed in the depressions of the weights. They should freely move through their arc against the force of the return springs.
Disassembly of dist Carefully remove CA springs. Remove circlip. See following:
After "C" clips retaining CA weights are removed, weights, fibre washers, and height bearing (three arrows) may be removed for inspection and cleaning.
CA weights can jam up when supporting fibre washers are damaged or worn below minimum thickness, it is important also to remove, inspect, and clean the (center) plastic (height) bearing.
Off-center wear is evident on centrifugal weight. This can occur with worn fibre washer, height bearing, or bent contact cam on lobeshaft.
Polishing the lobeshaft to perfection! A polished lobeshaft and just a bit of lube on reassembly makes for a happy, long-lived, points-rubbing-block! Visible are washer and circlip used for securing lobeshaft.
Polishing the mainshaft to an equal perfection! Note discoloration on shaft, probably caused by inadequate or overheated, and oxidized lubricant. A polished, well lubed mainshaft makes for a smooth, repeatable CA curve. The fibre washers seen here look to be in very good shape.
Distributor Lubrication: After careful disassembly, inspection and cleaning, reassemble with a film of engine oil...I now use synthetic motor oil for its consistent viscosity over a wide temperature range, and to possibly prevent gumming due to cooking which may have contributed to the jamming of the Snow Weasels CA mechanism. See: A Tune-up out of Guilt, Update II
Reassembly is, as they say, "the reverse of disassembly".
Don't forget a couple of drops into the recess on the top lobeshaft, and to soak and replace the felt, and to fill the little (turn cover) oil reservoir at the outside beltline of the distributor with (normal) engine oil (this lubes the mainshaft in the housing, eventually draining into the sump, and it's not right to mix wine and beer)...better yet, since it wasn't included in many manuals, here is the official exploded distributor lubrication diagram, showing how important, and extensive the recommended distributor lubrication really is. 4,5 and 8 are the really important ones!
Source: intereurope Workshop Manual 162 ISBN 0-85666-066-3
From a Forum posting of mine ( http://www.volvoforums.org.uk/showthread.php?p=2051541#post2051541 ) :
A quick check on Centrifugal Advance is
something that can, and should be performed whenever Dist Cap is off (as well as
adding a drop or two of oil to felt "reservoir" at top of Lobeshaft under
Rotor...remember, the Distributor is strictly a mechanical system, no computer
in sight(!), and mechanical systems need to be lubed. See here for all the other
places on Distributor which should be lubed:
By simply turning Rotor in the Counter(Anti)-Clockwise direction, a smooth, increasing spring counter-force should be felt, and rotor should return smoothly when it is released. If there is any non-smoothness, or high resistance to turning, or non-returning to starting angle is noted, CA has an issue which needs to be resolved.
Proper CA action is quite important to a good running engine! Ignition Timing which doesn't advance smoothly can cause engine surging like a bucking bronco, and timing locked at one place, and which does not advance at all with RPMs, results in an engine which feels like it's being held back (because it is!) with all the performance of a road-slug. Lube your CA!
The Bosch xxx003 distributor...reassembled with a new tune-up kit, gapped to .016", checked with an Ohmmeter and ready for installation in the Snow Weasel, static timing, and another 50k miles of trouble free service!...nah, I promise to do more regular tune-ups and maintenance! Rotational (Timing) Clamping Nut highlighted in Blue.
Vintage Volvo Ignition system and the Armored Cable
The vintage Volvo IGNition system is a classic, simple, points and coil design. It does feature two notable differences which set it apart from ignition system found on American Vehicles of the era, which a mechanic may be familiar with.
1. No Ballast Resistor. In IGN systems which employ a ballast resistor, the trick of running the coil at part voltage under normal operating condition (with the ballast resistor dropping part of the voltage), while applying full battery voltage during cranking, is employed (by shorting across the resistor with the IGN switch while in the Start Position). This improves the chances of starting by working the coil harder and increasing the spark voltage during starting, while letting the coil work at a less stressful and cooler operating point normally...but apparently designers at Bosch figured this was unnecessary, figuring out a way to reliably start and also eliminate this component and the complexity that switching it into and out of the circuit brings.
2. The Armored Cable and Internal-only Coil + Terminal. It is also not possible to “Hot-Wire” a vintage Volvo! [“Hot Wiring” is defined as bypassing the IGN Switch, and applying battery power with a “Hot Wire”, to the positive terminal of IGN coil]. In Vintage Volvos, there is simply no access to this node (see diagram), so there is just no way to get the IGN system to function. Only the IGN Switch can apply power, and it requires the key to turn. The connection between IGN Switch and coil is further protected by the Armored Cable of fame and lore. This is a pretty effective anti-theft measure...and we vintage Volvo owners like it that way!
On Left, a standard sixties Kettering IGNition System with Ballast Resistor,
and on Right, Volvo’s (Bosch) version without Ballast Resistor, but with the “Armored Cable”, and inaccessible + node.
Also, noted in GREEN, the fact that Ign Pwr can be checked at Points node when Points are open,
since it cannot be checked at Coil + terminal (there is no terminal!).
Further details of the internal switching of the IGN Switch can be seen in the diagram.
Position 1. “Radio” or Accessory Position: ONLY the IGN power terminal (54) is powered.
Position 2. “Neutral” or Off Position: No terminals are powered. (This is the only position the key can be removed in.)
Position 3. “Driving” or Ignition On Position: In addition to the IGN power terminal being energized, power is also applied to the coil positive node (not otherwise accessible, see text).
Positon 4. “Starting” or Momentary Start Position: Power is removed from IGN power terminal (to shed additional loads and eliminate the resulting voltage drop during starting attempts), and power is applied to the Starting terminal (50)...power continues to be applied to the coil positive (see IGN Switch internal diagram). This is a momentary position against the force of a Gorilla Return Spring (see below). Turning the key against this spring repeatedly is what causes metal fatigue in keys and results in them breaking...this why you can also call this IGN Switch position the “Torsional Key Test Position”, and why you should NEVER have just one key, and might seriously also want to consider installing a Sw-Em Start Switch Upgrade!
Here, in detail, is
everything one always wanted to know about the workings inside of the Ignition
See also: Ignition Switch Key Breakage Tech Article
Modifications: The internal connections and workings of the vintage Volvo IGN switch must be carefully considered when making modifications like the Sw-Em Start Switch Upgrade (and rest assured, the author has!), or upgrading to an electronic IGN module to eliminate the mechanical points....because of the disconnection of power to the IGN power terminal (54) during cranking (see inner workings of switch), it is not enough to simply power an electronic IGN module from this terminal...it doesn’t get power during cranking!...so wouldn't work so good! A Power ORing Cable consisting of two (or one) diode(s) connected in a power ORing circuit (power is routed from one OR the other source) must be used.
Power ORing Cable (Two Diodes)
"OR"ing power connection. OC = Other Connection(s).
Power ORing Diode cable (Single Diode) for powering electronic Ignition Modules, (as offered by IPD for instance).
This is a Single Diode version of the two Diode ORing cable shown above, and serves the same purpose: To supply an uninterrupted power to an Ignition Module. It can work in a single Diode version because this takes into account the fact that no power is present on Term 54 during cranking (with key)...it is disconnected anyway, so diode is really not necessary on terminal 54 while Key is in Pos 4.
Power ORing Cable employing a single Diode.
Understanding the Failure of a Diode ORing Cable used with Electronic Ignition Module: Recently a question came up on a 122 equipped with an electronic Ignition Module, plus a (single) Diode Cable, but still with the original Lock Cylinder and Key doing all the work (no Sw-Em Start Pushbutton - this is significant!). It seems that owner was having difficulty Starting in Key Pos 4 (actually, he reported it would NEVER Start in this Key Position, when formerly, it did!), but the interesting symptom that sometimes it would Start just as he released the Key to Pos 3. In reviewing these symptoms, it is actually possible for author to logically explain this action by the fact that the diode has opened (so no power is available from Terminal 50, while cranking, but becomes available from Terminal 54 the moment Key is released, enabling Electronic Ignition Module, which produces Sparks, and allows Engine to fire...if you're lucky!
Summarizing symptoms if Diode fails. Engine NEVER Starts while cranking with key (because Ignition Module is unpowered since Diode path is open), but seems to fire up and maybe even Start when Key is released from Pos 4 to Pos 3 (module then gets powered, so Ignition Sparks now occur while engine is spinning down from inertia)...if State of Tune, and State of Battery Charge is good (fast cranking), a Start may occur (Owner is Lucky!).
Reason why diode opened in the first place can only be conjectured...it might have been due to any number of reasons, including a Load-Dump Surge (Link: Supporting information: Load Dump Surge ), but most likely, the diode taking a lethal shot from the Reverse Voltage Spike from Starter Solenoid...this is a big inductive Load which will generate a major reverse Spike (shown in Ignition System voltage graph, in Red below) when Ign Switch is released from Pos 4 and contact opens, very much like Ignition Coil Primary, that the Blocking Diode must be sized with a generous Peak Inverse Voltage (PIV) rating to survive this significant Spike!
I am still awaiting failed diode information, so that I can see what the PIV rating is for the component, but request anyone with a Failed Cable exhibiting these symptoms to contact the author...I would like to do a post-mortem on one! [See Update below.]
Below a bit more info on this Spike, and a Concept to add a Clamping Diode (same component, different electrical location and function, shown in Green) to suppress this Spike.
Explanation of how ORing Diode is damaged, and a concept for adding a Clamping or Flyback Diode (or about a half dozen other names), preventing this.
See also: https://en.wikipedia.org/wiki/Flyback_diode
Bottom line again is to install the Key saving Sw-Em Pushbutton Start Switch (highly recommended anyway!)...then all tricks and complicated provisions necessary for providing uninterrupted power to the Ignition Module become moot, simply fall away and become unnecessary! Easy! See also Tech Article: 123Ignition in a Volvo with Armored Cable.htm
[Update: Diode was found to be a 1N4006, with a PIV rating of 800V, and it was confirmed failed OPEN. Without measuring the actual reverse Spike, to see what the diode is subjected to, I expect this is an adequate PIV rating which I doubt was exceeded by the Spike, so the diode failure was a random occurrence.
Open 1N4006 from power ORing cable.
After removal of the failed diode and associated wiring, and installation of the (clearly super-groovy) Sw-Em Pushbutton Start Switch, all is once again well, with the side-benefit that the key is now not subjected to high torques!]
Troubleshooting the Vintage Volvo IGNition System:
The manner in which the high voltage is generated in a Kettering (conventional) spark IGN system takes advantage of some special rules of electronics and inductors. What is important to remember is that the spark occurs due to the magnetic discharge (of coil primary) occurring at the moment of points opening, but that doesn'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 in the first place!. Both points closed and opening are critical…if either doesn't happen, no spark will result…period!
The IGN switch / Armored cable/ IGN Coil Assembly of fame and lore is a wonderful thing...it makes stealing so equipped vehicles difficult (Good!), because the Coil primary (+) connection just isn't available for "hot wiring" by a thief (see Graphic above)...it also makes troubleshooting IGN system failures by the rightful owner or his duly appointed agent, by measuring voltage on that point a bit more difficult for the same reason…but this should not be a problem for the owner who has the IGN key and understands what is happening, and that is what these notes are intended to help with!
Understanding and Troubleshooting the IGN System:
I am now leary of applying a voltmeter to parts of the IGN system because of the high voltages present...I have personally destroyed an expensive Fluke DVM with a bolt of lightning in this manner during power up tests...and not of the secondary circuit...and this is to say nothing of less expensive meters which are likely to have even less protection and tolerance for surge insults built-in! The spike which occurs at points opening apparently had enough voltage and energy to kill the meter in a millisecond. To spare others the agony, I therefore instead recommend the use of a test light (essentially a low power 12V light bulb with a couple of leads on it.. connected across to points in question, it will light to indicate voltage is present). A DVM can certainly be used without fear during a IGN OFF, unpowered condition, for continuity or resistance checks. Besides, initial checks without a meter can often be informative enough to narrow in on the root cause before one even needs to break out the measuring equipment.
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 as I have experienced)...
1. Shorted Points. The connection to chassis may not be opening to break primary current...sure, the points themselves may be physically opening, but the connection to chassis must also electrically opening! If the distributor through-bolt and its stack of hardware has become uncentered, or the (by now, ancient) piece of insulating paper between points-spring and dist housing has become dislodged or deteriorated and is not insulating that critical connection from touching the chassis, the electrical connection to chassis is not opening and your IGN system is dead in the water! [With this condition, a test light across point node and chassis will NOT light when points are physically open, to indicate voltage across points, because they are NOT ELECTRICALLY OPEN...remember, no voltage can occur across closed/shorted points! Correct and expected action is that when points are open (IGN ON of course), voltage is present across points and test lamp lights]
2. High Voltage Leakage: If no spark is seen at the spark plugs, it doesn’t by a long shot mean that the high voltage is not being generated...it's just that high voltage has a definite preference for jumping to the nearest and easiest chassis point available to it...and under normal conditions and as designed this is at the spark plugs, but if under abnormal conditions, this happens to be elsewhere from the spark plugs, you can be quite certain that it will jump there, and the High Voltage will never make it to the plugs. That is why it's always advisable to check for the High Voltage at the coil output wire first (by doing this, you separate the High Voltage generation part of the system, from the distribution part of the system for troubleshooting…divide and conquer is often an effective way of locating electrical problems!). Proceed by disconnecting the middle (Input) High Voltage wire from Dist cap and laying it on a convenient chassis location like the valve cover, with a slight spark-gap at which the output spark can be observed. Have an assistant turn ON the IGNition and then activate the starter to turn over the engine (or do it yourself by turning ON IGN with key and activating Starter with a Remote Starter or even more convenient, by activating your engine-compartment SwEm Service Switch). Having checked that the Points and Coil are making the high voltage, one can now move on to the distribution process for which this assembly is named...divide and conquer IGN problems!
3. Distribution Problem: Once it has been determined that High Voltage is being indeed generated, the routing or “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 contacts of the circle of contacts of wires running off to individual sparkplugs. 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 (well known!), it also must jump the small gap between Rotor and fixed contact for the wire running off to each cylinder's sparkplug (not so well known!)...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, especially conductive dirt (carbon dust!), is the enemy of a properly working High Voltage system!
X. The very last thing (on my personal list), would be a failure of the IGN switch or coil...while not impossible, I just wonder how many IGN switch / armored cable/ IGN coil assemblies have been 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! [No-one has taken me up on challenge yet!]
See also: Quick Ignition Troubleshooting Info
Waveforms of the Kettering IGNition System (See: Who is Kettering?) :
I have found some representative Waveforms on Picotech's site!
Review: When points are closed during operation, IGN coil current flows in the primary winding, building up current (relatively slowly due to primary inductance), thereby storing electrical charge magnetically (see: Primary IGNition Current). When (and exactly when!) points open, this current path is broken, the resulting reverse inductive spike, caused by the very rapid discharge of the primary circuit inductance, in addition to a voltage step-up transformation to the secondary winding, results in a very high voltage spark being generated at the secondary winding (see: Primary IGNnition System Primary and Secondary Voltage and Waveforms.). Both conditions are absolutely necessary for correct function of the IGN system. Points must cycle in order for the IGN 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.
Primary IGNition Current. Kettering Ignition System Primary voltage and current waveforms.
Timing: X= Points close, Voltage across points drops to zero, secondary current begins rising.
O= Points open, voltage across points spikes up, secondary current drops to zero.
Graphic Source: Shown
Primary IGNition System Primary and Secondary Voltage and Waveforms.
Timing: O= Points open, voltage across points spikes up, secondary voltage spikes way up!
Graphic Source: Shown (marked-up)
In updated IGN systems which are triggered by magnetic or optical sensors, a non-contact sensor provides the timing function, and a solid state electronic switch provides the high current controlling function of points, but the circuit action is essentially the same. Note that in the original system and the electronically upgraded systems, the spark only occurs once...and ignition of the mixture therefore only has one chance to ignite...wouldn't it be nice to give it another or multiple chances... In a further advancement of IGN systems, Multiple Spark or Capacitive Discharge Systems (MSD/MCD) give multiple opportunities for ignition to occur...less misfires...more power result.
Multiple Sparks during starting attempts is also the basis of the “Wifes Startomat”
PLACEHOLDER FOR MULTIPLE DISCHARGE SYSTEM STUFF
Quick Ignition Troubleshooting Info
From thread: http://www.volvoforums.org.uk/showthread.php?p=2203057#post2203057
My response and troubleshooting info to a non-functional Ignition Sys:
Note: My following comments apply to an
unmodified Points based Ignition System for vintage Volvos fitted with the Ign
Sw/Armored Cable/Ign Coil Assembly.
Ignition Coil is supplied by Ignition Switch, and since this node is internal to the Assy (only!, and not externally accessible!), presence of Ignition Coil power cannot be checked directly...it can however be verified indirectly (statically) with a voltmeter, by checking the Points to Ign Coil node for 12V, while Ignition Switch is ON, and Points are open (remove Distributor Cap to allow visual check of Points condition!).
Alternately, and next, a more comprehensive functional check of Ignition Coil can be performed (also with Points open), by turning Ign Sw ON, then shorting and unshorting across Points repetitively (with for instance a screwdriver), while watching for a Hi-V spark from Ign Coil (output wire from center terminal of Ign Coil removed from Dist Cap and placed near Chassis to make a spark-gap).
If Hi-V occurs every time connection is unshorted, Ign Coil function is fine...Ignition System should be reassembled normally, except, one Sparkplug Wire disconnected at Sparkplug and again, placed near Chassis with a spark-gap, Sparks should be evident, with Ign Sw ON, and Starter activated. Ignition Function thusly (dynamically) checked, Ign Sys can be fully restored to normal configuration, and Starting attempts can be made.
Who is Kettering? Answer: Apparently a pretty sharp fellow from 1910! See: https://en.wikipedia.org/wiki/Delco_ignition_system
External material sources are attributed. Otherwise, this article is Copyright © 2001-2016. Ronald Kwas. The terms Volvo, Bosch, and IPD are used for reference only. I have no affiliation with any of these companies other than to try to keep their products working for me, help other enthusiasts do the same, and also present my highly opinionated results of the use of their products here. The information presented comes from my own experience and carefully considered opinion, and can be used (or not!), or ridiculed and laughed at (or worshipped!), 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 and future!
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 the next revision of this article...along with likely the odd metaphor and probably wise-a** comment.