Last month's article was on my 1946 Packard Standard 8, 282 CID (see archives section).  The problem is loss of power at full throttle with backfiring.  This month, I will continue with a complete overview of the ignition system from the Packard Service Training Program booklet, with my personal notes added.  This is relevant for most old cars with points, plugs and condenser systems, and specific for 19th (1941), 20th (1942) and 21st (1946-47) Series Packards.  Our '46 is an Autolite, 6 volt, positive ground.  We are assuming a good battery, spark plugs and distributor.

CONSTRUCTION AND OPERATION:         Good ignition, plus good carburetion, plus good compression equals good engine performance.  Good engine performance can be obtained only when all three are functioning properly.  Since good ignition is one of the requirements of good engine performance, the function, construction and operation of the ignition system must be clearly understood, so that an accurate diagnosis of ignition troubles can be made and the ignition system can be properly serviced.         The function of the ignition system is to provide a spark of the correct intensity at the proper time to ignite the mixture of fuel and air in the cylinder.
DESCRIPTION:         The ignition system of Packard cars consists of the following essential units:        

A- A battery and generator as the source of power
B- An ignition switch to control the starting and stopping of the engine.        
C- An ignition coil to step up the voltage         D- A distributor to direct the spark to the         proper spark plugs at the correct time.        
E. Ignition cables to carry the current to the  spark plugs.        
F. Spark plugs to ignite the mixture.        

Actually, the generator is the source of all electrical energy in the car.  It supplies power for the ignition, lights, heater, radio and other accessories.  The battery stores some of the generated energy in chemical form to be used when the generator is not operating.  But, for the purpose of simplifying the ignition circuits, we will assume that the battery is the source of power for the ignition system.         The function of the ignition switch is to close and open the circuit between the battery and the ignition circuit.  The voltage of the generator and battery is limited and is not great enough to cause a spark to jump the spark plug gap.  Therefore, the voltage must be increased.  This is accomplished by the use of an ignition coil.

IGNITION COIL         The function of an ignition coil is to transform the low voltage supplied by the battery into the high voltage necessary to jump the spark plug gap.  In simple language, it is a transformer.  The ignition coil is an electrical unit having two windings:  a primary and a secondary winding.  The secondary winding, which consists of many thousand turns of fine wire, is wound around a soft iron core.  The primary winding, which consists of a few turns of heavier wire is wound over the secondary winding.  A soft iron shell encloses both windings and provides an outer path for the magnetic field.  Thin insulation is placed between the winding layers of the primary and secondary windings and between the outside of the primary winding and the coil outer shell.  The coil is a sealed unit to protect the windings from moisture and air.         When the ignition switch is closed, current flows through the primary winding.  As long as the flow of current is steady in the primary winding, there is no flow of current in the secondary winding.  But, if the flow of current is suddenly stopped in the primary winding, a high voltage will be induced in the secondary winding.  The flow of current in the primary winding is stopped by the use of a set of breaker contacts which are connected in the primary circuit and are located in the distributor.

TESTING THE COIL:         The symptoms of a bad coil are hard starting, chronic high speed missing, and cutting out during acceleration.  To test the coil, first remove the high tension cable between the coil and the distributor at the distributor cap.  Hold the end of the cable about 3/16" away from some grounded part of the engine and crank the starter with the ignition switch ON.  A blue spark should jump the gap, indicating a good coil, or a weak yellowish or red spark indicates a bad coil.  The test must be done with the battery, points and condenser in good condition.         Another test using a 6-12 volt test light with two leads can be done:  Remove the distributor cap, then crank the engine until the points open.  Turn the ignition switch on, connect one test light lead to ground on the engine and the other lead to the coil's primary terminal that goes to the distributor (this is the + on our car).  If the test light bulb lights, that shows the coil is getting current and the primary windings are right.  If the bulb lights when the test lead is touched to the coil's other terminal (one not to the distributor) the coil is bad and the primary windings are faulty.

DISTRIBUTOR:         The distributor has two functions:        
1. To provide a ground for the primary circuit through the contact points and to interrupt the flow of primary current at the right time.        2. To distribute the secondary high voltage to  the proper spark plug at the proper time.
The Packard distributor is of the singer breaker type using centrifugal governor advance and vacuum advance for automatic timing control.  Four models of distributors are used on the 1946 21st Series Packard cars:  The Auto-Lite IGC 4505 and the Delco-Remy 1110132 are used on the Six, the Auto-Lite IGP 4502A is used on the Eight, and the Auto-Lite IGT 4203 is used on the Super Eight.  Ours is the Auto-Lite IGP 4502A.         The distributor drive shaft is driven by a slotted coupling of the oil pump gear.  The oil pump gear, which meshes with a gear on the camshaft, rotates the distributor shaft at camshaft speed which is one-half engine speed.  The other end of the distributor shaft is connected through a governor mechanism to the distributor cam and rotor.
PRIMARY CIRCUIT:         The distributor primary circuit contains a set of breaker contacts, one of which is on a stationary bracket but is adjustable, the other on a movable arm.  The contacts are opened by the distributor cam acting against a molded insulated rubbing block attached to the movable arm.  The contacts are closed by the action of a flat spring attached to the contact arm.  The contacts are mounted on the distributor plate and are connected in the primary circuit.        
When the breaker contacts are closed, current flows through the primary winding creating a magnetic field around the primary winding.  As the cam is rotated, it opens the contacts, breaking the primary circuit.  This collapses the magnetic field around the primary winding and induces a high voltage in the secondary winding.  The collapse of the magnetic field also induces a voltage in the primary winding.  The effect of this inductance is a tendency to keep current flowing in the same direction in the primary circuit.  The voltage induced in the primary winding is great enough to cause an arc at the contact points.  If it were not for the condenser, this arc would prevent the sudden collapse of the magnetic field and, consequently, a low secondary voltage.

CONDENSER:        The condenser is provided to bring the flow of current in the primary winding to a quick controlled stop.  The condenser prevents arcing at the contacts by absorbing and momentarily holding a charge of primary current.  When the condenser discharges the current, it speeds the collapse of the magnetic field and helps to induce the high voltage in the secondary winding.         The condenser is made up of two layers of metal foil, insulated by two layers of hallo wax impregnated paper.  To save space, these layers of foil and wax paper are rolled into a small roll and enclosed in a small metal shield.  The outer layer of foil is connected to the outer shell which is grounded to the distributor plate and the inner foil is connected to a lead wire which is connected to the contact arm terminal.  The condenser shell is sealed by a gasket to protect it from moisture and air.  The gasket is retained by the crimped edge of the shell.
CONDENSER TEST:         Condensers help the coil by the reduction of arcing and giving longer point life.  They are rated specifically for your car's ignition system in MFD (microfarads).  Our '46 is .20-.25 MFD.  A grounded primary circuit with misfiring at high speed can be the result of a bad condenser.  Fortunately, condensers are inexpensive and easy to replace.  But you may want to run a few tests before replacing it.          A common problem is the condenser's mounting strap becomes loose.  Before tightening it, lightly sanding the strap and condenser at strap contact with emery cloth can help to make a good ground.  A loose condenser can cause an erratic ignition.  When the points are burned or pitted, it's usually the condenser, or the points set too close.          To test the condenser, you can buy a coil/condenser tester, or use a multimeter.
MULTIMETER TEST: First, remove the condenser (the metal case is the ground and the lead wire is the hot).  Discharge the condenser by shorting the lead wire to the car.  Switch the meter to Ohms.  Set the resistance range to the highest setting.  Connect the test leads together and zero the meter.  Touch the red lead to the "hot" lead on the condenser and place the black lead to the metal case of the condenser.  On an analog meter, the needle should jump slightly to the right toward 0 ohms, then drop back to the left towards infinity.  By holding the test leads in place for 20 seconds will charge the condenser.  If this test shows any other readings, the condenser is leaking and is bad.        
In addition to closing and opening of the contacts, the purpose of the distributor is to deliver the high voltage to the proper spark plug at the proper time.  The exact instant at which the spark must occur for most efficient engine operation is determined by the:        
1.  Speed of the engine
2.  Throttle opening of the carburetor        
3.  Engine load. The exact ignition timing to satisfy these conditions is accomplished automatically by the centrifugal governor advance and vacuum advance mechanisms.

CENTRIFUGAL GOVERNOR ADVANCE:         The centrifugal governor advance is so designed that, as engine speed increases, the centrifugal force of the rotating flyweights will gradually throw the weights outwardly and will automatically advance the distributor cam in relation to the distributor shaft.  The rate and amount of advance is controlled by the design and calibration of the flyweight springs and the centrifugal governor flyweights.

VACUUM ADVANCE:         During part throttle (or part load) operation, there is a great vacuum in the intake manifold.  Consequently, the charge taken into the cylinder is not so highly compressed as it is when the engine is under heavy load.  With this condition, an additional spark advance will increase fuel economy.  This is accomplished by the use of the "part load" advance or vacuum advance, as it is commonly known.  The vacuum advance mechanism consists of a spring-loaded diaphragm operating in a vacuum chamber and is connected through a linkage to a lever on the distributor.  The chamber on the spring-loaded side of the diaphragm is air tight and is connected through a vacuum line to a small opening in the carburetor throttle body.  This opening is located just above the throttle valve when the the throttle is in idle position.  There is no vacuum at this opening during idle and, consequently, no vacuum advance.         When the throttle is opened, it uncovers the opening of the vacuum passage, which is connected by a vacuum line to the distributor vacuum chamber.  The vacuum acting on the diaphragm moves the diaphragm and compresses the spring in the chamber.  The diaphragm, connected by a linkage, rotates the distributor in its mounting to advance the timing.  On the Super Eight distributor, the vacuum advance mechanism rotates ONLY the breaker plate.  Under heavy load or full throttle operation, when the manifold vacuum drops, the spring pressure on the diaphragm will rotate the distributor backward, retarding the timing to prevent detonation.  The spring load is calibrated to give most efficient operation under any operating condition.  It is adjustable by the use of shims in the spring seat.

SECONDARY CIRCUIT DISTRIBUTOR CAP:  The distributor cap covers the distributor and is molded of a non-conductive material.  It contains one center carbon contact, to which the secondary wire from the coil is connected, and a series of brass contacts, each of which is connected to a spark plug by a spark plug cable in the correct sequence of the firing order of the engine.

DISTRIBUTOR ROTOR:  The rotor also is molded of a non-conductive material.  It carries a steel segment that makes contact between the center contact of the distributor cap and the brass contacts.  Actually, the segment does not touch the brass contacts, but it comes so near to them that the high tension current can jump an arc to the brass contacts.  The rotor is rotated by the distributor cam and is so timed that the secondary current from the coil is distributed through the radial contacts and the spark plug cables to each spark plug at the proper time and at each opening of the breaker contact.

IGNITION CABLES:  The ignition cables carry the current to the spark plugs.  These cables contain several strands of low resistance wire and are covered by a rubberized insulating material.  The insulating material is protected by a cotton braid and a lacquer coating.  High tension conduit is used to support the cables and keep them from chafing.  We always use stranded wires on vehicles with points and condenser ignition systems.  These wires will help produce the 20,000 volts at the spark plugs these old cars require.  Suppression wires won't do that.

SPARK PLUGS: The spark plugs are rated according to their temperature range.  A plug with a long porcelain exposed to the combustion chamber is "hot" plug.  A plug with a shorter porcelain is a "colder" plug.  The spark plugs used in Packard cars are the AC-104, The Champion Y4A, and the Auto-Lite P-4.  The thread size is 10mm.  Each is of the proper heat range and should always be replaced with the same type plug.


        Our backfiring problem happens happens when the engine is held at high revs.  Idling is fine.  The car is an evolving project car (sort of my Harley Earl's Y-job) with the drive train rebuilt.  When we rebuilt the engine, the distributor was mistakenly set one tooth off.  Number 1 timing plug tower on the distributor cap was at 6 o'clock instead of the correct 7 o'clock.  This is a problem on "vacuum advance" cars because it changes the degrees of advance.  This does create high rev problems and has been there since the rebuild, but the problem was getting worse, so we knew something else must be going on.

        We only start this car about every three months, always with fresh gas and a little Marvel Mystery Oil down the carburetor.  Even so, straight 8's are known for sticky valves, so that was the first place we looked.  We removed all of the spark plugs and filled the cylinders with MM Oil, also removing the side covers (valve covers) and sprayed down the valve train with MM oil, then let everything soak for a week.  At week's end, with the plugs removed, I turned the engine over, laying rags over the open cylinders as the MM oil blew out.  Then, using air, I blew into the cylinders to dry them, and installed a new set of AC M-8 10mm spark plugs gapped at .028 and started the car.  Same problem.

        To test further for sticky valves, using my tablet I shot video of the valve train as the engine ran.  Looked good.  Then I removed the 1/4" pipe plug from the intake and connected my vacuum gauge to check vacuum at warm idle.  It was a perfect 20 inches.  As I revved the car, the gauge moved to different readings, but they were all okay.    Next, I put an inline fuel pressure gauge right before the carburetor.  The engine idled at around 450 RPM's and had 5 PSI fuel pressure, and when  held at approximately 1500 RPM's, the fuel pressure dropped to 2 PSI.  Even though the engine had been rebuilt, I decided to check the compression.  It was  90 PSI on all cylinders (acceptable) and a good indication of no stuck valves.  I could now be pretty sure that the problem would be in the fuel or ignition systems.

        With the fuel pressure dropping so low at high revs, I decided to go through the fuel system first.  The manual fuel pump runs off of the cam, and a worn cam can cause the fuel pump pressure to be erratic, but the cam was checked at the time of rebuild, with almost no miles on it since that time, so a bad cam wasn't likely.  But I put an electric fuel pump on to eliminate that possibility.  I made a steel plate and capped off the old manual fuel pump opening in the block.  The electric pump I installed is a Carter #P-60430, as recommended by our buddy Ron at Daytona Carburetor.  This pump is a 6/12 volt, positive/negative ground.  At 6V, fuel pressure is 4-5 PSI; at 12V it is 5-6 PSI.  These pumps are gravity fed and should be mounted below the fuel tank and pointed toward the front of the vehicle.  I have seen electric fuel pumps mounted above the tank in the trunk as in our '67 Jaguar Mk II.  However, we ran out of gas once in the Jag and had to prime the pump by blowing air into the gas tank.  Not much fun out on the road!  To completely bypass our old fuel system, we put a 5 gallon gas can (full) on a stool above the fuel pump, then new gas line to the front of the car to the carburetor.  We wired a manual switch to the electric fuel pump so we could cut it on and off while testing the system.  It is recommended to run it through the ignition switch, but ours is for testing only.  If it didn't work, we would go back to the manual fuel pump.

        Now with the new fuel system on, we turned on the fuel pump and almost immediately the fuel pressure test gauge went to 4.5 PSI.  As I started the car, the fuel pressure dropped to 4.  As it warmed up, I held up the throttle.  Pressure dropped to 2 PSI with the same missing and backfiring through the tail pipe.

        The only thing left in the fuel system was the carburetor.  A bad accelerator pump can cause our problem.  With the engine turned off, I pushed the butterfly open and throttled the carb, and was able to see two squirts of gas go into the throat.  That told me that the accelerator pump was working, but not how well, so I replaced the Carter carb with a rebuilt one from our longtime Packard buddy David Moe, then started the car.  

        S-s-s-same problem !!!  

        The fuel system was all ok.  It was now time to go to the ignition system.  Before remedying our distributor-one-tooth-off problem, I checked the timing.  We hadn't touched it since rebuild, so it should be on spec of 6 degrees before top dead center (BTDC).  The Packard 1946 motors manual specs timing at 7 degrees.  Motor's Manual specs 6 degrees, and another motors manual says 5 degrees.  The car runs best at 6 degrees.  I have a 6V and a 12V timing light, but decided to use the 6V to be in period with the car.  To do this, you have to turn off the garage lights to see the timing mark on the harmonic balancer.  With the lights off I could see fire jumping around the spark plug wires at the cap and the timing was now on 8 degrees.  How did that happen?  It was time to straighten all of this out.    First, to set #1 plug on my distributor cap from 6 o'clock to 7 o'clock.  I set the harmonic balancer pointer to top dead center, and using a paint marker, I put a dot on the distributor cap and a dot next to it on the engine block, then dots on the rotor and distributor plate where the rotor pointed and carefully pulled out the distributor.  I noted the position of the end of the distributor shaft (oil pump side) was at 9 o'clock and I moved it to 10 o'clock, which would move my rotor to point at the correct 7 o'clock on the distributor cap.  The distributor runs off of the oil pump on the other side of the engine, so I went to the right side of the car and pulled the oil pump, marking the pump to the engine block for reference.  After removing the oil pump,  I turned it around to check the drive gear to see its position.  It was at 9 o'clock, the same as the distributor had been.  I moved the drive gear's shaft to 10 o'clock, marking reference marks on the gears (front side) so the gears wouldn't be moved when I put it back in.  This would make the oil pump's drive blade parallel with the cam when installed in the engine.  The oil pump has a shaft with a blade that inserts into the distributor shaft groove.   After doing this several times out of the car, I reinstalled them both.  They fit right together (the oil pump has to be rotated about one quarter turn to go in and come out of the block.)

        I had cleaned up the distributor while it was out, putting in new points, condenser, rotor, cap and spark plugs and wires.  I found the reason that ignition fire was jumping at the cap.  The wires' insulation was cracked on most of the wires (we use the stranded, lacquer cloth covered wires).  When the distributor was out of the car, it was easy to see the vacuum advance and how it connects to the distributor.  This is an Auto Lite system, and the vacuum advance moves the distributor body as the advance kicks in (over 500 RPM's) as opposed to the Delco centrifugal type, also used by Packard, that moves the distributor plate inside the distributor, not the distributor body.  At first look, the advance hookup is genius.  The vacuum control arm attaches to the distributor calibration plate (octane selector) with a #10 cam screw that goes down through the vacuum advance control arm, through the calibration plate and through to the bottom side, where a pointer with downward tabs on each side keeps the nut below it from turning.  When the desired timing is reached, the pointer shows the degrees on the distributor calibration plate and you turn the screw inward, thus locking down the whole assembly.  Here's what's wrong with that:

        When the distributor is in the car, it is so low on the engine that the cap covers the pointer and the pointer/lock nut spins when you tighten it down, even though the pointer has two tabs that face downward to keep the nut in place, and a tab on the back of the lock nut that is supposed to push up against the distributor body to keep the nut from moving.  I didn't appreciate how comical all of this was until Jason was holding the timing light as I moved the distributor to get my 6 degrees with my left hand (rubber gloves on, of course) then with my right hand I tightened down the lock screw, not realizing the lock nut was turning, then I turned the car off and restarted it.  Back to 8 degrees!  After doing this five times, I realized I was doing the same thing over and over again, expecting a different result.  This is one definition of insanity.  So I made my own distributor lock down.  I used the same cam screw, passing through the vacuum arm and distributor calibration plate, then on the bottom side I added a star washer, deleted the tabbed pointer, used the threaded lock nut from the old assembly and added a thumb nut at the bottom to double-nut it.  Packard changed to a very similar setup as evidenced on the cover of their Ignition Training Booklet dated April, 1947 (see next page).

        To base time an engine, #1 plug is removed, put your thumb over the hole and crank the engine over (coil wire off) to bring #1 piston up on its compression stroke.  You will feel the air from the cylinder pushing out against your thumb.  Stop when the pointer points to TDC on the harmonic balancer and the rotor points to #1 plug (ours is at 7 o'clock.  If it had been at 1 o'clock we would have been 180 degrees out.)   Also, to confirm, #1 piston's intake and exhaust valves will be closed (down on our straight 8), which is correct for the compression stroke.  

        To static time using a test light, put one lead on the distributor's primary terminal (the wire from the coil's + side [ours is a positive ground car]) and the other lead to a ground on the engine.  Turn the distributor until the light goes out (points closed).  Then turn the distributor toward #1 firing plug (clockwise on our car; this is opposite of cam rotation).  Turn until the instant the light goes on (points open).  Lock down the screw and you're done.  

        To time with a timing light, warm the car to operating temperature with low idle and disconnect the vacuum advance and cap off the carb end of the line.  This will keep the vacuum advance from kicking in and advancing the timing.  I backed off the #10 lock screw and advanced my timing (this distributor advances clockwise and retards counter-clockwise), setting the timing to 6 degrees on the harmonic balancer using the timing light, then locked down the screw.  When I started it, it idled nicely, no miss, 20 inches of vacuum, 5 PSI fuel pressure at idle, 3.5 PSI at "snap" throttle, then back to 4.5 PSI at fast RPM's.  (I found that fuel pressure drop can be caused by bad ignition timing, causing the engine to shut down as engine speed decreases.)  When I brought the revs up.  500, 800, 1000, 1500.  No missing, no loss of power, no back  fire!  The old straight 8 was back!  One thing about these old L-heads is, I've found they love to idle and be throttled, but not to just hold them up at 3,000 RPM's with no load.  They were not designed for that.  

        Now, what exactly caused my problem?  Here's how the clues add up.  Most every time we started the car over the years, we removed the distributor cap to file the points because of oxidation (Georgia's wet climate!).  We would unclip the distributor cap and hold it back toward the spark plug wires.  This cracked the insulation on the spark plug wires causing cross-firing, and this moved the ignition timing itself.  And the distributor being off one tooth with a vacuum advance secondarily contributed.  Next time we file the points, the cap will be carefully moved to the side with no stress on the wires.  This fixed the chronic after-fire problem when the engine was raced, but on occasion when the engine revs were held up with no load, it might occasionally backfire through the tail pipe.   The only thing that wasn't done was to rebilt the distributor.  Out distributor was sent to our good buddy Ron Carpenter.  He is a specialist on these old Packards and has the knowledge and equipment to go through the distributor.  After we got the distributor back totally rebuilt including a new vacuum advance, we dropped it in.  The idle was now smoother and never any after fire through the tail pipe!  I would suggest having your distributor tested and rebuilt before going through the carburetor and othe rparts of the ignition system.  As for us, we wanted to go through all of our systems to ensure many more years of dependable service from our old friend.  Keep 'em driving!


Our thanks to   Ron Carpenter, California Packard restorer