Chrysler Master Tech - 1973, Volume 73-11 Electronic Ignition Diagnosis

In recent years - has pioneered the high-volume use of electronics in automobiles and trucks the effectiveness of these innovations is clearly shown by the wide acceptance from owners plus the service life performance and reliability of these electronic components another factor to consider is the ease of servicing these electronic components take ignition systems for instance the breaker point ignition system served its purpose satisfactorily for many years one of the disadvantages. However, was the frequency of periodic service required to maintain satisfactory ignition performance the weak link in the breaker point ignition system are the points themselves they wear out and as a result ignition performance falls off with the exception of the spark plugs which eventually wear out the rest of the ignition system components the coil condenser and ballast resistor had been improved to the point where they should last the life of the car.

The task at hand was to find another way to duplicate the function of the breaker points the breaker points are simply an electromechanical switch when they open the current flowing through the primary side of the ignition coil is interrupted and high voltage is induced in the ignition coil secondary windings to fire the spark plugs the chrysler engineers came up with a product to replace conventional breaker points instead of depending on a mechanical method of switching they thought why not use electronics to do the job.

They came up with a way to stop current flow in the primary side of the ignition coil electronically instead of mechanically here's how they did it from past experience they knew a transistor could be excited by a small amount of electric current and made to act as a switch to open a path to larger amounts of electric current they built a transistorized electronic control unit to use as a switching station when the unit receives a signal it interrupts the current through the primary side of the ignition coil which in turn induces voltage into the secondary coil winding and fires the plugs the transistor would handle the switching part. Okay, but they needed something to signal the transistor when it was time to do its thing well the people who deal with electronic gadgets know there's a simple way to create a small amount of electric current and came up with a solution to demonstrate we will use a bar magnet small coil of wire piece of iron and a galvanometers first we connect the coil wire ends to the galvanometer the galvanometer is simply an instrument for measuring small amounts of electric current next we move the piece of iron near the end of the bar magnet with a coil around it the galvanometer needle begins to move this indicates a small amount of electricity is being generated when the piece of iron is moved near the end of the magnet here's what happens the magnetic attraction between the magnet and the iron causes the magnetic field to increase as the iron is moved closer the increase in the magnetic field strength excites the electrons in the wire coil and a small amount of electric current is generated the electric current at this point has a positive charge when the piece of iron is moved away the magnetic field begins to fade and the current begins to flow in the other direction and changes from positive voltage to negative voltage now let's look at how this principle is applied in the electronic ignition the distributor housing for the electronic ignition contains essentially the same equipment that was used for the demonstration a permanent magnet is fastened to a fishhook shaped piece of steel a coil of wire is wound around the hooked end of the steel piece the ends of the coil wire lead back to the electronic control unit now as you saw in the demonstration electric current was produced when the piece of unmagnetized iron was moved near the end of the magnet in the case of the electronic ignition the reluctor does the job of the piece of iron you'll notice the reluctor looks like a gear with teeth one for each cylinder as each reluctor tooth passes the pole piece with a coil around it a small amount of positive electric current is produced when the tooth passes the pole the polarity changes to negative and signals the switching transistor in the electronic control unit to fire the spark plug the reluctor and pickup coil work as a team with electronic control unit to fire the plugs at precisely the right instant the reluctor and the pickup unit determined the ignition timing the control unit determines the dwell air gap does not affect dwell or timing since the dwell has been predetermined elect on eclis in the electronic control unit it's no longer necessary to use a dwell meter when testing or checking an electronic ignition system the ballast resistor for the electronic ignition system plays a dual role the primary side has a half ohm resistor which controls primary current as engine speed varies the auxilary side of the dual unit has a 5 ohm resistor to protect the control unit by limiting current in the electronic part of the circuit in the electronic ignition system the battery current flows through the primary winding of the ignition coil and through the electronic control unit to ground when the reluctor moves past the pole piece the pickup voltage changes from positive to negative and deactivates or turns off the control unit circuitry this interruption of current flow in the primary circuit induces voltage in the secondary windings of the ignition coil to fire the spark plug the first tester available for testing the electronic ignition system was the c40 166 unit as it stands this model can be used to test 1971 and 72 electronic ignitions. However, to test 1973 electronic control units an electronic adapter number c41 66 1 must be used in conjunction with the original tester this adapter must be permanently installed to the electronic ignition tester wiring harness with the locking collar the c41 66 1 adapter is mounted permanently because 1971 and 72 electronic control units can also be tested with this adapter using the 1973 adapter does not alter the test procedure instructions which appear on the back of the c40 166 electronic ignition tester a second generation tester c41 66 a has been released recently this unit is the same as the c41 66 tester in all respects except the adapter circuitry has been built into the unit also an additional red light and a toggle switch used in checking both the 5 ohm and the half on circuit in the ballast resistor has been added the electronic ignition tester is a valuable diagnostic tool and a delicate test instrument therefore it should not be exposed to excessive dirt and dust for long periods of time also the test seeds were designed to be a specified length another thing to remember is the leads with the - alligator type battery clips and the dual male and female connector are used only for bench testing they are not to be used for on the car testing let's get into on the car testing before you connect the tester make a quick check for other component problems which could cause the ignition to perform unsatisfactory remove the distributor cap and check it for hairline cracks or corroded terminals check the condition of the rotor while you're at it if it shows signs of electrical discharge corrosion pitch it and install a new one give the spark plug cables a thorough going-over if you suspect they're not performing at peak efficiency test them out as outlined in the service manual one of the requirements of accurate electronic ignition analysis with the tester is a fully charged battery in good condition check the battery before you begin work otherwise you'll be wasting your time if you attempt to check out the system with a weak battery. Okay, let's go to work before you remove or install the wiring harness connector at the control unit make sure the ignition switch is turned off if it isn't there's a good chance you'll damage the control unit remove the hold down screw from the electronic control unit and remove the wiring harness connect the female tester lead to the control unit next connect the male tester lead to the system control lead the tester is now wired into the cars ignition system circuit don't connect any other leads on the car turn the ignition switch on but be careful not to crank or start the engine this light the ignition input voltage light must come on and remain on throughout all the tests if it goes off at any time while you're making your tests it means there's not enough input voltage from the battery to the tester to complete the tests if it didn't come on at all check the battery terminal connections and make sure the control unit is properly grounded also check the ignition switch and its wiring for an open circuit if both of the green lights come on and all the red lights remain off you're in good shape. This means all the components and wiring in the primary circuit are good ok let's say the ignition input voltage light is on but the other one the control unit green light is off you found the problem after that the electronic control unit is bad and must be replaced incidentally each of the test lights in the tester is completely independent of the others if the control unit is. Okay, this green light will be on even if there's something wrong with the pick up unit ballast resistor or the rest of the ignition primary circuit to complete checking the system disconnect the ignition coil secondary wire from the distributor cap tower and hold it about a quarter of an inch away from the engine actuate the high voltage coil test switch on the tester and watch for a good spark between the wire and the engine a long hot spark indicates the coil output is. Okay, while you're still holding the coil test switch move the wire away from the engine until the spark stops watch the coil tower to make sure arcing doesn't occur if it doesn't the coil is. Okay, this completes the checking of a good system as you probably already know instructions for using the tester appear on the back panel of the instrument if the auxilary ballast circuit light is on for instance check the instruction chart in this instance it means the five ohms side of the dual ballast resistor is bad and needs replacement here's something to watch for if you have the early tester seen 4166 the half on side of the dual ballast resistor is checked with the rest of the primary circuit by the tester if you have the new tester c41 66a use the toggle switch to test the ballast resistor momentarily hold the switch in the five ohm then the half on position if the light is lit in either position check the ballast resistor and its associated wiring if the light is lit in both positions check for crossed wires in ballast circuits if the red light labeled primary circuit comes on check the ignition coil primary the half on side of the dual ballast resistor and the wiring harness for an open in the circuit replace any faulty parts if the pickup circuit light comes on the pick up unit or its wiring is faulty and must be replaced even if the light doesn't come on it's a good idea to flex the wiring from the pickup unit to double check it if the red light blinks replace the pickup unit now let's get into bench testing once again a fully charged 12 volt battery is absolutely necessary tester to analyze the components connect the pickup connector to the tester if the pickup circuit light comes on the unit is faulty flex the wires to see if the light will blink incidentally the components do not have to be grounded when their bench tested as you can see the green control unit light is off and the red primary circuit and auxilary ballast lights are on. This is normal because there is no input for these circuits when your bench testing the pick up unit when you bench test the control unit you need only be concerned with the green input voltage light and the green control unit lights being on the red lights will also be on but you can ignore those the ballast resistor pick up unit and coil primary circuits are not connected into the tester circuit if the green control unit light does not come on replace the unit well that about covers troubleshooting with the electronic ignition tester there's one more simple test you can make if a customer complains of heart starting the air gap between the reluctor and the poll piece may be too wide it should be eight thousandths of an inch if it's necessary to reset the gap loosen the pickup adjusting screw align a reluctor tooth with the pole piece and insert an eight thousand non-magnetic feeler between the tooth and the poll piece tighten the adjusting screw and remove the feeler remember the air gap does not affect timing or dwell after setting the air gap run the distributor on a test stand and apply vacuum to the vacuum unit to make sure the reluctor teeth do not hit the pole piece during vacuum advance on a final note the teeth on the reluctor are supposed to be sharp.

They can decrease the magnetic field quickly and induce the negative voltage in the pickup coil don't try to clean them up with a file you may round off the edges well that's about it for this session as always see the reference book for additional information and remember don't touch the switching transistor when the engines running or you adapt you.

Chrysler Master Tech - 1973, Volume 73-11 Electronic Ignition Diagnosis

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