Pontiac Cranking Systems
A fairly common occurrence after a lot of miles, or after we rebuild our Pontiac engines, is poor operation of the cranking system. This column will discuss the separate parts of the cranking system, the function of each part, and some suggestions that may help improve your Pontiac's cranking system.
The cranking system of a Pontiac V-8 (and all similar GM vehicles) consists of:
1. Battery and two battery cables
2. Starter motor
3. Starter solenoid
4. Electrical starter controls
(See drawing for a typical starting system.)
Brief Theory of the Cranking System
The negative battery cable connects the negative post of the battery to the engine. The engine is electrically connected to the frame and body via ground straps. This combination of engine, body, and frame provides a conductive path (called "ground") from all devices on the vehicle that are connected to ground back to the battery negative post. The positive cable is connected from the positive post of the battery to the large + post on the battery to the large + post on the solenoid. A smaller wire is also connected at the same point on the solenoid and conducts the 12V power to the remainder of the vehicle's electrical system.
The starter motor is a very high current and powerful direct drive electric motor that rotates and turns the engine via the ring gear (flex plate) when the solenoid operates. The starter includes the starter drive gear that is equipped with an over-running clutch. The drive gear is splined to the motor shaft and designed to slide on the shaft so it can be driven in to mesh with the ring gear when the solenoid operates. The over-running clutch protects the starter from excessive engine speed when the engine fires.
The solenoid is an electrical relay that has two major functions when the ignition start circuit is activated. It drives the starter gear outward on the starter motor shaft in order to engage in the starter gear with the ring gear teeth. That movement almost simultaneously closes a high current switch (located within the solenoid) between the positive battery cable and the starter motor. A third minor function of some Pontiacs is to furnish a full 12V to the ignition coil during "start" (bypassing the ignition ballast resistance).
The starter/cranking controls include the "start" position of the ignition switch, the neutral start switch on automatic equipped vehicles, and all of the wiring and connectors from the smaller positive wire on the solenoid + terminal, through the bulkhead (firewall), through the ignition switch, through the neutral start switch, back through the bulkhead, and finally to the "S" terminal on the solenoid.
Sequence of Operation
1. Power is switched to the "S" terminal on the solenoid causing the solenoid to operate. It requires 40 to 50 amps to operate the solenoid.
2. The solenoid drives the starter gear out and against the ring gear and closes the high current switch between the battery positive post and the starter motor windings.
3. The starter motor begins to rotate causing the drive gear to rotate and slide into the mesh with the ring gear (if it was not initially engaged). The starter motor requires as much as 550 amps to operate normally.
4. The engine rotates (cranks) until the ignition switch is released from the "start" position.
5. Upon release of the ignition switch from the "start" position, the solenoid reverts to a normally off condition. The solenoid return spring causes the high current switch to open and pulls the starter gear out of the ring gear back to its normal off position.
Troubleshooting the Cranking System, Battery and Cables
A. The engine turns very slowly and may quickly stop.
B. The solenoid turns on and then immediately kicks off and then back on. In this case, the starter motor load drops the voltage so low that the solenoid cannot stay energized and it opens and disconnects the starter motor from the battery. The battery voltage immediately rises enough to reenergize the solenoid and the cycle repeats itself causing a click-click sound from the solenoid.
C. Dirty or faulty connections on either end of both battery cables can also cause intermittent operation of the solenoid as described in B above.
B. Badly worn or broken brushes will cause motor failure.
C. A defective armature, either electrically open or shorted or mechanically damaged by dragging within the case will cause an inoperative part.
D. The starter motor may rotate, but the engine will not turn. This indicates a defective starter drive gear.
E. The starter/drive gear may engage one time but slips the next. This is an indication of a badly worn section of teeth on the ring gear.
B. The solenoid clicks on and off. In addition to the reasons listed above under Battery, a faulty hold-in winding in the solenoid will cause this condition.
C. The solenoid operates but the starter does not turn (you can hear the solenoid click on when the start circuit is energized). Assuming the starter motor is okay, the switch portion of the solenoid is defective. A temporary repair can be made by disassembling the solenoid, filling/cleaning the switch posts and switch disc. The switch post for the battery cable can be rotated 180 degrees (with the solenoid apart) to expose a new contact area.
D. The solenoid operates normally, or when the engine is cold, but fails when hot. The solenoid normally requires about 50 amps, but when it is very hot, it will require even more current. The solenoid may be defective, but a failure is normally permanent and not intermittent.
A. The ignition switch can wear and become erratic or inoperative in the "start" position.
B. The neutral-start switch associated with the transmission shifter mechanism can fail or become misadjusted.
C. The firewall connections of both incoming wiring carrying 12V power and outgoing wiring carrying the ignition switched power to the "S" terminal on the solenoid can fail. These circuits carry about 50 amps during start operations and the terminals can expand, loosen, burn, and/or otherwise become defective.
D. The wire to the "S" solenoid terminal can become worn or broken and/or the wire/connector junction faulty.
2. Make absolutely sure that all high current connections are clean and tight. This includes both ends of the battery cables. If in doubt, remove all four and carefully wire brush both sides of the four connections. Assure that the battery post terminals are secure and cleanly attached to the cables. Make sure that the cables are equivalent in diameter to the original cables.
3. Check that both engine wiring and firewall cable connectors are securely fastened to the firewall on the engine side.
4. Assure that the starter and solenoid are in good condition.