Mach1 Driver
Well-Known Member
Our well known member Aussie67 is having trouble with his PMGR starter and requested a post about how to fix run-on.
A. First positively identify your type of starter. My 69 351w came with the OEM starter that has field coils (as opposed to field permanent magnets) and is a type called “movable pole shoe” with an overrunning clutch:
There as at least six types of starters:
1) Overrunning Clutch and movable pole shoe, Ford 60s, as above
2) DD- Direct Drive which is also movable pole shoe, Ford 73-90
3) PMGR- Permanent Magnet Gear Reduction, Ford >=93
4) PMDD- Permanent Magnet Direct Drive
5) PLGR- Planetary Gear Reduction (uses field coils)
6) OSGR- Offset Gear Reduction, Denso (uses field coils)
B. The common Starter Solenoid looks like this:
You’re probably saying “so what?” Well, if you’re like most of us you need to use the stock starter solenoid, because it has the “I” terminal output that feeds 12v to the coil when starting (to make it easier to start). That said, you really need to know if your new starter is one of types 3 or 4 above that have permanent magnets.
Below is how the stock system works: power from the battery runs through the ignition switch (in run or start), through the neutral safety (in park or neutral), and to “S” terminal on the solenoid, which connects to the coil. The coil pulls-in the two NO (normally open) contacts, and power from the battery is routed directly to the coil from the “I” terminal (bypassing the resistor wire) so the coil has 12 volts for easier starting. Power is also routed through the top solenoid switch to the starter motor and the engine cranks. As soon as the key is released, the ignition switch contact feeding the “S” terminal opens, the solenoid opens the two NO contacts, turning the starter off, also turning off the 12v bypass through terminal “I”, and power is forced through the resistor wire instead of around it, making the coil run at a reduced voltage, and allowing the points to last longer and preventing the coil from overheating.
C. The PMGR and PMDD starters have their own internal solenoid to pull the pinion into the ring gear on the flywheel or flexplate, and it also opens and closes a switch to turn the motor on and off.
One of the interesting things about permanent magnet motors is that they become generators if you spin them. The schematic below shows how that becomes a problem. The starter below is wired incorrectly, and the engine has been started, then the key released. Notice the NO contacts in the starter solenoid are open, and power can’t flow from the battery, but the permanent magnet motor is still spinning from cranking the engine and it instantly switches from being a motor into a generator, outputting power through the jumper wire to the solenoid, which keeps it engaged for several seconds, causing an irritating noise and damage to gear teeth. This is called run-on.
D. Since the PMGR starter has its own internal solenoid, route the cable to the front of the starter solenoid mounted on the inner fender. This removes the starter motor solenoid from any connection to power when the key is released, and it turns off right away. Ford used this very method for several years when first switching to PMGR starters.
A. First positively identify your type of starter. My 69 351w came with the OEM starter that has field coils (as opposed to field permanent magnets) and is a type called “movable pole shoe” with an overrunning clutch:
There as at least six types of starters:
1) Overrunning Clutch and movable pole shoe, Ford 60s, as above
2) DD- Direct Drive which is also movable pole shoe, Ford 73-90
3) PMGR- Permanent Magnet Gear Reduction, Ford >=93
4) PMDD- Permanent Magnet Direct Drive
5) PLGR- Planetary Gear Reduction (uses field coils)
6) OSGR- Offset Gear Reduction, Denso (uses field coils)
B. The common Starter Solenoid looks like this:
You’re probably saying “so what?” Well, if you’re like most of us you need to use the stock starter solenoid, because it has the “I” terminal output that feeds 12v to the coil when starting (to make it easier to start). That said, you really need to know if your new starter is one of types 3 or 4 above that have permanent magnets.
Below is how the stock system works: power from the battery runs through the ignition switch (in run or start), through the neutral safety (in park or neutral), and to “S” terminal on the solenoid, which connects to the coil. The coil pulls-in the two NO (normally open) contacts, and power from the battery is routed directly to the coil from the “I” terminal (bypassing the resistor wire) so the coil has 12 volts for easier starting. Power is also routed through the top solenoid switch to the starter motor and the engine cranks. As soon as the key is released, the ignition switch contact feeding the “S” terminal opens, the solenoid opens the two NO contacts, turning the starter off, also turning off the 12v bypass through terminal “I”, and power is forced through the resistor wire instead of around it, making the coil run at a reduced voltage, and allowing the points to last longer and preventing the coil from overheating.
C. The PMGR and PMDD starters have their own internal solenoid to pull the pinion into the ring gear on the flywheel or flexplate, and it also opens and closes a switch to turn the motor on and off.
One of the interesting things about permanent magnet motors is that they become generators if you spin them. The schematic below shows how that becomes a problem. The starter below is wired incorrectly, and the engine has been started, then the key released. Notice the NO contacts in the starter solenoid are open, and power can’t flow from the battery, but the permanent magnet motor is still spinning from cranking the engine and it instantly switches from being a motor into a generator, outputting power through the jumper wire to the solenoid, which keeps it engaged for several seconds, causing an irritating noise and damage to gear teeth. This is called run-on.
D. Since the PMGR starter has its own internal solenoid, route the cable to the front of the starter solenoid mounted on the inner fender. This removes the starter motor solenoid from any connection to power when the key is released, and it turns off right away. Ford used this very method for several years when first switching to PMGR starters.
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