The Basics...
Yes I searched around but could not find something like this.
I'm not surprised - nobody EVER has intermittent starter trouble. Ever.
Yes, this is a very rare problem.
This just occurred to my 86 Runner again today, but this time I felt starter relay click. Possible problem that I need to verify:
Starter relay contact has high resistance
Ignition switch ST1 contact has high resistance
Starter solenoid stuck
jlewis74,
Please search harder
Many things could go wrong with the starting circuit. Do not simply guess, replace parts and waste time and money - verify.
Start with the basics:
- Understand how the starting (cranking) circuit works.
- Make sure you have clean wiring, good contacts including ground strap on starter.
I hope this simplified explanation of how the starting (cranking) circuit works would help:
- Putting Ignition switch in "Start" position sends power (low current in green) to energize starter relay (located here). Have someone start the truck and listen to/feel the starter relay click. (It also sends power to Circuit Opening Relay to start fuel pump, but that's a separate system)
- Starter relay contacts close sending power (higher current in orange) to starter solenoid though this connector, that plugs into starter solenoid here. (Starter solenoid piggy-backs on starter.)
Starter solenoid has larger coil than a relay because it has to pull in a plunger that closes heavier starter contacts to handle extremely large cranking current, and possibly actuate clutch to engage flywheel and starter gears (I'm not sure whether 4Runner starter has bendix drive or clutch)
- Starter solenoid contacts sends power from heavy wire (directly connected to the battery) to starter to turn it.
Voltage drops/Corrosion/Resistances
Poor (loose/corroded/pitted) contacts have high resistance. It is quite possible to have high resistance on ignition switch ST1 contacts, relay contacts, solenoid contacts, and wire connections, including ground straps. This will result in too much voltage drop across the contacts when there is current flowing through it.
Starter solenoid needs high current through its coil in order to actuate the plunger. Even if the individual components of the starting system seem to work/energize/click, there may be too much voltage drop across these components. Once you add up these voltage drops, you may end up with too little voltage (hence current) to energize the starter solenoid.
Pitting/corrosion of relay contacts will cause too much resistance across them, that altho relay clicks, you may not be getting full power though it.
A starter that works when smacked could mean:
- Starter solenoid plunger mechanically hard to actuate and there is not enough current to move it. Smacking may get it unstuck.
- Plunger actuated and attempts to close contacts but because contacts are pitted/worn out it takes a little help to make them close all the way.
BIG BOO-BOO:
Note on schematic that starter
solenoid control (coil) power is also taken from ignition switch ST1 contact, same contact that the start relay is supposed to relieve of the solenoid control current in the first place -
DUH!
My next mod to bypass ST1 contact would be to move terminal 4 of starter relay to fused wire directly connected to battery. (This is similar to what the Painless Wiring Hot Shot relay mod accomplishes.)
