Electronic Ign. Control Unit (ECU) Heat condition
Using orange arrows to indicate current flow with key switch in RUN, engine off.
View attachment 1715382114
All power comes from battery. Voltage does not drop until it reaches a device with resistance. As current passes through those devices, voltage drops.
With the engine running, alternator provides the power. But in terms of voltage, same deal.
In an ideal world, if the alternator output is at 14.1 Volts, then everything up to the devices will be at 14.1 Volts.
View attachment 1715382121
All,
I continue to appreciate (& be amazed by) the amount of advice and level of detail you have all provided. (I owe you all a drink sometime...) sorry for length of this note.
--Current situation(same): Car still starts strong when cold and will do nothing when the key is twisted after car is hot (~10-minute drive). After cool-down, it starts normally again. Here are some updates on my troubleshooting.
1) Wrapped about 2/3 of the header pipes on the driver side all around/under the starter to minimize heat-soak.
2) Checked for voltage at the IGN lead to the Starter relay with key Off and in On position = 0V. (Need to get a helper so I can check when key is fully turned to Start.)
3) When car is hot (and turning the key results in nothing at all), the car will CRANK STRONG and start fine if I turn key to On and JUMPER THE Starter relay between the Pos+ post and the square Sol post just under it.
4) I have not taken any Ohm readings on the Ballast resistor, but it is very hot after a short drive (I expect this is normal.)
5) Idling Voltage reading taken between the Starter Relay Pos+ post and engine block = 13.9V.
6) Though I am not sure of what the correct readings should be, I decided to check the Voltage regulator (VR) internal resistance between the two pins with the alternator plug removed. With multi-meter set to 2000K-Ohm setting, I get: COLD reading = ~1850; HOT reading= ~1250. Are these values O.K.? I am just too ignorant to understand if/how the VR resistance would impact the signal to the starter relay when the key is turned. Does it?
7) NEXT Steps: a) Carry a screwdriver with me whenever I take the car for a drive so I can start it by shorting across the Starter relay(Like I stated in (3) above); b) Get some voltage readings at the Ign wire leading to the Starter relay when the key is twisted for both Hot & Cold conditions; c) check the resistance of the Ballast resistor; d) look for references to help determine if the VR is good or bad.(The battery is charging.)
FOOTNOTE: I don't think I mentioned this before, but FYI. The Pos+ lead from my trunk-mounted battery goes directly to my starter. A large (maybe 3-gage) wire connects between that same +lug and the Pos+ post on the starter relay. Most wiring diagrams show a separate Pos+ lead from the battery to the starter relay, but since my wiring set-up still puts both these connections in parallel, I think it is O.K. (Right?Wrong?)
-THX for hanging in there with me on this...-Scott
