12v system ignition on cranking

[Redleg130]

My M37 is difficult to start. I have found that when connecting a battery charger while attempting to start, the engine starts immediately. This leads me to believe that the added power, which I assume give a hotter spark, is helping give a quick engine startup.

I have a simple three post solenoid, and the ignition (and secondary fuel pump) are behind a standard resistor, which my understanding is that 12 volts is too much power for normal running ignition and without this resistor, the points burn up too quickly.

I have seen mention of a 4 post solenoid, with the 4th post providing an alternate path for cranking coil power, apparently to provide a hotter spark but only during cranking. This sounds like it might help?

I assume this 4th post is only connected when the ignition key (my M37 has a non-original key based starter instead of foot pedal) is in the 'start' position.

If this is something that could help with rapid starting, what is a good method of hooking this up? Google searching is not giving things that are consistent or detailed, probably because I am using inaccurate terms.

Should I be using a resistor, less ohms than the stock one I would assume, or use bare 12v? Should there be diodes blocking if I have this alternate path? Just imagining how this might be setup, the coil would have two connections, the 4th post solenoid connection and resistor connection, any risks with that?

 

[G744]

From the starter post relay 4th post to the + feed side of your coil. It will only go hot when in the start mode, no additional devices needed.

A 6-Volt starter is the ticket, you may have a 12-Volt one. Won't hurt things a bit.

G744

 

[John Mc]

First thing is clean all the related electrical connections including the grounds.

Also check the voltage of your battery when actually cranking. A weak battery can often measure at acceptable voltage when not under load, but can drop to unacceptable levels when cranking. If your battery is dropping under load, you can try connecting it to a charger with a desulfation feature - sometimes it can recover a battery (though it might take some time). However, if a battery is dropping significantly under load, there is a good chance you will need to replace it. The fact that your truck starts fine with a charger connected makes me suspect the condition of the battery is a factor here.