Voltage drop at HEI in "crank"
 

Can someone explain how the voltage drop occurs in the factory pink wire going to the distributor on a 77 C10 originally equipped with an HEI distributor?

I'm getting 12 v in "run" but it drops to 8 or 9 in "crank." All of the wiring is original and hasn't been monkeyed with. It's my understanding on points equipped vehicles, this lower voltage while cranking was normal and done through a ballast resistor.

I thought with HEI trucks this was not supposed to happen. Is this normal?

Re: Voltage drop at HEI in "crank"
 

On a points setup, it was the other way around. You got full 12V during crank and a lower voltage during run. That gave a hotter spark during start when battery voltage was lower due to the drain from the starter.

Check your voltage at the battery during cranking. Possible your battery is near EOL. Also possible your battery cables are going bad.

Re: Voltage drop at HEI in "crank"
 

Through the magic of YouTube tutorials on voltage drop testing, I was able to dive into the shallow end of the pool with some troubleshooting this evening. Results are as follows:

Voltage at battery terminals during cranking: 10.2v

Voltage from pos terminal to battery lug on starter during cranking: 0.25v
Voltage from starter case to neg bat term during cranking: 0.45v

I think I have the additive effect of a marginal battery along with some battery cables/connections that could be improved.

Re: Voltage drop at HEI in "crank"
 

Edit: Did some more research and the .25v drop from starter to positive is in the normal range. Starter case to negative terminal of .45 is borderline (general accepted limit of .5v drop).

So I'll be checking ground connections and replacing the battery. Battery is only a 500-ish CCA so that is a marginal power source even on its best day.

Re: Voltage drop at HEI in "crank"
 

On the steering column there is a sliding switch.

At our vehicles age this can be a source of near endless issues

Re: Voltage drop at HEI in "crank"
 

I think you need to upgrade to a higher CCA battery. Maybe 700 or 800.

Re: Voltage drop at HEI in "crank"
 

I never saw a mention of it being hard to start, just an interest in voltage drop. IS the thing having starting problems?

My suggestions on order of things to replace if needed:
1. Battery cables. Old but nice looking cables can be rotted on the inside.
2. Have the battery tested. It may be good.
3. Have the alternator tested. Low battery issues can be due to lack of good charge.
4. Only if needed, replace battery. No point in spending $100+ if not needed.

Re: Voltage drop at HEI in "crank"
 

Never any issues of hard starting. Just discovered this during some troubleshooting after a couple of fried HEI modules. I was getting low voltage at the distributor during cranking. Performance Distrubutors gave me their troubleshooting guide which said I needed at least 10.5 at the distrubutor wire during cranking or else it's hard on modules.

I will look at having the battery/alternator tested and check the ignition column switch. The reading of 10.2 volts was directly at the battery terminal bolts during cranking was taken after a full overnight charge.