adpostel

I just converted from points to HEI. My question is concerning voltage during cranking. I replaced the original (I assume) resistor wire at the fuse junction block on the firewall with a new 10 ga. wire and a new packard style connector. I get 12+ volts on this wire when ignition is in run position, but when cranking, I see a voltage drop to around 8.4 to 8.8 volts when motor is turning over. I am getting spark at the plugs, because I took one wire off and held it close to plug, and can definitely see the spark jump to the plug. So I know I have spark, but why the voltage drop when cranking? I realize that the battery is having to turn the motor over, but is the voltage drop during cranking pretty normal?

Lady72nRob71

What car and year? Almost sounds like the resistor wire is still there...
What color was the wire you replaced?

adpostel

Its a 1968 Cutlass with original 350 and still had the points ignition and externally regulated alternator. I am doing both conversions. And yes, it almost seems like the resistor wire is stil there, but once the key goes back to the run position, I get the 12 volts again. The wire that I replaced was right by the purple starter wire and a black wire w/ an orange stripe that should go to a TH400 trans if you have that trans. The wire was black and had very few strands in it, I used a wiring diagram and it is definitely the spot where the resistor wire went. Does the resistor wire go all the way through the firewall and end up somewhere? I may have the 10 gauge wire from the firewall to the HEI, but still have resistor wire from the fuse block back?

Lady72nRob71

Now that I am waking up, I realized there should be 12V on crank and ~9V in run for a typical points type setup.
In 72, the resistor wire ended at the firewall connection - it was pink, but colors changed throught the years.
There might have also been another wire on the ignition coil that went directly to the starter solenoid to give the 12V boost during crank.
Check your body grounds. Measure at, say the cigar lighter during crank to verify 11-12V. If less, check those grounds.

gearheads78

Its been a while since I have done one but I remember having to tie two wires together at the ignition switch. I think there might be two resistor wires off the switch.

adpostel

Another question I have, is how can you get 12 volts to any wire during cranking if there is a voltage drop on the battery when cranking? My battery is new and charged to about 12.8 volts, but when turning the motor over, there is a voltage drop to about 8.8 - 9.2 volts. This is pretty normal voltage drop under load correct? So how do you get 12 volts during cranking?

MDchanic

8-9 volts when cranking sounds about right to me.

That's why the points system switches from resistor to direct when cranking.
The coil runs on 8v through the resistor,
you get 8v when cranking without the resistor.
That way the coil always gets about 8v.

Your mistake was checking the voltage when you didn't have a problem in the first place.
If it ain't broke, don't fix it.

- Eric

MDchanic

You can't.

- Eric

adpostel

Haha! I was just double checking things because I couldn't get the motor to crank last night. But after doing some more research this morning, I figured out my problem. I did have all electrical connections for the conversions right. It was the CCW rotation on Oldsmobile distributors that stumped the pooh out of me. I restabbed the new HEI dizzy about 5 times and redid and rechecked the plug wires, TDC, and firing order. But I am so used to CHEVY, that I put the wires on the dizzy in a CW rotation. I read that it should have been in a CCW rotation which makes sense as to why I couldn't crank the motor.

adpostel

And thanks for your input Eric. Sounds more like someone who has actually checked voltage during cranking. Every post about HEI conversions says you should have 12v in the RUN and START position. But that is impossible. The HEI BAT wire needs to have 12v in the RUN position and needs to be "HOT" during cranking, not neccesarily 12v.

Another thing is that I didn't see the CCW rotation listed on any firing order during my searches.....maybe I just missed it....you learn something new every day.

MDchanic

There may be some cars with small low compression engines that don't drop the voltage much when cranking, but you can expect it to go down to 8-9v when cranking any of ours.
The load-shedding feature of the ignition switch (goes through a separate relay on newer cars) kills the heater fan and wipers when you crank - if you look ALL the other lights will dim, and if you've got a newer digital radio, it may turn off for a second.

That's just normal, and that's why the points have a switched power source.
The HEI doesn't need the extra volts, since it can make so much anyway, so they did away with the added complexity when they designed its system.

- Eric