Hi All - just joined and was hoping one of you can assist. I have a 1971 Skylark Custom Convertible with a chevy 350 small block (yes, I'll apologize now, but that is how I purchased it) Been having some ignition issues and have swapped out the distributor, wires and plugs. When the car starts, it runs beautifully, but have been having issues starting it. The engine turns and fuel supply is good, but fails to spark sometimes. My question is... how many volts should the power source to the HEI distributor deliver at time of ignition? It is currently showing 12 volts prior to crank, but drops down to around 10 volts at crank... I'v also noticed that when I replaced the distributor, there is only 1 wire from firewall feeding the distributor and I've read somewhere that some 71 GMs require 2, 1 from the firewall to feed when engine is running and a 2nd from the starter solenoid to boost the voltage during start-up. Can someone clarify this for me and let me know if I need that 2nd power source from the starter solenoid and if this may be causing my start issue? If so, please provide clear description of where the wire from the solenoid comes from, what gauge wire to use and if I can just splice the 2 power source together to feed the distributor (pictures would be even better) as I am not as proficient as most of you seem to be on this forum. Thank in advance for any advise.
Make sure the hei system is not running on the original coil power wire because it is a resistor wire. Hei will run on full battery voltage at all times. No start boost wire needed because there is no resistor wire in the circuit.
Being as your car is a '71 and HEI for Skylarks/Regals didn't come until '73 (maybe late 72), you probably have the resistor wire coming from the ignition circuit thru the firewall. You should replace that wire with a non-resistive wire and your starting problems will be cured. You might even notice some improved performance due to a hotter spark as well.
The fat HEI distributor introduction was 74 at the earliest. A 71 factory wiring harness has the pink resistor wire. To the OP. Do not make any changes based on your understanding. Wait for some pictures.
Run the resistor wire to a relay that gets a FULL 12 volts. The resistor wire will trigger the relay. Some GM cars have NO voltage in the start position during cranking & one reason the yellow wire from the starter to the dist. + side is also used.
Thanks for all the great advice, folks. Especially the VERY detailed write-up on the HEI conversion For now, I think I'll just try re-wiring with the correct gauge wire and hope this resolves the problem as I noticed that the current wire feeding the distributor is a mess (3 splices with different gauge wires, yikes!).
Update... and need further advise. I just measured the voltage directly from my battery (fully charged) and I'm seeing the same readings... 12.9v and then at crank, it's dropping down to around 10v?! Is this enough voltage for the HEI distributor? Do I need to upgrade to a stronger battery? I currently have the Diehard Gold with 700 CCA.
Sounds normal to me. A 12 volt battery should not measure 12 volt. It will be 12.5 -13.0 volts fully charged. When a lot of amps are being drawn to turn the starter motor, the battery voltage will drop as would be expected under Ohm's law in light of the Thevinin equivalent for the circuit. Another consideration, not previously discussed, is the performance advantages of staying with a non HEI distributor body. You could convert it to eliminate points and perhaps have more flexibility in tailoring the curve of the ignition advance. If your goal is more performance this could be a better option.
For right now, I'm just trying to get the car started again so I can enjoy it for the limited number of days I have in the summer . Just can't explain why no spark... I bench tested the HEI coil and all numbers seem to be in range and I'm reading that 9-10v to the HEI should be plenty to generate a spark...
