Not to sound silly but have you verified the 12 volt power at the battery Positive position on the distributor power connectors on the HEI system? My C4 has a HEI and the Battery + wire connector was broken allowing it to make and break and this caused the engine to run poorly. You need a steady 12 volts at the battery positive input on the HEI distributor to make the ignition work. It is on the side of the distributor and is marked on the case.

Have you double checked the timing? I would rotate the engine around to verify that you are on the TDC and the distributor's rotor is pointing at the #1 cylinder spark plug connection on the distributor cap. With the engine at TDC be sure the harmonic balancer is showing on the timing marks. I would verify that you have a spark at all eight cylinders to be sure that your spark plug wires are working properly.

A weak or failing coil can manifest itself in several ways. Some just die, some die s-l-o-w-l-y causing misfires and some work great until they warm up or get hot. You might want to try another coil. I have a replacement coil and pickup sensor for the distributor as I heard bad things about the HEI. I installed a DUI cap and coil and it makes a wicked spark for my L98. Not to sound silly but have you verified the 12 volt power at the battery Positive position on the distributor power connectors on the HEI system? My C4 has a HEI and the Battery + wire connector was broken allowing it to make and break and this caused the engine to run poorly. You need a steady 12 volts at the battery positive input on the HEI distributor to make the ignition work. It is on the side of the distributor and is marked on the case.

My brother likes European junk and had a 1974 (?) Triumph Spitfire. The engine ate a valve at speed so he had the block rebuilt and re-installed. After putting all the parts on the engine it would crank but not start. My brother let the car sit as he worked on it and could not get it to run. It had air, fuel , Compression and ignition but the engine would not start or run. A buddy of mine who is a professional mechanic helped me for over 8 hours trying to figure it out. As we were getting ready to close down for the night I saw a small component that was called a "Drive Resistor" and it appeared totally useless so my brother didn't put it back on. I plugged the resistor in and the engine started right up and ran like a champ. The device was a single wire piece that attached to the distributor It was connected the ignition system and when removed the engine would die. I hate little British cars to this day. I won't tell you about his MG Midget with a 1962 Buick 215 (?) aluminum V8 in it. I am not a believer in LUCAS "The Prince of Darkness" as they are truly dangerous.

Corvettes are so much easier to work on.....

 

Also verify 12v at the distributor while cranking. Some power sources are on with key on, but drop out during cranking. I have my HEI power source from the "IGN" terminal in the fuse panel.

 

Thanks for the detailed response. In terms checking the 12V supply to the distributor I am checking this pin (see photo below). I am also checking the output of the distributor by inserting a plug test tool inline between the distributor cap and a spark plug lead. I see a flickering orange glow when cranking. My understanding is that I should see a bright blue/white glow for a healthy spark and orange signifies a weak spark. So I think the no start problem is that the spark is insufficient to ignite the fuel. It seems to me this is suggestive of a fault in the coil, fault in the HEI / rotor / cap, or a voltage drop under load. My next step is to check the 12v input to the dizzy while actually cranking and see what it drops off to. I also want to try a different plug tester to see if the result is consistent. I don't think its the leads as I think its unlikely that all leads would go out at the same time(?). I really like your suggestion to double check the timing and also plan to do that.

Easy to work on? Hmmm, maybe compared to British cars!

 

Hi, Thanks for your ongoing help. Here is my voltage data:
- Fully charged battery with no terminals connected: 12.99V
- Battery with terminals connected and everything off: 12.99V
- Ignition pin in fuse panel with ignition on: 12.7V
- Distributor BAT terminal with ignition on: 12.58V
- Distributor BAT terminal while cranking: 9.96V
- Inline plug tester while cranking: no glow at all now
So.... looks like the resistor wire is still in place?? I do have a wire coming off the IGN terminal in the fuse panel but it is light gauge (16 AWG) and runs up behind the speedo somewhere. It is not the same wire that runs to BAT which is 12 or 14 AWG.

 

I meant some sources drop voltage completely during cranking (I think the wipers is one). Sounds like you still have some voltage while cranking.
Not sure about how low is an issue. I know I've seen someone state on here that an HEI will fire with a little as ~6 volts. But, I'm guessing everything else in the system - wires, plugs, coil, Module, would all have to be in tip top shape for that scenario to work.

To find out, get another good, fully charged battery (steal it from the wife's car), and ground the negative to the car frame, and run the positive to the BAT terminal on the distributor. But connect it in such a way that you can disconnect it easily, since that is how you will shut the car off if it does start.
This way you are separating the cranking power from the distributor power and supplying a good 12 volts always.

 

Its good suggestion, I plan to try that this afternoon with a new 800CCA battery. However because the output test went from a weak glow to nothing under the same conditions and voltages, I suspect that there is also a failure in the coil or HEI. My HEI distributor looks older and is a "no brand" of dubious quality. It's a good opportunity to replace the whole distributor with something of known quality (what's another $250 at this stage of the game?). I just want to figure out the battery and voltage drop first so as to not fry a new HEI. Not sure what to believe with respect to acceptable voltages for an HEI. Some say must be 12V in order to work. I do know that based on Ohms law if the voltage drops the amperage has to increase and its amperage that can fry electronic components and wiring. My hope is that a ne battery reveals just slight voltage drop during cranking and if so I'll put in a new dizzy.