75 chev 350 cu in with hei no spark

[blazer74]

http://macsblognotes.blogspot.com/2011/10/troubleshooting-gms-hei-ignition-system.html?m=1

[Irish_Alley]

im going to give you this. Distributor componets test

but im really doubting its in your distributor. is the engine turning slow? 7v is sufficient to keep the spark of the engine but not sufficient to turn the engine fast enough. if your engine is turning fast enough i would trace the B+ wire that goes to the distributor and see if you can find any issues with it. if its the yellow wire it should have full battery voltage. if your battery is really hitting 7v then its time to replace it anything under 10 is questionable. keep in mind that wire gets its power from the big wire on the starter. if your only getting 7v while cranking your starter might be only getting 7v and will slow it way down but since you can start it with a jumper wire i would think its just resistance in the wire or its connection

if all else fails you could just hot wire a 12v wire from your fuse box thats only on with the key "on" and "start" to the distributor but i would much rather fix the issue than rigging something 

[blazer74]

Do you have a pink wire to the distributor or a yellow wire?

Pink will be 12 volts from the fuse panel to dist.   

Yellow will be to the R on the starter and be 12 volts when ign is in start. This wire is spliced with another resistance wire purple/black which drops voltage to 8 volts for run and goes to the firewall junction pass-thru at position 3.
From there it breaks off to 2 wires, 1 to the ignition switch 12purple3A and the other to the ignition fuse 12 purple3B

If the yellow wire to the starter is broken, burnt or bad and not providing 12 volts for start.

You can run a jumper wire as before except from the R terminal on the solenoid to the (existing wire leave it hooked up) at the distributor and see if it starts/runs and stays running.
If it does that wire is bad.
Could also be bad contacts in the starter solenoid on a long shot.

[Henry]

Hi Rocker:
Your HEI problems sound very similar to mine I had about 10 years ago on my 1976 V8 HEI. I followed my factory service manual troubleshooting for the unit and it diagnosed the coil and module as bad at two separate troubleshooting occasions. After replacing both of these and everything seeming ok for a short period of time, the starting problems occurred shortly after. Replacing both these parts repeatedly after following the troubleshooting guide, the whole process was repeated...still intermittent starting problems. So I finally decided that the only old electrical part left in the HEI system was the pick-up coil at the base of the distributor...I could not find this as a spare part and so I just bought a complete new HEI distributor with the pick-up coil. This solved the problem and so I think the pick-up coil was intermittent or bad...I followed the GM troubleshooting guide very closely and it did not lead me to this little coil.
Hope this helps,
Henry

[Outacontrol]

Did you replace the cap and rotor? Just because it's only a year old doesn't mean the rotor contact doesn't have a hole in it, sending the spark down to the distributor shaft.