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Bob, Auto Tech
Category: Chevy
Satisfied Customers: 4087
Experience:  Plus 40 years GM, over 30 certified with Chevrolet, ASE certified Master Tech. (Expired, Retired)
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did a complete tune up on chevy 350 hei charged ...

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did a complete tune up on chevy 350 hei charged battery but still have weak spark
The spark to the ignition system is regulated by the HEI system, not the battery. Some of the components can be tested separately to see if they are with in specs or not. The items that cause the most problems are the module, the coil and the pick up coil. What year is the car?
Customer: replied 9 years ago.
Reply to Bob's Post: 41 chevy pickup not sure of engine yr best guess   early to mid 70"s set up for 2yrs alot of old wiring ran fine before setting up

I am sending you the test procedure for the HEI, all you need is a volt meter and an ohm meter. This is out of the factory service manual and should help you find the problem. Even if the battery was dead, as long as the car will run, the battery has no say so as to how hot the spark is. All it does is supply a 12 volt source for the distributor. Let me know what you find. Thanks, XXXXX XXXXX May take more than one post. Just follow the instructions.


Bob and 4 other Chevy Specialists are ready to help you
Customer: replied 9 years ago.
whats number 5. get spark at plug very weak new coil cap rotor and module could poor ground or bad wire to dist
I would suspect the wire before the ground, only because if the ground were bad, it should affect all of the cylinders. You could try a wire from a different cylinder, just swap them and see if it changes.
Customer: replied 9 years ago.
new super stock 8mm wire all have weak spark would poor groud connection or low volts to ignition reason really old wiring
It is possible. Have you checked the voltage going into the distributor? It needs 12 volts. A ground also may cause that. Have you run the chart that I sent you to eliminate the coil and module and pick up coil? The module can be tested out of the car by most parts stores. Also be sure there is no resistor in the power line to the distributor. It needs 12 volts
Customer: replied 9 years ago.
the ground from battery is bolted to trans is that best place also replaced weights and springs old cap had crack they were rusted up     could rust affect pickup coil
If it is an aluminum trans, you would be better off having it grounded to the motor. Aluminum is not a great conducter. And yes, rust could change the resistance values on anything electrical. Have you checked the voltage supply going into the distributor yet? I will be off line for a couple of hours, but will check my mail as soon as I sign back on. Thanks
Customer: replied 9 years ago.
one last thing do you have picture diagram of plugwires from dist to plugs bad memory

Sure, here you go.


Click image to see an enlarged view
Fig. 4: V8 firing order-1967-74 engines

Customer: replied 9 years ago.
thank you
You are most welcome. Thanks for the accept and feedback and for using JA