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Mike S.
Mike S., Chevy Mechanic
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Experience:  ASE Certified Master Technician
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My chevy 350 isnt firing. I replaced the ignition module after

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My chevy 350 isn't firing. I replaced the ignition module after having it tested and it being bad. But I still have no fire.

Is it an external coil? Do you have spark from the coil?

Customer: replied 7 years ago.
The coil is located in the top of the distributor cap.

Ok, If no spark occurs, check for the presence of normal battery voltage of the battery (BAT) terminal in the distributor cap. The ignition switch must be in the ON position for this test. Either a voltmeter or a test light may be used for this test. Connect the test light wire to ground and probe end to the BAT terminal at the distributor. If the light comes on, you have voltage on the distributor. If the light fails to come on, this indicates an open circuit in the ignition primary wiring leading to the distributor. In this case, you will have to check wiring continuity back to the ignition switch using a test light. If there is battery voltage at the BAT terminal, but no spark at the plugs, then the problem lies within the distributor assembly.


Fig. Fig. 3 Ohmmeter 1 shows the primary coil resistance connection (the meter should read 1 ohm or less); ohmmeter 2 shows the secondary resistance connection (the meter should read 6k-30kohms)-replace the coil if any readings are off

Click image to see an enlarged view


Fig. Fig. 4 The coil on all but the 1975-77 six-cylinder engines is accessible by removing the four attaching screws-be careful when installing the coil into the cap, as the screws can strip the plastic mounting holes if overtightened

Click image to see an enlarged view

Fig. Fig. 5 Check the condition of the arc seal under the coil

Click image to see an enlarged view

Fig. Fig. 6 Ohmmeter 1 shows the connections for testing the pickup coil; ohmmeter 2 shows the connections for testing the pickup coil continuity-move the vacuum advance arm during this test to ensure no change in the reading

Click image to see an enlarged view

If the trouble has been narrowed down to the units within the distributor, the following tests can help pinpoint the defective component. An ohmmeter with both high and low ranges should be used. These tests are made with the cap assembly removed and the battery wire disconnected. If a tachometer is connected to the TACH terminal, disconnect it before making these tests.

  1. Connect an ohmmeter between the TACH and BAT terminals in the distributor cap. The primary coil resistance should be less than 1 omega .
  2. To check the coil secondary resistance, connect an ohmmeter between the rotor button and BAT terminal. Note the reading. Connect the ohmmeter between the rotor button and the TACH terminal. Note the reading. The resistance in both cases should be between 6,000 and 30,000 omega . Be sure to test between the rotor button and both the BAT and TACH terminals.
  3. Replace the coil only if the readings in Step 1 and Step 2 are infinite.

These resistance checks will not disclose shorted coil windings. This condition can only be detected with scope analysis or a suitably designed coil tester. If these instruments are unavailable, replace the coil with a known good coil as a final coil test.

  1. To test the pick-up coil, first disconnect the white and green module leads. Set the ohmmeter on the high scale and connect it between a ground and either the white or green lead. Any resistance measurement less than infinity requires replacement of the pick-up coil.
  2. Pick-up coil continuity is tested by connecting the ohmmeter (on low range) between the white and green leads. Normal resistance is between 650 and 850 omega , or 500 and 1,500 omega on 1977 and later cars. Move the vacuum advance arm while performing this test. This will detect any break in coil continuity. Such a condition can cause intermittent misfiring. Replace the pick-up if the reading is outside the specified limits.
  3. If no defects have been found at this time, you still have a problem, then the module will have to be checked. If you do not have access to a module tester, the only possible alternative is a substitution test. If the module fails the substitution test, replace it.


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