One of the greatest things about the internet is the amount of tech help you can find about different automotive topics when you’re surfing the webs. Our focus is primarily aftermarket automotive, so we get a chance to see what all the major manufacturers are doing.
Recently we stumbled onto Performance Distributor’s Pro Tips page on the company website and found an interesting jewel. This tip deals with troubleshooting the DUI HEI distributors made by the company, but the tip can really be used across the board for any HEI distributor.
When Your Distributor Won’t Fire
Under the heading “When your distributor won’t fire,” we found a seriously great Pro Tip for anyone that is troubleshooting an HEI distributor. While the tech crew at Performance Distributors intended this information to center around troubleshooting the installation of a new DUI Distributor, we felt that steps were universal and would apply to diagnosing a fault with any distributor. That goes for a new installation or one that has installed for years – things happen over time, screws loosen, and electrical contacts are broken.
According to Performance Distributors, if you are experiencing a no-spark problem with your HEI distributor, you can use the following information to help check and test the installation, connections, and components of the unit.
Where To Start
First and foremost, check the 12-volt wire that you are using for power to the distributor. This wire should be a minimum of 12 gauge and have no resistors inline. Make sure your 12-volt wire is fully connected to the “BAT” terminal (the terminal located on the front right of the cap). Also, make sure the three wire harness is fully connected to the three terminals behind the BAT and TACH connections. Included is a warning to ensure the hot wire is never connected to the “TACH” terminal or damage to the module or coil can occur.
If all of your connections check out good, then check your battery voltage as you are cranking the engine. Since the HEI is a high-performance ignition system, it requires more voltage than a standard ignition system. If your battery voltage drops below 10.5 volts, this is usually not enough power to get the distributor to fire correctly. This condition can be due to a weak or old battery or if you are using a hot wire that has a resistor inline.
Use a voltmeter to test the hot wire while someone else cranks the engine over. If the voltage drops below 10.5 volts, check your battery. To make sure it is not the hot wire, run a temporary jumper wire directly from the positive side of the battery to the distributor. If the distributor fires using the jumper wire, run a new hot wire from your switched 12-volt source to the distributor.
A bad ground can keep the distributor from firing as well. The distributor grounds itself to the engine when installed. Make sure your ground to the engine block is secure. If the intake or the distributor hold-down clamp has been painted, remove any paint from the surface where it makes contact with the distributor. To ensure a solid ground, a secondary ground wire can be attached to the distributor by connecting a wire anywhere on the housing and running it to the chassis, body, or negative side of the battery.
If you suspect an electronic part to be defective, the following steps will allow you to test the coil inside the cap and the magnetic pick-up coil. You will need a ¼-inch nut driver and a multimeter to check these components. To test the resistance of the coil, loosen the three screws (two on six-cylinder models) holding the top coil cover. Remove the cover to expose the coil and you will see a red and yellow wire.
Using the multimeter set on the ohms setting, touch the positive lead to the red wire terminal and the negative lead to the yellow wire terminal. The primary resistance value should be 0.3 – 1.5 ohms. To check the secondary resistance, remove the four screws that hold the coil in the cap. Pull the coil out of the cap and turn it upside down. Touch the negative meter lead to the ring terminal on the black wire (between the red and yellow) and touch the positive lead to the bottom of the coil where the rotor bushing makes contact. Your secondary reading should be 6.0k – 10k ohms.
Pick-Up Coil Test
If the resistance-checks on the coil are within spec, the next test would be to test the magnetic pick-up coil. The pick-up is located underneath the top plate of the shaft and has a green and white wire coming from it that plugs into the module. Remove the green and white wires from the module and touch the positive meter lead to the terminal on the green wire and the negative lead to the terminal on the white wire. The normal reading should be 800 – 1,000 ohms.
The remaining electronic part that would keep the distributor from firing is the module. The module is located inside the distributor and has the green and white wires from the pick-up attached on one end and a terminal block on the other. Unfortunately, there is no test that can be performed with an ohmmeter on this part. You will need to remove it and take it to an auto parts store that has a module tester. Have them test the module 3 – 5 times as the module may not show to be bad until it develops some heat.
For more information on distributors, DUI HEI distributor, or any product made by Performance Distributors, visit them online at performancedistributors.com.