How many of you reading this remember a time when distributor diagnosis meant checking the points? If so, you probably remember that distributor issues were usually fixed with a fingernail file and a matchbook. Well, those days are gone, and the HEI-style distributor is a mainstay with hot rodders. That also means that a fingernail file is no longer the repair tool for roadside fixes.
Since diagnosing the module, pickup, and the coil of an HEI distributor is a little trickier than an old-school points distributor, we checked in with the folks at Performance Distributor to get some diagnostic input.
If, for some reason you have no spark coming from your distributor, the following will help you check and test the installation, connections, and components, of the unit so that you can get your engine running.
The first area they suggest you check is to make sure all the wire connections on the cap or solid. If a connection is loose, current cannot travel to where it needs to go. If the connections are good, you next need to make sure the unit is getting a strong 12 volts. Many times, a low-voltage issue can cause a myriad of problems. The wire carrying the 12 volts should be a minimum of 12 gauge, and have no resistors in line. Make sure your 12-volt wire is connected to the spade connector labeled BAT.
When checking for 12 volts, do so while you are cranking the engine. If the battery voltage drops below 10.5 volts while cranking, you probably have a bad battery. This low voltage could be insufficient to get the distributor to fire. Use a volt meter to test the hot wire while a buddy cranks the engine over. If the voltage drops below 10.5, check your battery.
If the battery is fine, make sure the wire feeding the distributor is sufficient. 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 also keep you scratching your head. Typically, the distributor grounds itself to the engine when installed. But, if the ground from the engine to the battery is making a good connection, ignition spark will be none existent. To test for a good ground, a jumper wire can be attached to the distributor by connecting it anywhere on the housing and running it to the negative side of the battery.
If all of that checks out, the following steps will help you to test the coil inside the cap, and the magnetic pick up. To do this, you will need a 1/4-inch nut driver and a multi-meter. To test the resistance of the coil, remove the coil cover so you can see the red and yellow wire. Using the multi-meter 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 between 0.6 – 1.5 ohms. To check the secondary resistance, remove the screws that hold the coil in the cap, remove the coil and 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 between 6.0k – 10k ohms.
If the resistance tests verify the coil is fine, you’ll need to test the magnetic pick up coil next. The pick up is located underneath the top plate of the shaft, and has a green and white wire coming that plugs into the module. Disconnect the green and white wires from the module and touch the positive meter lead to the green wire and the negative lead to the white wire. The normal reading should be between 800 – 910 ohms.
The remaining electronic part that would keep the distributor from firing is the module. This 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 ohm meter on this part. You will need to remove it and take it to an auto parts store that has a module tester. Sometimes, heat can cause these to not work properly, so it is recommended to have them test the module 3 – 5 times as the module may not show to be bad until it develops some heat.
For more distributor tech tips, check out Performance Distributors’ Professional Tips page on their website, it’s chock full of useful information.