One of the hardest issues that can keep your truck inoperable is the dreaded downed ignition system. The second issue is, there are a million different diagrams etc that conflict with each other. So today I'm going to give you a comprehensive look at how to diagnose your ignition system.
Step 1: Check your battery.
Yes it's obvious but with a low voltage reading your ignition coil will not be able to provide adequate spark to your plugs.
Step 2: Check for power at the ballast resistor.
Turn the key to the on position and probe the ballast resistor side with two red or pink wires coming to a single connector, this is usually the top connector. Check for voltage here, you should see 12 volts with the key on and nothing with the key off. If it does not have power when the key is turned on then a broken wire or bad connection into the cab needs to be looked for.
Step 3: Check ignition coil.
Turn the key to the on position and probe the power side of the coil. You should see roughly about 5 volts here. If you fail to see power then you have a break in the wire between the ignition coil and ballast resistor. Next probe the negative side of the coil. If there is no voltage present then check the wire to the ECU (it is almost always a black with green stripe wire). If there is no break in the wire then go to step 4. If you do have ground at the coil test your coil resistance for the primary and secondary windings.
Remove the coil from the vehicle to test it. First test the primary windings in ohms. To test put one volt meter probe on the power side and the other on the negative side of the coil. Your reading should be between 0.4 and 2 ohms. Next test the secondary windings. Put one probe on the positive terminal of the coil and the other in the distributor plug hole and you should see between 6,000 and 10,000 ohms reading. If either of these readings are different chances are you need a new coil.
Step 4: Check all grounds to the fire wall and fenders.
If your ECU doesn't have a good ground then it will not be able to send a good signal or signal at all to the coil. If in doubt run a ground jumper wire from the batter to the ECU mounting bolt to ensure that you have a good ground. Look an see if the ECU is leaking. Look for a sticky black or clear substance on the fire wall just beneath ECU, also remove ECU from fire wall and inspect back of ECU. It should be a perfect surface not melted or distorted. If it is or you have no ground output to the coil, then something internal to the ECU has failed and it needs replaced.
Step 5: Check distributor.
First remove the cap and check for worn out contacts and do likewise with the rotor. Next check the distributor to ECU connector and check for corrosion and make sure there aren't any broken wires from the distributor to the ECU. If all that checks out then it's time to test the distributor itself. (Electronic ignition) Unplug the distributor plug and put one end of the multimeter (set in ohms) in one terminal and the other probe in the other terminal of the same plug. Turn over the engine and watch the reading. You should get a reading between 600 - 1400 ohms. If this reading is not seen then your distributor is likely bad.
And there is a comprehensive look at checking your electronic ignition system. If you have any questions still or have other questions feel free to contact us and keep an eye out for more posts.