Replacing a distributor cap and rotor is a great job to tackle yourself on your late model vehicle and can really give a lot of benefits to the way your vehicle runs. Before we add details to the video here, we want to talk more about distributors so you know how they work and why your vehicle may or may not have one.
Every vehicle had a distributor for the longest time. They were a great idea that really got the job done pretty well. The distributor not only gets the spark to the right spark plug it also gets the spark to fire at a very specific time in the combustion process. Too early and you can damage things, too late and you don’t get much power. The timing of the spark is first set by connecting the distributor rotor to the camshaft so it makes one revolution every time the crankshaft goes around twice. The next step is setting your base timing so you have a starting point. The step after that is adding some fancy spark advance devices like mechanical or vacuum advance to help your engine run great at different loads and RPMs.
The other thing a distributor does is help create the energy for the spark. This was done originally with a set of points and a condenser, then electronic ignition (not to be confused with coil-on-plug) took over which reduced vehicle maintenance by using current technology. If your vehicle has points in the distributor you may consider checking the condition of the points and the gap while you have the distributor cap off.
Now that you understand what you’ve got, it’s time for replacing a distributor cap and rotor in your car! Once you’ve located the distributor the first and MOST IMPORTANT part of the job is making sure you know where all the spark plug wires go. You may consider writing yourself a note, taking a picture, drawing a map or whatever you have to do to make sure you can remember where each wire goes before you pull things apart.
With your map in hand, yank the plug wires off and remove the distributor cap. We already mentioned checking your points if your vehicle doesn’t have electronic ignition, but now might also be a good time to check the condition of your spark plug wires. This includes a visual inspection and a resistance measurement of your wires. If the wires are melted or the resistance is too high or too low it can your engine to run rough.
You’ll notice in our video and on your distributor cap and rotor that the rotor and contacts are worn down. This isn’t from direct contact as the rotor and contacts on the cap never actually touch. This wear is simply from the spark jump the gap as the rotor spins under the cap. Since this spark jumps multiple times every second it will wear down the contact causing poor and erratic energy transfer. Bad energy transfer means poor spark quality and poor sparks mean poor combustion. Less than optimal combustion leads to engine deposits, low power, poor fuel mileage, and a rough running engine. Since a distributor cap and rotor will set you back less than a tank of gas, we recommend getting out there and changing yours today!
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