Engine Tune Up Basics

This article will guide you through a generic tune up on most any car or light duty gasoline-powered vehicle built within the last 20 years or so. We will presume that you are tuning up your engine because it has reached the mileage or time point to do so, and that you are NOT performing a tune up to cure an engine performance defect. We make this distinction because not all running/performance issues will be solved via a simple tune up.

You are working on an automobile engine, so please follow these simple precautions which will go a long way toward ensuring your safety and comfort:

For most vehicles built since the early 1990s, an “engine tune up” will include:

  1. Replacement of the air filter.
  2. Replacement of the fuel filter.
  3. Replacement of all spark plugs.
  4. Replacement of spark plug wires (if equipped).
  5. Replacement of distributor cap and rotor (if equipped).
  6. Checking and setting distributor timing (if equipped).
  7. Overall check of underhood fluids and connections.
Air Filter Installation

1. Let’s start with an easy step, replacement of the air filter. The air filter is always located close to the engine air intake in the engine compartment. On most late model cars, it’s a rectangular shape (also called a panel filter) located in a black plastic housing or box. Accessing the filter is as easy as releasing or unscrewing the clips which hold the top of the air box in place. You may need a screwdriver to release the clips. Once the filter is exposed, no tools are needed to replace it.

a. PART NEEDED: NEW AIR FILTER
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b. TOOLS NEEDED: SCREWDRIVERS
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Fuel Filter Replacement

2. The fuel filter replacement is a little more involved. It is usually under the vehicle near the fuel tank. Some vehicles require removing an access panel. You will almost certainly spill some fuel, so be absolutely certain that you are comfortable performing this step. Make sure that there is no open spark or flame, have a pan available to catch the fuel, and also some cloths or rags to clean up the fuel. (These rags must be properly disposed of.) Check to see how the fuel lines are attached. You may only need wrenches or screwdrivers. If there are special clips, these require special tools which you can purchase. Remove the fuel filler cap to release any residual fuel pressure. Position your pan or rags under the filter, then loosen the fuel line fittings. Undo the clamp holding the fuel filter, remove it, and replace it with the new filter. Follow the directional arrow on the new filter, with the arrow pointed toward the engine. Reinstall the fuel lines. Don’t forget to put the gas cap back on!

a. PARTS NEEDED: NEW FUEL FILTER
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b. TOOLS & EQUIPMENT NEEDED: OPEN ENDED WRENCHES, SCREWDRIVERS, FUEL LINE DISCONNECT TOOLS, DRAIN PAN, RAGS
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Note that Steps 3 (spark plugs), 4 (plug wires) and 5 (distributor cap) all involve removal of the spark plug wires. If you’re a novice at this, do these steps one at a time. If you’re confident, read through all these steps with the understanding that you can perform these replacements simultaneously.

Spark Plugs Replacement

3. Let’s now move to the engine’s spark plugs. For most engines, you need one new spark plug for each cylinder (some rare engines use 2 plugs per cylinder). So you’ll need to know how many cylinders your engine has: 4, 6, 8, etc. Removing the plugs is not difficult, however, there are some important steps to follow: NEVER remove plugs from a ‘hot’ or ‘warm’ engine. If you’ve recently driven the vehicle, wait at least 4 hours for the engine to completely cool down before removing the plugs. Some vehicles have access covers which must first be removed. You need to take off the spark plug wire or coil, depending on ignition design. You can either remove one wire at a time, replace that plug, and reinstall the wire, OR tag each wire with a cylinder number before removing all of them. This is important because it matters which wire goes to which plug. You do not want to mix that up, as that will cause an engine misfire.

To remove the plugs, use a ratchet wrench, long extension bar, and a special spark plug socket. Why not use a regular socket? Spark plug sockets are thinner, to fit inside the spark plug opening, and they have an inner layer of foam or rubber. This material not only protects the plug from breaking, it provides a snug fit so that the plug will stay inside the socket as you retract the old one and lower the new one.

Break the plug loose, and completely unthread it. As you lift the socket, the plug should stay inside. Take a quick look at the spark plug electrode (tip). It should be brownish in color. Very wet or oily spark plugs, or plugs which appear to be missing their tips, are indications of other problems which a fresh set of plugs will not fix!

Check the gap on the new plugs and adjust to spec, using an appropriate plug gapping tool. (Some spark plug manufacturers claim that their plugs are “pre-gapped” and do not need checking/setting.) Begin the installation of the new plugs by hand, which helps avoid stripping threads. Finish the installation with a torque wrench set to the vehicle manufacturer’s specs. Reinstall the plug wire or coil, and move to the next cylinder.

a. PARTS NEEDED: NEW SPARK PLUGS, ONE PER CYLINDER
http://www.carid.com/spark-plugs.html

b. TOOLS & EQUIPMENT NEEDED: SPARK PLUG SOCKET, RATCHET WRENCH, EXTENSION BAR, SPARK PLUG GAPPING TOOL, TORQUE WRENCH
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Spark Plugs Wires Replacement

4. Spark plug wires are next. Many modern vehicles have switched to a coil-on-plug ignition, and plug “wires” have become old fashioned. If your vehicle has plug wires, they do wear out. They are subject to tremendous heat, as well as dirt, oil, etc. Over time, they lose their ability to conduct the necessary high voltage. Again, be very careful not to mix up wire locations: the correct wire MUST go to each plug. Before removing the old wires, consider numbering them (use masking tape and a felt marker). Look at your new set: each wire is likely a different length. Change the wires one at a time, starting with the shortest wire. This will ensure that you are using the correct length wires. If your engine has wire separators, or clips to help keep wires away from hot or moving engine parts, reuse those.
If the wires are difficult to remove, there is a special spark-plug wire tool. It looks like a pair of pliers, with rubber coated tips. It can help provide extra grip if the old wires are stubborn about coming off.

a. PARTS NEEDED: NEW SPARK PLUG WIRE SET
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b. TOOLS & EQUIPMENT NEEDED: SPARK PLUG WIRE PLIERS, MASKING TAPE, MARKING PEN
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Spark Plugs Wire Set

5. Distributor service, like spark plug wire replacement, went away in the early 1990s as vehicles moved to distributor-less ignition systems. If your vehicle has a distributor, at a minimum you should replace the cap and rotor. Vehicles over 25 years old likely also used distributor points and condenser, which we will not cover in detail here. Replacing the distributor cap is rather easy. AGAIN: you will be removing and reinstalling spark plug wires, and they must remain in the same order! You can replace the cap at the same time you replace the wires if you’re methodical.

One trick is this: number all your old spark plug wires. Remove the wires and distributor cap as a unit. Take the new wires and cap, and using the old parts as a template, install the new wires into the cap. Number the new wires. Reinstall the distributor cap, then reinstall the wires onto the plugs.

Distributor Cap and Rotor

Look at the underside of the distributor cap: there is usually a tang which allows it to be installed in one direction only. The cap itself is held on with screws or clips, and its removal and installation is straightforward.
The rotor may be held on with screws, or may be a pull-off, push-on affair. Again, it is indexed to go onto the shaft only one way.

a. PARTS NEEDED: NEW DISTRIBUTOR CAP AND ROTOR
http://www.carid.com/distributors.html

b. TOOLS & EQUIPMENT NEEDED: SCREWDRIVERS, MASKING TAPE, MARKING PEN
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6. Distributor timing is the last step in our basic tune up outline. You’ve replaced the air filter, fuel filter, spark plugs, plug wires, distributor cap, and distributor rotor. Note that all these operations must be done with the engine OFF; indeed, there are some technicians who will go so far as to disconnect the battery to avoid any potential short circuit (not necessary, but could be considered a best practice). If your vehicle has a distributor, then its “timing” is adjustable. This refers to how the distributor is geared or “timed” in relation to the engine crankshaft. If adjustable, a clamp at the bottom of the distributor can be loosened, and the distributor rotated.

Timing Light Tool

In preparation for checking and setting distributor timing, do the following:

  • Find the engine’s timing marks, usually on the crankshaft front pulley/harmonic balancer.
  • Look up the timing specs, given as “degrees BTDC” (Before Top Dead Center). For example, 10oBTDC means 10 degrees before top dead center.
  • Mark the pulley so that the timing mark is visible. Use a dab of paint or a piece of tape.
  • Install a timing light on the engine, ensuring its wires are out of the way of any moving parts.
  • Note in this photo that the timing light has 3 connections: two onto the battery posts, and one onto the “#1 plug wire”. You MUST look up which cylinder is considered “the #1 cylinder” by your vehicle manufacturer.
Understanding TDC - Top Dead Center and ATDC - After Top Dead Center

Start the engine and allow it to reach operating temperature. Loosen the distributor hold-down clamp (on some engines, a special distributor wrench is useful for accessing this).
The timing light is aimed at the timing marks (the timing light acts like a strobe, with a flashing light timed with the #1 cylinder). If the correct timing mark lines up with the pointer, no adjustment is necessary. If it does not, slowly rotate the distributor until it does. Turn off the engine, tighten the clamp, then recheck the timing once again to ensure it did not change.

In this illustration “TDC” stands for Top Dead Center, and “ATDC” stands for After Top Dead Center.

a. PARTS NEEDED: NONE

b. TOOLS & EQUIPMENT NEEDED: TIMING LIGHT, DISTRIBUTOR WRENCH, TAPE AND MARKING PEN OR PAINT
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7. While the hood is open, your hands are dirty, and you have some tools and supplies at your disposal, it is a best practice to perform some basic checks. Do the following:

  • Check engine oil level (car on level ground, engine off for at least 5 min.) and top off.
  • Top up windshield washer fluid (use 100% washer solvent in the winter).
  • Check power steering, brake, and transmission fluid levels. Top up, however, be prepared for further checks if any of these levels are significantly low.
  • Perform a visual check of the battery terminals: they should be clean and tight.
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  • Perform a visual check of the underhood fuse box. All fuses should be present, without any signs of stains, oils, or scorch marks.
  • Perform a visual check of the engine drive belt or serpentine belt. There should be no signs of fraying or cracking. Press your thumb against the belt to make sure there is adequate tension. In general, you should be able to deflect the belt about ½”.

Of course, if anything under the hood appears abnormal, you will need to continue your diagnosis, or take the vehicle to a professional for further assistance. To complete your tune up, take the vehicle for a ride. Allow the engine to fully warm up. Listen carefully for any abnormal sounds. Overall performance should at least be equal to what you had previously; ideally, you will notice some increased performance as well as better fuel economy. Finally, take pride in a job well done!


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