The words "engine tuneup" are doubtless familiar, and you may well have asked for one. But are you sure just what ought to go into one?

Let's take a typical tuneup for a late-model car, the actual sequence for your own car may be slightly different - check your service manual.

The first step is to check the battery, testing its specific gravity with a hydrometer, adding water if needed and cleaning and tightening battery connections.

Next is to test the starter motor's cranking voltage - basically, cranking the engine and checking (with a volt-ammeter) to see how much current it takes to turn it over. Too high a reading can indicate problems that should be fixed before going any farther, corroded wires, loose connections, faulty starter, etc.

Then the mechanic should check the bolts that hold the intake and exhaust manifolds on and tighten them to service-manual specifications, since air leaks can affect performance and mileage.

The next step is to test the compression of each cycliner, by removing all the spark plugs, disconnecting the coil wire from the distributor and grounding it, and inserting a compression guage in each spark-plug hole and cranking the engine. If the readings are within the service-manual specs, it's on to working on the plugs.

Clean and gap them or, if they've been in the engine past the manual's recommended time, replace them. Then gap the new ones (using a plug gauge to be sure the distance between electrodes is what the book calls for) and install them.

Now check the secondary ignition system: The plug cables' insulation for cracks and each wire's resistance with an ohmmeter. A wire with excessive resistance or cracked insulation (which can let electricity escape rather than throwing a strong spark at the electrodes) should be replaced.

Following the service manual's instructions, check ignition timing with a timing light. (With an older car, points are replaced, timing reset and centrifugal and vacuum advance are also checked.)

Next adjust the carbuteror, its idle mixture and throttle-stop screw. Test the fuel pump to be sure it's supplying the card with enough fuel.

Make sure the manifold heat-control valve is working freely and lube its bushing and shaft to be sure it keeps doing so. Check all fuel and air filters, clean or replace them as the book says. Check the crankcase ventilation system for proper ventilation. Check out every hose and belt.

And that, basically, is the tuneup.

Even if you don't have some of the equipment we've mentioned - an ohmmeter, say or timing light - you might be able to do the job at one of the do-it-yourself places where you can rent a bay and tools for a reasonable fee.