The Tune-Up Book

How can I tell if my car needs a tune-up?

First, keep a running check on your gasoline mileage. Figure your average mileage for every three tankfuls. When this average has dropped by over 15%, chances are you need a tune-up or other work.

Other symptoms of an out-of-tune engine are listed below. Check each problem that occurs frequently with your car. The more problems you check, the more likely it is that your engine needs some sort of tune up.

Check these problems that occur FREQUENTLY:

Idles fast when warm
Stalling
Low power
Idles rough
Knocking or pinging

Hard starting
Misfiring
Hesitation
Rough running
Engine runs on with key off
Black exhaust

Caution: Be especially aware of changes in your car's behavior. Look for things it's doing today that it hasn't been doing. Some models, for instance, will exhibit hard starting, knock or run-on, even when they're perfectly tuned.

I checked several of those problems. Am I facing a big bill?

Not necessarily. For instance, of the 116 cars we checked, 54 needed only minor adjustments normally costing less than $10.

A common problem was idle speed. When it's too low, your car could stall out. When it's too high, your engine might continue to run on, even after the key is turned off. A mechanic can often adjust your idle speed quickly, using simple tools.

Incorrect ignition timing was found on many cars. Timing is often the culprit when you experience hard starting, pinging under acceleration or loss of power. Like idle speed, ignition timing can be easily adjusted on most cars.

Ask your mechanic to check the engine before he replaces anything. If a few minor adjustments will do the trick, why should you pay for parts you don't need?

So as long as my car runs fine, I can forget about tune-ups, right?

Wrong. Even if your car exhibits none of the symptoms discussed in this book, I recommend that you have it tuned periodically, as specified by the car maker:

As a rule of thumb, do it every 12 months or 12,000 miles if you use leaded gasoline, every 24 months or 24,000 miles with unleaded. It's a good investment in preventive maintenance that pays off in your having a reliable, smooth-running car.

Isn't a tune-up just changing the points and plugs?

No. A thorough tune-up is a four-step process, of which "changing the points and plugs" might be only one step. Here's what I think a tune-up should include:

1. Checking cylinder compression first, which determines whether a mechanical problem exists that a tune-up couldn't help. Then ignition, carburetion and pollution systems are checked against specifications (usually found on the underhood decal).

Engine idle speed, ignition timing, vacuum and mechanical advance, points and dwell, plugs, condenser, distributor cap and rotor, ignition coil, spark plug wires and PCV system should all be checked with engine-testing equipment.

Air and PCV filters, battery, automatic choke and vacuum hoses are checked visually.

2. Replacing points, plugs, condenser, and those parts that cannot be brought up to specifications by cleaning and adjustment.

3. Adjusting slow and fast idle speeds, idle mixture, ignition timing, point dwell (or gap) and automatic choke. (NOTE: I always spray-clean the carburetor before making adjustments.)

4. Road-testing to make sure the car really runs as it should.

What's all this going to cost me?

I asked a dozen service men in Nashville how much a tune-up would cost and what work would be done.(The car was a 1974 Ford LTD.) The lowest price was $29.50 and included only points, plugs and condenser. The highest was $75, and that included a complete diagnostic checkup, including compression check, and all parts, even air and fuel filters.

Of course the price could vary widely, depending on where you live. My best guess for a national average would be somewhere between $45 and $65 for a thorough tune-up.

My gas mileage is lousy. Will a tune-up help?

Only if you've kept an accurate record of your gas mileage and have noticed a decline. (Remember what I said earlier about watching for a change in mileage.)

Some cars, especially 1973 and 1974 models, aren't going to get very good mileage, no matter how well they're tuned. And there are many factors that affect fuel economy. You might want to write for Shell Answer Book #3, The Gasoline Mileage Book, for more information.

Will a tune-up make my car peppier?

Usually. Providing you have no major mechanical problems (like burned valves), your car's performance depends heavily on how well it's tuned.

If your car has become sluggish (remember: look for a change in performance), a tune-up could give it more pep.

Sluggish performance can be dangerous. On the chassis dynamometer, we tested two cars under full-throttle acceleration from 35 to 55 mph. This is the situation you might face if you were passing someone on a two-lane road with oncoming traffic in the distance.

After getting a good tune-up, both cars cut their acceleration times by at least 1.2 seconds. That kind of performance boost could give you a greater margin of safety in a passing situation.

Can I do it myself?

Maybe you can. A recent survey showed that over one-third of all tune-ups are now being performed by do-it-yourselfers.

If you have a little mechanical aptitude and the ability to follow directions, chances are very good that you could do your own tune-ups. Use the manufacturer's specifications for your engine, usually shown on a decal found in the engine compartment.

Note to owners of fuel-injected cars

While your ignition is tuned like any other, fuel injector adjustments should be done by trained specialists.

There is one thing you need to watch closely, and that's your fuel filter. Fuel-injected engines are more sensitive to dirt than carbureted engines.

Make sure you always have your fuel filter replaced on schedule. If you do it yourself, be careful not to get any dirt in the injector side of the fuel line.