Most engines (except diesels) use an electric spark to ignite the fuel/air mixture which burns to power the car. This electric spark has to happen at exactly the right time or the engine will not run properly. When a mechanic SETS YOUR TIMING he is adjusting the time the plug fires relative to the position of the piston. Piston position is like this: at the very top of the cylinder the piston is said to be at TOP DEAD CENTER. At the bottom of its stroke it's said to be at BOTTOM DEAD CENTER. The crankshaft is marked in 360 degrees. At top dead center, the crank is at 0 degrees. At bottom dead center the crank is at 180 degrees.

Timing is measured in degrees before (or, rarely, after) top dead center . (Degrees BTDC)
It is measured either with a timing light (which is a "stop motion" strobe light which fires with the spark plug and "freezes" the crankshaft timing mark for observation), electronic timing probe (engine must be set up for this), or mechanical setup (static timing).

On older cars the ignition timing was controlled completely by the distributor . On many modern vehicles the ignition timing is completely controlled by the computer using crankshaft sensors and cannot be adjusted.

Your ignition timing changes as you drive. The number of degrees BEFORE TOP DEAD CENTER (BTDC) is called the ADVANCE. This is done mechanically (centrifugal advance), or by vacuum (vacuum advance), or by computer, or by a combination of these. Whatever the setup, advance increases with engine RPM and decreases as the engine goes under a load.

SYMPTOMS OF INCORRECT IGNITION TIMING

Symptoms of incorrect ignition timing are poor fuel economy, sluggish acceleration, hard starting, backfiring, or "pinging" or "spark knock". Too little spark advance will cause low power, bad gas mileage, backfiring, and poor performance. Too much advance will cause hard starting and pre-ignition.

PINGING, SPARK KNOCK, OR PRE-IGNITION

Pinging or spark knock is properly called "pre-ignition" and is often incorrectly called "valve noise" because it sounds similar to loose valves that need adjusting. The difference is that loose valves will make noise all the time, whereas pre-ignition happens on acceleration or under a load.

Pre-ignition can be caused by too much spark advance or too low octane gas. Many newer cars have "knock sensors" that retard the spark when pre-ignition occurs.

If your car does this from time to time, you may not need to do anything. you might use a higher grade of gas, but that costs a lot of money! I tell people to just not let their car do it: either get on the gas or get off the gas and the "ping" will go away.

---

DON'T BE STRANDED!
AT ECONOMECHANIX WE CAN CHECK YOUR TIMING AND SPARK ADVANCE! GIVE US A CALL AT 352-376-5624.

---

Help support this website! Check out these products!

---

>>>>>>>>> CLICK HERE>> The Economechanix Cyber Mall

---

RETURN TO THE ECONOMECHANIX HOME PAGE

---

We also serve the surrounding communities of Alachua, High Springs, Hawthorne, and Newberry!

Thank you for visiting the ECONOMECHANIX WEB SITE. Please feel free to comment. We also serve the surrounding communities of Alachua, High Springs, Hawthorne, and Newberry! Gainesville has been my home since 1974, and I've loved Gvl and the Gators since I came here in the fall of 1974 to attend the University of Florida. I loved it so much I stayed and opened my car repair business. Originally it was out of the back of a 1963 Chevrolet wagon, but in 1977 a fellow mechanic and I opened an auto repair shop with actual walls, etc. I stayed in the same location for 26 years, and recently moved my operation to property I bought 15 miles east of Gainesville. I am doing most all the repairs myself now, having reduced my overhead from $1500 per month to practically nothing. I do work by appointment only. I mostly work only on my established customers cars, but I will occasionally take on new clients. E-mail me and I will either make arrangements to look at your car, or I will recommend you to someone who will.

George G. Scott, Jr.