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Spark Plugs

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Spark plug replacement: $50-$200 (Prices good for most domestic or import cars and light trucks)
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What Spark Plugs Do

Your spark plugs ignite the compressed fuel/air mixture in your engine. This then powers your car down the road.

Spark plugs last longer today than they used to, however plugs still should be checked every 10,000 to 20,000 miles or so. Some manufacturers recommend replacing plugs at an even longer interval: many recommend 50,000, even 100,000 miles before replacement. These plugs may last that long, but GOOD LUCK getting them out of an aluminum cylinder head after 100,000 miles!

With today's electronic ignition your plugs can be worn out and your engine still run fairly well. On the flip side, if your engine isn't running right, chances are just a new set of plugs aren't going to help anything. I say this because today a "tuneup" basically consists of replacing the plugs. Period. I've worked on a lot of cars where the customer has had 3 tuneups in the past year to fix a rough run situation and has only gotten 3 new sets of plugs. The problem lay in a computer sensor or some such thing.

Avoid this problem!
If your car is running rough, take it to your regular mechanic and tell him the symptom : like " My car is hard to start in the morning" rather than just "getting a tuneup"!!!!!!!!!

HOW PLUGS FAIL

NORMAL FAILURE

Even in a normal engine, eventually the plug electrode will get eaten away by the electric arc and combustion chamber temperatures. This is the normal way a plug fails, and this takes at least 10-15 thousand miles before engine performance is affected. Some newer cars advertise 100,000 miles before they need plugs.

ABNORMAL FAILURE

Plugs can fail much sooner than this due to other defective components. This may mean changing plugs more often, or repairing whatever else is wrong with the car, depending on how bad the problem is and how much you can afford to fix.

FOULING

Fouling is where a buildup of deposits accumulates on the plugs electrode or insulator. In extreme fouling the plugs will stop firing and the cylinder will "go dead".

OIL FOULING

A crusty buildup covers the tip of the plugs. Light brown is minor oil fouling. Black, dirty, oily stuff is severe oil fouling. Oil fouling is caused by too much engine oil getting in the combustion chamber. Usually caused by bad valve stem seals, bad valve guides, or bad piston rings.
TRICKY CAUSES OF OIL FOULING:
Oil fouling plugs can be from tricky causes other than the usual engine stuff. Plugs can foul from transmission fluid being sucked through a Vacuum modulator (early GM, Ford).

Turbocharged vehicles have engine oil lubricating the turbocharger, and the turbo can leak oil into the engine and foul the plugs.

FUEL FOULING

With fuel fouling plugs are black and literally wet with gasoline. The spark will travel down the cone-shaped insulator rather than jump the plug gap and make spark. Cause: extreme rich run condition

CARBON FOULING

Carbon fouled plugs are black with charcoal like deposits, but dry, no oily texture.
Cause: extreme rich run condition

MODIFIER FOULING

Modifier fouling is from fuel additives. It's a whitish scaley deposit.

OTHER CAUSE OF PLUGS FAILING:

SHORT TO GROUND

Any time the plugs insulator is cracked, or a plug wire gets wet, the spark will follow that path rather than jump the spark gap. Often spark plugs with these problems will idle fine, but misfire under a load or while accelerating or passing. If your engine is missing going up a hill, but runs fine the rest of the time, you probably need new spark plugs and ignition wires.
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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.


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Auto, Car, and Truck Article List

A
ABS: Anti-Lock Brake Systems
ADVANCE: Car ignition timing
ALTERNATORS and Car Battery
AUTOMATIC TRANSMISSIONS
B
BAD CAR DESIGNS
BATTERIES: Auto, Car or Truck
BELTS AND HOSES
BEARINGS
BODY AND BUMPER REPAIRS
BRAKE REPAIRS: Car or Truck
C
Car Washing and Care
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CHECK ENGINE LIGHT
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D
DISTRIBUTORS (IGNITION)
E
ELECTRIC WIRING REPAIR
ENGINES: Car & Truck
ENGINE CLEANING
EXPANSION PLUGS
F
FREEZE PLUGS
FUEL AIR MIXTURE
FUEL INJECTION: Car & Truck
FUEL PUMPS: Car & Truck
G
GAGES AND "IDIOT LIGHTS"
GASKETS AND SEALS
GLASS: WINDOWS AND WINDSHIELDS
H
HEADS & HEAD GASKET
HOSES AND BELTS
I
"IDIOT LIGHTS" AND GAGES
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J
AUTO JACKS: lifting cars safely
K
L
LEAN "Car runs lean"
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Limp Home Mode
M
MIL Light
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N
NO START: Car Won't Start
O
OIL CHANGES
OIL: What's right for your car?
OIL LIGHT ON OR GAGE LOW
P
PCV Valve
Q
R
RADIATORS: Car and Truck
RICH: Car runs rich
S
SEALS AND GASKETS
SERVICE ENGINE SOON LIGHT
SPARK PLUGS
STARTERS: Auto, Truck
T
THERMOSTATS
TIMING: IGNITION TIMING
TIMING BELT & TIMING CHAIN
TIRE REPAIR
TRANSMISSIONS: AUTOMATIC
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U
V
VACUUM ADVANCE
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