Serving the Gainesville and Hawthorne Florida Area

How Your Car Works: auto system descriptions Get Estimates and Advice by E-mail Think you've been ripped off? Click here for some information that might help Links to other Auto sites and More questions and answers form other readers The Tales of Linda's Lemons Noise Library: got a funny noise? See if it sounds like one of these! Auto articles, tips, and advice Car Killers!!! A list of simple things that can kill your car Car won't start? click here for help!

Return to the Econofix Home Page

Coil: ignition coil


All gasoline engines need good spark to run

All gasoline engines have spark plugs which ignite a fuel / air mixture. This burning fuel propels the vehicle down the road. A gas engine MUST have good spark to run. About half of engine failures (car won't start) are from spark failure (no spark, or no "fire"). The ignition coil takes a low voltage (12 volts on most vehicles) and multiples it into thousands of volts. (low voltage won't make a good spark. High voltage does.) Older vehicles had coils that put out 8000 volts or so. Modern vehicles have colds that produce 20,000, even 50,000 volts.

types of coils and ignition systems

Ignition systems on older vehicles

Older cars had ignition systems consisting of a single coil, and a distributor cap and rotor that "disributed" the spark to the different cylinders. The distributor also had points at first, and later an electronic pickup coil to operate the coil, via an ignition module.

Computer Controlled ignition systems

When car engines started to be computer controlled, at first they used the same distributor/ rotor/coil setup. Later, they moved the ignition pickup coil to the crankshaft, and the distributors didn't have anything in them besides the rotor. Other vehicles (like Honda) had a distributor, rotor, pickup coil, and ignition coil all in one package. The next step was getting rid of the distributor, and firing coil packs directly from a module controlled by the computer. These cars have 1/2 the number of coil packs as they have cylinders. (A 4 cyl will ahve 2 coil packs, a V-6 will have 3, and a V-8 will have 4) Each coil pack will fire 2 plugs at the same time: one cylinder will be on the exhaust stroke, the other on the power stroke) The newest engines have a coil for each cylinder, often a small coil which sits on top of the spark plug. Each coil is controlled directly by the computer.

TESTING FOR SPARK!!! (COULD BE DEADLY if you have a pacemaker, otherwise unpleasant if you get a shock: careful now!!!)!!!

Remove a spark plug wire. They sell spark testers at any parts store, fairly reasonable. (Follow the directions: don't ground to the battery! It will explode! Otherwise, Insert a screwdriver or other metal object in the plug wire end. Hold this wire about 1/8 to 1/4 inch from a metal part of the engine. Have the friend turn the motor over. (making the rrrrr sound like you were trying to start the engine). There should be a nice blue spark jumping off the screwdriver to the engine metal part (pick a part: any part).
DON'T LET THE SPARK GET NEAR THE BATTERY: IT WILL EXPLODE!!!!!!!!!!!!!!!!!!!!
CAREFUL!!!! IT CAN BITE!!!!!!!!!!!!
No spark can be from a bad coil, rotor, distributor cap , electronic igniton module, pickup coil assy., or wiring defect.

Bad Coil symptoms and repair

No spark: total coil failure

A coil in total failure is easy to diagnose. There is a positive and a negative side of the coil. If there is no spark from the coil, disconnect the two wires that feed the coil, and connect a test light between them. Turn the engine over. The test light should blink on and off. If the test light blinks on and off, but the coil when connected makes no spark the coil is bad.

Coil resistance tests

A coil can be checked with an ohmmeter. A typical good coil will measure .6 ohms or so on the primary side, and 8 K Ohms on the secondary side.

Coil testing

On any car, especially a new one, a coil can be bad and still make spark. A good repair manual will have resistance specifications for the primary and secondary coil windings, but sometimes these can mislead you. At one dealership I know, the mechanics take all the plug wires off and spin the engine over. A fireworks show of 3 inch bright blue sparks should arc across the coil teminals on the coil pack, enough to scare you if you're not expecting it. Those are good coils. A wimpy yellow spark that's not that frightening: the coil or coils are bad.

Marginal coil symptoms

When a coil starts to go bad, but hasn't totally failed, it can be hard to diagnose. Sometimes it will run fine, then it can act like it's running out of gas, and then run fine again. As a coil heats up, the internal resistance increases, so a bad coil can start to fail when it heats up, and the run OK when cold.

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
Bad Drivers: How NOT to drive
BATTERIES: Auto, Car or Truck
BELTS AND HOSES
BEARINGS
BODY AND BUMPER REPAIRS
BRAKE REPAIRS: Car or Truck
C
Car Washing and Care
CARBURETORS:Car & Truck
CHECK ENGINE LIGHT
CLEANING: Engine Cleaning
CLUTCH REPAIRS: Car & Truck
COIL (IGNITION)
COMPRESSION: Car Engine
COMPUTER CAR CONTROLS
CV JOINT OR CV AXLES
D
DISTRIBUTORS (IGNITION)
E
ELECTRIC WIRING REPAIR
ENGINES: Car & Truck
ENGINE CLEANING
EXPANSION PLUGS
F
FILTERS: OIL, AIR, ETC.
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
IGNITION COIL
IGNITION TIMING: Car & Truck
J
AUTO JACKS: lifting cars safely
K
L
LEAN "Car runs lean"
LIGHTS: WARNING OR "IDIOT LIGHTS"
Limp Home Mode
M
MIL Light
MANUAL TRANSMISSIONS
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
TRANSMISSIONS: MANUAL
U
V
VACUUM ADVANCE
WARNING LIGHTS OR "IDIOT LIGHTS"
Car Washing and Care
W
WATER PUMP REPAIR
WINDOWS AND WINDSHIELDS
WIRING REPAIR
X
Y
Z

only search Econofix.com


RETURN TO THE ECONOMECHANIX HOME PAGE

Thank you for visiting the ECONOMECHANIX WEB SITE. Please feel free to comment.



>> CLICK HERE: The Econofix Cyber Mall!!! >

The Economechanix Cyber Mall