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IGNITION TIMING

Lewis

Lewis

Member
IGNITION TIMING

Most engines (except diesels) use an electric spark to ignite a fuel/air mixture. The fuel burns and powers the car. This electric spark has to happen at exactly the right time or the engine will not run properly. This is called "Ignition Timing". When a mechanic "Sets your timing" during a tuneup he is adjusting your ignition system to fire the plugs at the proper time. 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. You might hear it when going up a hill on the interstate: a rattling sound that goes away when you downshift or get off the gas.
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. Official word from the manufacturers is that a"little" ping is normal, although they don't define "a little".

Basic Ignition System Components

Your ignition system supplies that spark to a spark plug via a set of spark plug wires, or ignition cables. The thousands of volts used to fire the plug comes from one or more ignition coils. Over the years manufacturers have used several different ways to operate these coils: BREAKER POINT IGNITION

Cars used to have BREAKER POINTS to fire the ignition, and as they wore the timing would change and need to be adjusted. Whenever you replaced the points during a tuneup (about every year) you had to reset the timing. This was when you needed a tuneup every year or so. ELECTRONIC IGNITION

Since the 1980's most every car has some type of electronic ignition. Since there are no points to wear, the timing should never need to be adjusted unless you take the distributor out of the car. On a lot of newer vehicles you can't adjust anything: it's all controlled by the computer. WATCH OUT! A lot of people have a rough run problem with their car, take it to 3 different shops for a tuneup, and end up just getting 3 new sets of plugs without fixing the problem.AVOID THIS! Don't go in just asking for a tuneup: give a specific complaint: like, "It's hard to start in the morning", or "It's getting bad gas mileage".
COMPUTER IGNITION

Newer vehicles have their ignition and fuel controlled partly or entirely by the vehicle computer. Many of these have no distributor: the computer fires multiple coils directly. You cannot adjust the timing on a vehicle that has no distributor, unless you reprogram the computer. SPARK ADVANCE

To get the most power out of a motor the spark has to happen a bit before it gets to the top of the cylinder. As the engine goes faster the spark needs to happen earlier and earlier. This is called "Spark Advance". Older cars had vacuum advances, centrifugal advances, or a combination of both. On newer cars the computer controls the spark advance. TYPES OF ADVANCE MECHANISMS

VACUUM ADVANCE

A vacuum advance is on the side of the distributor, usually a cone shaped metal unit with a vacuum hose connected to it. As an engine comes under a load it cannot tolerate as much spark advance. Also, when an engine comes under a load, intake manifold vacuum decreases. So the vacuum advance works out well by retarding the spark (less advance) when the engine comes under a load. CENTRIFUGAL ADVANCE

As a motor goes faster it needs more spark advance. Picture the old flyball governors on the old steam engines (and Frankensein movies) Centrifugal advance mechanisms are inside the distributor. They have weights that oppose springs, and engage a pivot mechanism that advances the spark as the distributor spins fasrter. COMPUTER CONTROLLED ADVANCE

Newer cars use computer controlled electronic ignition to advance the spark. They use a number of sensor inputs to calculate ideal ignition timing. TIMING MARKS

Timing is measured in degrees of crankshaft rotation. When a piston is at the top of it's cylinder, it is said to be at "TOP DEAD CENTER, or TDC. A mark is placed somewhere on the crankshaft to indicate this position and labeled "ZERO DEGREES OR TDC. This mark is used to set the ignition timing. BEFORE TOP DEAD CENTER (BTDC)
 
The spark advance varies as to engine speed, but it is set to an initial base setting, called BASE TIMING. This is measured in "DEGREES BEFORE TOP DEAD CENTER". In a manual, or on a sticker under the hood, you'll see something like this: IGNITION TIMING: 12 DEG. BTDC. Rarely a car will set BASE TIMING to a few degrees AFTER top dead center (Some VW Rabbits: 3 degrees ATDC), but these cars have VERY agressive advance mechanisms that put the timing into the BEFORE top dead center range really quickly. TIMING MARK LOCATION

Somewhere on the motor's crankshaft there is a timing mark (usually on the front pulley, or Harmonic Balancer.) Sometimes it's just a tiny pointer which you align with notches on the front pulley. Some cars have a piece of tin about an inch long by the pulley with dregrees embossed on it. Some have degrees engraved on the harmonic balancer, with a pointer to align them with. Some vehicles have the timing marks at the back of the engine on the flywheel: you view them through an acess hole in the bell housing.A CUTE TRICK
WITH THE ENGINE OFF !!! clean off your timing marks. Very often they are hard to see because of dirt and grease. With some chalk or paint go over the timing mark so it will be easy to see.
The typing correction fluid "White-Out" works really well for this.
ADJUSTING IGNITION TIMING: METHODS OF "SETTING YOUR TIMING"

On newer vehicles you can't adjust the timing without reprogramming the computer. You CAN buy performance computer chips, but that doesn't really count. Basically, if you don't have a distributor, you can't adjust your timing.
WARNING!!! BEFORE YOU BEGIN: DISABLE THE ADVANCE
Many cars run a lot of advance at idle. If you don't disable this advance and set the timing to the mark the spark will in reality be very retarded and the car will run poorly.
DISABLING THE SPARK ADVANCE

Vacuum advance distributors

Disconnect and plug the vacuum line(s) going to the vacuum advance on the side of the distributor Centrifugal advance distributors

Set timing with engine RPM as low as possible: under 1000 RPM
Some folks with centrifugal distributors static time them: (see below) Computer controlled distributors

On many cars you disconnect a wire, some you jump a wire between 2 terminals on a connector, others you put into diagnostic mode. Check out the manual for your car: the manufacturers have too many ways to list here!
TIMING LIGHTS

A timing light is the most common way to check ignition timing. It is a strobe which is activated by whichever cylinder the engine "times" off of: #1 cylinder on most every vehicle, except some International Trucks, which for some resaon time off the back cylinders (6 or 8), and have timing marks on the flywheel . Some other motors, especially front wheel drive motors, DO also have timing marks on the flywheel, visible through a small hole in the bell housing. Some motors have timing marks both places. The strobe "stops motion" and shows the timing mark and pointer. You can also check the advance operation: rev the engine and you'll see the timing mark move.
ELECTRONIC TIMING PROBE

Mostly on GM, a magnetic sensor fits into a tube by the front pulley (harmonic balancer). You view the timing degrees on an LED digital readout. All cars set up for this have traditional timing marks next to the hole for the timing sensor probe.. STATIC TIMING

When you put a motor together you HAVE to static time it or you'll never get it started. Align the timing pointer on the harmonic balancer (front pulley) with whatever degree setting the motor uses for its base timing. Loosen the distributor and move it back and forth. Then use one of the following methods: THE SPARK METHOD: WATCH OUT! IT BITES!

Turn the ignition on, remove the coil wire from the distributor, leaving it hooked to the coil. Put the loose end of the coil wire near a good ground AWAY FROM THE BATTERY: IT WILL EXPLODE!!!
As you rock the distributor the coil will spark. After you "play with it" a bit you can see where the spark is happening as you rotate it. Find that spot and bolt the distributor down. THE VISUAL METHOD

When you build an engine the coil isn't working yet, but you can still static time it. Remove the cap. On the older point ignitions set the distributor where the points are just about to open, but are not open yet. Electronic ignition distributors use 2 different sensors to fire the coil: the RELUCTOR and the HALL EFFECT SENSOR.
RELUCTORS

Reluctors are star shaped and located just below the distributor rotor. The reluctor is magnetic, and it induces a current in a PICKUP COIL (WHICH IS REALLY A SENSOR) which fires the IGNITION COIL. Align one of the points on the reluctor even with the center of the pickup coil and you are static timed. . HALL EFFECT SENSORS

Hall effect sensors are also under the rotor, but they have a series of windows cut in a piece of tin. These windows pass between a pickup assembly, where they interrupt a magnetic field in a HALL EFFECT SENSOR.
These fire when the window just clears the center of the sensor. In all cases static timing should be done like this: your "finishing turn" should be in the direction OPPOSITE the rotor rotation direction. This way you are moving in the direction the engine rotates and you get an accurate setting.

RACE TUNING, OR TUNING BY EAR

To get the most power out of an engine you really need to give it as much advance as it will tolerate without preignition, or pinging, also more accurately called "spark knock" This setting is varies according to how good your gas is, outside temperature, humidity, and altitude above sea level, to name a few. A lot of racers (and mechanics) I know set their timing by specs, but then leave their distributor slightly loose. They'll advance the spark until it pings, then back off it a bit. For a rough timing setting you can turn the distributor one way until the engine starts to die. Turn it the other way until it starts to die. The correct timing is approximately halfway between these 2 points.
A "CUTE" SETUP: MID 60'S TO MID 70'S TOYOTA COROLLAS
These Corollas had a small white knob on the side with "R" and "A" and a couple of arrows. This knob when turned advanced or retarded the ignition timing a bit. The reason was to allow drivers to compensate for various octanes of gas. Get a cheap tank of gas and your engine pings a bit? Turn the knob a bit. Find some good gas? Advance it a bit for better gas mileage. This in effect gave the driver the ability to easily "race tune" his motor without tools or major hassle.
 
:lol i can still set the timing on 03 nissan frontier as has the older style distrubitor ignition, but unless you move those things there no need to set base timing. i have over 130k miles on my nissan and i have never reset base timing.
 
Jason I think when my drive belt snapped on my Ford Escort and wrapped around the crank pulley, it threw the timing off, stretched the belt, because I timing belt slap on the cover when it first starts when cold. And also very poor low end power as well as poor gas mileage. The car has been sitting mostly since last November, now I am ready to fix it. But before that belt wrapped around that crank pulley, I did not have this problem.
 
hmm no valves bent? set the timing and check vaccum and see if it has that sign of a bad vavlve or other things.
 
It is a 2.0 non interference engine so the valves are okay. I am going to change the belt and reset the timing, an the d also change the fuel filter car is a 98 and I think that is the original filter. I am not going another winter without a car, I always has to borrow my moms wheels.
 
i dont think you can set base timing in that. hmm you dont have acess to lab scope to look at the ignition system do you. that would tell you alot.
 
jasoncran said:
i dont think you can set base timing in that. hmm you dont have acess to lab scope to look at the ignition system do you. that would tell you alot.
Click to expand...
No I don't have one. But when the timing belt popped, it popped while driving and cut the car off by wrapping in between the crank and pulley. Now when AAA showed up with a flatbed, I had already unwrapped the belt. So when he lowered the flatbed and asked me to drive up on it the car had very little power, so he had to put the cable on it and pull it up. So I am thinking jumped timing, from that belt all off a sudden jamming a running engine. Also what if it knocked out the crank position sensor.
 
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a code scanner with the ability to look at pid data would tell if that happened but well if the timing belt jumped time and it had to be towed. first fix the belt and set the timing that way. i bet that is the problem. exhaust valves opened at the same time intake is doesnt allow for much compression.
 
Yeah I am going to replace the belt and the tensioner. I can drive but the power is real low, I have to floor it almost to get decent power. But I think that it has jumped time.
 
lewis, did it ever occur to you that the tranny might be bad and the converter isnt putting the oil pressure needed?

try putting it in first and see if that occurs.
 
The trans is in great condition. The only problem with the trans system is the neutral safety switch, which has nothing to do with the internal parts.
 
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jasoncran said:
ok, i dont recall you saying that you verified the timing belt jump or the tensioner on it whent bad.
Click to expand...
Well before the wrap around the crank shaft, there was no timing belt slap against the timing cover. So that should tell me and you a lot.
 
did you check the harmonice balencer often those do go bad if they have rubber in the middle of them? still that shouldnt affect power. my mom topaz had one that sounded like timing belt slap.i took that off and it fell into two pieces and all it was the first time was age and the second time the water pump locked up and throw the belt and the harmonic balancer went as well.
 
Well when I take it off I will see. But today's belts really don't give, it is more than likely the tensioner failing I will change all that along with the timing belt idle pulley.
 
what they give, i have seen them come off. its either from the tensioner or an accessory locking up. you did check the ac and ps and altenator for bearing play or seizure i hope.
 
From Wikipedia, the free encyclopedia

A timing belt is typically rubber with high-tensile fibres (e.g. fiberglass or Twaron/Kevlar) running the length of the belt as tension members.[6]
Rubber degrades with higher temperatures, and with contact with motor oil. Thus the life expectancy of a timing belt is lowered in hot or leaky engines. Newer or more expensive belts are made of temperature resistant materials such as "highly-saturated nitrile" (HSN).[citation needed] The life of the reinforcing cords is also greatly affected by water and antifreeze. This means that special precautions must be taken for off road applications to allow water to drain away or be sealed from contact with the belt.
Older belts have trapezoid shaped teeth leading to high rates of tooth wear. Newer manufacturing techniques allow for curved teeth that are quieter and last longer.
Aftermarket timing belts may be used to alter engine performance. OEM timing belts "will stretch at high rpm, retarding the cam and therefore the ignition.[7] Stronger, aftermarket belts, will not stretch and the timing is preserved.[8] In terms of engine design, "shortening the width of the timing belt reduce weight and friction".[9]

 
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