1990 ACURA INTEGRA IGNITION TIMING
IGNITION TIMING
General Information
Ignition timing is the measurement, in degrees of crankshaft rotation, at the instant the spark plugs in the cylinders fire, in relation to the location of the piston, while the piston is on its compression stroke.
Ideally, the air/fuel mixture in the cylinder will be ignited (by the spark plug) and just beginning its rapid expansion as the piston passes top dead center (TDC) of the compression stroke. If this happens, the piston will be beginning the power stroke just as the compressed (by the movement of the piston) and ignited (by the spark plug) air/fuel mixture starts to expand. The expansion of the air/fuel mixture will force the piston down on the power stroke and turn the crankshaft.
It takes a fraction of a second for the spark from the plug to completely ignite the mixture in the cylinder. Because of this, the spark plug must fire before the piston reaches TDC, if the mixture is to be completely ignited as the piston passes TDC. This measurement is given in degrees (of crankshaft rotation) before the piston reaches top dead center (BTDC). If the ignition timing setting is 6 degrees BTDC, this means that the spark plug must fire at a time when the piston for that cylinder is 6 degrees BTDC of its compression stroke. However, this only holds true while your engine is at idle speed.
As you accelerate from idle, the speed of your engine (rpm) increases. The increase in rpm means that the pistons are now traveling up and down much faster. Because of this, the spark plugs will have to fire even sooner if the mixture is to be completely ignited as the piston passes TDC. To accomplish this, the distributor incorporates means to advance the timing of the spark as engine speed increases.
The Acura PGM-IG ignition system uses various inputs from engine sensors to change the ignition timing in accordance with the needs of the engine. This is all done completely by the engine control computer, in place of the traditional vacuum and centrifugal means of timing adjustment.
If ignition timing is set too far advanced (BTDC), the ignition and burning of the air/fuel mixture in the cylinder will try to oppose the motion of the piston in the cylinder while it is still traveling upward. This causes engine ping. If the ignition timing is too far retarded (after, or ATDC), the piston will have already started down on the power stroke when the air/fuel mixture ignites and expands. This will cause the piston to be forced down with much less potency. This will result in rough engine performance and lack of power and gas mileage.
Vigor
CAUTION
All SRS electrical wiring harnesses are covered with yellow outer insulation for easy identification. To avoid the possibility of personal injury, if it is necessary to disconnect the SRS harness, install the short connector on the air bag, then disconnect the wire harness. Replace the entire affected SRS harness assembly if there is an open circuit or damage to the wiring.
Start engine and allow it to warm up until the cooling fan comes on.
Pull out the service connector, located under the middle of the dash. Connect the WHT/GRN and BRN terminals with a jumper wire.
Check the idle speed and adjust as required.
Connect the timing light to the No. 1 plug wire; while engine idles, point light toward pointer on timing belt cover.
Inspect ignition timing at idle. Timing should be 15 plus or minus 2 degrees BTDC, using the RED timing mark, at 700plus or minus50 rpm in N.
If timing adjustment is necessary, complete the following:
Remove control box upper cover and ignition timing adjuster from control box.
Drill 2 rivets off with a 1⁄8 in. drill bit, then separate stay cover from adjuster.
CAUTION
To avoid the possibility of personal injury, always wear eye protection when drilling. Do not damage adjuster when removing rivets.
Adjust timing as necessary by turning adjusting screw on adjuster; turn adjusting screw counterclockwise to retard timing, or clockwise to advance timing.
After adjustment, reinstall stay cover to ignition timing adjuster with new rivets, then reinstall adjuster to control box. Reinstall control box cover.
