How to Test an Ignition Igniter in a 1987 Toyotaby Don Bowman
The 1987 Toyota ignition system consists of the distributor -- which houses the coil and crank sensor -- ignition igniter and the engine computer. The crank sensor sends a signal relating the position of the crankshaft relative to top dead center on compression stroke to the engine computer. The computer determines the appropriate timing and sends the signal to fire the spark plugs to the igniter. This activates a transistor in the igniter, which fires the coil. The igniter then sends a return signal to the computer of confirmation of firing. The computer uses this to regulate the firing of the fuel injectors.
Locate the igniter. It is a 2-inch square box located either on the driver's side fender well or on the side of the distributor. Inspect the electrical harness plug in the igniter. Notice that there are five wires in the plug. The only two that you are concerned with are the top and bottom wires to the extreme left side of the plug. The top wire is the signal from the computer, and the wire below it is the confirmation of firing going back to the computer. When the ignition system fails in a Toyota, generally it's because the igniter transistor has gone south. To confirm your diagnosis, the crank sensor and the coil should be checked in the process of elimination.
Push a needle or pin through the top left wire in the igniter connector. Connect the voltmeter's red lead to the pin and the black lead to any good ground, preferably on the engine. This test will work with the voltmeter only if the engine will not start. When the engine is cranking over, the voltage should rise to 5 volts followed by a drop to 0 about three times a second. If the engine starts, the signal would oscillate at a rate of 15 to 25 times a second. At that rate it would be impossible for even Superman to see any dropouts or glitches. This is where an oscilloscope is needed, because it shows a sine wave taken at intervals.
Watch the display for a pulsating signal, while a helper cranks the engine. If the signal is present, go to the wire below it to the left and repeat the same procedure. If the signal is not present or erratic replace the igniter.
Check the coil to confirm the diagnosis. Remove the distributor cap with a Phillips screwdriver. Look at the coil, located right below the rotor, for carbon tracks or cracks. Make sure the key is off. Pull the two wires off the side of the coil.
Connect the red and black voltmeter leads to the vacant terminals on the coil. Turn the voltmeter to the 1k ohm scale. There should be 1.2 k to 1.5 k ohms. If the resistance is other than this, replace the coil. If it is good, replace the wires.
Check the crankshaft sensor for operation. Turn the voltmeter scale back to volts. Look for the three-wire connector on the side of the distributor. Push the needles through the upper and lower far right wires. Connect both voltmeter leads to these pins. Crank the engine over and watch the display for oscillating voltage from 0 to 5 volts just like the ones seen when testing the igniter. If the signal is there, the igniter is definitely bad. If the signal is deficient, replace the distributor.
Items you will need
- Sensitive digital voltmeter or an expensive oscilloscope scanner
- Sewing needle or pin