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mr2greasemonkey · 05-20-2007, 03:14 PM

Ignition system basics:

The basic components to the ignition system: igniter, coil, distributor, distributor cap, distributor rotor, spark plug wires, spark plugs. Now if the system is coil on plug or distributorless than you wont have some of the parts. The igniter needs a signal to fire the coil. On vehicles with distributors the sensors ( or pick-ups as we like to call them) are located inside the distributor.

The first test is to see if we have spark. A spark tester is a handy cheap tool that generally plugs into the end of the spark plug wire and then is grounded. You are looking for a nice sharp blue spark. If you don't have a spark tester you can use a screw driver in the end of the plug wire and hold it a couple millimeters from a good ground and crank on the engine to see if there is a spark.

If there is NO SPARK generally the first thing we check is power at the coil and if the igniter is controlling it. The simplest quick test to do is ground the secondary side of the coil ( so you dont burn it up) and then crank on the engine with a test light on the negative side of the coil. The light should be nice and bright with the key on and then flicker quickly when the engine is cranking. If you dont know what the seconday side of the coil is, it's the contact that goes to the center of the distributor rotor. If the light flickers, that will tell you that the pick-up is generating a signal and the igniter is grounding the primary side of the coil.

Now if you have a coil on plug system it gets more complicated because you need an inductive device to check the coil operation. You can try pulling the coil packs and using a spark tester.

So let's say you have power at the coil and still no spark, but the test light only dims on the negative side of the coil when you crank the engine. That's usually a sign of a bad igniter that can no longer properly ground the primary side of the coil. If you get no change at all then you need to check the signal from the pick-ups. Since most MR2s are distributor systems we will only discuss this particular application. The pick-ups are inside the distributor so take a good visual inspection to make sure they are not damaged or coated with oil. You will need the BGB for wireing daigrams and a good mulitmeter to check the signals. Unless you have a good graphing meter to check pick-up wave forms the best that you can do with a digital meter is checking power and resistance across the sensor. This is generally about the time when most people start looking for a "known good part" to swap in for testing. I generally keep a few good spare parts like distributors and airflow meter and oxygen sensors and ecu's around for testing purposes.

Let's assume that you've done all the basic tests and the coil/igniter/sensors all come out good but still no spark. Now you will have to test resistance/continuity through the distributor cap and wires. That white crusty stuff that grows inside the distributor cap can be enough to stop the spark from traveling across it. High resistance, like worn out spark plugs or chaffed wires can cause the spark to prematurely jump to ground before it gets across the spark plug. A couple of quick tests for random ignition misfires are a light water mist with a spray bottle over secondary ignition components. You can actually see the spark jump sometimes or the engine misfire increases. You can also run a jumper wire along the secondary components with one side grounded. If there is a weak point then you're supplying a great groung path and the spark will go to your jumper wire. Snaping noise generated when an errant spark jumps to ground. Even a decent timing light will show intermittent flashes on a bad wire.

more to come....

05-20-2007, 03:14 PM	#6 (permalink)
mr2greasemonkey Once again....yups Join Date: Sep 2005 Location: Portland, OR Posts: 1,440 Thanks: 4 Thanked 54 Times in 39 Posts iTrader Rating: (0/0% )	Ignition/spark Ignition system basics: The basic components to the ignition system: igniter, coil, distributor, distributor cap, distributor rotor, spark plug wires, spark plugs. Now if the system is coil on plug or distributorless than you wont have some of the parts. The igniter needs a signal to fire the coil. On vehicles with distributors the sensors ( or pick-ups as we like to call them) are located inside the distributor. The first test is to see if we have spark. A spark tester is a handy cheap tool that generally plugs into the end of the spark plug wire and then is grounded. You are looking for a nice sharp blue spark. If you don't have a spark tester you can use a screw driver in the end of the plug wire and hold it a couple millimeters from a good ground and crank on the engine to see if there is a spark. If there is NO SPARK generally the first thing we check is power at the coil and if the igniter is controlling it. The simplest quick test to do is ground the secondary side of the coil ( so you dont burn it up) and then crank on the engine with a test light on the negative side of the coil. The light should be nice and bright with the key on and then flicker quickly when the engine is cranking. If you dont know what the seconday side of the coil is, it's the contact that goes to the center of the distributor rotor. If the light flickers, that will tell you that the pick-up is generating a signal and the igniter is grounding the primary side of the coil. Now if you have a coil on plug system it gets more complicated because you need an inductive device to check the coil operation. You can try pulling the coil packs and using a spark tester. So let's say you have power at the coil and still no spark, but the test light only dims on the negative side of the coil when you crank the engine. That's usually a sign of a bad igniter that can no longer properly ground the primary side of the coil. If you get no change at all then you need to check the signal from the pick-ups. Since most MR2s are distributor systems we will only discuss this particular application. The pick-ups are inside the distributor so take a good visual inspection to make sure they are not damaged or coated with oil. You will need the BGB for wireing daigrams and a good mulitmeter to check the signals. Unless you have a good graphing meter to check pick-up wave forms the best that you can do with a digital meter is checking power and resistance across the sensor. This is generally about the time when most people start looking for a "known good part" to swap in for testing. I generally keep a few good spare parts like distributors and airflow meter and oxygen sensors and ecu's around for testing purposes. Let's assume that you've done all the basic tests and the coil/igniter/sensors all come out good but still no spark. Now you will have to test resistance/continuity through the distributor cap and wires. That white crusty stuff that grows inside the distributor cap can be enough to stop the spark from traveling across it. High resistance, like worn out spark plugs or chaffed wires can cause the spark to prematurely jump to ground before it gets across the spark plug. A couple of quick tests for random ignition misfires are a light water mist with a spray bottle over secondary ignition components. You can actually see the spark jump sometimes or the engine misfire increases. You can also run a jumper wire along the secondary components with one side grounded. If there is a weak point then you're supplying a great groung path and the spark will go to your jumper wire. Snaping noise generated when an errant spark jumps to ground. Even a decent timing light will show intermittent flashes on a bad wire. more to come....