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- Dec 19, 2015
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This DIY Article is not VW/Audi specific, but same principles apply to any engine. this is a guideline for info. Please refer to model specific RTFB.
If your engine cranks normally but will not start because it has no spark, or it stalls and won't restart because it has no spark, the problem may be due to any of the following: * A bad crankshaft position (CKP) sensor (on engines that do not have a distributor), or broken, loose or corroded wires from the sensor to the PCM. * A bad ignition module (on engines that have a distributor or use an ignition module separate from the PCM) * A bad pickup inside the distributor (on engines that have a distributor), a stripped distributor drive gear (common problem with plastic distributor drive gears), broken, loose or corroded wires from the pickup to the ignition module or PCM. * A bad ignition coil (on engines that have a distributor and a single coil) * A bad rotor or distributor cap (cracks or carbon tracks that are allowing the spark to short to ground) * Faulty ignition switch. HOW TO CHECK FOR SPARK To confirm your engine is not starting because it has no spark, you can do any of the following to check for spark: CAUTION: Secondary ignition voltage can shock you. Do NOT hold or touch a spark plug wire while cranking the engine. spark plug firing If your ignition system is working, you should see a strong hot spark at the spark plugs when the engine is cranked. If your engine has spark plug wires, disconnect one of the plug wires from a spark plug and place the end of the wire near a metal surface on the engine. You can insert a small Phillips screwdriver into the end of the wire (the plug boot), or a small bolt or nail to provide a conductive path. Then crank the engine and look for a spark to jump from the screwdriver, bolt or nail in the end of the plug wire to the engine. If you do not see a spark, there is an ignition problem. Remove a plug wire and insert an old spark plug or a spark plug tester into the end of the wire (the plug boot). Place the spark plug on a metal surface on the engine, or ground the spark plug tester to the engine. Then crank the engine to check for a spark. No spark indicates an ignition problem. If an engine has a coil-on-plug ignition system with no plug wires, remove one of the coils from the spark plug and insert an old spark plug, a spark plug tester or a screwdriver into the end of the coil. Ground the spark plug or plug tester to the engine, then crank the engine and look for a spark. No spark indicates an ignition problem. Spray some aerosol starting fluid into the throttle (CAUTION: Starting Fluid is Extremely Flammable!). Then crank the engine. If the engine starts, you do NOT have an ignition problem. The no-start is fuel-related. typical distributor ignition system NO-SPARK DIAGNOSIS If the engine has no spark, check for voltage at the coil positive terminal when the ignition key is on. If there is voltage, the problem is on the trigger side of the coil (pickup, crank sensor, ignition module or primary wiring circuit). If there is NO voltage at the coil, the problem is on the supply side (the ignition switch or ignition wiring circuit). If the coil has voltage, the problem may be a bad high voltage output wire from the coil to the distributor, hairline cracks in the coil output tower, or cracks or carbon tracks inside the distributor cap or on the rotor. . . . distributor cap SCAN TOOL IGNITION DIAGNOSIS If you have a scan tool, plug it into the vehicle diagnostic connector and look for an rpm signal when cranking the engine. No signal? The problem is either a bad distributor pickup (on engines with a distributor), a stripped distributor drive gear (common with plastic gears), a bad crankshaft position sensor (on engines without a distributor), a wiring fault (broken or shorted wire, or a loose or corroded wiring connector). If the Check Engine Light is on, use a scan tool to check for ignition-related fault codes. Any coil-related codes (P0351 to P0358) would require testing the coil(s). Misfire codes would tell you the spark plugs and/or plug wires need to be checked. IGNITION COIL CHECKS The ignition coils in DIS ignition systems function the same as those in ordinary ignition systems, so testing is essentially the same. But the driveability symptoms caused by a weak coil or dead coil will be limited to one or two cylinders in a DIS ignition system with a bad coil rather than all the cylinders on an engine with a distributor and single coil. distributorless ignition system Most DIS no start problems are caused by a bad crank position sensor. Many DIS systems use the "waste spark" setup where one coil fires a pair of spark plugs that are opposite one another in the firing order. Others, including the newer coil-over-plug systems, have a separate coil for each spark plug. Individual DIS coils are tested in essentially the same way as epoxy-filled (square-type) ignition coils. First, isolate the coil pack by disconnecting all the leads. Set the ohmmeter in the low range, and recalibrate if necessary. Connect the ohmmeter leads across the ignition coil primary terminals, and compare the primary resistance reading to specifications (typically less than 2 ohms). Then connect the ohmmeter leads across the coil secondary terminals and compare the secondary resistance reading to specifications (typically 6,000-30,000 ohms). If readings are outside the specified range, the coil is defective and needs to be replaced. If measuring the secondary resistance of a DIS coil is difficult because of the coils location, try removing the wires from the spark plugs and measure secondary resistance through the plug wires rather than at the secondary terminals on the coils. Just remember to add in a maximum of 8,000 ohms of resistance per foot for the plug wires. DIS MODULE & SENSOR CHECKS Here is a little trick that will literally show you if a DIS ignition module and its crankshaft sensor circuit are working: connect a halogen headlamp to the spade terminals that mate the DIS module to the coils. A headlamp is recommended here because it puts more of a load on the module than a test lamp. If the headlamp flashes when the engine is cranked, the DIS module and crankshaft position sensor circuit are functioning. Therefore, the problem is in the coils. If the headlamp does not flash, or there is no voltage to the module or coil pack when the engine is cranked, the problem is most likely in the crankshaft sensor circuit. On most vehicles, a bad crank position sensor will usually set a fault code, so use a scan tool to check for a code. Or, check the crank sensor itself. Magnetic crank sensors can be tested by unplugging the electrical connector and checking resistance between the appropriate terminals. If resistance is not within specs, the sensor is bad and needs to be replaced. Magnetic crank position sensors produce an alternating current when the engine is cranked so a voltage output check is another test that can be performed. With the sensor connected, read the output voltage across the appropriate module terminals while cranking the engine. If you see at least 20 mV on the AC scale, the sensor is good, meaning the fault is probably in the module. If the output voltage is low, remove the sensor and inspect the end of it for rust or debris (magnetic sensors will attract iron and steel particles). Clean the sensor, reinstall it and test again. Make sure it has the proper air gap (if adjustable) because the spacing between the end of the sensor and the reluctor wheel or notches in the crankshaft will affect sensor output voltage. If the air gap is correct and output is still low, replace the sensor. Hall effect crankshaft position sensors typically have three terminals; one for current feed, one for ground and one for the output signal. The sensor must have voltage and ground to produce a signal, so check these terminals first with an analog voltmeter. Sensor output can be checked by unplugging the DIS module and cranking the engine to see if the sensor produces a voltage signal. The voltmeter needle should jump each time a shutter blade passes through the Hall effect switch. If observed on an oscilloscope, you should see a square waveform. No signal would tell you the sensor has failed.