Auto Service Professional

OCT 2018

Magazine for the auto service professional

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O c t o b e r 2 018 A SP 25 primary side of the coil or an air fuel ratio prob- lem. A Chevy Express van came in with an in- termittent stall and intermittent no-start with a PO316 CKP code. e crank sensor had been replaced twice by another shop. e crank sensor on these engines is mounted on the front timing case cover and triggered by the reluctor on the end of the crank. A common problem on these Vortec engines is created by main bearing wear which causes the loss of the air gap between the reluctor and the tip of the sensor causing mechanical interfer- ence. GM will sell you a shim to restore the air gap. On my inspection of the tip of the sensor I found no interference. Let's look at a secondary ignition waveform during the misfire symptom in Figure 24. Notice the loss of the point of pri- mary turn-on. We know that the whole ignition process begins with the CKP input. Notice the waveform in Figure 25 of the CKP signal. You can see the intermittent dropouts of the CKP sig- nal. We simply ran a redundant circuit between Figure 20: 1998 Mustang #5 secondary after fix Notice the good secondary waveform after the plug wire was replaced. Figure 21: 2003 Honda Odyssey Notice the waveform from a V6 Honda with a dead miss and no codes. Channel 2 is accessing the igniter control signal from the PCM to the number 4 coil. Channel 1 is the amp probe clamped around the B+ feed wire to the coils and is set at 200 millivolts per division which converts to 2 amps per division. Notice that there is no primary event to the number 4 coil. COURTESY OF ROBERT BOSCH LLC Figure 19: 1998 Mustang 3.8L #5 secondary Another example from a 3.8L Mustang with an engine misfire from #5 cylinder. Look closely at the secondary ignition waveform from #5 cylinder. Do you see the split firing line and the extremely short spark duration period? There are only two possible causes, one being an open plug wire or two, or an open spark plug resister. The cause in this case was an open plug wire. Figure 18: Secondary cranking KV test Here we're looking at KV demand during a WOT (wide-open-throttle) cranking clear flood mode on a distributor-equipped engine, using the bar graph function. Notice the 24 to 28 KV demand. This is another way of doing a relative compression test. COURTESY OF VETRONIX CORP.

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