Re: Need tech explanation, ignition switch
ill agree on the erratic or no spark condition. no agument there, but the capacitor discharge is measured in milliseconds and the voltage across the M terminals is the same as the voltage in the coil primaries. there is little current and a very short duration. not enough to go both ways, it will either arc across the kill circuits or flow through the coil primaries. unless somehow the impedance is matched, I use impedance here due to the fact we are looking at a very rapid rise and fall of the circuit voltage. its amazing how little resistence is required to turn the pack off. I have had to many issues with corroded kill switches, some of them will read 5-8 Kohms and shut off the spark. I have also seen a bad kill switch kill one pack and not the other on twins. I got that one after 3 other techs gave up.<br /> Alden, contact stevens instruments for a set of coil primary terminal extenders, also snap-on sells a nice Kv tester to oberve secondary spark voltage. <br /> but you need to either have it run up on a dyno or the correct test wheel with a known good inductive tach to insure its a motor issue and give a baseline for further testing.<br /> if you suspect a kill circuit issue simply dissconect the black/yellow wire from the pack harness at the pack.<br /> I have seen kill ciruits with high resistance break down the circuit resistance at high speeds and not at lower speeds. I have also seen internal pack faults,usually in the voltage regulating portion, create a high speed loss of spark thats actually rather smooth.<br /> I prefer an analog meter for this type issue personally because it reacts so much faster.<br /> but if its a kill circuit failure or an internal pack problem your DVA readings will reflect it with a decrease in coil primary voltage. once coil primary voltage drops much below about 60V it quits sparking.<br /> its actually amazing how much voltage those charge coils can put out, thats why the pack has an internal regulator, the faster you rotate a set of magnets around a coil of wire the more voltage is generated and the higher the frequency. be careful playing with the blk/yellow wire, its at the same potential or slightly higher than the individual coil primaries, most run around 200 volts. its non lethal but it will make ya jump.<br /> back when we used ign systems that ran all the ign voltage through the keyswitch we had a lot of low current/weak coil primary voltage problems, now on modern systems the ign switch either opens the circuit for the capacitor ground path or completes it. once completed the capacitor will discharge to ground rather than the resistance of the coil primary circuit.<br /> test each stator charge coil leads for shorts to ground, if no shorts to ground are noted test the loaded stator output, it should be above 150 volts. the coil primary voltage should remain within 10 volts of the stator input voltage, the pack does not step up the voltage, whatever the loaded chargecoil voltage input is the output is about the same.<br /> it does not happen often and I have never seen it on single pack motors but the potential for having one bank run at a different timing is there, thats why I say verify the marks and add one for #2 cylinder so timing on both banks can be confirmed.<br /> I hate to keep saying it but if you suspect a kill circuit issure remove the black/yellow wire from the amphenol connector and retest. be careful as there will be no good way to imediatly shut the motor off. if there is an improvement in engine performance then test the switch and harness, if no improvement is noted odds are the problem is elsewhere.
