84B23F
Well-known member
- Joined
- Feb 11, 2008
- Location
- Kansas, USA
Coil Dwell - I did a duty cycle test with a Fluke 78 Automotive Meter today at idle speed on 1993 B230F NA, and it showed 6% duty time. At 800 RPMs, it takes 75ms to rotate crank once, so 6% times 75ms equals a calculated coil dwell time 4.5ms. Using Mac Automotive Multimeter ET 332, it shows at idle rpm an average pulse width of coil around 5.7ms. Since these valves of 5.7ms vs 4.5ms should be similar, this indicates one of these values is bogus.
From my reads, these higher energy coils, like Bosch LH 2.4's coil, do not take much dwell time to charge. A GM HEI coil, for instance, takes 3.6 milliseconds at 13 volts. Further, as RPM increases, there is less time to charge a single coil. Consequently, to have a good spark throughout engine's RPM range on EFI vehicles, a coil's dwell time should match up to higher RPM, when possible.
On a 4 cylinder engine @ 6000 rpm with a single coil, there is about 5 ms of time to charge a coil. Fluke meter showed via duty cycle calculation above to a coil dwell time of 4.5ms at idle.
It's going to take a good scope to measure dwell time, unless Bosch's single coil specs can be found, but I suspect that Fluke meter's measurement might be more realistic. If true, using GM's LS2 (D585) coils should not be an issue, with respect to coil's dwell time.
From my reads, these higher energy coils, like Bosch LH 2.4's coil, do not take much dwell time to charge. A GM HEI coil, for instance, takes 3.6 milliseconds at 13 volts. Further, as RPM increases, there is less time to charge a single coil. Consequently, to have a good spark throughout engine's RPM range on EFI vehicles, a coil's dwell time should match up to higher RPM, when possible.
On a 4 cylinder engine @ 6000 rpm with a single coil, there is about 5 ms of time to charge a coil. Fluke meter showed via duty cycle calculation above to a coil dwell time of 4.5ms at idle.
It's going to take a good scope to measure dwell time, unless Bosch's single coil specs can be found, but I suspect that Fluke meter's measurement might be more realistic. If true, using GM's LS2 (D585) coils should not be an issue, with respect to coil's dwell time.