Quote:
Originally Posted by spoke
Thanks for the tip. Before I change the CDI I want to make sure the CDI is at fault. I think to get a better idea on the alternator performance I'd need to find a different place to measure its voltage. Measuring at the CDI introduces all the current drops of the CDI wiring, connectors, and relay.
One thing I noticed on the CDI battery voltage was intermittent negative pulses between the normal idle pulses. I couldn't capture these rogue pulses before the engine died.
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You will always get a fair amount of noise on the 12V line, even measured at the battery.
A 'working' Bosch CDI will still fire down to around 7v (albeit with less energy) but below about 10v the tacho is wandering all over the place. Above 18v (failed alt or external regulator) the Bosch CDI is toast as there is no internal regulation but this takes out the power supply so no whine from box.
If it were me I would disconnect the CDI and look at the distributor signals across pins 7 and 31d at the 6 pin connector. On cranking, you should get a zero crossing 'jaggedy sine wave', maybe 10v pk-tp-pk. Post the trace if you can.
Having said that, on a Turbo the most common CDI fault is the signal input circuit failing. We get lots of boxes that still make the whiney noise but they do not fire at all or when the box heats up. Turbo is so cramped in there, hard for the heat to escape.