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Weak spark 175 HPDI Low Voltage to Coils??
Been working on a 175 HPDI running poorly, won't idle unless I bypass the neutral switch to make it idle on 6 cylinders and it still runs poorly. After finding no codes and everything showing normal on YDS, I began testing everything as per yamaha manual. The fuel system is pristine, new pumps, injector pump, and injectors. The plugs are wet and not burning well. Coils all tested within spec.
I attached a CDI spark board and spark was very weak. I tested the wire pairs going to the coils with a DVA and had 9 volts cranking and 12.5v-13v running. The manual says the voltage should be 270vdc cranking and 250vdc running. Is that a misprint? Or is my ECU bad? Pulser coils tested in spec.
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What manual and where within it are you getting your data?
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Yamaha VZ175 manual under "Testing ECU".
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I think the manual is hosed. Confusing at best.
HPDI's use transistorized ignition systems. Not a capacitor discharge ignition system.
Battery voltage to and through the ignition coil to ground. ECM simply disconnects the ground at the appropriate time to cause the primary coil to induce enough voltage in the secondary coil to fire the spark plug.
Seems they are trying to measure the voltage induced within the primary coil as it collapses.
Last edited by yam911; 04-29-2021 at 01:04 PM.
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YDIS can be used to fire the plugs. To check ignition spark. Do you have YDIS?
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Yes have ydis and am familiar with it. I can use this to fire the plugs. All are weak. Barely visible on spark board. I thought there was a misprint in the manual. 270vdc seemed very high to send to a coil. I was aware the positive side was constant and negative intermittent so the manual saying 270vdc is confusing.
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Strange that all of them would be weak. Presumption being that you are seeing battery voltage to each coil as it is being tested. Only thing I can think of is a significant voltage drop to all of the coils.
Have you tested the coils when removed from the motor?
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This from Yamaha literature. Only thing I can guess is they are trying to measure the ~ 250 volts induced in the primary coil.
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