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Post by airindestrangler on May 16, 2024 14:55:35 GMT -5
The "mysterious" sensor mounted close to the clutch bell on EFI models from 2018 and later, is nothing more than a pickup coil fed to the ECU, that again measures the frequency (and possibly the voltage, but it's not that likely) and messes with the ignition timing when the frequency reaches the set limit (about 400Hz) internally in the ECU. To circumvent this we need to lower this frequency somehow. A lot of people have removed two of the magnets on the clutch bell to halve the frequency that way, but this method is more or less irreversible and if you want to revert things back to legal, you will probably have to pay dearly for a new clutch bell with all the magnets intact. We can do this a better way by carefully feeding the ECU with a fixed frequency generator working below 400Hz, since it's only the max frequency ECU is looking for and it doesn't seem to care for anything else in this world. I used the venerable NE555 timer chip. The same result can be achieved with a tiny micro controller or a two-transistor bistable flip-flop, too. I used a small two channel relay, where one channel is used to switch between the two signal sources and the other is used to latch the circuit on when a hidden push button switch is pressed. I'll try to answer questions if any.  |
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Post by FrankenMech on May 17, 2024 13:01:36 GMT -5
Nice 'fix' using the very widely available 555.
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Post by GrumpyUnk on May 20, 2024 7:58:08 GMT -5
Have you charted or measured what happens to ignition timing above 400Hz? IOW, does the ECM remove any spark advance to lower power produced? ... Or does it interrupt spark once frequency is reached?
The old(late teens) machine I had with a sensor inside the CVT did something. I never checked prior to selling. The PO disconnected it, and I suspect it was an interruptor to limit top rpm.
Nice job. I have no idea what you are doing with the stacked diodes.
tom
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Post by airindestrangler on May 20, 2024 11:05:59 GMT -5
Sorry, no I didn't do any extensive measurements because my old Keysight scope decided to quit on me so I had to use a multimeter with TRMS and a counter instead. Yes, it definitively messes with the igtn. timing when the frequency is reached. I'm not sure, but I've heard it retards the timing(?)- not cutting the spark, which would cause all sort of problems with unburnt fuel and screaming Greta's.
The four diodes are for reducing the voltage to the NE555 (max. 15V for most versions). I thought it was a simple solution to implement and it will also "ruggedize" the circuit a bit. We are after all in an automotive environment. The voltage divider on the 555's output is just there to be a bit careful with the ECU. An afterthought that I've had is to put a somewhat high value resistor across the pickup coil, just to keep the "freewheeling" voltage down a bit. Don't know if this actually necessary though.
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Post by FrankenMech on May 22, 2024 9:12:52 GMT -5
Rather than stacking diodes use a resistor and zener diode. The automotive environment can see 400V load dump transients and the system regulator is cheapo trash.
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Post by airindestrangler on May 22, 2024 17:30:39 GMT -5
True enough about the diodes, but then you probably have to buy at least a pack of five, or maybe ten, zeners and the same for the resistors, if you're not having them at hand already. Some diodes in series creates less heat, is dirt cheap. simple and just as reliable.
Yes, automotive environments can be extremely noisy.
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Post by FrankenMech on May 22, 2024 23:17:12 GMT -5
The diodes in series does not work near the same way as a zener/resistor to regulate voltage.
I do happen to keep zeners and other parts in my junk stores...
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Post by airindestrangler on May 23, 2024 3:51:29 GMT -5
My intention wasn't to regulate the voltage to a smooth and stable level, but to lower it to be safe for the 555.
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Post by FrankenMech on May 23, 2024 8:49:44 GMT -5
Stacked diodes won't do that.
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Post by airindestrangler on May 23, 2024 9:24:57 GMT -5
Voltage drop is about .7 Volts per diode, dropping 2.8 Volts in total for a normal current draw.
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Post by FrankenMech on May 23, 2024 14:34:18 GMT -5
Read the datasheet again. The voltage drop is current dependent. It varies with the current and while the voltage drop may be 0.7V on some diodes at rated current the 555 does not draw that much.
I am just trying to help you understand what is going on. I am just telling you a zener and resistor is a better solution. Stacked diodes will do no good when the voltage rises to 20 volts or higher. Get your scope working and check out a scoot's electrical system.
I was a mechanical engineer but I also had to do electronic design for many of my years. Now that I have had three strokes I don't do that anymore but I have forgotten more than many people know.
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