PWM logic assistance

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Tapps33

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Hey guys! I’m hoping someone in the forums understands how the LR ECU handles PWM signals?

Long story short, I’m in the process of swapping to an electric water pump and electric cooling fans. The only real problem I haven’t solved (aside from how to route the serpentine) is how to fool the computer to think the fan is still there.

As far as I can tell, the ECU sends a PWM signal to the fan for rom requirements, the fan in turn sends a PWM return signal indicating how many rpm’s it’s actually turning. Thus, if it ever gives out, the fan won’t meet the required speed and you’ll throw a code.

So the big question is, does anyone have any idea how I could fool the computer? I’m guessing there’s got to be a simple logic circuit I could put together to simply mirror the rpm request into an rpm output?




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Nechaken

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Have you been able to capture output from either of the circuits? Might be as simple as optocoupler ? Is the RPM return signal really PWM, and not just a tach signal ?
 

Tapps33

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As I understand it, the fan, even at full lock turns at a different rpm than the engine. This is just due to the crank pulley vs fan pulley diameter difference. Take it one step further, and when the fan isn’t at full lock, which in theory is most of the time, is spinning completely different than the engine. So it’s definitely not a tach signal.

Unfortunately, I don’t have any signal capture. I suppose at some point I could go unplug the fan wire and connect to it and record it somehow? To be 100% honest, my experience with PWM signals is pretty limited, I’m not even sure how to capture one...an o-scope is all I can think of to visualize it.

I wonder if it’s something as completely simple as looping the signal directly back to the ECU....so the ECU sees exactly what it sends...[emoji848]




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