GDT70-49 Posted May 16, 2023 Report Share Posted May 16, 2023 Hi guys and gals, first post from me. I'm stumped I am trying to control the low pressure fuel pump on my system using the GP PWM1 output in conjunction with AUX 6. The pump is controlled using a high side MOSFET controller (couldn't break into low side as loom already made etc etc). The circuit looks like this The ECU looks like this Ignition switch active is the only condition and the speed is controlled against engine speed from the table as follows But...it won't work, either in test mode or properly when the engine is started. It does run the pump when started but goes to full 12V and flat out. I've tried swapping the logic and setting the PWM to LOW active state on the GND side and feeding the PWM pin on the board with 12V through a resistor without any joy! However, if I use an Arduino Nano to provide the PWM signal, it works fine... What have I missed?? Quote Link to comment Share on other sites More sharing options...
Vaughan Posted May 16, 2023 Report Share Posted May 16, 2023 What do the Aux 6 Duty Cycle and Frequency runtimes show when testing? Note the pump won't run until the engine is running based on the above Duty Cycle table which is going to make it awfully hard to start it. Note setting active state to high means that 100% Duty cycle is output floating with slight pullup to 12V and 0% Duty Cycle being pin held low (Grounded). Active state low is the opposite way around. Quote Link to comment Share on other sites More sharing options...
GDT70-49 Posted May 16, 2023 Author Report Share Posted May 16, 2023 Sorry, this fuel pump is only maintaining the volume in the swirl pot. I have a HP fuel pump supplying the fuel rails. So engine starts fine as HP pump runs on cranking. I’ll look at the duty cycle and frequencies in the morning. Just in case it’s not obvious, where do I find those? Quote Link to comment Share on other sites More sharing options...
Adamw Posted May 16, 2023 Report Share Posted May 16, 2023 Also dont mistake active state with drive type. Regardless of active state a PWM output will always be a low side drive - that is it can only supply significant current to ground. It is pulled-up to 12V when not driven low but it will only be able to provide about 5mA in the high direction. I would expect that device you have if it is designed for PWM wouldnt require any significant current but who knows. You can check by measuring voltage at the device when the aux is in a high state. TTP 1 Quote Link to comment Share on other sites More sharing options...
GDT70-49 Posted May 20, 2023 Author Report Share Posted May 20, 2023 Tested AUX 6 and logged outputs. All good. Then did something I should have done before, but didn't because how could I possibly have got that wrong....??? Turns out its a little hard to control anything when AUX 6 isn't connected to anything - crimped terminal in wrong connector hole!!! All works fine and as expected now. Apologies for wasting your time. dx4picco 1 Quote Link to comment Share on other sites More sharing options...
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