bherd Posted July 25, 2008 Share Posted July 25, 2008 I have a high volume fuel pump on an 83 ZXT. I have built up a PWM fuel pump speed controller to give the pump a second speed, so there are two outputs from the MS of pump ON/OFF and half/full speed. The initial FP rules are still intact, the pump runs for a few seconds after crank and stops with no CAS and I have selected the logic for adding the high/low speed relay which seems to work, was simple so far and kinda cool to do. Initially my thought was above a certain RPM then full speed fuel but that doesn't account for WOT or coasting. So I would love to hear suggestions for pump speed logic or as it relates to the VE table for fuel demand and not just RPM or other paramters that are important (such as WOT?) Hope this makes sense. bherd Quote Link to comment Share on other sites More sharing options...
mobythevan Posted July 25, 2008 Share Posted July 25, 2008 Use the second VE table when pump is in hi mode maybe. Are you using this because your injectors are so large that it won't idle with the pump running full voltage? Just curious. Quote Link to comment Share on other sites More sharing options...
bherd Posted July 25, 2008 Author Share Posted July 25, 2008 Hi Moby, Thanks for all of the helful info posted everywhere, it was invaluable getting to where I am at so far. No, primary reason is that the pump is LOUD. Secondary would be pump life and even heating of the fuel going round and round. I actually have the stock ecu and injectors right at the moment (bigger ones on the shelf to match the T3/T4 I have installed) and am running the MS in parallel (I built a little isolater circuit for the CAS so that they both can run without clamping the signal) so modulating the fuel pump is a natural thing to have it do. The IGN, and INJ wires are taped off waiting to do a cutover one day to MS, but still working through getting the car on the road after a long revbuild Thanks Moby, Bil Quote Link to comment Share on other sites More sharing options...
mobythevan Posted July 25, 2008 Share Posted July 25, 2008 Actually I wasn't thinking it through on the first post. As long as either speed of the pump provides enough flow to build the same pressure in the fuel rail(depending on injector duty cycle at any given spot) then you wouldn't need to do anything special. The only time you would need different VE tables would be if the fuel pressure changes because of the PWM. I bet that won't happen on a stock engine. I would be interested to see if you could run the pump at half speed all the way through WOT and still get enough fuel. You could use a fuel pressure gauge that you could log with megasquirt to see if the pump can keep up with the engine at the lower speed. Quote Link to comment Share on other sites More sharing options...
bherd Posted July 25, 2008 Author Share Posted July 25, 2008 I have already set up fuel pressure to be one of the recorded parameters as I dont trust my abilities to catch a problem like not enough pressure (also have an FMU) by sight sound or smell. My other I/O's are set up for knock detection and boost control. Quote Link to comment Share on other sites More sharing options...
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