- Mon Jul 12, 2021 3:14 pm
#51751
Hi everyone, I've built a Lotus 7 replica using a Miata engine, redoing all the electronics from scratch (including coil-on-plugs, slightly beefier injectors, inline fuel pump: it's not turbo-charged, but wanted to keep that as an option). Anyways, soldered together a 0.4.4b, did a lot of tinkering, and to my great surprise, I'm able to start the engine and it idles indefinitely.
Before digging into the tuning, I noticed something un expected (to me): I have it set so the fuel pump just runs continuously. It's rated at 225LPH, and I have a regulator set to ~35 psi. The pump needs to prime to get the engine to start, but after that, by flipping off the pump (cut-off switch) the idle gets much smoother, and doesn't seem to ever get fuel-starved (I've let it run for ~10 minutes with no problems). In fact, flipping it back on will usually kill the engine.
So, my theory (bear in mind I'm new to this) is that the setup is far too rich (dwell time too long etc) so the engine is flooding, but this also makes it possible for piston suction/gravity to provide sufficient fuel when there's no actual load (I can rev the engine just fine etc, but maybe if it was actually moving the car it would stall out due to fuel starvation?).
OK, with that background, my questions are basically 1) does any of this sound wrong/more of a problem than I'm seeing and 2) what best practices are for fuel pump control here? Is it OK to just run the pump all the time (other than some unnecessary electrical load)? And a more specific question, I've heard people talk about how their Miata's fuel pressure goes from ~30 psi "up to X", where "X" might be 60 psi etc...how does this happen? There's just a single pressure regulator, so are these people setting that to the highest value and having a combination of sensor/pulse/ECU dial in the pressure on-the-fly? I hope not, because for the moment I'd like to just set the pressure, turn on the pump at full blast, and drive it a bit...
Thanks for any help/advice, I'm genuinely amazed at how approachable Speeduino made this whole project, this is the first time I've had to even ask something I couldn't quite grasp from the documentation!
Before digging into the tuning, I noticed something un expected (to me): I have it set so the fuel pump just runs continuously. It's rated at 225LPH, and I have a regulator set to ~35 psi. The pump needs to prime to get the engine to start, but after that, by flipping off the pump (cut-off switch) the idle gets much smoother, and doesn't seem to ever get fuel-starved (I've let it run for ~10 minutes with no problems). In fact, flipping it back on will usually kill the engine.
So, my theory (bear in mind I'm new to this) is that the setup is far too rich (dwell time too long etc) so the engine is flooding, but this also makes it possible for piston suction/gravity to provide sufficient fuel when there's no actual load (I can rev the engine just fine etc, but maybe if it was actually moving the car it would stall out due to fuel starvation?).
OK, with that background, my questions are basically 1) does any of this sound wrong/more of a problem than I'm seeing and 2) what best practices are for fuel pump control here? Is it OK to just run the pump all the time (other than some unnecessary electrical load)? And a more specific question, I've heard people talk about how their Miata's fuel pressure goes from ~30 psi "up to X", where "X" might be 60 psi etc...how does this happen? There's just a single pressure regulator, so are these people setting that to the highest value and having a combination of sensor/pulse/ECU dial in the pressure on-the-fly? I hope not, because for the moment I'd like to just set the pressure, turn on the pump at full blast, and drive it a bit...
Thanks for any help/advice, I'm genuinely amazed at how approachable Speeduino made this whole project, this is the first time I've had to even ask something I couldn't quite grasp from the documentation!