![]() I've been trying to figure out this same problem for awhile by poking around other systems. The VW common rail TDIs use glow plugs which also function as cylinder pressure transducers, so being able to implement them into Megasquirt firmware for use as a limit spec would save people from blowing head gaskets or worse. Without the cylinder pressure transducers there is no way of knowing how much boost and fuel is safe. It really requires a steady state engine dyno (preferably A/C) and cylinder pressure transducers to safely tune a diesel. I do not see street tuning as a feasible way to tune a common rail on a theoretical megasquirt for common rail diesels. I will say that common rail tuning is much more complex and precise than port injection on a MS3X on my 13b RX-7. At high speeds and loads being able to crank up the rail pressure improves power by giving us a smaller pulsewidth, which offers us more flexibility over SOI (start of injection) timing and less concern over just getting all the fuel required into the available injection window. At low speeds and loads there is no need to run 2000bar, and sometimes a longer pulsewidth improves emissions and BSFC. Being able to control rail pressure allows you to vary the required injection pulse duration. One tuning parameter being underestimated in importance is HPFP command. ![]() There is typically only one pilot and the main injection pulse under most operating conditions. We use two different pilot injections and two different post injections so that we can have greater resolution in the fuel maps. The pilot injection is the big difference between an 80s Merc diesel and a modern common rail in terms of NVH and noise levels at idle. I would recommend keeping the pilot injection on a car that would see any street use. A good percentage of the diesel fuel used is for everything besides making power. The two pilot pulses are used to reduce clatter. Post 4 - 165-185* ATDC - DPF active regeneration via in cylinder dosingįrom a pure performance standpoint, there is absolutely no need to for any more than 1 main injection pulse. ![]() Post 3 - 155-165* ATDC - DPF active regeneration via in cylinder dosing There are typically 7 possible injection pulses: We use a current probe on the #1 injector to give us feedback and I am sure they are not variable voltage. I'm not sure of the voltage they run, but I will look into. The injector wires are 22ga, and you must keep in mind how small of an injection window there is for up to 5 injection pulses, not included post 3 or 4 injection (in cylinder dosing for DPF active regeneration). These injectors do not need anywhere near the power discussed in this thread. The current standard is the Bosch ECM, injectors, and HPFP running up to 2000bar. I am also a CPE engineer so here's some input from tuning 4 banger oil burners:Īll the modern common rail fuel systems I've worked with use piezo injectors. I have a whole bunch of information I can use at my disposal I also work at the local International (Navistar) dealership which is who produced these engines for Ford. If this is true, then the factory IDM could be used and the MS3 just needs to supply 3 circuits to the IDM to control the injectors, 4 if it is ultimately ground switched. It's the only way I can see how it would work. Let me know if this makes sense and is even plausible. The PCM supplies voltage through one, two, all or none of the wires to the IDM and then completes the circuit with ground when that injector is called up. I assume that the way this works is this: There are 3 signal wires and a ground that run from the PCM to the IDM. The kicker is, you only need 4 wires going to the IDM from the MS to activate the IDM the way the factory PCM does. I read some of this thread as I have a 97 250 HD with a powerstroke that I was thinking about seeing if it was possible to run a diesel with MS.
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