Changing Injector Flow Rate Fuel Pressure Multiplier - Will this do anything bad?

[radz28]

Good day all.

Is there any reason that changing Injector Flow Rate Fuel Pressure Multiplier (e.g. [33355]) would "hurt" anything? I'm talking changing the commanded pressure (20mPa) to something like 18 (or even 16)mPa. Would that hurt anything, or cause some sort of torque-reporting issue?

My build is pretty simple (for specific reasons no one else might understand, but there is a method to my madness), and, basically, I just want to be able to push boost up some, and run full-pump E' (my Summer max' content is about 75%). I'm on a stock long block, so no cam or heads (just a 2650 and 103 - stock exhaust/DSX low side). I have been exploring an alternate method of integrating a separate PORT INJECTION controller to the E92 ecosystem. I've been, largely (and apparently), successful in being able to pull fuel from the fuel model and maintain a correct airflow model. My EQs and STFT/LTFTs have been getting closer toward zero-correction as I've driven and corrected more and more. I've been trying to use this method to keep the torque model correct (as correct as I can make it anyways), and have hit a road block, I think.

Until recently, I've been able to use [33355] to remove enough fuel to keep IPWs around 5.2ms and maintain about 20mPa in the fuel rails. BUT - I recently added an upper (came from a 90mm to 85mm), and with full pump E', and temperatures getting into the 60's during the day, that's been enough to completely wreck havoc. Cooler temps' and smaller upper have demanded more fuel, but even after reducing the PE to about .95 (from about .83), and pulling about 5% from the MAF curve, I'm still at the edge from what I can tell. I can still get the E92 to go crazy with the IPWs and drop fuel pressure WELL below 20mPa. Low Side pressure under control, except for when the DI goes bananas, but comes back immediately.

I am at the limit of what HPTuners will allow me to change the multiplier I've been using. I've max'd it out at "2.0000", and it was working just fine until boost weather came and I changed the upper. I've been max'ing out the table above [33355] at 20mPa (and blended down), but it's just not enough now. I can really only drop fuel flow rate by about 25% or so with that value (i.e. the OEM value in [33355] at 20mPa is 1.4456, and I've changed the value {multiplier} to "2.0000"), but I think I need closer to 30-35% in order to keep the E92/DI happy. As far as I can understand, that requires, either HPTuners increase the limit, OR can I drop commanded BASE FUEL PRESSURE (DESIRED) [17071] to less than 20mPa, like it is stock? I mean - can I command 18mPa (or even 16mPa) at airmass near, and at WOT? Would that hurt anything? What am I not thinking of?

So that's my question: Can I lower BASE COMMANDED/DESIRED FUEL PRESSURE to less than OEM's 20mPa? Is there a reason I couldn't? Maybe this is a fruitless effort, but this method seemed to work, up until now, but I'm sure I'm missing something, or this is just not a good idea

Thanks for anyone's time and input. Have a great day.
Chuck

[TriPinTaZ]

It's much easier to drop the high side fuel pressure commanded vs injector multiplier. However, this isn't going to lower the amount of fuel delivered. The ECU is still going to try and deliver the fuel it thinks it should with the MAF and the PE tables. Dropping the rail pressure will just exacerbate your problem by commanding a longer injector pulsewidth. The Injector multiplier will cause the same thing.

You should use Mass Airflow and PE to get injector pulsewidth inline. Then use the port system to make up for the extra fuel. Then adjust the torque model to keep reported torque inline. The injectors can handle longer pulsewidths at lower RPM's as long as fuel pressure isn't dropping hard, but since the injection window has more time (due to lower RPM) you can let the injectors creep up a bit here to like 6-7ms. Then as long as they are coming down the higher the RPM climbs and are around 5.5ms in cold weather. This will give you enough overhead for a real cold day in regards to injectors. Then make up the difference with the port system to get your total fueling in line.