FPR vacuum source for VVT engine swap and MS3X?
 

Hi, I swapped in a 2003 VVT 1.8 engine into my 97 Miata earlier this year. I have it running pretty well on a Reverant built MS3X Basic ECU (no power adder yet). However, now that I have more experience with the setup, I want to take care of a couple of loose ends and go over the entire tune.

One part of the swap which I still have some doubt about is the FPR. I am running a reworked set of OEM NB2 injectors with a 99-00 fuel rail and the original 97 FPR in a return style configuration (OEM 97 fuel pump). The original NA FPR setup had the vacuum source going to an ECU controlled valve. Per the NA factory manual, that valve was used by the ECU to lower fuel pressure at times, presumably for fuel economy or emissions. I ripped out all of the OEM emissions controls, including the valve for the FPR vacuum source during the swap.


1) I currently have the FPR vacuum line disconnected (not connected to any vacuum source). With a NA application, is there any reason to reference the FPR to intake vacuum full time?

2) If I connected the FPR to a vacuum source and retuned, I am thinking that it would flatten out my VE map, which currently ranges from about 40 at low pressure to about 90 at atmospheric.

3) Also, I am thinking that having the FPR not referenced to vacuum may have impacted my required fuel setting... I ended up setting it to 11.3, which may not be normal for NB2 injectors run at NA fuel pressure levels.


I can test all of this out when I have a chance to work on the tune again, but getting some pointers would be appreciated.



Note: I understand why the FPR is normally connected to the intake manifold in boosted applications (ie so that fuel pressure can increase relative to pressure above atmospheric). However, with a NA engine, it isn't as clear that fuel pressure needs to be varied like that.

OP, what did you end up doing or finding out? I understand that it should just pull from an intake manifold vacuum

Hi there. I now have the FPR connected to a manifold vacuum port.

I recently upgraded the firmware on the MS3X to the latest Beta build and have noticed solid improvements across the board in drivability, stability of PID's, etc.

The main culprit of tuning issues for me has been VVT. Looking through the logs, it is easy to have VVT making angle changes while cruising at highway speeds. This causes oscillations in the MAP signal, causing fueling to fluctuate.

I have been working on my tune the past couple of days. My latest VVT map and VE table can be seen in the screenshot. I avoid VVT angle changes near idle. It is also important to implement the right AFR and Timing values to help out idle recovery (i.e. go richer below your usual idle RPM, add timing below your usual idle RPM).

Hope this helps.