TheMiataOwner

I recently finished my VVT swap on my 91 and I got it to start cold on a base tune, warmed it up, and had someone tune the idle while the car was hot. It ran pretty decently that night, but I didn’t drive it as it got late.

The setup:
MSLabs MS3 Basic for 90-93
'91 Miata
2001 engine
NB1 intake with VICS wired
VVT wired
NA6 FPR
NB1 fuel rail
AEM Wideband O2
GM IAT
NB2 coils
NB2 injectors
Let me know if you need further details.

Fast forward to the next day, I try to start it up in order to warm it up and auto tune it while driving when it’s warm, however it starts, runs for a few seconds, then the AFR leans out and the car dies. Nothing changed between the previous night and today, except for a firmware update I performed on the standalone ECU as recommended for a better idle. I went from version 1.4.1 to 1.5.1.

An observation I made while this happened is that when the car dies this way, the fuel line has little fuel pressure. I noticed this when attaching a fuel pressure regulator to the fuel feed line to check, where I confirmed I had good fuel pressure while priming the fuel pump and running. I think my ECU is cutting fuel too much but I’m a pretty big novice at tuning so I’m not sure what to look at.

Here are the things I’ve checked and noticed were fine:
Fuel pressure is definitely good, and the pump is strong
Battery voltage when running
Injectors fired
NB2 coils fired
MAP reading looked good
AFRs remain at a safe, if not slightly rich levels before it suddenly leans out and dies
Compression is good around 175-180psi across all cylinders.

The car sounds extremely rough when it starts to lean out, and if I disconnect the FPR (fuel pressure regulator) vacuum line and cap the open port, the car goes on for longer, but then it tries to lean out and the car sounds very rough to the point where I’m afraid to keep it running.

Link to a log of it dying seconds after startup and the current tune:
https://drive.google.com/drive/folde...M6?usp=sharing

Video with FPR vacuum line connected: https://streamable.com/upks84

Video without FPR vacuum line connected: https://streamable.com/vzs602

Attached is a photo of the fuel pressure looking good while running the fuel pump in test mode:

Stoffl

As I've already told you on miata.net you fucked up by updating the FW to 1.5.1 AFTER getting startup and idle tuned.
https://forum.miata.net/vb/showthread.php?t=764998

Pay someone to tune idle and cold-start for fw >1.5.1 engine states or revert FW and tune...