Starts, runs for 15 sec, dies... read on
 

Okay, posted up a little bit back, still can't seem to solve this one. It'll cold start, fires right up, seems to only run on the start map, soon as it transitions over, falls on its face. Street ported motor, rebuilt less than 10k ago. Compression is good, 90+ on all faces. Emissions harness ive been through over and over. Brand new injector clips. High impedence injectors, no resistor pack. Brand new water thermo sensor, new plugs, new fuel filter, new fuel lines, tried swapping coils, 3 different tps sensors, 2 different boost sensors, 2 different maf sensors, different ait sensor, tested afm, all tps, coil packs, boost sensor, variable resistor, swapped throttle bodies for a stock one in complete working order, tried 2 different fuel pumps, tested fuel pressure - spot on, checked spark - good, checked fuel injector signals with a noid light, confirmed only vacuum leak is the factory metered leak at the thermo valve on the throttle body using a pressurized system and soapy water, redid all grounds, pin out tested ecm per fsm and EVERY value is spot on, no codes using original mazda oem code scanner, verified pin 3b sees starting signal, verified circuit opening relay is functioning properly, hard wired fuel pump direct to battery to confirm plenty of current... yeah, im out of ideas. Oh yeah added 2 additional 16 gauge ground wires soldered at oem junction to connectors 2 and 3 on ecm grounded directly to chassis. This problem started about 2 years ago. I attributed it to bad plugs, deleted emissions and cold start and a possible bad water thermo sensor. The more throttle input the worse it gets, at least til it warms up. Eventually if i start it enough times and the battery doesnt die itll clear out but i havent dared attempted to drive it since shortly after it started this. I notice if i hold the throttle at say 2000 and watch the a/f it just dumps lean and dies, however fuel pressure never changes according to my inline gauge. Sorry for the disastrous list. Here's the video, im open to any and all suggestions. Thanks. https://www.youtube.com/watch?v=9thn...e_gdata_player

Have you tried swapping out the AFM?

Yes tried another afm off my brother's tii, exact same outcome. Both are s4 tii's 332 ecms with 318 pressure and afms

My brother's car obviously runs fine, i checked pin for pin all afm wires from afm to ecm also, i also dont find any loose pins on the afm connector

Also note when i zoomed in on the af gauge i wasnt letting off the the throttle it leaned out on its own, at the very end i tried to give it more gas, then it pops and dies. The door does move freely on the afm.

How is fuel pressure? It is way too lean even for a fully warmed up motor; and yours is cold. It needs more fuel.

Have you tried running it with the afm disconnected to see if it'll stay at idle? Just asking because im dealing with a similar problem.

Monitor fuel pressure during the startup/run. It seems like a fuel issue.

fuel pressure is 36 psi and never varies. Walbro 255, stock fpr, stock primaries, aftermarket 720 secondaries, brand new fuel lines, brand new fuel filter. afm disconnected doesnt run for half that time.

Check that the injectors are wired correctly. This started 2 years ago though? Has the car sat since then until now?

The car isnt a dd but i used to drive it regularly, well that drivetrain anyhow. It was all in a coupe and i swapped it. The problems started in the coup but wasnt as bad. It progessively got worse so i assumed plugs and possible bad water thermo sensor. So when i tore it out i replaced all the exterior gaskets and hoses, installed new plugs and sensors, deloomed the harness and checked all the wiring and connectors, installed new injector clips tested all the harness with a fluke meter to confirm proper repairs and connections

check to make sure fuel lines are not clogged. seems like a filter, line or pump issue. afm would not allow it to run that long If dead or leaking.

I seriously suggest checking the return line or making sure your vent line is open, watch it be as simple as vapor lock ;)

Lines and filter are brand new front to rear. I get fuel and the appropriate pressure at the rail and return line has fuel in it. If i fight with it long enough and the battery doesnt wear out itll eventually run. Used to just start shitty at first but if i held the throttle at 1500-2000 for a bit it would be fine. I attributed that to the lack of cold start help from the throttle body as the old.one was modded. I had it running a few weeks ago just by fighting with it for 30-45 minutes. Then it finally started idling and quite dying and i set tps and verified ignition timing was on but it still hesitated pretty bad til the secondaries kicked in then it would take off. So i swapped the primaries with a set of spares and still same problem. When it was idling on its own it read lean when id stab the throttle under 3500 rpm.

I had the same 15second and die issue it was the fuel pump wiring
Just do the fuel pump re wire on it
i ran 14ga wire from battery to a switch then to the pump and it solved my issue

Fuel pump related............