Tuning Boosted Miata
Finally tidied up all the parts and pieces. Took a few tries and guessing to get the ancient AEM FI6 running. First started and warmed up with stock ECU under the concept that at idle the engine really isn’t any different from stock.
Drive from Concord to Blacktrax in Fremont was uneventful and a mild test of my patience because no boost was allowed. On ride down she cruised at 60-65 well out of boost, 75 -80 °F outside temp. Intake temps staying around 90 °F despite no shield for filter and coolant was happy at 185 °F. Zero leaks and even A/C still working!
At this point I was stoked because all the work was doing what it should do without any drama….. Oh the stock Miata injectors were running out of capacity at around 6300 rpm so for now I’ll stay below that point until I can get ahold of Mazdaspeed ones to get a little more fueling.
And then Jei turned off the engine. It would not restart. Sending us down a rabbit hole of troubleshooting.
First concern was tack showing zero rpm while cranking (trivia for those curious a miata doesn’t show RPM until it actually starts)
They had a Mazdaspeed Miata in the yard so we borrowed crank and cam sensors to see if they had died on me. No change, still not starting.
Next up was to jiggle wires to find something loose. Found a fun resonance from the IAC valve against the intake tubing, but no issues.
Gave up and reconnected stock ECU, fired up no problem. At this point we were tired and I wanted to go home. Babied the car home staying out of boost.
Next Day…
Checked piggy bank wiring and AEM settings, found no issues with the harness or connectors so just tried to start the car with AEM plugged back in. Hesitantly started…. then went for drive around block at which point I was curious does it restart when I turn off/on the key while moving in gear. Logic says if it restarts the starting issue is not wiring related, if it doesn’t then I’m walking home and it is clearly wiring.
Three times it started right back up when key turned on while moving. Meaning I need to look at AEM settings.
Found the section of tune at 400 rpm and in vacuum had an ignition timing offset and fuel offset. AEM interpolation between cells meant it was pulling a tiny bit of timing and adding fuel while cranking. I wiped out that cell and the car started roughly. After a few adjacent cells were adjusted it reliable starts even when warm. Cool minor problem solve.
So remember engine computers interpolate between cells so it might be a cause of your headaches!
Dyno Results with 10 psi
AEM FI6 tune file - hopefully it helps someone like the fellow I found to start my tuning from.
Updated tune that actually allows close loop ECU control and sets all smog readiness checks - FIC CA Smog Tune
