'90 NA6 Miata with DIYPNP - Engine starts but dies quickly.

[mj1176]

Hey y'all. I have a 1990 NA6 Miata (naturally aspirated) and I just installed my DIYPNP. Specs of the megasquirt install:

-DIYPNP v1.5b board, MS2/E 3.4.2 firmware, TunerStudio MS (registered) v3.0.28
-Sequential injection add-on board, outputs from DB15 added to stock harness
-AEM UEGO X-Series 30-0300 Wideband O2 sensor / gauge (O2 signal output sent to MS directly via jumper from O2 main board to DB15 port.)
-GM IAT sensor placed just before the throttle body
-Stock TPS disconnected, megasquirt using MAPdot

Car specs:

Stock motor, RoadsterSport catback exhaust, K&N cone-style intake filter installed on the end of stock crossover tube w/ 45-degree fitting

I did all the peripheral sensor installs, modified my injector harness for sequential injection, and got the DIYPNP in the car. Tried to start it and it stumbles a bit around 400-500 RPM, then slowly surges up to around 1500-1700rpm before falling back down and dying. I've done a ton of reading, all the msextra manuals and as much of the idle-related tech articles from DIYAutotune as I can find, as well as guides on Miataturbo and miata.net. But everything I'm seeing sort of requires that you have a stable idle or at least can keep the motor from dying without throttle in order to have a starting point for tuning. If anyone can take a look at my tune / log file and point me in the right direction towards achieving a stable idle I'd really appreciate it.

Only thought I've had so far is maybe I should change the idle cells in my AFR table to 14.7 since I'm running sequential injection? I spent a bunch of time getting the wideband O2 signal properly wired into MS and grounded to the DIYPNP board's signal ground so I only had time to try starting it a couple times and it did the same thing each time.

[mj1176]

Welp, between the time I submitted this and when it was approved I was able to get the car idling. Turns out tunerstudio wasn't seeing an AFR signal so I double checked everything and apparently the new version of the UEGO X Series widebands need a sensor ground in addition to the sensor output wire you send to megasquirt. Also had a minor vacuum leak at the T fitting where I spliced the megasquirt vacuum line due to a size mismatch. Got that sorted. At that point the car started and idled, but roughly, and I was able to autotune the WUE and dial in the idle cells in my VE table well enough to get it to idle smoothly so I could verify the base timing. Now that that's done the car idles pretty darn good, so I did 2 quick laps around the block in autotune to see how the car drives. Seems fine so far.

I still haven't done anything with Afterstart Enrichment, Acceleration Enrichment, or Closed Loop Idle. If anyone has input on how and in what order to best tackle those things next, or general advice as to how to proceed with tuning the car, I'd greatly appreciate it. I'll also comment with an updated copy of my tune file and a log from a cold start / short test drive, I'd be thrilled if anyone wanted to look at those and let me know if anything still looks obviously out of whack.

One last thought: As I was reading last night I realized that all the DIYPNP base maps are intended for 91 octane. While I was autotuning today I remembered that I'm still running on about a third of a tank of 87 from before I started the megasquirt assembly/install, about a week ago. If I intend to run 91 in the car, is it as simple as running this tank of 87 down then filling with 91 and re-autotuning the fuel map? If not, can anyone guide me in the right direction?