Replaced injectors with flow-matched ones from Dave Wheeler @ Advanced Autosport, car has a "good" (read: lean-running) OE pressure regulator from Drago (East Street Racing). Post injector replacement, the car seems to stumble a small bit just on initial crank, almost like the car isn't getting enough fuel pressure, but runs fine within 2-3 seconds.
For the entire time I've owned the car after putting a cat-back on, it seems to pop/burble a bunch when lifting off throttle (indicative of really rich condition, or so I thought). The dyno seems to run lean (this is a tailpipe sniffer, so would run a bit leaner), but I'm really curious as to why the early-on lean condition would occur. My first thought is to put the original FPR back in, in case Drago had screwed it, but dyno time isn't cheap and I'd really like to get my AFRs back in a "stock" range, and not have a car 15 wheel down to the rest of ES for next year. (It has the 9:1 pistons, and 82K on it, so I don't expect it to be RIGHT up front, but I'd be a lot happier being 5 down than 15).
Peak power levels are right what I'd expect on a stock 1994, honestly.
Get a wideband gauge and put a non-modified FPR back on.
Keith, thanks for the help.
Most of my concern is how lean it is in general, yet the engine SEEMS to be running rich (the popping/etc off-throttle). Also, the hyper-lean and VERY low power at low RPM. Is that typical? Any thoughts on the 3200RPM jump?
You really do need a WB on it to see what's really going on. The dillution of a sensor in the tailpipe changes a lot, and will likely give you odd information.
Popping off throttle can also mean that the throttle isn't closing enough to trigger the fuel to turn off- either way, rich misfire or lean misfire, it's hard to tell without the right information.
It's not that unusual for Miatas on a stock ECU to make a single pop! on a shift, about 1 second after you lift. It's endearing.
That first run (the blue one) is odd. I was assuming dyno operator problems, the car wasn't being held at WOT before the run was begun.
I don't think the TPS on the 1994 engine can be adjusted. You could check that the idle switch is engaging on closed throttle, there should be continuity between two wires on the TPS in that case. Sorry, don't have the wire colors handy.
It was pointed out to me that the FPR is "good" on a 1.8 SM, but without a plate, understandably could cause the super-lean stuff that I'm seeing. Since I've got that laying around and it takes ten minutes to replace including the fuel depressurization, I'll give that a shot first.
Also, looking at the graph, it's been pointed out to me by a couple folks that the curve looks REALLY jumpy for something with a smoothing factor of 5. Possibly a CAS/ignition issue? Plugs + Wires are fresh.
I wouldn't call it totally out of line for a stock ECU. Our old Dynojet files used to look like that - there was a characteristic wave in one of the model years. I never ran much smoothing on them though. It's possible that the stock ECU is compensating for low fuel pressure by jacking up the short term trim and you're seeing the results of the O2 signal dithering - but I'd expect a '94 to be in open loop for most of the run.
First two runs are a stock ECU, this is a 1994. You can see the car go into closed loop at 4000 rpm: http://www.flyinmiata.com/tech/dyno_runs/Bernhart_021800.pdf
Thinking I may be a tooth off on timing, meh.
