Just about to wrap up the megasquirt install and I got to thinking, how much worse is my open loop AFR compared to others? I saw Emilio in an older thread quote the worst he has seen is 12.5:1 on stock ecu. I see around 11.5 in the mid range tapering to about 10.2 at redline. Lots of breathing mods, but stock BP5A ecu.

How bad were your AFR's on a stock ecu?

 

The last few people that observed oem ecu afr's on an nb seem to have observed the same: pig rich up top, mid 11's to mid 12's midrange, and stoich pre 3k or something

search scenturions posts, he did testing on this and posted plots IIRC

 

It's been a really long time since I put a wideband on a stock miata but I was remembering it dropping to 11:1 at anything over 4000rpms.

I did a 2hr drive at 90mph with the top down in a stock 10AE and got like 14mpg.

 

Mine is pretty far into the "pig rich" area, and my cruising rpm at 80 is almost 4500 rpm (6 speed and 4.30). I can get in the mid 20's cruising, but it all goes to hell with hard driving.

I am basically just curious if the old "more airflow mods makes it richer on stock ecu" is true or if I made poor choices with modifications.

 

more airflow on stock ecu should cause it to lean out.
if you're richening up, it's more indicative of losing power or not gaining any.
for the most part

 

Or possibly moving to a different, more poorly tuned part of a table(s).

Mazda's never done a good job at tuning. Miata, MSM, and RX8 are all pretty bad, even with a MAF. I'll try not to hate on earlier stuff with AFMs too much as the metering is poor, but I'll just say that the OE system as a whole on the pre MAF leaves a lot to be desired.

 

I've got a dyno of my completely stock nb2 making 107hp I can post tomorrow. Only mod was a mazdaspeed muffler.

 

with afr plot?

 

My bone stock, no breather mods at all, 95 with a BPE9 hit its 14.7 at idle, 15.3 at cruise, and 11-12 up top. Seemed like it kept it running pretty nice

 

I'm curious what the oem ecu triggers around half throttle
anyone try this?

 

Of course.

Here's three engines.

Green: Dopples 170k VVT rebuilt by me running in an NA, MS3
Red: My Smurf post-turbo 1.6, MS2
Blue: 187k '01, again bone stock beyond a MSM axle back.

 

is that afr plot legit? that looks crazy (terrible)

 

I have 2 more runs, although looks like we lost the WB signal on the blue line, but yeah, it's terrible.

 

Just for comparison, this is the same car a few thousand miles later after I installed an Rev MS3. Made 10hp more and obviously had a much better fuel curve. Still a little rich but no WB yet, so I erred on the safe side for fueling.

 

Mine goes into low 11's at anything over about 40% throttle. It goes into open loop admirably well for a miata ecu (BP5A ecu from japanland), but is equally terrible when it comes to the AFR.

 

13afr is safe?
in that case I tune my cars way too safe

thanks for the feedback. it's impressive that these cars still get the mpg they do if that's how they react to part throttle

 

It occasionally hits 13.0, but it's in the 12s most of the time...13.5 is where it's at for N/A.

 

Misquoted a bit. Leanest I have seen at WOT with a 100% stock NB is 12.5. On the rich side, the stock ECU can get down to low 11's. I have seen high 10's on bone stock NA's. Any stock ECU with a modified engine can quickly run way leaner than stoich at WOT though. Bottom line is, if it is modified, either verify you are safe with a WBO2 or stop being cheap and find some way to trim fuel via a standalone, AFPR, piggy back or whatever your budget will allow.

 

hmm, I usually trigger 12.5

 

When my 1994 was bone stock the AFR would stay 14.5 until 3k, then would drop to 13 fast, by 5500 it was dipped down to 10.5 then at Redline it had worked its way back up to 12.0. Looked like a big "V" shape. Pretty terrible.