BP5A ECU Experiment

[Ciotti]

99' STR Built Miata (Intake, header, midpipe, exhaust, and a bit of extra compression from a slight head deck during a recent motor rebuild)

I've never been all that happy with the stock tune of the car especially when cold, after doing a bunch of research it seems that many of those cold tune problems popped up after a fuel efficiency TSB where they replaced/retuned the ECU's in the 99/00 NB's.

I picked up a Greddy E-Manage and Boomslang harness for local tuner to dial the car in with but in order to work with the cold tune I would need to leave the car there for days and pay a good bit of labor for him to take the car on and off the dyno over and over again each time it heats up and cools down.

SO, I had an idea...

The JDM BP5A computer didn't have such strict fuel economy guidelines, had a higher 7,500 rev limiter, and was tuned for a more free flowing intake and exhaust. For $100 it would be a hell of a lot less expensive proposition than a few hours of dyno time so why not give it a shot!

Nobody seemed to know for sure if the pinout was the same so I just said to hell with it and ordered one up.


Luckily for me... IT WORKED!

Plugged right in and the car fired right up!


First impressions: Since it was dark when I put it in, I noticed that the check engine light is constantly on but juuuuust barely, you can't see it during the day but in the pitch black of night you can just barely see that it's ever so slightly lit up which is odd.

It's definitely got a different tune, the first thing I noticed is that the revs don't drop quite as quickly and it idles a bit high at around 1,200 when you're coming to a stop, hangs there for a second, and then comes down to where it should be.

There's definitely a higher rev limit, according to the tach it's not quite the 7,500 I had read probably closer to 7,400 or 7,300 but who knows how accurate the OEM tach is up there and it's definitely higher than before so I really dig that.

Power feels about the same but I did notice that the car doesn't burble under deceleration like it used to when I would give it just the tiniest bit of gas although I have gotten it to do it once or twice which is fun.

Most importantly, the cold tune is GREAT, it runs pretty much exactly the same on the cold tune as it does on the regular tune which is exactly what I was looking for so to me the $100 was well spent right there.

I just sorta stuffed it up under the dash so that I can swap back and forth between it and the regular ECU to get some back to back comparisons and with the impending dyno time to tune the Greddy E-Manage soon I may get some head to head numbers between the two ECU's, I'm curious as hell



Next up, disabling the EGR since the JDM cars didn't have it and zip tying the VICS opened to more closely resemble the flat top intake manifold air delivery

[etikoner]

Cool results.

FYI most people don't recommend swapping out to JDM ECU's or rom chips cause they're tuned with higher Japanese octane ratings, which could cause some cars detonation issues.

but it seems your gamble is paying off.
good stuff. interested in the numbers before and after the ecu swap

[wannafbody]

Might want to throw the BP5A cam in as well.

[Ciotti]

Cool results.

FYI most people don't recommend swapping out to JDM ECU's or rom chips cause they're tuned with higher Japanese octane ratings, which could cause some cars detonation issues.

but it seems your gamble is paying off.
good stuff. interested in the numbers before and after the ecu swap

They tune for higher than 93?

[silvermazda]

NO, I think its a RON vs the other standard of measuring. KAI? lol Also, I think I read that japan is more humid, different tunes for different weathers. But then again, the bayarea is kinda humid..hm? Oh wait, bay area doesnt compare to island weather.

Anyways, like you said, its about the cold tune. Keyword, tune. Personally, with a aftermarket ecu I noticed a smooooth idle. And what my butt felt like 20% more umph. I would recommend an ECU because when it comes down to it its about the fuel and timing aka the tune. Not saying your wrong, heck you can play around with it and achieve similar results, but you'll need to learn how to trick the stock ecu to achieve that I would guess. Thanks for your research so far.

[Ciotti]

What aftermarket ECU do you have?

[silvermazda]

I got a megasquid Currently a on and off project. It's difficult to start, so i'm back indefinantly to the stock ecu. Really a love/hate. But when it works, man its worth it.

[atlnb]

in for dyno results

[Ciotti]

Ran out of time on the dyno to hook up the BP5A ECU, I have to go back after Miatas in Boone though so I'd like to try and hook it up then.