At what RPM does an NA Miata go open loop?

My hazy memory suggests at around 3500 rpm, or am I misremembering that?

I had my Meotter dyno'd by a local race shop last week to get a base line and an idea as to how healthy the engine is. They mentioned that it was running very lean below 3.5k - I believe their words were "dangerously lean" - with a corresponding dyno graph to match as there's about a 15 hp power jump at slightly above 3500.

Current suspect is either the intake causing the MAF to misread, or a dirty MAF - what say the font?

The good news is that once the lean condition clears up it makes decent power (around 110 whp) with just an intake, header and free flowing exhaust + cat.

However, without a wideband mounted on the car (shop was using theirs) I can't tell if I manage to fix the lean condition by cleaning the MAF and trying to make sure I didn't have any air leak. Guess Thunderhill is out on Wednesday then as I don't like the idea of potentially blowing the engine...

IDK about a mazda ECU, but the trigger is typically not RPM, but manifold vacuum, open happens when you dip below 10-12 inches.

MAF sounds like something to look at.

I thought it was around 3900-4000.

I always thought this was load based - Like a combination of RPM, throttle position, and pressure.

The stock miata tune stays lean until 3500-4000ish depending on the year, model, fate, the weather, and Andy Hollis's mood. This is part of the reason why you can gain 10ftlbs down low by going to a stand alone.

Keep in mind we're talking "I can't give it full throttle without the engine sputtering" lean.

Oddly enough the amount of soot in the exhaust suggests that it is/was running rather rich in other parts of the RPM range.

Oh, and the injectors were cleaned and flow tested less than 5k ago.

Normally you see 14.7ish until 3500-4000ish and then it drops to 10-12ish depending on what end of the tolerance the FPR is at and what angle the flappy maf thingy is at for 1.6 cars.

Well, mine's a 1.8 so it doesn't have the flappy MAF. Either way, it still seems to run slightly lean after cleaning the MAF with the correct cleaner.

Looks like if I want to continue the saga of the Miata I need to get the MAF sorted out or the OEM airbox back on as it wasn't having the problem with the OEM intake.

Sure you didnt tear the according piece or otherwise have a leak between the maf and the throttle body?

I've got an aluminum ARC intake on the car with the ARC airbox, and thus no accordion piece. I did check for leaks, didn't find any but I was in a bit of a hurry...

I thought it went open loop closer to 4200 rpm... /yells/ KEITH! Get in here.

4000 was the number that I have always been told.

Full throttle open loop is controlled by the TPS. At any rpm. It ignores the EGO.

Coast down with closed throttle it goes back to closed somewhere around 2000 rpm.

TPS either way

iceracer wrote: Full throttle open loop is controlled by the TPS. At any rpm. It ignores the EGO. Coast down with closed throttle it goes back to closed somewhere around 2000 rpm. TPS either way

Thats what you would think.

It changed over the years. If you really want to know, the info is in the OBD-II stream (if applicable). 4000 is a rough number for most NAs, although the ECU did get more sophisticated.

It doesn't really matter in this case, the car has a definite problem.

Thanks Keith.

It's a 95, so no OBD-II. I'll check the TPS, the MAF and then go from there. Probably put the original airbox back on, too, to eliminate the ARC intake as a potential issue.

As to this car having a problem five minutes before a track day, that's almost traditional with this thing.