Yep, had some problems at the track tonight. When I try to launch, I bog real bad, and when i start to build boost, it's like i'm hitting fuel cut and the car bucks real bad and i hear that loud popping sound like fuel cut does. I could not accelerate at all through 1st and only about the latter half of 2nd. Once I was into third, the car would boogy quicker than the word of God, but not enough to make up for the dismal start. Anyone have any ideas why it would do this?

 

OEM AFM Still in place?

 

Bruce what the hell are you doing up at 4:46AM?!

Super, sounds like a fuel issue. Maybe a misfire from running lean?

I see you have a Vortech FMU, 1.8L injectors, 190HP @ 8psi, correct?

Is this the first time you've run the car through the gears hard?

Has it always done it?

Is your FMU hooked correctly?

What ratio disc is in it?

What do you idle at?

What's your vacuum reading?

O2 clamp installed?

 

Yah, how the hell did you get it to the track like that?

 

Mostly not sleeping.

I know it almost sounds like a crusade since I had the AFM trouble, but the characteristics are about the same. If the AFM signal is low or non-existant, the ECU thinks you are at full air flow and is throwing in maximum fuel.

 

Bruce:
Yeah, it's the stock AFM. However, it appears it has been disassembled at some point because the top cover has silicone around it.

Braineack:
This is not the first time, however I have noticed an odd phenomenon. The first time i run the car hard (enter boost suddenly) i get this problem. For instance, when i first get on the highway when leaving my subdivision. Every time after that first time, i can enter boost just fine without hesitation. The problem with the track is that you sit in the staging lanes so long, every run is my bad "first time".
To my knowledge the FMU is installed properly.
Don't remember the disk ratio right off hand. It's whatever Bruce is running, as he recommended it to me.
I idle at 1000 rpms (though it's been up to closer to 2000 since it got cold. it drops down to around 1000 if i blip the throttle a few times)
Vacuum levels at idle are nice and low.
Yes, i have Bruce's autotune installed.

samnavy:
oddly enough, the car is perfectly streetable as long as I take it easy in 1st gear and easily transition into boost. I can beat the heck out of it in 3rd and 4th though.

 

Your O2 sensor could be cooling down(or not yet heating up) so that you are getting a full rich shot of fuel as it references the O2 when the Autotune kicks in. If you have a 4 wire, the heater may be bad. (Sorry, I don't associate screen names with real names very well and didn't realize you had Autotune by your signature)

 

Sounds very similar to when I had a large voltage offset between the EMB/Autotune and the O2 sensor. As soon as the pressure switch would trip all hell would break loose and the car would fall flat on it's face from too much fuel.

 

sounds like its an AFM issue to me. I would rip open the AFM and check spring tension.

 

I'll look into these suggestions. The O2 sensor IS kinda old, and i've been meaning to replace it for a while now, since i went ahead and bought a 4-wire replacement. It's just a pain to get to where it is on the downpipe. Also, i'm getting like 15 mpg, and i regularly get a CEL when cruising at the same speed for very long, probably from the O2 sensor.

 

15 mpg! Do you get tons of black crap at your exhaust tip?

I don't think the O2 signal modifys the calculation that much, does it? I know the AFM can screw up the car that bad, my old turbo rx7 ran like crap like that when the connection was corroded at the afm.

 

The Autotune works off of the NB signal. If that signal is low due to the O2 not being hot enough, a bad connection, etc, the Emanage maps default to rich.

Further, if the Autotune is activated when cruising at high speeds because the pressure switch is set too low, you will throw a CEL and waste a lot of fuel. At 75-80MPH in a 1.6 the vacuum/pressure hugs -0- and can trip the switch at its' lowest setting.

 

This is the EXACT thing thats happening to me /subscribe

no, but really I've tried like 3 O2 sensors now. Do you notice at around 3.2k rpms cruising highway the car kind of glugs right before the check engine??

 

Haven't really noticed any issues when the CEL comes on other than the light itself. No hesitation, surging, or bucking. If I let off the gas ever so slightly, the CEL goes right back off and I can continue for another minute or two until the light comes back on.

 

Adjust the boost switch so the Autotune comes in 1~2 psi

 

Will do. thanks.

 

That will take care of the cel and running at 12.5 AFR while cruising, the O2 sensor needs to be checked out for the bogging.

 

I already have a 4-wire Bosch unit that I originally bought way back when i got the autotune.

I'm going to be following this info to set it up.
http://mymiata.paladinmicro.com/Miata4-WireO2.htm

If that doesn't alleviate the problem, i'll move on to the AFM, since the one i have is suspect (appearing to have been opened at some point).

 

Well, it's not the AFM. I swapped it with one from a wrecker. Doing the same thing.

Has anyone been able to get the O2 sensor off the downpipe without removing the downpipe? I can't see how to get a tool in there. Also, did any of you have any clearance issues with the steering shaft? The 1-wire sensor on there now comes awfully close to it, and i believe the 4-wire replacement may hit it.

 

HOLY MOTHER OF GOD

It was the O2 sensor. I found a way to get it off and there is just enough clearance.

Apparently, I need a clutch now though because it was sooooo not up to the task of boost in 1st or 2nd gear.