Changed my exhaust now I have a stutter
 

Ok to start with I am running a 94 with stock internals, and a Flyin Miata turbo II with a hydra nemisis. I got my initial tune after the turbo kit installand the car pulled like a mofo up to redline. It was making about 230 hp and about 210 tq. It had a 3 inch exhaust with a high flo cat, and a backwards glass pack at that time at about 12 psi. Again the car drove great, and pulled really really nice all the way up to 7 grand.

My only real complaint was that it was just too loud. I was not a big fan of my neighbors giving me the eveil eye as I drove past them, not to mention the fact that it was a great reason for the highway patrol to mess with me. So I had a racing beat 3" can installed to quite it up a little.

After the install I would get a hesitation from about 6500-7000 rpm. Not horrible but defiantly noticeable. My guesses that it richened things up and that was my problem. Soo I took it to get another tune this last weekend. Umfortanatly I went to a guy who has never tuned with a hydra, and actually tunes rotaries for a living. He claimed that I was getting some knock and that was my problem. He also shaved a crap load fuel from 6-7k, and took some timing out. Now granted he made it better but there is still a stutter at 6600 rpm up. He kept saying it was a spark issue and even replaced the plugs and gapped them down to .25. My ignition is also still stock by the way. He also said the boost was only holding about 11 psi now.

Again he helped it out, but I want it back to the way it was. Spark is not the issue as it drove great before the addition of the can. What do you guys think? Is it still that I might be too rich and I need to take more fuel out and put a little more timing back? The tuner kind of gave up due to the fact that there was another customer waiting and, and he made like twenty pulls that got only slightly if any better with each one. I just got a battery for my laptop so now I can start to do some of my own data logging and tuning, but I am the ultimate noob when it comes to this tuning thing. I appreciate the advice, and like always can't wait for the snide comments to pile up. That's what forms are really for after all. Thanks.

If you can, post a datalog of a pull and also post a screen shot of your fueling and spark.

Wait, your tuner said you were knocking and shaved " a crap load" of fuel from 6-7k rmp which happens to be the same spot were you're having the hick up? Wtf O_o

What AFR and what level of boost are you seeing at the hick up?

Yeah, wtf is right! Let's say the AFR's were good...who would shave fuel out of it to keep from knock? Is that what they do with rotaries? If so, no wonder they eat apex seals all the time...
Everybody knows, knock = retard timing, Power= advance timing. Goal is to advance timing to make the most power before knock occurs.

That's not all OP says the "tuner" ran the car for an additional 20 times and the issue persisted. O_O

I guess I wasnt really all that clear. The first thing he did was pull timing. Then he did a pull. Shaved more timing. Did a pull. That went on for like five pulls. Then he started to trim fuel. Sorry if I wasnt clear enough. I will try to get a data log in tomorrow if I have the time, as well as some screen shots for you guys. The afr's were staying at like 10, even as he pulled lots of fuel out of the top end towards the end. I think he got it to around 10.5 when he finished. Again I think he just gave up on it. He kept claiming that the hydra was really slow to tune with. My guess is it's a learning curve thing.

I don't see how you went from a "perfectly" running car to extremely rich AFRs from an exhaust change.

10 and 10.5 is really rich. I'd say at 11psi, it should be 11.5 at the very richest. What turbo is on your car?

OP do you know how to datalog and export the log in the hydra?

If you do, then please upload the .csv of a pull. Make sure your default hydra log data profile shows RPM, AFR, advance (timing, knock voltage, knock retard, boost.

This is a pull:

Floor it in 3rd or 4th gear all the way to redline.

Upload that here, along with your hydra map.

I'm going to post a FAQ on tuning soon.

This just in:
Most people who own dynos are fully retarded with sometime 3-5 extra chromosomes.

Actually I can't knock the guy. When it comes to rotaries he is really good at what he does. Again I kinda feel like he was behind the learning curve and kinda gave up because of time. Do you think spark could possibly be my issue? I will try to get some shots up tonight for you guys. Just gotta figure out how to do it. Again I'm a noob so Please bear with me.

I'm not sure if a stock ignition, even with gapped down plugs, is sufficient for a FMII at 12 psi. :confused: I'm thinking the wideband reading stupid rich could be a symptom of a misfire rather than too much injected fuel. That would explain why it's still stupid rich even after pulling a bunch of fuel, and why you can't hold 12 psi.

We stuck in his wideband to make sure mine was reading ok, and they were both dead even. He thought maybe mine was miss reading. Again though it ran great at 12 psi with no hints of missing at all before. It's a GT2560R by the way.

This. Your tuner sucks.

If you don't upload a data log and your hydra map i'm going to unsubscribe.

First thing I would have done would have been to put the other exhaust back on just to make sure.

Ok so here we go. I got a couple of pulls in today, and actually what I previously thought was wrong. It looks like the AFR's are way better than I thought. The boost is way lower than I thought as well. What do you guys think? It seemed like when I got to the fourth pull it started to buck and hesitate more at 6500 up. Lame. I realize that being in the 12's afr wise at 6700k might not be all that great for the motor. I need to put some more fuel in right? I did talk to Jeremy today at Flyin Miata, and he told me I might want to try bumping the dwells up one. Again thanks guys. I really appreciate it. And faeflora chillax my friend. Some of us have jobs. And the can is welded in so i can't exactly remove it that easily.

Where's your hydra map???????

What map do you mean man? I thought the fuel and timing were what you were looking for. Sorry please elaborate.

The .s26 file.

Looking at the logs it doesn't look like you are having spark misfire. That would be characterized by lean or rich spikes in your AFR.

Your timing is very very wussbuckety but that wouldn't cause stutter.

Your AFRs look rich from 3000-6500 and then a little lean above that. 12:1 or even 12.5:1 AFR won't break your motor at that boost level and high RPM.

You are down 2.5psi at redline. That means your power will fall off. In the driver's seat, that will feel like you lose power, or power feels flat, or the motor feels weak in that RPM. That could have been caused by your exhaust system change.