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Bringing foxy back.
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Discussion Starter · #1 ·
Hey guys!

I have done a few preparations on cars so far, including a friend's car, who had his full exhaust system replaced and a remap. We noticed when we added the exhaust system, that the car started popping from the exhaust, and I reckon that could be due to either a rich or lean condition on overrun. I'm guessing rich, because we remapped the car since, done away with his O2 sensor and made the mixture slightly rich, and the popping noises increased.

Either way, I was expecting my miata would do the same when I added my cat-back system and test pipe. And to my surprise... It doesn't. My car is running a bit on the lean side (between 14,5:1 and 15,5:1 AFR) with stock ECU, therefore, it has overrun fuel cut, which I reckon should also prevent this situation from happening.

Now you're probably asking, if this is about exhausts, why is it not in the exhaust section, or if I have some experience with engine tuning, why can't I figure this out on my own?

Well, this question isn't really about the exhaust, or the tuning of the car. It is about the engine. I have seen many cars (mostly, if not all, euro cars), and they all share some things in common. For starters, they all have a throttle position sensor and they all have a MAP sensor. So that makes me pretty puzzled when I look at a car like the miata, which has a closed throttle switch, and a mass air flow sensor.

So the real question here is... Can I disconnect the throttle switch to disable overrun fuel cut? Will it have any adverse effects? What can I do with what I have (if I can do anything at all) to add some popping to my exhaust?

That or I can just add a switch to my O2 sensor, to be able to select between the currently lean feedback, a slightly rich feedback, or no feedback at all.

PS: No, I'm not going to ride around like that. Just experimenting, and getting acquainted with the way this car works. It will definitely come in helpful at a later stage when I get on with seriously tuning it!
 

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Lit like a BranchDavidian
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Ghettorigging or disconnecting sensors just to get your exhaust burble is really.....dumb. As long as you are on the stock ECU, you're not going to get what you are looking for. It's hard to compare other cars to a Miata because OE ECU tuning is completely different. If you have an aftermarket ECU or plan on getting one, disabling decel fuel cut will get you popping/burbling on decel.
 

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Bringing foxy back.
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Discussion Starter · #3 ·
Put it this way ... I'm not "ghettorigging" the car to get anything out of it bug rather to understand how it reacts to disabling systems and other failures. This may seem dumb to you but that is how I learned about my other car before turboing it. Nobody had done it like that before.

Quite unlike the miata, which has been so overdone that nobody cares how or why things happen... People just know they work. I'm not one to take things for granted.
 

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I get lots of burbling in my exhaust on stock ecu. And at 14.5-15.5 is pretty much stoich range during cruise on stock ECU, especially if you are using narrowband simulator from a wideband o2+gauge (which is my guess here since you know your AFR, but are on a stock ECU).

The burbling is from unburnt fuel in the exhaust (ie if you are running rich there is more fuel in the exhaust and more burbling). You will tend to get it more when cold or if you can do a pretty perfect shift, you can get a slight bit of backfire.

I normally get backfire only when my exhaust is slightly cold as the fuel tends to burn on the catalytic converter rather than in the header or the pipes before the cat.

If you want to hear the burbling, remove your resonator.

As for the rest of the junk you are talking about, its total bullshit. The miata is not overdone in any way. Fuel cut, MAFs, Stoich AFRs, Throttle position are all about get the most out of what you got. MAF + Throttle position allow for higher efficiency (ie good fuel mileage with good performance). Stoich AFRs are used to make sure you engine doesn't pop, give you good fuel economy on cruising, yet still allow the ecu to turn up the power on full throttle.

If anything the miata is basically about as unover done as you can get without being carb'd. Unless you really want to use some of the shitty EFI systems of the 70s and early 80s.
 

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If I do a half throttle and shift at 4-4.5 backfires everytime am I super cool yet?
 

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~Foo's Best Friend~
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Lol 1/4 throttle at 3k I get a pop xD
 

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Bringing foxy back.
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Discussion Starter · #10 ·
I think you guys are all missing the point here...

brontosaurus and BLU-PR!NT, yes, I am going to buy a megasquirt, and then I MIGHT disable the deceleration cut-off, but right now I'm only experimenting with what happens. Like I said, I won't be keeping it ghettorigged like somebody said before, I'm just trying to get a grasp of how everything works on this car. I know my **** enough to know what is well done and what is not.

lebowski, I know that and there's not many reasons you'd want to do spark cut-off only either way. Thanks for the tip though ;)

RedemPhex, yes you are right, I'm using a wideband O2 sensor. I have no cat converter and both my mufflers are a direct design, so it's already pretty loud as it is. Also, by overdone, I didn't mean it comes tuned to perfection or anything like that. I meant that people have done turbos, aftermarket EFI, compressors and all that stuff so much, that when presented with a project of tuning their miata, they just assume things are done that way from other peoples' knowledge, and that they work. I want to know why things are the way they are, and what things can be improved and especially why.

adam, no sorry, you ain't cool yet :lol:


With that said, you guys all missed my point, which is: I EXPECTED the car to do some popping, but it didn't. I WONDER WHY it didn't and came to the conclusion it's either fuel mixture, or decel cutoff or both. And I WANT TO KNOW simply what are the effects of disabling the throttle switch, and if it will lead to decel cutoff deactivation or the car not working properly or at all. That is all ;)
 

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I just cut off my stock muffler and mine pops, release the inner ricer.
 

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If you disable the throttle switch, the car will probably run in open loop mode. It will run rich, you will lose some performance, gas mileage will suck, and you might get some backfiring.
 

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turning off fuel cut off will just prevent any burbles and pops. all those lovely sounds come from fuel cut off. easiest way to get them is to have bigger pipes and a free flow exhaust system.
 

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no Cat.. more pop.... Haters, i still pass my emissions :p
 

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Lit like a BranchDavidian
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Add a turbo, deactivate decel cut, richen decel fuel cells, retard timing and let the games begin.
 

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Bringing foxy back.
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Discussion Starter · #19 ·
Ain't that basically the same as having ALS?
 
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