Slight emergency: Need to set up alpha/N quick. - Miata Turbo Forum - Boost cars, acquire cats.

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Old 06-15-2010, 09:37 AM   #1
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Default Slight emergency: Need to set up alpha/N quick.

I'm in kind of a bind. On my way to work this morning my map sensor crapped out (I'm likely the one that broke it, but that's a different story). It's reading a constant 150kpa. So you can imagine how undriveable it is. Thank god I brought the laptop with me. I was able to play with the VE table enough to make it to work. I want to set up alpha N so I can drive home. I tried switching to Alpha N in "constants", but that only made it run even richer. I just need to make my 40 mile trip home without dumping fuel. I'm also running tunerstudio if it makes a difference.
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Old 06-15-2010, 10:28 AM   #2
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On a turbo car, if you break the MAP sensor, tow it.

With no way of reading boost, you can get yourself in pretty serious trouble.
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Old 06-15-2010, 10:36 AM   #3
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Oh that's not a problem. I already have the wastegate actuator rod disconnected so the wastegate is wide open all the time. It ain't making any boost.
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Old 06-15-2010, 04:11 PM   #4
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Is your MSPNP modified to read a vtps?
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Old 06-15-2010, 04:24 PM   #5
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94+ doesn't require any mods to do so.
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Old 06-15-2010, 06:30 PM   #6
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So if I understand this correctly, when you switch to Alpha-N mode, the vertical scale on the VE table represents throttle ADC instead of map?
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Old 06-15-2010, 06:47 PM   #7
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That's basically the idea. You are telling it to assume that for any given combination of TPS and RPM, VE must be a constant.

Part of me wants to side with Matt, and tell you that driving like this is a bad move. Even with the wastegate wired open, that turbo is still entirely capable of making several PSI. In fact, some folks around here wind up having to port their wastegate passages oversize, because they can't get the boost to stay below 10 or 12 PSI even with the WG fully open.

Another part of me wants to be a realist and say that you're probably capable of driving the car 40 miles gingerly enough that you're not going to start making boost. Where you'd get an Alpha-N scaled map that's anywhere near close enough to drive on is a whole 'nother* story.


* Yes, I must now be sent to a work camp.
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Old 06-15-2010, 08:40 PM   #8
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Well I made it home unscathed. Yes, you're right. I'm perfectly capable of driving without entering boost, however it wouldn't have mattered anyway. I wouldn't be able to make boost even if I tried. Anything less than 10in of vacuum and it falls on it's face. I couldn't get alpha-n to work though. I was expecting the VE table to react to throttle input but it didn't. Seemed like it was still following the map sensor (which was stuck at 150kpa). Anyway. What I ended up doing is setting up the VE table to run at pretty much stoich when traveling at 65mph on flat ground. Since the majority of my drive is highway, that worked fine. Accelerating was tricky. I could barely breathe on the throttle to accelerate and that was it. Naturally that meant slowing down when encountering hills. Taking off from stoplights was a chore. Whatever. I'm home.

As far as how I fucked the thing up? I took the board out to add a wire to one of the unused inputs (for a/c idle up). I forgot about the map sensor being attached to the board (and the case for that matter) and pulled it off the goddamn PCB. It's tiny. It's surface mount. I thought I would get away with just pressing down on the little legs with the heated tip of my soldering iron, melting the solder beneath and effectively re-sticking it to the PCB. It worked for about 2 weeks. I'm not messing with it anymore and I'm sending it in for a proper repair. Live and learn.
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Old 06-17-2010, 10:40 AM   #9
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To answer the original question, by the way: The only realistic way to make a good alpha-N map from speed density would be to comb through a large number of data logs with the engine in the same configuration it would be driven in, plot the MAP readings as a function of throttle opening, and use that curve to figure out how to create a new VE and spark table. Not easy by any stretch of the imagination, and probably wouldn't be possible if the logs all were done with the wastegate connected.

As Anarchy demonstrated, making a map that simply runs is a bit less complicated.
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Old 06-17-2010, 10:58 AM   #10
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Would you recommend alphaN/hybrid for a boosted miata running cams that idles in the 45-50% load zone, and has a 70mm TB that's overly sensitive to throttle input?
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Old 06-18-2010, 10:33 AM   #11
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Might not be a bad idea; we had to use a hybrid alpha-N / speed density tune on a Dinan M6 a while ago that was running a turbo with ITBs and wild cams.
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