Hydra in normally-aspirated NB, won't rev over 7000rpm? - Miata Turbo Forum - Boost cars, acquire cats.

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Old 02-03-2010, 03:35 PM   #1
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Default Hydra in normally-aspirated NB, won't rev over 7000rpm?

I recently installed and tuned a Hydra in my SCCA ITS race car--stockish normally-aspirated engine. While it's way better than the previous ECU I experimented with, for some reason neither my tuner nor I can figure out why it still limits to 7000 RPM. I've set both hard and soft limiters well above that (~7800 and ~7500) and haven't found any other limiter in any of the settings screen. The maps are all programmed up to 8000 and beyond.

When sitting in neutral, once everything is warmed up I can rev the engine all the way to 7500 (though I'll always hear a slight stutter crossing over 7000), but on the dyno and at the track it will not rev over 7000. It seems to be hitting some really soft limiter... I can barely feel it, can't really hear it (over all the road/exhaust noise), but watching the tach I see the revs completely hit a brick wall at 7k.

Any idea why? I've attached the map file if anybody wants to look... Thanks!
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Old 02-03-2010, 05:59 PM   #2
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unfortunately not many people are running the 2.6 version here.

did you look for any flat shift / launch control type setting that might be enabled on the wrong clutch switch? or maybe a valet mode?
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Old 02-03-2010, 06:03 PM   #3
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That's a good point, the clutch switch in my car is hardwired so the car always thinks the clutch is pushed in. (Did this with the stock ECU so I could start the car from the outside.)

Re: 2.6, do most people have an earlier or later version?
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Old 02-03-2010, 06:20 PM   #4
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I didn't see anything out of the normal. Have you noticed any Knock? It could be one of the Trim maps. I didn't look at any of those.
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Old 02-03-2010, 06:54 PM   #5
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Can't say that I've noticed any knock, or even that I could or would notice it when going WOT at the track with my helmet on and the windows down... kinda noisy. :-) But I haven't felt any misfire. Furthermore, we observed the same problem on the dyno, where we could have tuned out any knock. My tuner (Mike Warfield, GST Motorsports) knows his way around the Hydra fairly well.

I'll have to see if it's a clutch switch-related issue.
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Old 02-08-2010, 01:59 AM   #6
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Do you have a datalog of what it does when it hits this phantom limiter?

--Ian
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Old 02-08-2010, 02:35 AM   #7
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I glanced at your map and your tables only go to 7750 RPM. Did you upload the correct map?

Also

Does your tach needle match up with your RPMs in the Hydra? Mine is off by almost 400PM. My tach actually reads high.

And

The flat-shift/launch control RPM activations themselves can be a little wonky and not kick in where you set them to. If they're the cause, they might need futzing.

Lastly

Ditto ^ Log please
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Old 02-16-2010, 01:24 PM   #8
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Are you going lean at 7K?

Are you exceeding your knock threshold?

If you go to Settings 2 -> Aux Input configuration and turn Aux 4 (launch low) Off, does it stop?

Do any of your real-time inputs get weird when it happens? What is the RPM in the Hydra when it occurs?

Is it a (2G Engine Calibration) Dwell Trim issue?

P.S. looks like you have a "USB" load glitch in your 3D Engine Cal -> Aux Ign Trim & Backup tables. Have to watch out for those.

P.P.S. remember that your clutch override switch and your clutch neutral switch are different switches..
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Old 04-19-2010, 03:00 PM   #9
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Thanks everyone, I hadn't realized there were more replies as notifications for this thread somehow didn't work for me.

I tried reinstalling the clutch override and it didn't help. Looking at the factory wiring diagram, it's obvious it shouldn't, because there are two switches/sensors connected to the clutch pedal: the sensor which is wired to the ECU, and the starter "interlock" which is the big white switch that I overrode, which is simply connected in series with the starter circuit (hence why it has big honking wires to and from it) and which the ECU knows nothing about.

@faeflora: my tach is fine; I have a digital sequential shift light and it agrees with the tach, as does a connected laptop, etc. Also, judging from shift points, lap times etc. on the track vs. the stock setup I'm confident revs are being reported correctly.

I suspect the reason I can't rev much above 7000 RPM has to do with a limitation of the wasted-spark ignition and dwell settings; I'm running the stock coils and wasted-spark setup and if you do the math, with each coil firing twice per revolution the time between sparks at 8000 RPM is 3.75 ms, whereas the dwell time (at ~14.4V, 8000 RPM) with trim is about 4.5 ms. Clearly that isn't going to work (or am I missing something?).

Furthermore it seems this misfire issue has gotten worse; the past few track/race days I've been getting intermittent misfires around 6500 RPM. It feels very similar to the "phantom 7000 RPM limiter" I felt before. I've replaced the plugs, plug wires, coil packs, cam & crank sensors, fuel filter to no avail; new injectors and fuel pump are next.

I have the sneaking suspicion that my alternator control isn't set up quite right and that the voltage isn't where it should be, resulting in increased dwell times and causing my misfire. To that end I'm swapping to an NA 1.8L self-regulating alternator.

Unfortunately I haven't had my car on the dyno since I last posted, and as the track/race officials frown upon me driving around the track with a laptop in the passenger seat/footwell, I have not been able to collect any datalogs.

Thanks again everybody, I'll keep you posted on any new developments.
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Old 04-19-2010, 03:19 PM   #10
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And before anybody suggests it, no, I can't go to a sequential-COP setup, much as I would like to, as the rules don't appear to allow it.
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Old 04-24-2010, 12:49 AM   #11
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Quick update:

Installed a 1.8L NA alternator, did a bit of wiring underdash to make it work, now I reliably get a stable 14.3V at the battery terminals.

I replaced the injectors with ones newly blueprinted by WitchHunter Performance, and also replaced the fuel pump with a newer unit.

But tonight just sitting and revving the misfire issue cropped up again, occurring reliably at ~6500 RPM. So I use the Dwell Trim map to take a fifth of a ms off the dwell time and lo and behold, the misfire started happening at 6700 RPM. I kept reducing the Dwell Trim curve, until I could reliably rev without misfire all the way to the 7500 RPM limiter that I set.

The question is, with the reduced dwell time will the spark still be strong enough at full load? (And if not, what I do about it if I have to use the stock coil packs? Anybody here tried the HKS ignition amplifier which claims to be compatible with a coil pack with built-in ignitors?)

We'll find out when the car goes on the dyno next Wednesday...
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Old 05-01-2010, 01:29 AM   #12
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Dyno testing didn't happen due to unforeseen circumstances on their end, but in today's practice and qualifying sessions at Laguna Seca I was able to rev well over 7000 RPM without a single misfire.
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Old 06-15-2010, 02:23 AM   #13
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Quote:
Originally Posted by vtluu View Post
I suspect the reason I can't rev much above 7000 RPM has to do with a limitation of the wasted-spark ignition and dwell settings; I'm running the stock coils and wasted-spark setup and if you do the math, with each coil firing twice per revolution the time between sparks at 8000 RPM is 3.75 ms, whereas the dwell time (at ~14.4V, 8000 RPM) with trim is about 4.5 ms. Clearly that isn't going to work (or am I missing something?).
Each coil fires once per rev with wasted spark (twice per power stroke per cyl. which happens every second rev., allowing 7.5 ms at 8000 rpm.
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