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Old 12-19-2012, 05:02 PM   #1 (permalink)
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One more EFI question re: rev limit

I've been tuning a map and have it in the ballpark. It's pretty fair for street use, but I'll be taking it to a dyno to tune for MBT and power. Appointment is shortly after Christmas.

While I've been working on it, I've had the rev limiter set at 7800 spark cutout and 7900 fuel cutout. When the map is dialed in I'll make a street version with those limits, but the primary track map will have the limit raised.

So, to get ready for the dyno session, I went out today with the cut outs set at 8500 spark and 8600 fuel. After a good long warmup, I tried to pull the revs up there with a low to moderate load. But at about 78-7900, the tach quickly rolled back to about 2000; I was able to keep it revving just a bit more, perhaps 80-8100, then the limiter hit. And it didn't just bounce off the limit, it basically cut back to idle power...

Is the stock ECU causing the limit? Or is there another EFI constant to set?
Any advice is appreciated.
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Old 12-21-2012, 06:06 PM   #2 (permalink)
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Bump!

Anyone? Hope to get this sorted before Xmas Eve, last chance before dyno session.
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Old 12-24-2012, 05:04 PM   #3 (permalink)
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Nobody has any idea?

Well, here's what I've been speculating. The cutoff I'm trying to set is effectively 8500. The Injection and Spark maps top out at 8500, so I thought maybe it would help to have a little headroom. I reset the last couple of breakpoints to stretch the maps to 8600 rpm. A long warmup and short spirited drive later, I found that didn't help. It still cutout abruptly at 78-7900.

I remembered the Engine Protection section has an rpm limit, which was also at 8500, so I bumped it to 8700. That didn't fix the problem, so I disabled Engine Protection entirely. Success? No, let's say partial success. I can roll it up to about 8400, but only if I creep up on it gradually. A normal pull still cuts out before 8000. Since the rate of approach is apparently a factor, I'm wondering if one of the Derivative Gain settings is at issue.

I'll do a 150 mile drive tomorrow if the weather allows; maybe I'll get a chance to play with the gain settings a bit on the way. Merry Xmas or holiday of your choice, everyone!
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Old 12-25-2012, 02:15 AM   #4 (permalink)
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Are you sure that the tach is telling the truth? I would run data logs to check that the feedback from the ECU matches the dash display. Considering the EFI system is a stand alone I don't see how the factory ECU would have any control over rev limit.
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Old 12-25-2012, 05:49 AM   #5 (permalink)
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You got a problem.
Your engine will rev right up to the efi rev limit if everything is working right.
Limited rpm can be a few things. Are you getting high lift cam ? Running voltage ?
Crank sensor. Did you get the crank sensor upgrade for the efi?
I wouldn't disable the engine protection. The cut off is usually 5000 rpm.
Most times I can't figure it out. I have to call Phil.
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Old 12-25-2012, 12:32 PM   #6 (permalink)
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Thanks for the input, guys!

No datalogging, but I have carefully cross-checked the dash against the laptop readout.

Crank sensor upgrade. Hmmm. I haven't heard of this. I am running the latest firmware and editor, would that cover it?
I do get lift, which I have set at 5300. Battery is always better than 14v.

I'm out for a few days of work, check you later...
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Old 12-25-2012, 01:04 PM   #7 (permalink)
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Just thinking out loud.... have you checked your spark plug/coil health? Maybe you are suffering from a spark energy issue. Are your gaps set excessively high? Spark is much harder to maintain under high cylinder pressures and less so under light load, might explain why you can "creep" up on a high rev cut when you are easy on the go pedal.....
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Old 12-26-2012, 09:31 PM   #8 (permalink)
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Thank you, Mike, interesting thought. I'll investigate when I get a chance.
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Old 12-26-2012, 10:39 PM   #9 (permalink)
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Sounds like you're working w/ an old 1.2 that hasn't had the crank trigger upgrade. Send it to EFI and they will update it for you. Without the upgrade, some will lose tach sync and do as you describe.

The stock ecu has nothing to do w a rev limiter. It jus interprets the EFI generated tach signal and that signal can become obfuscated by a poor crank pickup when the problem crops up. Hence the wonky tach reading. The problem is typically in the upper rev registers.

I agree with jim. Leave the engine protection rev down low. I cut it at 1000 rpm to force shut down when on the track and then 5000 rpm for street tunes to limp home. On the track, if something isn't right I know there's a tow vehicle close by, so no sense in even limping back to the pits if protection has triggered.
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Old 12-27-2012, 03:55 AM   #10 (permalink)
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Okay, got it now. I'll contact Marc at EFI and arrange to send it in when I hibernate the car. And restore the protection function. Thanks for the info.
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