Rev Limit Issue

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Rev Limit Issue

imtheman0313 Wed Jun 12, 2019 1:49 am

I have a couple problems that are completely baffling me atm. The first being one with the rev limiter. Symptoms are:

Rev limit in 1st, 2nd, 3rd normal set @ 6800rpm
Rev limit in 4th limits at 5500rpm
Per gear limits are not set

I know the issue is actual rev limiter because when I turn on and off the ign and fuel cut switches, the issue shows as which ever I have turned on. If I turn off the limiter altogether, the problem disappears.

Other possibly related issues:

VSS readout incorrect in Neptune, gauge shows 0 or 4mph only. Speedometer functions correctly on dash
Gear indicator only ever reads 1 (could be because manual transmission, not sure if ecu calculates a gear w manuals)

Also, a note on possible program bug. If usb connection is disconnected while logging, the program locks up. It will respond again once usb is reconnected, or it must be shut down by task manager. I'm not certain anything can be done about that.

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Coupe-r Wed Jun 12, 2019 3:14 am

Post up a datalog to help but.

Do you have launch control enabled? No VSS means it COULD be hitting a tps based launch control if its always on based on being below 10kph.

No VSS signal is not a software issue, check ya VSS wiring to the ecu (sometimes the sensor can be faulty and gauge reads ok but intermittent on the ecu readings)

Posting a datalog showing the RPM reading while you experience the issue. (could even be a dizzy trigger issue where RPM is reading incorrectly sometimes).

I had a faulty VSS that would only show an issue at higher speeds in 4th gear, then the signal would drop out and i would hit a launch control limiter.

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HRTuning Wed Jun 12, 2019 2:15 pm

VSS will be the issue. Either wiring or the unit itself.

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imtheman0313 Wed Jun 12, 2019 2:51 pm

Launch control is not enabled in program, so barring some odd issue there, I think we can rule that out. The VSS error at higher speeds is a possibility, I have no idea the age of the sensor. I'll hook up the Oscope this weekend and watch the data input to the ecu, see if it's dropping out on me. If it's not that Ill grab a log and post it up. I wonder if you could be a little more specific with RPM reading incorrectly? Is that going to be sensor or wiring that you have in mind? The dizzy is less than a year old, brand new (not reman), so if that's the case, warranty here I come. But I would think that that should present regardless of gear?

A little more specific on the issue, actually. When the limiter does engage (again only in 4th gear) the cut lights turn on in neptune, and I holding the throttle WOT, I see the RPM drop to around 3k, up to 4500, back to 3k....The AEM UEFI shows --- (far lean, no fuel)

I will also check free rev this weekend to see if it does it at a standstill. It could very well be some weird launch control thing, maybe I have to turn it on then back off for the program to set it? Not exactly sure.

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HRTuning Wed Jun 12, 2019 4:11 pm

If it's bouncing off of the low rev limit RPM that you have set, that's a clear indication.

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imtheman0313 Thu Jun 13, 2019 1:40 am

The rev limiter is set to 6800, and resume is set at 6700. Its hitting 5500 and dropping to 3k. That don't make any sense to me. It's not even close to the limit. When I turn off both fuel and ignition cut in the limiter section, it stops limiting, but why would it be cutting only in 4th gear, and so early? I set both low and high cam to the same settings even, no gear specific limiting.

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HRTuning Thu Jun 13, 2019 8:08 pm

That suggests a pending error code then perhaps. Fix your issues and I bet it gets resolved.

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imtheman0313 Fri Jun 14, 2019 6:53 pm

Update, I noticed the issue arose only under heavy load, indicative of dizzy problem. At 5500rpm, neptune was indicating 5k-5900, erratic. Replaced dizzy today. Next thing is to retest for problem, make sure it was just a mechanical failure. Then off to futz with the VSS and try and figure that out. Another question presents itself, however; should the ecu calculate which gear I am in? Or is that an automatic thing only?

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HRTuning Fri Jun 14, 2019 7:25 pm

It does, as you'll find gear settings in the software. VSS would need to work for that to work.

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imtheman0313 Sat Jun 15, 2019 7:12 pm

That's what I figured. Right this moment I'm trying to get Win7 installed on my machine (new Lenovo laptop) beside 10. Ahhhh M$, how you refuse to work. I've spent the better part of the last 4 hours trying to get it installed, so I can use my USB Oscope, and watch the VSS signal (I don't like replacing parts willy nilly), to verify an issue. I will update again as soon as I have answers, or more questions. Thank you so far for your help.

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imtheman0313 Sat Jun 15, 2019 10:17 pm

Update: replaced VSS, signal slightly smaller than old VSS, but still clean. Speedo works normally, no change. Neptune still reads either 0 or 4mph. Any pulse train into ecu causes the speed reading to be 4mph. So I guess the next thing is to figure out why neptune doesn't see the speed correctly. I have not tested the rev limit issue yet, that will be tonight, when I don't need to use the A/C, but I have a feeling that's probably solved at this point. On my test drive tonight I will save a log and stick it on here for someone smarter than me to look at. Do we (collectively) know the signal path through the ecu of the VSS? I wonder if its possibly an old electrolytic or a damaged trace.

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imtheman0313 Sun Jun 16, 2019 4:09 pm

Either I'm old, or not all too bright. How do I go about posting the datalog I recorded last night? Did some searching, and found nothing.

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imtheman0313 Sun Jun 16, 2019 4:17 pm

Oh, other things I have noticed recently. Aside from VSS not functioning, I also do not have battery. Batt voltage always shows at .2v. Clutch switch input not being read from ecu, neptune does not register it. I'm wondering if the ecu could be faulty, but I'm pretty sure it's ok. The dash speedo works fine, and I know the altc system/ELD system functions because the voltage will drop on warm days in town. Is there a bug that could cause these issues? Should I try reinstalling the program?

On a more positive note, everything else seems to function impeccably. With new dizzy, the rpm now read correctly in neptune, and the rev limiter issue seems to be resolved. I do like neptune over crome quite a bit, I like the little things it has, like the ac idle up control, for instance.

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HRTuning Mon Jun 17, 2019 2:19 pm

If you're seeing other live data in datalogging then battery should also be reading correctly unless the ECUs input for that is damaged.

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imtheman0313 Mon Jun 17, 2019 7:20 pm

I have checked the input to the ecu, and everything is fine. VSS signal is there, battery reads correct voltage (although I dont remember if I have checked the clutch input). Have you ever seen an ecu fail such that a couple of readings show incorrect, while everything else is nice and friendly? I do have 3 ecus available, but I would rather rule out possible bugs or software issues before putting the labor into chipping another ecu. Where does the demon get the data from the ecu? Does all data come from the CN2 header? Or does some of it come from the board itself, the socket?

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