09-16-2018, 01:10 AM | #1 |
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4th gear stumble
I'm posting this here with the idea someone may know what's happening. I went to the track today in terrible heat and humidity...it was awful and odd for this time of year where i live. Anyway best of the day was 12.7 at 110mph. 1.8 sixty. My question is in the vid if you listen to the car go thru the gears once it goes into 4th it stumbles....anybody have any idea what it could be...I'm thinking tune related but I'm not sure thank you.
https://youtu.be/3oEmLH751S4 |
09-17-2018, 07:34 AM | #2 | |
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It sounds like you might have tickled the knock sensor pretty good and it sucked out some timing for a bit. I didn't hear a stumble (actual mis-firing) but more of just laying over and then recovering, which is what you'll get if the PCM grabs a bunch of timing out from under you (it recovers pretty fast - stock tune will roll that timing back in much slower). The fact that you mentioned it was very hot and humid may support this this theory, as heat will lower the threshold for knock anyways. If it was a one time thing I wouldn't get too concerned, but if that starts being repeatable, you're gonna want to get on some sort of data acquisition platform and see what's going on. Good lick against the Mustang!
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09-17-2018, 08:27 AM | #3 | |
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09-17-2018, 09:37 AM | #4 | |
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I do think lay over is more appropriate - I don't hear it misfiring at all, it sounds like it loses some power, and then comes back in. No hint of that in the first three gears, just 4th where the load is the highest. It almost sounds like the converter locking - I don't know if that's a thing with 6L80's or not, but it's about the right spot in the pull to do that. I would make sure it's not that before going any further.
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09-17-2018, 01:13 PM | #5 | |
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09-17-2018, 02:26 PM | #6 | |
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GPI Max Package 2.0: Brodix BR7 heads/GPI porting, MAX3 cam, ST2116LSR, BSR Max Lift rockers, LS7 LSXR with 103mm TB, Vararam OTR, Mcleod RXT, G-Force/Strange 9" IRS setup with 4.63 gear. 551whp, 11.1@124mph.
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09-17-2018, 02:53 PM | #7 |
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Its a Circle D 3200. Seems to work well but i guess Wed will be the day to fined out.
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09-17-2018, 02:57 PM | #8 |
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Let us know what you find - but I'll bet that's by design. It's become a fairly common practice to lock the converter on the back half of the track once to make up some of the efficiency lost with a torque converter. It's usually worth a couple MPH.
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09-17-2018, 02:59 PM | #9 |
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Ok....i appreciate your advice.
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09-19-2018, 09:52 PM | #10 |
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Yep it was the converter locking up. So the tune has been changed ...went with the tuner for a wot pull and its just fine. He reduced some more tq management and it seems to have a little more grunt down low.
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09-20-2018, 07:25 AM | #11 |
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Makes sense - good to know. If you don't know it's doing that I can see how you'd think it was something like a stumble. Probably not something you notice on the street all that often, because how many wide open 3-4 shifts do you get to make on the street?
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09-20-2018, 07:45 AM | #12 |
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Your right....i didn't notice on the street. I usually get to the track way earlier ..like May. But its all good. Now we are talking about how much torque can be safely removed for alot better hole shots. He only has 15% removed but I've read 50% plus and even completely removed...that's another story lol
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09-20-2018, 09:01 PM | #13 | |
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I'm going Saturday finally. Two broken diffs, an axle, a slave cylinder, the whole cam job, I've been down nearly 11 weeks this season. It if doesn't go 11s I'm lighting in on fire!
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09-20-2018, 09:23 PM | #14 | |
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