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Old 07-02-2010, 02:15 PM   #1
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Default overrun fuel cut is driving me nuts

No matter what I do, I always get lean spots between shifts. Seems overrun fuel cut kicks in almost instantly (PW drops with TP) although it's turned off. My AFR calibration doesn't go leaner than 19.5 BTW.
Weird thing is that PW / dutycycle don't drop entirely to zero, suggesting it's not overrun fuel cut? Is there some other setting that I'm overlooking?
Autotune always leans out the bottom row, but adding fuel there, doens't make a difference.




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Old 07-02-2010, 02:37 PM   #2
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Weird, have you tried increasing the MAP and RPM thresholds to something very high(110kPa, 10000rpm) to at least disable it that way?

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Old 07-02-2010, 02:40 PM   #3
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yup, I have 3 seconds delay and only > 100C and that makes no difference.
Weird thing is that sometimes overrun does not kick in.
This is a bit earlier in that same log.
Overrun is turned off during the entire log.

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Old 07-02-2010, 02:44 PM   #4
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What is your decel fuel amount set to?
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Old 07-02-2010, 02:47 PM   #5
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100%
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Old 07-02-2010, 02:55 PM   #6
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Sounds like you need to post a datalog at msextra.com...
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Old 07-02-2010, 03:01 PM   #7
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good suggestion, will do.
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Old 07-02-2010, 03:15 PM   #8
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Is there an indicator for overrun fuel cut that I can add to the dashboard?
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Old 07-02-2010, 03:59 PM   #9
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Overrun fuel cuts always drop to zero. That is running off the VE table and possibly the acceleration wizard.
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Old 07-02-2010, 05:39 PM   #10
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that's what I found weird, that it doesn't drop to zero. The VE table has no lean spots though and decel fuel is 100.
To rule out msq errors, I reflashed to 3.0.3u and started a new project from default.
I'll turn on decel fuel and do some more logging.
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Old 07-02-2010, 06:37 PM   #11
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your MAP is dropping down to 13ish kPa? what's your fuel there look like?
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Old 07-02-2010, 07:07 PM   #12
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It would just fuel whatever is in his bottom most cell at that rpm on his ve table.
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Old 07-04-2010, 07:08 AM   #13
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Well, it's not overrun. Switched on overrun and duty drops to zero.
So it must be something else. My bottom fuel row is only 2 points leaner than my idle row. Autotune always leanes it out to 30ish, but raising it to where it is now does not seem to make a difference. I'll try raising more.
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Old 07-04-2010, 10:00 AM   #14
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That is strange. Are you sure it's leaning out and not dumping too much fuel? It drops to full rich and then goes lean. Your cells are 2/3 the fuel they are at 60kpa. That sounds like a ton of fuel to me. Increase it more and I'd bet you'd start getting backfires. What does your timing map look like? When autotune leans it out to 30, does it run the same?

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Old 07-07-2010, 02:18 PM   #15
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I have lots of backfire. Nearly between all shifts a fat fart (especially hi rpm) and a rumble when coasting. Thought that was because of running too lean, is it not?

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Old 07-07-2010, 02:25 PM   #16
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are you using EAE? Is your sucked-from-walls too aggressive?
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Old 07-07-2010, 02:49 PM   #17
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I thought backfire was from unburnt fuel, not lack of fuel.
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Old 07-07-2010, 03:04 PM   #18
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Frank needs to post his MSQ and logs
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Old 07-09-2010, 12:17 PM   #19
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logfile here. Look at 1018s
msq here
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Old 07-09-2010, 05:03 PM   #20
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it is odd that your PW goes to 1.2 and isn't completely cutting. what would happen if you added 10 points to your 20kPa row on your VE fuel table? My logs look similar, but the leanness doesn't kick in right away, think it's cause my lowest kPa row in my VE table isn't so leaned out like yours...it hovers at 1.3PW, fully lean, and then kicks off completely with overrun.


Have you tried using EAE? Looks like you're really not getting much reacting from the TPSdot, dunno why you arent using EAE, should really help improve the AE between shifts.
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