Unloading in third - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 01-03-2007, 04:56 PM   #1
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Default Unloading in third

Jesse in Fast and Furious would tell me my fuel map has a nasty hole in it, but I need more info than that.

Ok, with my AFC at a certain level, my LTFT is high, so I know it'* adding fuel. I raise my setting, my LTFT gets closer to where it should be, but then I get KR and dump boost in third (sometimes second) when I give it some good throttle but not quite enough to downshift.

Any ideas? I've had this problem before and after my AFC scrambled its display. Letting off then getting back into it sometimes makes it go away, but not always. I have the wastegate set towards the conservative end of actuation.
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Old 01-03-2007, 10:28 PM   #2
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Bump.
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Old 01-04-2007, 02:12 PM   #3
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Beuler...
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Old 01-04-2007, 02:34 PM   #4
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Apparently someone didn't agree with my response? Looks to have been deleted.
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Old 01-04-2007, 02:41 PM   #5
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Twas off topic. Funny, but off topic.
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Old 01-04-2007, 02:52 PM   #6
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Quote:
Originally Posted by J Wikoff
Twas off topic. Funny, but off topic.
I viewed it as a free bump letting you know the GH community was looking but didn't have a more valuable response. You have a good valid and good question on this one.
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Old 01-04-2007, 05:19 PM   #7
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KR? Air temps? Fuel pressure? STFT?
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Old 01-04-2007, 05:28 PM   #8
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KR, yes, a few degrees. 40-50 degrees F. Wasn't watching STFT when it happened.
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Old 01-04-2007, 05:48 PM   #9
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STFT is going to have more of an effect on cutout or pulled timing than LTFT. Could your AFC be running you slightly lean it ONE step? Causing a momentary spike in KR that the PCM sees? That'll dump boost and pull timing like a bad dog.

You may not be able to catch it with the frame rate and display refresh rate of your scantool.

LTFT'* are more likely to look normal, even in a situation of low fuel pressure, simply because the amount of averaged data where you're not under extreme fuel demand.

Also remember that in some cases, it'* possible that low fuel pressure can make the PCM think you're running rich. Lower pressure doesn't atomize the fuel as well from the injectors, allowing for an incomplete burn. That fuel can be detected by your O2, which will try to lean you out a little.
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Old 01-16-2007, 09:16 PM   #10
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Hmm, code 57 while accelerating today for about 10 seconds. Boost control error. I verified it'* (BCS) hooked up properly. I replaced it less than two years ago.
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