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Old 12-10-2007, 09:00 PM   #1
williaty
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Default Why Does The ECU Dump Fuel In After Shift?

I'm frequently getting patterns in my log like the one below. I shift, a few lines later, it dumps in A LOT of fuel. Anyone have any idea why/what's going on?

Code:
Time	RPM	g/rev	AFR	A/F-C	A/F-L	CL/OL	FBKC	FLKC	IAM	TotTime	IAT	MAF g/s	Throt%	Gear
4594	3975	0.56	14.59	0	2.34	8	0	0	0.875	36	54	37.03	21.57	1
4875	4115	0.48	14.36	0	2.34	8	0	0	0.875	39.5	54	30.78	18.43	1
5156	4191	0.29	13.9	-2.34	1.56	8	0	0	0.875	44	54	16.07	12.16	1
5453	4146	0.19	15.04	0	1.56	10	0	0	0.875	35.5	54	13.57	12.16	1
5734	3947	0.19	17.92	0	1.56	10	0	0	0.875	25	52	12.93	11.37	0
6031	3491	0.19	20.33	0	1.56	10	0	0	0.875	25	52	9.92	10.2	0
6313	3041	0.16	20.33	0	2.34	10	0	0	0.875	30	52	8.17	9.02	2
6609	2793	0.33	20.33	0	1.56	10	0	0	0.875	34.5	52	20.09	15.69	2
6891	2805	0.59	20.33	20.31	2.34	8	0	0	0.875	38	52	29.81	20	2
7172	2682	0.69	14.7	29.69	2.34	8	0	-1.47	0.875	32.5	52	32.26	21.57	2
7453	2762	0.77	12.17	17.97	2.34	8	0	-1.47	0.875	30	52	35.24	23.14	2
7750	2878	0.78	13.32	3.12	2.34	8	0	-0.26	0.875	31	52	37.03	24.31	2
8031	2989	0.86	14.36	0	2.34	8	0	1.4	0.875	29.5	52	42.74	27.84	2
8313	3119	0.88	14.59	0	2.34	8	0	1.4	0.875	29	52	45.33	29.02	2
8609	3266	0.87	14.47	-0.78	2.34	8	0	1.25	0.875	29.5	52	46.57	29.41	2
8891	3397	0.87	14.59	-0.78	2.34	8	0	1.25	0.875	30.5	52	48.81	29.8	2
9172	3515	0.88	14.7	-0.78	2.34	8	0	1.25	0.875	30.5	52	50.9	29.8	2
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Old 12-10-2007, 09:18 PM   #2
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Just a guess do you have an aftermarket intake or bov???
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Old 12-10-2007, 09:19 PM   #3
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Stock engine, stock tune
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Old 12-10-2007, 09:19 PM   #4
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And no turbo, btw
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Old 12-10-2007, 09:21 PM   #5
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so you havent done anything to the car at all....
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Old 12-10-2007, 10:12 PM   #6
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Quote:
Originally Posted by williaty View Post
And no turbo, btw
Well THERE is your problem....

I have no specific knowledge of the factory Subaru ECU, but this type of strategy is typically done for one of two reasons:
1) Typically, some amount of fuel gets "stuck" on the walls of the intake ports with a port injected engine. Go into fuel shutoff (on a shift, long decel, etc.) and you tend to suck all that leftover fuel through the engine. When you turn fuel back on (after a shift) you need to throw "a little extra" in to make up for the wall etting effects. If this was "perfect" you wouldn't see it on the A/F meter, but it's safer to make things a bit rich here to cover production variability. (If you're a bit lean, the car stumbles when you get back on it)

2) More likely this is for emissions. When you're in fuel shutoff (see above) the catalyst(s) take all that extra oxygen you're pumping through the engine and store it up. When you turn fuel back on, the high temperatures and "extra" O2 stored in the cat make the car puke NOx. You can't make this NOx burp go completely away, but if you dump in some extra fuel, you can deplete the extra O2 quicker and reduce the effects on your cumulative tailpipe numbers. Incidentally, it also hurts fuel economy a teeny bit...

Your mileage may vary.
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Old 12-11-2007, 02:44 AM   #7
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If this may be something the ECU is doing deliberately, is there a way to tune it out?
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Old 12-11-2007, 08:02 AM   #8
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Looks like tip in enrichment.
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Old 12-11-2007, 09:29 AM   #9
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Quote:
Originally Posted by TheMadScientist View Post
Looks like tip in enrichment.
I'll second this. When you're opening the throttle after the gear change, I'm sure it's quick enough to trigger tip-in enrichment. Try either logging the tip-in enrichment throttle plate % (it's called something like this) value if it is available with NA and see if the tip-in corresponds to the fuel dump. To test this, try rolling on the throttle slowly after a shift, keeping the tip in % value as low as possible or 0 and see if the AFR still goes rich.
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Old 12-11-2007, 05:28 PM   #10
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whatever it is - that engine aint a happy thing even if it is standard.

Are you running it on poor quality fuel?
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Old 12-11-2007, 05:30 PM   #11
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Shell 89oct. Remember that it's an RS, so it's only supposed to run on 87. It's got some serious knock issues that no one can seem to explain. While looking at the knock problems, I noticed this weird fuel thing.
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Old 12-11-2007, 09:27 PM   #12
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OK, more logging tonight. The fuel dump isn't caused by tip-in. I logged Tip-In Throttle* (%) tonight and it's un-correlated to the huge positive AF-C#1 values. However, this scares me more. A LOT MORE.

Code:
Time	RPM	Throt%	g/rev	g/s	AFR	AFC#1	AFL#1	Tip-in	CL/OL	FBKC	FLKC	IAM	Advance	KC	Gear
112782	1986	16.08	0.58	19.22	14.7	2.34	3.12	0	8	0	0	0.875	7.26	7	5
113125	2002	16.47	0.6	19.69	14.59	2.34	3.12	0	8	0	0	0.875	7.9	8	5
113469	2010	16.86	0.6	20.01	14.59	1.56	3.12	0	8	0	0	0.875	7.71	7.5	5
113828	2014	16.86	0.59	19.85	14.7	2.34	3.12	0	8	0	0	0.875	7.32	7.5	5
114219	2024	16.86	0.6	18	14.7	2.34	3.12	-0.12	8	0	0	0.875	7.7	7.5	5
114563	2039	16.86	0.59	19.38	14.59	2.34	3.12	0	8	-1.05	0	0.875	7.12	6	5
114907	2042	16.86	0.6	21.03	14.59	2.34	3.12	0.12	8	-1.05	0	0.875	7.99	6.5	5
115266	2036	17.65	0.64	22.32	14.24	0	3.12	0	8	-1.05	0	0.875	9.02	8	5
115610	2053	17.65	0.65	21.66	14.59	0	3.12	0	8	-0.7	0	0.875	9.08	8	5
115953	2041	17.65	0.65	22.15	14.59	0	3.12	0	8	-1.75	0	0.875	9.04	7.5	5
116297	2044	17.65	0.65	22.32	14.59	0	3.12	0	8	-2.8	0	0.875	9.35	6.5	5
116657	2046	17.65	0.65	22.07	14.59	-0.78	3.12	0	8	-3.85	0	0.875	9.16	5.5	5
117000	2050	18.04	0.65	22.49	14.59	-0.78	3.12	0	8	-3.85	0	0.875	9.25	5.5	5
117360	2060	17.65	0.65	22.32	14.59	-0.78	3.12	0	8	-3.85	0	0.875	9.16	5.5	5
117703	2062	17.65	0.65	22.32	14.7	-0.78	3.12	0	8	-3.5	0	0.875	9.16	5.5	5
118047	2070	17.65	0.65	22.49	14.7	-0.78	3.12	0.12	8	-3.5	0	0.875	9.15	5.5	5
118407	2077	17.65	0.65	22.4	14.59	-0.78	3.12	-0.12	8	-3.5	0	0.875	9.04	5.5	5
118750	2078	18.04	0.65	22.82	14.59	-1.56	3.12	-0.12	8	-4.2	0	0.875	9.01	5	5
119110	2081	18.04	0.65	22.74	14.7	-0.78	3.12	-0.12	8	-4.2	0	0.875	8.75	4.5	5
119453	2090	18.04	0.65	22.07	14.59	-0.78	3.12	0	8	-4.2	0	0.875	8.82	4.5	5
119782	2100	18.04	0.64	22.65	14.7	-0.78	3.12	0	8	-3.85	0	0.875	8.67	5	5
120141	2110	18.04	0.65	22.49	14.59	-0.78	3.12	0	8	-3.85	0	0.875	8.64	5	5
120485	2114	18.04	0.65	21.99	14.7	-0.78	3.12	-0.12	8	-3.85	0	0.875	8.49	4.5	5
120844	2116	18.43	0.66	22.74	14.59	-0.78	3.12	0	8	-3.5	0	0.875	8.82	5	5
121188	2136	18.43	0.66	23.07	14.59	-0.78	3.12	0	8	-4.55	0	0.875	8.69	4	5
121547	2133	18.43	0.66	23.49	14.59	-0.78	3.12	0	8	-4.55	0	0.875	8.7	4	5
121891	2146	18.43	0.66	23.32	14.7	-0.78	3.12	-0.12	8	-4.55	0	0.875	8.61	4	5
122250	2154	18.43	0.66	24	14.7	-0.78	3.12	0.12	8	-4.2	0	0.875	8.73	4.5	5
122610	2156	18.43	0.66	23.66	14.59	-0.78	3.12	0	8	-4.2	0	0.875	8.4	4	5
122953	2168	18.43	0.65	23.24	14.7	0	3.12	0	8	-4.2	0	0.875	8.23	4	5
123297	2172	18.43	0.65	23.24	14.7	0	3.12	0	8	-3.85	0	0.875	8.15	4.5	5
123657	2172	18.43	0.66	23.83	14.7	0.78	3.12	0	8	-3.85	0	0.875	8.31	4.5	5
124063	2180	18.43	0.66	23.66	14.59	0	3.12	-0.12	8	-3.85	0	0.875	8.16	4.5	5
124407	2192	18.43	0.66	24	14.59	0	3.12	0	8	-3.5	0	0.875	8.16	4.5	5
124750	2198	18.43	0.65	23.24	14.7	0	3.12	0	8	-3.5	0	0.875	7.58	4.5	5
125094	2188	16.86	0.61	21.5	14.59	0	3.12	-0.12	8	-3.15	0	0.875	5.69	2.5	5
125438	2201	16.08	0.55	18.59	14.59	0	3.12	-0.12	8	0	0	0.875	3.05	3	5
125782	2202	14.12	0.5	15.71	14.81	0.78	3.12	-0.24	8	0	0	0.875	1.02	1.5	5
126125	2198	12.55	0.39	15.3	15.04	2.34	3.12	-0.12	8	0	0	0.875	0	0	5
126422	2200	9.8	0.29	9.22	14.59	2.34	2.34	-0.12	8	0	0	0.875	0	0	5
Gulp.
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Old 12-11-2007, 10:02 PM   #13
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It is very difficult to catch tip-in %. You need to log an absolute minimum number of parameters. If your other log, which you didn't show, has the same number of parameters selected as this one, then the tip-in % values will be worthless. Log only RPM, tip-in %, throttle opening angle %.
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Old 12-11-2007, 10:28 PM   #14
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No, I've never tried to log tip in before. I only added it to tonight's logging because someone mentioned it in this thread yesterday.
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Old 12-12-2007, 12:51 AM   #15
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Is that the stock O2 sensor reading? If so it isn't anywhere near close to being accurate off of stoic (14.7), you cannot use that sensor for tuning. If you are richer than 14.7 it will read much richer than actual, and if you are leaner then it will read leaner than actual.

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Old 12-12-2007, 01:15 AM   #16
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Master, before enginuity.org's forums disappeared, someone did a comparison of the newfangled not-quite-narrowband AFR sensor to a LC-1. The results weren't in perfect agreement, but they weren't bad either. IIRC, the worst error was ~0.08 near 11:1 where it stopped reading.

Obviously a true narrowband (which is what that graph looks like) would be useless as you say. Are you sure that still applies to the newer cars?
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