2nd Generation Specific 1986-1992 Discussion

goes lean during cruise, boost, and free rev

Old 12-28-2006, 09:12 AM
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i have a s4 TII. i noticed sometimes when cruising at around 2k-3k rpms in like 15" of vac i get a really lean condition. jumps from 14A/f to sometimes 17A/F! then a sec or two later it goes away and A/F drops back down to normal. sometimes when i boost (no FCD so i dont boost past 5 or 6 psi) AFRs stay high lke at 15 then starts dropping to 12s (is that normal)?also goes lean at free revving sometimes at around 3k AFRs go up to 15 or 16ish.i dont know why its doing it. any thoughts?

fuel filter was changed bout 3 or 4 months ago (only use 93 octance)

550/880 injectors

have a fd fuel pump

have tried 3 different ecus and the samething

replaced TPS still the same

i have a crane cam high on leading coil (maybe has something to do with it?)

removed emissions but keep twin scroll (" ")

running on stock ecu.



these readings are of course takin off of wideband, stock o2 is still connected (was put in new in march). got new exhaust in march (no cats).

voltage to pump was around 7vs if i remeber correctly, and sometimes 9 when revving it alittle (when bogging it would stay the same)

new wires, plugs put on about 3k ago. different tps, had a rtek2.0, and a geforce ecu in and still did the same.



after free reving today when it was booging out i disconnected pressure sensor and it went away. did it 3 times in a row, if that helps anyone.
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Old 12-28-2006, 10:16 AM
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if you're cruising its supposed to be in closed loop, and it will go between 15.5-14:1, although it will go leaner if you've got a really free flowing exhaust.



if you floor it, the stock ecu sometimes runs out of injector before the secondaries turn on @3500, so if you floor it, and its lean until 3500-3800, then it goes rich, then thats whats wrong. theres no good way to fix it, with the stock ecu, but you can do a few things to get around it.



1. rtek ecus are better about it

2. bigger turbo less boost, or more lag...

3. larger primaries and maybe a super afc
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Old 12-28-2006, 11:41 AM
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ok the boosting part makes sense. but under cruising it is annoying, itll cruise at 14.7:1 then itll jump to 16:1, or even 18:1! and it is a noticable loss in power (almost like driving thru a big puddle of water) and then a few seconds later it go back to 14.xx:1 AFR. and the car doesnt go in closed loop while at idle and free revving i dont think.
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Old 12-28-2006, 12:39 PM
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yeah they do that cruising, a freeflow exhaust leans it out, and the stock ecu does compensate, but not very well.



it looks at the o2 at idle, but its not in closed loop.
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Old 12-28-2006, 02:51 PM
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so you think its going into closed loop? but onlydoesit for a few seconds and then goes away,and feels like a dramatic lost of power. thats wat I dont get.
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Old 01-07-2007, 07:29 PM
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ttt
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