ok so heres the scoop. as i hear a lot of up here, i have a bad case of the 2500-2700rpm stumbles. it gets worse as there is more load on the car, i can baby it to where you cant feel it, but the wideband still pegs lean. all other rpms are fine as far as the way it runs and afr's. and at any low throttle, basically anytime not in boost, the LTFT's are at ~+30%!!!! i have tried pulling more and it got worse, i tried pulling less, and even adding....and it got a little better as far as afr's but ran like poo. i have also went up to 50psi static on the fpr and down to 35psi. still no matter what i have done, it still gets random lean spikes between 2.5k and 2.7k. and its way worse when the car is cold.
mods are:
s2 pcm and map
3" sri
tcc wga
ported intake mani
ported turbo
bfmic
55mm tb & 55-60mm tapered spacer
mbc @20~16
needswings v5 dp
walbro 255
returnline
03 rail
bottleneck fix
dw 650's
dtec fc
dcr oil mod
2.0L cams
fidanza gears @ +2/-4
solid mm's
$20cc w/cv
greddy type s bov
*data was acquired via autometer wideband and aeroforce scangauge pro*
returnline is set at 45psi static with boost only source from cold pipe
dtec is set by columns only for 25 50 and 75% at:
25% -8%
50% -6%
75% -3%
100% column doesnt matter since it runs fine at WOT but if you must know its between -12% and -15% for a very mild 11.2 afr for now...
please ask questions if necessary, i know this is a problem for many people and i really want to solve this. help me out guys. thanks
When I removed my return line and switched back to the stock fpr (58psi static) and changed my injectors from rc 750's to dw 650's the car runs flawlessly @ part throttle...LTFT never go too far out of whack. No stumbles or hesitations at all.
I had a lean spike when I first got my car back together last year, when I went from mostly stock to big turbo, etc. I never got rid of the stumble completely but I made it so it wasn't really all that noticable. I don't remember what I did exactly but I just did a lot of driving around and changing my tune, fuel pressure, etc.
ok ill try that this weekend. what gets me though, is my friend down the street has a 50 trim with 750s on a returnline at 28psi static w/boost source and his car drives like an n/a. smooth as a caddy. and my tune for low throttle isnt much different than his. but hes workin with an safc...
28 psi static??? was he going for the drip-affect with the injectors or did he actually want the fuel to atomize?
you're getting +30% LTFT's during your lean stumble? I get -30% LTFT's during my lean stumbles ... wideband hit's 16 and the car stumbles, then feels like it hits a brick wall and then it finally goes
ok ill try that this weekend. what gets me though, is my friend down the street has a 50 trim with 750s on a returnline at 28psi static w/boost source and his car drives like an n/a. smooth as a caddy. and my tune for low throttle isnt much different than his. but hes workin with an safc...
Every car is different...I'll go check my lower throttle maps if you want to give them a shot...just don't boost to high on them since I'm out of fuel at 17 psi
Edit: Nevermind this offer...the battery is sitting in my garage and I don't feel like putting it back in
28 psi static??? was he going for the drip-affect with the injectors or did he actually want the fuel to atomize?
you're getting +30% LTFT's during your lean stumble? I get -30% LTFT's during my lean stumbles ... wideband hit's 16 and the car stumbles, then feels like it hits a brick wall and then it finally goes
i dont know what his fuel trims look like, but all i can say is it drives GREAT, like i said, like a caddy. i havent looked at the LTFT when it hits a lean spike, but ill check that tomorrow and post up, but all the other time, its between +20 and +30% especially when cruising. but the kicker is im getting a consistant 28mpg with about 75% highway miles. and if i do all highway ill get 31. but i dont understand how it has to add 30% when i have about 660cc/min of fuel flow while stock is almost 100cc's less and drives fine.
I didn't have a scan gauge when I tuned the car before so I have no idea what it does
The farthest away from 0 my LTFT get is under decel they go to -9 or -10...but 30 in either direction is the max that it can read
right, and from what ive read you want the LTFT's and STFT's within 10% of each other. and thats not the case at all. STFT's are low, usually less than 5%
ok i did some testing today, when i get lean spikes the LTFT's get down to +9% and no lower. but i really dont care what the fuel trims are as long as the car runs good. the biggest issue is getting rid of the lean spikes. another thing that strikes me as odd, is it takes a sec or two for the FT's to drop to 0 when i get into boost, usually a few hundred rpms, like as if the pcm isnt seeing that im past 85% throttle and it just sees lots of boost and jumps into open loop mode. the scangauge reads a max of 76% throttle at 3.16v but the aeroforce guy said that is normal since that reading is taken from the pcm and not right at the tb...but idk how that would be different.
i just got back from a little tuning session around town and i set the fpr to 58psi static no boost source, it ran just the same, and i had to bring the dtec down to 0 on 25, 50, and 75% and bring the 100% column down to 5-6% to get the right afr's, which it ran fine at WOT and low throttle the LTFT's came down nicely below +10 hovering around+9.then i started looking at the afr's on low throttle, which were pig rich in the 12's and 13's, so i started to pull in the low throttle and the LTFT's shot back up to +30. i dont get it
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Tuning issues: Tired of lean spikes and LTFT's
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