2g tuning complications

[cuong1106]

hey guys i have a 97 gsx and im have complications tuning the short term fuel trim. i have checked for boost leaks and i only found a lil leak near the throttle body. i have denso 660cc injectors. im sure that are they 660cc too and i also have a 3kgt vr4 pump. the problem im having is that my car is currently at -20 all across the low and high side of the safc. while the logger is telling me that the short term fuel trim is a positve 17. so as i start to add fuel to the safc the number on the logger is getting near 0. well when im at 0 on the logger, im at -1 or 0 on the safc too. its wierd i thought that bigger injectors i would need to lean them out, but the logger is telling me to add fuel. i dont know what is going on. any suggestions on what can cause the short term fuel trim to be jacked up? some of my mods are 50 trim turbo, 660cc injectors, 3kgt vr4 pump, stock fuel pressure regulator, and the bov is recirculated too. please help!!!!!! need it bad. others have doubted that i dont have 660cc injectors in there but there are cause while i was trying to tune with the kpt4321 guide my low settings were -1 at 1k -4 at 2k and 3k and up was at around +5 and then car would run like crap cause of too much fuel. so i backed them back down and it drives ok but the short term fuel trims are still out of whacked. could it be that my stock fuel regulator is bad or maybe the fuel pump? and injectors are less than 6 months old. sorry for the long post, just need some advice from the pros.

 

[CanadianTSi]

Is your MAS hacked at all??

The logger doesn't lie, if that's where you have to set it to get your fuel trim right then thats how it's gotta be

 

[cuong1106]

i dont have a hacked mas. well the car doesnt run well according to the logger. its telling me to add alot of fuel for the 660 injectors, and making the car run like crap. dont know what is going on.

 

[Coldandafraid]

you have to add fuel (air) at idle for a number of reasons.

#1. Bigger injectors have bigger dead-time. Making a lean idle.

#2. A vacuum leak drawing air in past the mas.

With my 680s I added only a few percent for the dead-time. And a couple more when I had a small vac leak.

If you have to add 20% you must have a huge vac leak then. Are you venting your bov? it is possible that the bov could suck in air under vac, but unlikely with the stock spring in the HKS bov.

#3. A bad O2 sensor... telling you to add fuel when you dont need it.

Did you have the afc installed and tuned with the stock injectors before you put the bigger ones in?

 

[cuong1106]

well is it common for 660cc injectors to have a condition like at -8 at idle? is that okay and normal? cause from what i was told is that the 660cc injectors should be leaned out to be around -20 something percent. so that is kinda confusing, is it the brand of injector too? i have denso. i have a lil vacuum leak in the throttle body area, and i dont think its my o2 sensor cause i just changed it out not too long ago. and yes i did have the safc installed and tuned with the stockers before the larger 660 injectors. have for reference too, do u mind letting me see ur safc settings for the low and high settings. thanks cuong and please help a fellow dsmer in need of tuning out. thanks alos i am recirculated with my hks ssbov. i have vacuum leaked the car and only to find out the lil leak at the throttle body area only.

 

[Coldandafraid]

you say -8 at idle. What are you at the other rpms, for low throttle?

I cant rememeber what my afc settings where exactly, because I only had them for a few days until I got my ecu chip in the mail, and now I am almost zero'd.

 

[cuong1106]

hey the logger is telling me to add more and more fuel for the low settings. we i follow kpt4321 guide, the low settings came out to be something like -8 at 1k -3 at 2k and 3k and up was near 0 or even in the positive. i know something isnt right about this. and when i drove the car it drove crappy like too much fuel but that is what the logger is telling me to do. im stumped. please help

 

[Coldandafraid]

yes thats odd. it should be the other way around.

-8 at 1k, -15 at 2k, -20 at 3k and so on.

Just to be perfectly clear, by following kpts guide, you are making your short term and long term trim cancel eachother out right?

 

[cuong1106]

yes using that method does make the short term and long term trim cancel out. is there a easier or more preferable way to tune? so u suggest me to leave the settings like what u said in ur post? -8 at 1k -15 at 2k and -20 for the 3k and up? please let me know. thanks im very appreciated. respond asap

 

[Coldandafraid]

No, i would not suggest my numbers, they were an estimation, and just a rough example of where you might be.

With your trims where they ar now (balanced) are you positive you are running rich... even though the logger doesnt thing you are?

 

[cuong1106]

with the settings like that i dont think the trims are balanced. the o2 voltage says that im kinda rich but the egts are high. 1600 in 3rd at 6k rpm. not even redline, i dont know what to do. if i add some fuel to the high settings then the car would hesitate at around 4-5k rpm and then take off. i really dont know what i should do. the logger is telling me one thing but it doesnt run the best with what the logger is suggesting. and some say that the logger doesnt lie, so now im just kinda stumped and stuck, dont know what to do. thanks cuong please help. cuong

 

[Coldandafraid]

ok, first of all... low throttle and high throttle are two different things. For now, we will just stick with low throttle.

At low throttle you want your 2 trims to be zero, or to equal zero when added together. If they do equal zero, but you have a feeling that your car is running rich, then the logger doesnt lie unless your O2 sensor is not working properly.

 

[1fast97gsx]

-8, -15, -18, -18 ... is about where it should be imo. My idle settings were only -12 with 780s.

 

[cuong1106]

well at i think around -8k the short trim is at zero and the long trim is still high like around 10-15 i think. what do i suppose to do with that at idle? also how would i tune the short term for 2k-7k? same prodecure? please let me know. the o2 is working properly cause i just changed it out about 2 months ago. thanks reply asap

ok, first of all... low throttle and high throttle are two different things. For now, we will just stick with low throttle.

At low throttle you want your 2 trims to be zero, or to equal zero when added together. If they do equal zero, but you have a feeling that your car is running rich, then the logger doesnt lie unless your O2 sensor is not working properly.

 

[Blk_99gst]

Gosh I remember your first thread about this...

The whole business of adding the stft and ltft so that they reach zero is kind of bs. Short term fuel trim is instantlous what the ecu is doing (adding fuel or taking out fuel), ltft is basically the stft over a longer period of time. The real goal is to get ltft to be as close to zero as possible. Not adding the two together. If the ltft is +10%, then things are too lean and you need to richen up the safc. If it is -10%, things are too rich and you need to lean out the safc. You use stft to start to guide you when you are changing the safc.

You probably never tried the other scenario that I posted in your original thread did you. If you have the safc at near 0% correction with the 660's in there at idle; then my suggestion was to put the stock 450's back in, reset the ecu, and see what fuel trims do. IF they stay at zero-ish on the fuel trims with the safc still zeroed out, that would tell me the injectors you have aren't 660's. IF you're fuel trims shoot way the hell up (+20%), then you have something major wrong with the car; maybe air is being sucked in after the maf.

I think that's a good test to run. Otherwise, you've done things right and are asking people to explain why it is. No one can tell you why your safc settings are zero at idle with 660 injectors in the car, and near zero fuel trims. That's just not right, and not happening to other people. I have denso 660's in my car, and my low safc settins are as follows (actually going out to the car and checking):
1000 -27%
2000 -29%
3000 -37%
3500 -37%
4000 -37% (above 4000 rpm, low setting should be the same as the 4k setting)
5000 -37%
6000 -37%
6500 -37%
I haven't checked my trims with the logger in a few days, but they are within + or - 5% on the ltft (the one that matters).

 

[kpt4321]

The whole business of adding the stft and ltft so that they reach zero is kind of bs. Short term fuel trim is instantlous what the ecu is doing (adding fuel or taking out fuel), ltft is basically the stft over a longer period of time. The real goal is to get ltft to be as close to zero as possible. Not adding the two together. If the ltft is +10%, then things are too lean and you need to richen up the safc. If it is -10%, things are too rich and you need to lean out the safc. You use stft to start to guide you when you are changing the safc.

Why is it BS? Those two numbers mean the amount of correction that the ECU is applying to the IPW.

If it's adding 10% (10% LTFT) and then taking 10% back out (-10% STFT) then the IPW is in the end totally untouched, which means that your settings are correct.