Help with fuel trims

**00gpgtp** · 01-10-2009

I am new to the forums and I have a question. I have a 2000 gtp. Mods are: 3.4, open cone, 104's, 180* stat, zzp stage 1 tb, and pacesetters. The car was tuned on zzp's dyno. I got an aeroforce gauge a couple days ago and have been monitering my fuel trims. both short term and long.

My question is, what are the fuel trims supposed to be at? I know at WOT the long trim is supposed to be at 0 +/-3, I see 5.4, and also saw as high as 6* KR with 960 o2's. What about idle warm/cold? Sometimes they read as low as -21 but as high as +8. I know 16.4 is the max and usually means a vac or exhaust leak. Is there a time where 16.4 is normal? Sometimes when the engine is cold and i give it like light throttle (maybe 10%) in like 3rd gear itll jump to 16.4 but as soon as I let off it goes back down.

I reset my trims a couple days ago, and have driven about 80 miles since then at various speeds and rpms (never wot). The 5.4 wot ltft above was before I reset. Should the trims be relearned by now? I also read that the trims are learned when the short term and long term are close. What is considered close? Within 5 of eachother? Right now they are as much as 10 from eachother, is that "close".

Sorry for all the questions, I just wanted to be clear. I can't find clear answers doing a search. Thanks for the help!!

**chrisb** · 01-10-2009

well in a perfect world you want to be on 0 on your fuel trims but + or - 5 is ok. now when you go wot (pe mode) the car stops making fuel calculations based off the o2 sensor. it goes based off of maf tables. the only way to know where your fuel trims are at wot is with a wideband. also the last fuel trim the car was at before pe mode it will add or subtract that value from your pe table. so if your at -16 before pe it will take -16 from what ever your wot fuel air ratio is which can make a lean condition and causing knock.
i believe fuel trims take about 15 mins or so to be learned again, not 100% sure on that though.

hope that helps

**00gpgtp** · 01-10-2009

i get what your saying about the fueling being calculated from the maf when your at wot but why would it pull more fuel when its leaning it out already? so your saying that if its -16 right before pe mode, it will take it to -32 when it enters pe? or did you mean it would add it to make it 0 (in a perfect world). i know a maf tune should be done with the stage 2 tb since that hump is taken out but what about tuning for the stage 1? also, i heard zzp isnt good for a ve tune, true? what is ve mode anyway lol?

**chrisb** · 01-10-2009

Originally Posted by 00gpgtp

i get what your saying about the fueling being calculated from the maf when your at wot but why would it pull more fuel when its leaning it out already? so your saying that if its -16 right before pe mode, it will take it to -32 when it enters pe? or did you mean it would add it to make it 0 (in a perfect world). i know a maf tune should be done with the stage 2 tb since that hump is taken out but what about tuning for the stage 1? also, i heard zzp isnt good for a ve tune, true? what is ve mode anyway lol?

first off.
your car wants to run a base afr of 14.7 during normal driving.
in pe mode or wot its 12.4 afr. or what ever zzp set it to.

+16 ltft means your to lean
-16 ltft means your to rich. and the pcm is pulling 16% to get you back to 14.7 afr.

now when the car enters pe mode which is wot. it stops making adjustments to the afr via the o2 sensor and goes on whats stored on the maf tables.

the last fuel trim you hit before you go wot is the fuel trim the pcm will use to adjust your afr in pe mode. so if -16% is the last fuel trim u hit before you go wot (pe mode) the pcm will take that percentage away from your pe's base afr. of 12.4

-16% ltft in pe mode with a base afr of 12.4 would be
(12.4/100*16=1.98+12.4=14.38) 14.38 afr which is lean and would cause kock to show up!

even with a stage 1 tb your fuel trims will be off, some say it wont be that much compared to a stage 2 , but if you can tune for it then do it.
if zzp did a dyno tune i would say it would be good but who knows??

ve mode is just another set of tables to calculate air flow if the maf fails.
some people say tunning in ve mode helps the car out others say its a waste of time because the car isnt using the tables. im not sure on the whole thing.

sorry for the lecture!

**00gpgtp** · 01-10-2009

no no i wanted a lecture lol. its the only way to get answers. note: the car was dyno tuned before i put the tb on. its been about 3 days, plenty of start up/ shut offs, and a little over 100 miles so i think the trims are relearned by now. once the weather gets better (got about 5 inches of snow today) ill get a wot run and see what it does. does anyone know where zzp sets pe mode to begin? im thinkin about 60% throttle

**chrisb** · 01-10-2009

ok i didnt want to repeat stuff you prolly already know!
100 miles is plenty for your fuel trims to relearn themselves when i was tunning i would drive 15 to 20 mins before i would adjust them again till i got them on 0 or close to.
not sure where they set pe mode. stock should be sumthing like 70%, i would just ask them.

**00gpgtp** · 01-10-2009

is it ok for the trims to stray from 0 when driving normal? it goes up to 16.4 sometimes for a little bit and falls back down. also at idle the stft hang around 0, -1.5 to +1.5 usually, but the ltft are usually about +5 to +8.

i tried to scan my iac but get really weird values with my aeroforce. people talk about values of like 30 and 50 but i get like, 3500 or 6000... its always in the thousandths lol.

what should my boost gauge read at idle? i usually get about 17 or 18 in. hg. sometimes 20.

just trying to rule out a vac leak, especially since it threw a p0133 code today. either need a new o2, or its a vac/ exhaust leak. cant hear or feel anything... thanks

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