Fuel Trim and o2 trim questions. Please help...

turbo95dsm · 09-26-2003, 11:21 AM

Ok. First I have done a search and found some stuff that helped me a bit but not enough.

I'm needing some help understanding my logs a little cause I dont fully understand the datalogger with fuel trims and o2 trims.

How does the o2 trim relate to the fuel trims?

Let me also say, I have tons of black smoke coming out my exhaust and I can smell the unburnt fuel and it leaves a fuel taste in my mouth... I'd think I was running very pig rich, but it seems from what I've read on this board that I am running a bit more on the lean side??

Here is a sample of some data from a log of my 93 Tsi Awd:
**(3rd gear pull @ 12 psi on pump gas)

EGT's are never above 780-800c

Fuel trims: (these never change no matter if idle or WOT)
High - 108
Mid - 102
Low - 96

O2 at WOT: .86 to .88

injector pulse - 12.54
injector duty cycle at WOT: ranges from 22 to 58

timing is in the mid 20's

My mods are:
PTE 54trim, 680cc injectors, 2g maf, 4" FP MAF to turbo intake, SAFC, FMIC walbrah 255, rre 3" dp, ATR 3" catback, 3" cat, + tranny stuff

Any help would be wonderful... Thanks in advance.

turbo95dsm · 09-28-2003, 08:43 AM

ok. Basically all I really want to know is how do the 02 voltage and fuel trims relate to each other? Also what are typical readings for both.

Thanks.

sqhopeful · 10-01-2003, 05:54 AM

the ecu uses the o2 TRIM to help set the other trims as far as i know it. Also, keep in mind, the ecu ignores the trims for WOT so that is nto a factor here. From your trims you posted everything looks pretty good. all cars are different but the ecu take it's good'ol time adjusting the trims, in my car we are talking a day or so. To set the trims i had to make adjustments and check it in a couple of days.

My low trim is still acting up, it peggs at 140% at idle. but the 02 trim looks great boucing between 95% and 105%, if i let it sit idleing long enough it will fall down to something reasonable, but as soon i come to a stop again it's back at 130%+. ever run into this?

Mike 99GSX · 10-01-2003, 07:53 AM

I'd say you're in pretty good shape. I would start turning up the boost now and continue to watch the timing and knock. You've got plenty of room with injector obviously since you're only maxing 58%. You'll probably see your timing drop down from the mid 20s as you turn up the boost but you should still be able to get near 20 at the top of 3rd at around 18-29 PSI on good pump gas.

turbo95dsm · 10-02-2003, 02:04 PM

Thanks for the info guys.

I ran into a big problem though. I pulled the #4 spark plug and found it was soaked in oil.

The JDM 6 bolt I had put in the car has always sucked oil and I have never found where it was going... the motor place replaced the valve seals and well I dunno... guess the rings are bad.

I'll see what they want to do with this engine and then get my car tuned properly... lol this is not so much fun.

Mike 99GSX · 10-02-2003, 02:21 PM

Do a compression test.