What is causing my fuel trims to go negative?

[Mike H.]

Ok so long story short, car has 243 heads ls6 intake used to be 233/239 cam now has a tick polluter. The only change I made to car is polluter and th400 with a 3500 instead of my old 60e with 4000 stall.

I logged the car and from the logs looked like I had some negative fuel trims (log1t1 file). So I pulled 2% fuel from VE table just to get values closer, took it for another drive and got fuel trims that were way negative again. (log2t2 file). So pull another 2% out and car wont idle and trims climb positive. Can't even give car any gas it just goes dead. (log3t2).


So basically, was wondering what you guys thought? I will include the logs and also if you see anything else worth noting please let me know.

[jimbos'ss]

Ok so long story short, car has 243 heads ls6 intake used to be 233/239 cam now has a tick polluter. The only change I made to car is polluter and th400 with a 3500 instead of my old 60e with 4000 stall.

I logged the car and from the logs looked like I had some negative fuel trims (log1t1 file). So I pulled 2% fuel from VE table just to get values closer, took it for another drive and got fuel trims that were way negative again. (log2t2 file). So pull another 2% out and car wont idle and trims climb positive. Can't even give car any gas it just goes dead. (log3t2).


So basically, was wondering what you guys thought? I will include the logs and also if you see anything else worth noting please let me know.

tune the VE table(looks way too smooth like you used the smooth all button) then maf, then dial in the RAF table using a desired airflow histo. search on here and you can find how too's for all of that.

[Mike H.]

tune the VE table(looks way too smooth like you used the smooth all button) then maf, then dial in the RAF table using a desired airflow histo. search on here and you can find how too's for all of that.

I'm tuning the VE table. What my problem is, is that my fuel trims go negative as you can see in the log, so I pull fuel out of the VE table, and then it wont even run and the fuel trims start to climb positive. It seems like my STFTs are incorrect.

[cptinjak]

Don't pull 2% across the board because you see negative trims. Use the AFR Error histogram and multiply by percent.

Also try to keep the log under 24 bits for best resolution.

Jack

Edit: are you just revving it at idle and trying to tune VE off that? You need to actually go drive around to tune the VE.

[Mike H.]

Don't pull 2% across the board because you see negative trims. Use the AFR Error histogram and multiply by percent.

Also try to keep the log under 24 bits for best resolution.

Jack

Edit: are you just revving it at idle and trying to tune VE off that? You need to actually go drive around to tune the VE.

In the 1st two logs I was driving the car around. Speed is 0mph because I have a TH400 and no speedo. Will do on the 24bits. Only reason I pulled 2% is because it was less of a change than multiply by percent and I only pulled it from 0-4000rpm where my data was in the negatives.

I am also being told on another forum that I guess the overlap of the Polluter Cam might be throwing the fuel trims off and I might have to tune in OL.

[Beatdown Z]

Make sure you reset your fuel trims every time you start a new log.