Need basic help tuning my fuel trims.

[Scuba_Steve]

Sorry for the basic question, but yes I did search quite a bit. Regrdless, I still felt this is designed for the newbie forum, not the tuning section.

First of all, I am in Iraq right now, so I obviously won't be able to try to correct this for a while, but I want to be prepared when I return. When I was on my R&R, I tried tuning my car for the first time. I was following the Piggyback tuning guide, using MMCD and an SAFC. MAS, fuel pump, O2, and injectors are currently stock which should mean I should be around 0% across the board as far as I know.

When I first started it up, the previous owner had the SAFC set to +5% on the low side. The log showed about 110% on the low table. So I began playing around with the SAFC. No matter how extreme of a change I made, the trims wouldn't move.

I reset the ECU by removing a fuse, and of course they went back to 100%. I literally let the car idle for over an hour, and the trims again didnt change, stayed at 100%. I tried this at 0% and at 10%, same result. Same goes when I tried to hold the throttle at 1500, 2000, 3000. The only way I could get them to change was a LONG drive, then I saw changes up to 121%. This is way to difficult to do to make small adjustments though, or even get it in the ballpark.

So I decided maybe I was reading into everything wrong, and tried tuning so I could get my o2 table at 100% instead, but of course that value jumps all over the place being a nbo2. I did get it to stay in the general vicinity of 100% though.

All in all, I didn't get much time to mess with it, not much time with everything else going on in my short 2 weeks. Will this method of tuning to the o2 table work well enough to get in the ballpark, or does that value mean something completely different? What am I doing wrong?

Thanks in advance!

 

[red1993gsallmt]

First off let me say thanks for serving our country and keeping us safe. It sounds like your o2 sensor might be on its way out. Do you have a wideband?

 

[Scuba_Steve]

Thank you for the kind words. No I do not, but it is a high priority after I repair some much needed steering and suspension parts. From what I did find in my search I thought that might be the problem, but it does jump all over the place (20% swing on the o2 value of the log), which I thought was about normal for a nbo2.

 

[red1993gsallmt]

Next time u drive it watch your o2 trim and see what its doing

 

[Scuba_Steve]

That is what I was watching, the o2 trim. It bounced around about 10-20%. The last time I tried tuning the trims, I used that trim exclusively, and just got the 02 trim so it was jumping above and below 100% equally.

 

[JeffGST]

Your O2 is working fine. Just the fact that the trims are changing is proof enough that it is operational. A Front O2 that is on the way out, will show a voltage flatline and have the fuel trims locked at 0 or 100%.

If your Lo fuel trim was at 121%, it means that the ECU is trying to increase fuel flow due to a lean condition at low airflow readings of 0Hz-75Hz. Increase the low RPM sliders on the SAFC by +2% from where they are now. Then after a day of driving check back on the fuel trims.

For example... if the Lo trim is now 110%, you know now that a 2% change in the SAFC netted a 11% change in the fuel trim. Then I would go up 2 more percent on the SAFC and then be done with the Lo trim. That is the way to go about this with the SAFC.

The key to fuel trims is PATIENCE. The trims will not change in a minute or two. They will give you accurate readings after a good drive throughout the day.