After owning my car's hand-tuner for over 2 years, I finally decided to look into that little feature called 'data-logging'. I only chose the options of short fuel trim 1 & 2, long fuel trim 1 & 2, spark, and incoming air temperature. I figured fuel/spark/air are the basics. I just wanted to see if these numbers look healthy

On start up and while my engine was cold, the short fuel trims were hanging around 1.18-1.22. After driving a few miles and entering a long stretch, I hit cruise control (5th, ~55mph, 1600rpm) and they were slightly lower, being around 1.08-1.12.

Long fuel trims 1 & 2 said 1.00 and did not move.

Spark was around 20-23 while cold (dipped to 16 for a brief moment). Once warm and driving it went to high 20's, 28-30.

IAT surprised me a bit. It was 70-74 the entire time. The VFW's outdoor digital thermomater said 73. I expected it to be slightly higher than outside ambient temperature due to the engine's heat output, and particularly because my upper radiator hose slightly touchs my MAF housing.

Thanks!

 

I should look into doing that also. Since my Stang isn't my DD and will often sit in the garage for 2 weeks at a time AND my spare time is taken up with fishing and yard work, I haven't played with mine much other than swap tunes on occasion the 5 years that I've had it. My bad...

I'm a little surprised at your IAT #'s also.

 

I suppose, while driving, the air is coming in too quick to get heated up much at all.

I also suppose it is getting this measurment via the MAF?

 

short term of 1.18 is -18% I believe, so it is subtracting that much fuel. Spark while cruising is pretty pointless. it will fluctuate a lot.

Brenspeed turns off Long term fuel trims in some of their tunes, looks like they did in your case. They did in mine as well.

IAT while cruising is going to be close to ambient. You are moving the air by the sensor to fast for it to get heat soaked. Now if you are sitting at idle you should see it increase quite a bit.

 

Unless you are having cold start issues, i wouldn't worry about fuel trims until it's at operating temp. What is your short term at with a hot idle?

 

I will have to get that tomorrow when I arrive at work.

Truthfully I only selected the fuel measurments because I've always wondered if I am running rich. More soot on my exhaust than seem ordinary. Didn't know if it was too much fuel, my lack of a air/oil separator, or both.

 

Just for a point of reference, our cars are very different though, my short term fuel trims on a cold start are 1.06 or less and end up being around .95 after about 5 minutes of idle and 152*F coolant temps.

Now that you have a point of reference, i'd clean your MAF sensor and see if the 1.18 drops any.

With a coolant temp of 188, i'm getting +8-11% stft or .89-.92. Both banks are very close to each other. Interesting note is I have 3 tunes for my car and none of them are consistent with the fuel trims at idle. They range from +8, +15 and +28 at hot idle. That +28 tune was showing a 15.5:1 afr before the fuel trims kicked in, so it took 28% more fuel, than it was commanding, to bring the afr back to 14.4:1.

 

I'll check out my hot idle tomorrow morning as well as coolant temperature since I just flushed out all the old fluid.

If nothing else, I'll get someone from Brenspeed to look at my numbers and see what they think. Although, car runs fine, so I'm probably just splitting hairs

 

I ran another log this morning, this time with engine coolant temperature, incoming air temperature, and short fuel trim 1 & 2.

ECT was 50 upon ignition (ambient temperature) and slowly rose til it peaked at 192. Never budged from 192 once it got there, even when I got to my destination and idled for a few minutes. Seems normal since aren't the thermostats 193?

IAT was @ ambient temperature til I got to work and idled. Jumped like 20 degrees in a 3-4 minutes, lol. All normal

SFT was noticeably lower this time. ~1.16-1.21 on initial start up, but dropped slightly to 1.10-1.19 within a minute. A mile or two down the road it further dropped to roughly .99-1.06, and hot idle was a tight .97-1.02

 

OEM thermostat is 192.