Help understand these trims......

[BOBS90TURBO]

Can anyone help me understand why my Fuel trims look so wierd, the rest of my logs look great(I think) I know the car is screamin ass fast since the turbo upgrade.

Anyway a few days ago after logging for 10-15 minutes my trims were
FTRL 118.7%
FTRM 100.0%
FTRH 102.3%

Today after about 5 minutes they were FTRL 105.4%
FTRM 100.0%
FTRH 100.0%

I have been tuning all week with my safc and logger and I'm getting the hang of adding and taking fuel, but I can not figure out what the trims are and what they do. Thanks

 

[kpt4321]

but I can not figure out what the trims are and what they do. Thanks

From www.vfaq.com/TMO:

FUEL TRIMS HIGH, LOW, MIDDLE (range of 60 to 140% for 91+ cars, 80 to 120% on 90's)
These are the "long term" memory fuel tables in the ECU. When you drive the car in closed loop (normal to low-boost driving, rpm<4500), the ECU is constantly updating these trim values. The ECU takes the signal from the MAS and calculates how much fuel to add to maintain an a/f ratio of 14.7:1, then compares the O2 readings against the value it calculated and adjusts the fuel trims (adding more fuel or taking away) to try and stay at a constant "stoichiometric" value (14.7:1 air/fuel ratio). A trim value of 100% is stoichiometric, anything greater than 100% and you are running lean so the ECU is adding fuel, anything less than 100% and you are running rich and the ECU is subtracting fuel. The ECU always tries to run at a stoichiometric 14.7:1 ratio under closed loop operation and the values will be reset to 100% when the ECU is cleared.

These values will always be changing up or down a little depending on the air conditions and many other variables. Low, middle, high refer to the amount of airflow that the ECU sees while in closed loop. When the ECU goes into open loop, none of the fuel trims are updated.


From the piggyback tuning guide, http://www.dsmtuners.com/forums/showthread.php?t=58403:

The ECU is, in essence, just a big set of spreadsheets (also known as "fuel maps"). It takes input from the MAS (in the form of Hz, temperature, and barometeric pressure) and comes up with a final value that represents the amount of air entering the engine. It also looks at the engine's RPM. With the RPM and an airflow value in mind, the ECU will look to the fuel tables, and find the amount of fuel it should inject into the motor.

Then the O2 sensor comes into play. The O2 sensor tells the ECU what the a/f mixture looks like, if it is rich, lean, or right in the middle (stoich.). If the O2 sensor says that the mixture is lean, then the ECU will add a bit more fuel on top of what the tables tell it, until the O2 values get close to stoich. If it has to do this for a certain period of time, it will take note of that in the fuel trims.

Example: You are pulling in 30Hz of air at 800 rpm (idle). The ECU looks this up, and decides to inject 2.1 ms of fuel. However, the O2 sensor decides this is not enough. The ECU bumps this up to 2.2 ms, 2.3 ms, and finally 2.4 ms, when the O2 finally says that is perfect. If this keeps happening over a period of time, the ECU will increase the Long Term Fuel Trim to 114%, since 2.4 is 14% more than 2.1. It will, from then on, add 14% more fuel whenever it is in the range of that Fuel trim.

(note: This information is not correct, as the 1g fuel trims do not have a simple linear effect on IPW like that, it's more like a 4:1 ratio).


1g: 1g's have 4 fuel trims. The low trim is for idle and low rpm cruise conditions. The middle trim is for medium cruse rpm's (1500-2500ish) and the high fuel trim is for 2500+ rpm. The O2 trim is constantly changing with the O2 sensor, and it is what will cause the Long term fuel trims to change.

The approximate airflow ranges for the three trims are:

Low: 0-125 Hz
Mid: 100-175Hz
Hi: 175+ Hz

2g: 2g's only have 2 fuel trims, a long term fuel trim (LTFT) and a short term fuel trim (STFT). The STFT varies with the O2 sensor, an the LTFT goes for every rpm range. Since the STFT directly effects the LTFT, then you can just add the two together, and tune from there. For example, if the LTFT is +20%, and the STFT is -5%, you are at approximately +15%.

You can also do this addition trick on a 1g with a TMO/Pocketlogger type setup.

 

[BOBS90TURBO]

Ok, so after reading this I should trash my 1g mass that has the lower part hacked and screw backed all the way out

(((((If you have to correct your SAFC into the positive range, than the ECU will see more airflow Hz than the MAF is outputting, and could change the timing map you are following. The problem with this is, higher airflow levels get less timing advance for safety, and lower airflow levels get more timing advance))))))))

The strange thing is now that I understand fuel trims a lot better, I can't believe I am not hitting fuel cut, I have my lows set at like 1k+40, 2k+25 and the rest +10
my highs are at 1k+3, 2k+4 3k+5 and the rest +6

I get no knock and advance time up to 18, before I did the RRE mass hack mod I swear I would advance to like 21-22, man I wish I had not hacked my mass, whay does RRE even have that stupid mod on thier site...

 

[kpt4321]

There's nothing wrong with hacking a 1g MAS, I don't know where you got the idea that it was a bad thing.

If you advance is different it's because the overall airflow reported at the ECU (MAF hacking and SAFC correction) is different. That's something you can change with the SAFC.