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Fuel Trims

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J95GST

15+ Year Contributor
68
0
Jan 27, 2005
cocoa, Florida
Ok I have a question about fuel trims

My fuel trim are
Lo 139% Mid 116% High 101%

So does this mean Im running lean? Is anything above 100% lean and anything below 100% rich?
 
J95GST said:
So does this mean Im running lean? Is anything above 100% lean and anything below 100% rich?
It means that the ECU is adding fuel over the base calculations when the trim is >100% and subtracting fuel when <100%. While your in closed loop, when the fuel trims are being used, your not actually rich or lean because the ECU uses those trims and the feedback from the O2 sensor to keep the AF around 14.7:1.
Once you go open loop, you may be leaner than what the factory maps figure but since your trims move closer to 100% as the airflow increases it looks like your pretty close to what the factory figured at higher airflows.

Do you have a hacked MAF or 2G MAF installed in that 1G?
Did you understand that your not actually running rich or lean in closed loop, the trims take care of that?

Steve
 
Ok so how do I tell if Im running lean or rich?
When my low went up to 139 my car started idiling bad.
 
J95GST said:
Ok so how do I tell if Im running lean or rich?
When my low went up to 139 my car started idiling bad.

Perhaps the correct question is why did your low fuel trim max out low. Did your O2 sensor die? If it's bad and slow to react it will fool the ECU into thinking it needs to add more fuel and it will make you run rich.

What I posted is how things work when stuff isn't broke.
How does it idle bad?

Steve
 
Im actually experiencing the same problem except my trims are 118,95, and 81 (90 tsi) Im only running 15psi (look at mods) it seems as if i could run more than that on the stock fuel system, but my idc is VERY high. If i lowered my fuel trims, as in closer to 100, do you think my idc would be lower?
Btw, another thing is i actually think my 02 sensor is dead as well. It reacts fine but when im part throttle, the o2 voltage stays around .8-.89 which is rich for a 90.
 
Just thought of something, is it probable that im leaning out or maxing injectors because i have the GM Maf-t considering it flows 800% more air than stock? I really didnt even think about that till just now cause i could run 18 psi w/ my current mods and the stock MAS and get the same results i get w/ 15psi and the GM Maf-t.
 
94Jettameowpsst said:
Im actually experiencing the same problem except my trims are 118,95, and 81 (90 tsi)
You don't have the same problem at all. Your trims are saying that as the measured airflow goes up you getting richer and the ECU is pulling fuel up high to stay at 14.7:1. That and you saying your IDC are higher that you expect would suggest you leaking air.

J95 has bottomed out his trims on the low end and looks to go to 100% as he gains airflow so he's lean and the ECU is adding fuel down low. Either he's gutted his MAF, has some injectors with a bigger deadtime, or has an bad O2 sensor.

That's the best I can do with the data we have.

Steve
 
steve said:
You don't have the same problem at all. Your trims are saying that as the measured airflow goes up you getting richer and the ECU is pulling fuel up high to stay at 14.7:1. That and you saying your IDC are higher that you expect would suggest you leaking air.

J95 has bottomed out his trims on the low end and looks to go to 100% as he gains airflow so he's lean and the ECU is adding fuel down low. Either he's gutted his MAF, has some injectors with a bigger deadtime, or has an bad O2 sensor.

That's the best I can do with the data we have.

Steve

Steve,

My low trim is maxed out at 140. After all my tuning, I still cannot get the low trim off max.

I have 550's and had to set the MAFT for 600's because the car was running too rich.

The O2 sensor is working properly, and I was told that it's probably injector dead time. What do you think? How can you correct dead time if that is the issue?

BTW, I'm still hoping to get my EPROM socket, but I'm worried about turnaround time, since I only have the one car right now. St. Charles is about a 45 min ride, so I could probably come up on a Saturday to drop off--if I did that, when would you expect that I could pick up? I'd want a ZIFF and capacitor replacement.

Thanks
 
94EclipseGST said:
My low trim is maxed out at 140. After all my tuning, I still cannot get the low trim off max.

I have 550's and had to set the MAFT for 600's because the car was running too rich.

The O2 sensor is working properly, and I was told that it's probably injector dead time. What do you think? How can you correct dead time if that is the issue?

Most aftermarket injectors have larger deadtimes than the stock 450s. This impacts low trims more than higher ones because the deadtime is a larger percentage of the injector pulse width at low airflow. Setting up your MAFT for 600's only makes this worse by making the pulse width even shorter. The MAFT may make some corrections in it's calcs for deadtime but doing it in the EPROM works so much better.

email me or call me about the rest.

Steve
 
Steve,

I'll email you and try to set something up.

Thanks for the help. :thumb:
 
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