Hey guys, my datamaster log is telling me my short and long term fule trip values are lower then 128 (they fluctuate between about 108 and 128) What is this telling me about what is going on with the engine? My O2 readings seem normal. I know the car is running rich, but i don't know why. Any help would be great, thanks.

Mike

 

ttt

 

In general, its saying that under some conditions, the "standard" fuel calculation (long term fuel trim = 128) is producing a mixture that is too rich, or which the PCM erroneously perceives as too rich. The PCM is reducing the LT fuel trims to reduce the amount of fuel delivered. When the LT trim reaches 108, it has "bottomed out".... the PCM has pulled more than 15% fuel from the standard calculation, and it is (probably) still running rich.

The LT trims are arranged in "cells" that are a function of engine RPM and engine load (as approximated by manifold absolute pressure - MAP). As you move through the range of operating conditions, the LT's will represent the degree of correction being applied under those condition.

You need to look at:

-are the LT's for any operating condition the same for both left and right banks of the engine? That tells you whether you have a condition affecting the entire engine, or just one side.

-are the low LTs... e.g. 108... skewed toward any particular operating ranges.... all at idle (cell 16) and low loads/rpm, or all at high loads - Cells 14 and 15 for example.

Things that can cause a true rich condition on both sides of the engine would be a false MAF reading (higher than actual), excessively high MAP reading, fluctuating TPS voltage, excessive fuel pressure, leaking EGR valve, saturated EEC canister, FPR dumping fuel in the vacuum line.

Things that can cause a "false" rich condition would include leaky injectors.

For info on interpreting scan data, you might want to review my ScanMaster writeup. I think there might be some differences in the way DataMaster reports "cell #".... I think they have intermediate values, resulting in the appearance of more than the 16 normal cells in the RPM/MAP matrix.

 

Injuneer,

My mistake, the condition of the LT's that I stated above were not the most current. I belive those low readings were from a leaky injector. however, my most current test is showing abnormal LT's as well...

In Fuel trim cells 16 and 17, my left side LT's hold steady at 137 or 138, while my right side LT's hold steady at 157 or 158.

In almost all other cells the LT's are the same for both sides.

I'm not sure which side of the engine the program considers right and left.

What is the differance between true rich and false rich?

thanks

 

OK.... now you have the exact opposite problem, but only at idle (Cell 16). Ignore Cell 17, that is the "override" or coasting cell, and appears to be a problem mostly on the right side.

Bank 1 = left side = drivers side
Bank 2 = right side = passenger side

This would suggest its a problem that appears mainly at idle. Misfires, leaky exhaust before the O2 sensor are typical causes.

Seems odd that you would have a complete reversal from 108 LT's to 150+ LT's without having made some changes of some sort.

"True" lean means the engine is actually running lean and has to add extra fuel to correct to the desired 14.7:1. "False" lean means the PCM thinks the engine is running lean, and is adding fuel, but the information given to the PCM is incorrect (exhaust leak, misfire, faulty O2 sensor) and the PCM is adding fuel the engine doesn't really need, causing it to run too rich.

You might want to go back and collect your thoughts a little more clearly.... hard to understand how you could think you had 108 LT's when in fact you had 150+....... a lot of wasted time addressing a problem that didn't really exist.