those # are at crusing speeds of 65mph, but when the tune was first done they were at -3.45 to -2.45 at the same speed but since i've cut the tial pipes they have jump to those # and i think the truck ran better at the -2 -3 range and on the note they still went to 0.00 at wot, another ? is it running rich or lean at -12 thanks , kevin

 

Parish8- Do you think the varience in LTrims is only related to injector offsets or are changes in actual VE more responsible? Seems like there are a few folks out there that are making their LTrims vary less (more consistent) by adjusting their VE table. I know that someone has mapped all non PE cells to the VE table. Just wanted to know what you think with your experience.

 

whoa, right over my head. maybe i should just shut up cause i am not so sure i know what i am talking about now.

 

It's running rich at -12. The LTrim number represents how much fuel to change on the next calculation. I believe it recalculates fueling in all Fuel trim cells every 10 or 15 minutes.

 

I have been getting codes 172 and 175 (fuel trim rich) on my '94 truck ever since I put it together. The L trims were running around -13.5 at 75 mph where I usually set the cruise. I broke out the service manual and it states that one of the criteria for setting those codes is for LT's to be -13 or more for extended periods. I adjusted the IFR up a little and now the LT's are around -9.7 and the codes have not returned. Other than freak probs like mine I don't see any downsides to running them -10 to -15

 

ok i guess its fine but man it sure felt alot better when they were -2 to -4 and then going to wot and zeroing out ,but hey what do i know im just the driver lol later and thanks

 

there is an important 2nd step after you get your ltrims negative, you have to adjust your WOT fueling.

above we were just talking about weather it was really nesasary to get your ltrims down to -5 or so and it probably isn't but if you can you might as well. THEN work on your WOT tuning.

 

thanks parish8 and yea going to have to get with nelson tunning and see what we come up with later, kevin

 

YES hohl seems to know what he is talking about. When you mod an engine, the Volumetric Efficiency changes. The VE tables affect L-trim readouts. For example, your l-trims could be perfect while in the VE cells of 5 and 21, but when you are in cell 7, it could have some wierd readout of -20 on the L-trims. What hohl was saying about the mapping out of the VE table is also right. Someone on this forum discovered which VE cells are PE (Power Enrichment) cells and which ones are at cruise.

When tunning you should use your L-trims to calculate what your IFR number should be. Take a long cruise and log all of your L-trim readout. Average them and multiply it as a percentage to your existing IFR numbers. For example: if your averages for Bank1 come out to +3.2 and averages for Bank2 come out to +3.0 -->avg. those = +3.1, so to richen up the mixture, multiply the IFR table by 96.9% (this will yield a smaller number in the IFR table than when you started) The lower the number in the IFR cells, the richer the engine will run.

If you have messed up VE cell values, then it will affect the L-trim readouts, affecting the IFR number, which will mess with engine performance. Use the stock settings on the VE tables! Even with my pretty big mods, only one cell is giving me troubles in the VE. I see this when I let off the throttle after giving it lots of gas, but not enough to jump into PE. The L-trims when I am in that VE cell go to something like +20. I disregard any L-trim readings in that VE cell if I am tuning for IFR.

I hope some of this made sense.
Ryan

 

Just to clarify, its not actually running rich, its subtracting 12% fuel to acheive a 14.7 to 1 AFR.