LTFT RPM Boundaries
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TECH Enthusiast
Joined: Aug 2006
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LTFT RPM Boundaries Ok guys,
On the '98 in my sig, my LTFT RPM boundaries are 900, 1400, 2200. MAP boundaries are 37, 57, 77.
Should I raise the high rpm boundary up to get LTFT's in higher rpms or just not even worry about not having LTFT's above the stock 2200 rpms?
I'm not so much worried about the MAP boundaries, 77 as a high limit seems fine to me. But 2200 rpm seems low. Really low.
I know the later LS series have mid and high rpm limits above 6000, is there a reason the early models don't? Not enough processor speed or memory on the '98's maybe?
On the '98 in my sig, my LTFT RPM boundaries are 900, 1400, 2200. MAP boundaries are 37, 57, 77.
Should I raise the high rpm boundary up to get LTFT's in higher rpms or just not even worry about not having LTFT's above the stock 2200 rpms?
I'm not so much worried about the MAP boundaries, 77 as a high limit seems fine to me. But 2200 rpm seems low. Really low.
I know the later LS series have mid and high rpm limits above 6000, is there a reason the early models don't? Not enough processor speed or memory on the '98's maybe?
I read a approach to setting these, it made sense and I have used it and doesn't seem worse, so it maybe helped, my settings are 900, 1600 and 2400 rpm and map is 50, 70 and 90 using the idea from the discussion...can't remember where I read it.
BTW the lower is based on idle, as mine is 825 and about 47 kpa
BTW the lower is based on idle, as mine is 825 and about 47 kpa
Once you go into PE mode you don't need fuel trims.
So you might look at something like a histogram of
commanded AFR or EQ (logging a well-rounded drive
cycle) and see where the EQ (minimum mode) pops
up from 1.000. That's the highest you care about.
Discarding free-revving, which is also so-what and
ought not to be part of the drive cycle. Then go
subdivide the remaining space. Figure you should
favor the lower RPMs because that is where the
motor breathing characteristics change a lot with
RPM. Where you have a high slope on the VE table
you also have a greater chance of error and need
for trimming.
I would put the first MAP line just above your idle
MAP, and the last should be at / just below your PE
enable MAP threshold.
So you might look at something like a histogram of
commanded AFR or EQ (logging a well-rounded drive
cycle) and see where the EQ (minimum mode) pops
up from 1.000. That's the highest you care about.
Discarding free-revving, which is also so-what and
ought not to be part of the drive cycle. Then go
subdivide the remaining space. Figure you should
favor the lower RPMs because that is where the
motor breathing characteristics change a lot with
RPM. Where you have a high slope on the VE table
you also have a greater chance of error and need
for trimming.
I would put the first MAP line just above your idle
MAP, and the last should be at / just below your PE
enable MAP threshold.
To find the best compromise on the LTFT boundaries, you need to log a long, typical drive and make sure you have MAP and RPM in your log config. Export the log file and import it into Excel. Build a chart with MAP on one axis and RPM on the other with each data point plotted. You'll get a bunch of dots spread throughout the whole thing.
Take a look at how they tend to bunch up and what RPM and MAP value might represent the boundary of each group. There's the number you put into your tune. For me, it worked out to:
RPM: 900, 1800, 3500
MAP: 40, 58, 72
Take a look at how they tend to bunch up and what RPM and MAP value might represent the boundary of each group. There's the number you put into your tune. For me, it worked out to:
RPM: 900, 1800, 3500
MAP: 40, 58, 72
