low rpm ve help please
08-17-2014, 01:26 PM
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low rpm ve help please How do yall usually go about tuning the ve in the low rpm areas (idle area) with a good size cam? I know you can't really trust a wideband or narrowbands with overlap in the mix.
08-18-2014, 10:47 PM
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I have asked this question in the past and was told to use vacuum as a guide and extrapolate based on what a normal table looks like. I believe that the wideband will read very lean due to the unburned gasoline at idle from a large cam even though it's not lean. If I remember correctly, an AFR of 17 or 18 is typical.
A question I always wondered was if your running a car in closed loop with a big cam, wouldn't the car keep adding fuel so it would always be rich (long term fuel trims) based on what it sees at idle.
A question I always wondered was if your running a car in closed loop with a big cam, wouldn't the car keep adding fuel so it would always be rich (long term fuel trims) based on what it sees at idle.
08-19-2014, 09:46 AM
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That's exactly what I was thinking also when I wrote the post. I would think running closed loop is going to give a rich idle so I might just stay open loop.
So add or take away fuel until my map reads the lowest value? It's kinda hard to pinpoint exact values when your map is fluctuating at idle huh.
So add or take away fuel until my map reads the lowest value? It's kinda hard to pinpoint exact values when your map is fluctuating at idle huh.
08-20-2014, 05:05 PM
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I am one who says not to trust wideband readings at
idle, if your cam has any more overlap than stock. And
almost any worth having, does.
You're better off sitting in the parking lot and playing
with bidirectional controls target AFR, looking for the
minimum MAP you can get at your desired RPM. This
will show you what the motor likes (you might fiddle
advance, too). When you find your happy place then
record the AFR and the NBO2 average voltage, the
former you'd use to scale VE table (by ratio of
BestMAP_AFR/14.7) roughly - but you need to hit the
400RPM column harder than the 800RPM; you could set
your idle RPM to 800 on the dot and get that colum
right, then set idle RPM target to what you really
want and bump the 400RPM column until you again
achieve that minimum MAP, indicated AFR position
indicating that the interpolation where you live, is OK.
Then put that NBO2 switch voltage into the vs-airflow-
mode table in the airflow ranges where you idle. That
will make closed loop seek what works for open loop,
not some arbitrary value.
idle, if your cam has any more overlap than stock. And
almost any worth having, does.
You're better off sitting in the parking lot and playing
with bidirectional controls target AFR, looking for the
minimum MAP you can get at your desired RPM. This
will show you what the motor likes (you might fiddle
advance, too). When you find your happy place then
record the AFR and the NBO2 average voltage, the
former you'd use to scale VE table (by ratio of
BestMAP_AFR/14.7) roughly - but you need to hit the
400RPM column harder than the 800RPM; you could set
your idle RPM to 800 on the dot and get that colum
right, then set idle RPM target to what you really
want and bump the 400RPM column until you again
achieve that minimum MAP, indicated AFR position
indicating that the interpolation where you live, is OK.
Then put that NBO2 switch voltage into the vs-airflow-
mode table in the airflow ranges where you idle. That
will make closed loop seek what works for open loop,
not some arbitrary value.
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08-20-2014, 05:06 PM
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VE table can add to surge problems if the slope in the
MAP dimension mismatches what the motor really does.
This gives you fuel surge, directly. I have played with
this to the point of getting clean idle, without gaining
any useful understanding really. Other than, it has effect.
MAP dimension mismatches what the motor really does.
This gives you fuel surge, directly. I have played with
this to the point of getting clean idle, without gaining
any useful understanding really. Other than, it has effect.
08-20-2014, 10:24 PM
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That post is much appreciated jimmyblue!!! that is the exact answer I was hoping for and will help me alot. The only question I have now is I noticed map kept decreasing as I increased timing from 20. I only went to 25 because I got scared of going too high. Should i keep going or is that too high for idle? Also since map fluctuates a bit at idle I'm guessing the best way to do it is log it in a histogram and get the average over a few hundred counts. Make a change then get another average? The cam i have is a torque v2 in an ls1 with prc225 heads with fast 90/90. Sorry for the long post I just want to pick your brain a bit