VE tuning question
08-26-2009, 01:59 AM
#1
VE tuning question Maybe a dumb question but if the pcm can compensate the fueling of our cars using the ST and LTFT's what is the point of fine tuning them? I am in the process of "TRYING" to get mine dialed in and just wondered what I am going to gain if I am ever able to get them in line! I know I then have to dial in the MAF and after that I dont know. But what is the benifit of the VE table being +- 5%
08-26-2009, 04:46 AM
#2
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Well, not knowing what your final goal is..but if you are keeping the MAF and utilizing the narrowband O2 sensors, you will want to get the LTFT's in line, especially if they are positive.
The way the PCM works, any +LTFT's will be added to your fueling at WOT or when you hit all the PE Enablers.
Under the above conditions, the VE Table/MAF influence is intertwined below 4000RPM's. Above 4000Rpm's, it is presumably all MAF.
How much work you do with the VE Table (on a MAF-based tune) has been the subject of intense debate and numerous threads over the years. My view is to first get the VE Table as accurate as possible using a wideband. I do most of my LTFT tuning via the MAF..I just make sure I get the VE Table as accurate as possible, especially below 2000 Rpm's.
I have not had much success using the narrowbands/LTFT's tuning method with the VE Table ( on a MAF-based tune).
The bottom line is not getting those Trims in line will result in inaccurate fueling under heavy throttle. You will risk either being too rich and lose performance, or worse too lean and risk detonation/engine damage.
That is my personal 'Cliff note' version of Trims. There are numerous tutorials and writing on it, so dig in and do your research before deciding on your ultimate tuning method.
Good luck.
..WeathermanShawn..
The way the PCM works, any +LTFT's will be added to your fueling at WOT or when you hit all the PE Enablers.
Under the above conditions, the VE Table/MAF influence is intertwined below 4000RPM's. Above 4000Rpm's, it is presumably all MAF.
How much work you do with the VE Table (on a MAF-based tune) has been the subject of intense debate and numerous threads over the years. My view is to first get the VE Table as accurate as possible using a wideband. I do most of my LTFT tuning via the MAF..I just make sure I get the VE Table as accurate as possible, especially below 2000 Rpm's.
I have not had much success using the narrowbands/LTFT's tuning method with the VE Table ( on a MAF-based tune).
The bottom line is not getting those Trims in line will result in inaccurate fueling under heavy throttle. You will risk either being too rich and lose performance, or worse too lean and risk detonation/engine damage.
That is my personal 'Cliff note' version of Trims. There are numerous tutorials and writing on it, so dig in and do your research before deciding on your ultimate tuning method.
Good luck.
..WeathermanShawn..
08-29-2009, 02:49 AM
#3
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Weatherman is right on, if your tune is too far off for your cam, it will run better with a good tune. You will never hit the correct A/F ratio when you go WOT.
08-29-2009, 05:35 AM
#4
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Trims are only there to fix slight errors and remember LTFT's are segment based so you dont get a separate trim value for each cell (would be nice though). Using them to supplement an inaccurate air flow model is just plain dodgy.
08-29-2009, 09:04 AM
#5
Tune the MAF first (MAF only mode) then tune the VE table (SD only) with a good Wideband O2.
Get your MAF within 1-2% and the VE within 2%
Under 4000 RPMs its a blend between the MAF and VE table. If the weather never changed and you tuned the MAF and VE to within 1% then when you went back to closed loop your LTFT will be within 1-2% but since the weather does change so will your LTFTs.
WOT fueling is open loop, you need a Wideband O2 to dial that in, NEVER go by narrow band O2s. Set your PE table to 1.13/1.135 then tune the MAF for WOT, 6,000hz to 10-11,000hz.
Get your MAF within 1-2% and the VE within 2%
Under 4000 RPMs its a blend between the MAF and VE table. If the weather never changed and you tuned the MAF and VE to within 1% then when you went back to closed loop your LTFT will be within 1-2% but since the weather does change so will your LTFTs.
WOT fueling is open loop, you need a Wideband O2 to dial that in, NEVER go by narrow band O2s. Set your PE table to 1.13/1.135 then tune the MAF for WOT, 6,000hz to 10-11,000hz.
08-29-2009, 09:14 AM
#6
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Whats the best way to calabrate the Maf on a procharged car? I don't want to go lean If I am out flowing it at WOT.
/threadjack
/threadjack
Last edited by kjhallex; 08-29-2009 at 09:20 AM.
08-29-2009, 12:52 PM
#7
If its a pre 2005 LSx based system, you will max the MAF out at 12,000hz. gotta scan to see whats going on. Depending on mods and boost, anything over 6-7lbs your maxed out, check with the FI guys for more info/suggestions.
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08-30-2009, 10:00 PM
#8
Thanks for all of the reply's, problem is I do NOT have a wideband and will have to do what I can with the narrowband stock O2 sensors. They are reading good and cycling as they should be, I am not goint to do any wot tuning just going to try and get the fuel trims as close to 0 as I can and move on to MAF, Spark, and idle. By then I should have a wideband and can hit the WOT tuning. Hope it sounds right and hopefully I will be able to figure all this out!
