Are LTFTs directly applied to the VE table?
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Originally Posted by TT_Vert
if you reset your Fuel trims after making a VE change shouldnt the change be instant? A while back I had -10 Ltrims and attempted to scale the appropriate VE table cells by about 75% then reset Fuel Trims and it went back to -10 at idle again again.
Dave
Dave
I have a theory on why the VE table will make the car run better. I think that when you use the IFR to adjust the LTRIMs you still end up with some highs and some lows that average out. In the long run you probably (I think) end up with lean spots (or maybe spikes?) and rich spots while you are driving. Using the VE table will allow you to create a smooth transition at all vacuum and RPMs.
Originally Posted by HumpinSS
The Ltrims are applied to closed loop fueling. LTrims are figured out between the o2 sensors and the maf. With these two sensors you get fueling that is supposed to equal 14.7 during closed loop. If the fuel deviates from this value any between the o2 sensors and the maf sensor the pcm will figure out how much more/less fuel is needed. If you force the computer to run in open loop you wouldnt need LTRIMS as a measurement for anything. All you would need is a wideband to figure out what fuel ratio the engine makes the best power rather than having it forced to run at 14.7
If you are lean up top you can adjust that two ways either the pe vs rpm table or the open loop f/a table. A well known tuner on the forum (NoGo) suggested tuning through LTrims doesn nothing but trick tune the pcm. Even more so when you have a cam with a lot of overlap since reversion skews the results/readings from the maf.
If you are lean up top you can adjust that two ways either the pe vs rpm table or the open loop f/a table. A well known tuner on the forum (NoGo) suggested tuning through LTrims doesn nothing but trick tune the pcm. Even more so when you have a cam with a lot of overlap since reversion skews the results/readings from the maf.
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Originally Posted by Another_User
I wondered that too. I don't think that the computer can accurately calculate LTRIMs at idle. Why? Because as we have found out the MAF is not reliable at low vacuum so it is using the VE table to fill in the gaps. I think they just need to get tuned until you get them to 0. After I made my VE table change I saw 0 (amazing) LTRIM adjustment at idle for minutes and minutes. I was baffled, but the car ran really nicely.
I have a theory on why the VE table will make the car run better. I think that when you use the IFR to adjust the LTRIMs you still end up with some highs and some lows that average out. In the long run you probably (I think) end up with lean spots (or maybe spikes?) and rich spots while you are driving. Using the VE table will allow you to create a smooth transition at all vacuum and RPMs.
I have a theory on why the VE table will make the car run better. I think that when you use the IFR to adjust the LTRIMs you still end up with some highs and some lows that average out. In the long run you probably (I think) end up with lean spots (or maybe spikes?) and rich spots while you are driving. Using the VE table will allow you to create a smooth transition at all vacuum and RPMs.
Read the "VE Cracked" thread above. Don't worry about the math. Also read gameovers referenced "Airmass " Thread . Then more of PCM Fueling will make sense. Good Luck - as NoGo would say.
Joel 
