Fuel Trims
10-04-2005, 09:42 PM
#1
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Fuel Trims I did use search a few times but still havent found what I am after. First off if my short or long term fuel trims are negative then that means the computer is pulling fuel or adding it if they are positive correct? Well with a good tune should they stay close to zero and at what range of #'s? At part throttle street or highway speeds my trims jump all around from -12 to +15 (it was close to these numbers but I dont remember the exact numbers) At wot the short terms went to 0 and the long term went to +3.xx So to those of you who know where these numbers should normally be because I really dont know. And I was using the Predator to get these #'s also. Thanks in advance for all help. 
10-04-2005, 11:12 PM
#2
Negative trims means pulling of fuel
Positive trims means adding of fuel
The part throttle ltrims need to be zero or slightly negative. This will allow the WOT ltrims to be locked at zero. If the ltrims are positive just before WOT, the PCM will try to add fuel. This will lead to inconsistent fueling. So, need to work on the part throttle and a good range would be 0% to -5%. I am sure that the Predator will does not allow tuning of part throttle ltrims. Since you are stock internals, the MAF table would be the place to start.
Positive trims means adding of fuel
The part throttle ltrims need to be zero or slightly negative. This will allow the WOT ltrims to be locked at zero. If the ltrims are positive just before WOT, the PCM will try to add fuel. This will lead to inconsistent fueling. So, need to work on the part throttle and a good range would be 0% to -5%. I am sure that the Predator will does not allow tuning of part throttle ltrims. Since you are stock internals, the MAF table would be the place to start.
10-04-2005, 11:35 PM
#3
Originally Posted by Blacker
Negative trims means pulling of fuel
Positive trims means adding of fuel
The part throttle ltrims need to be zero or slightly negative. This will allow the WOT ltrims to be locked at zero. If the ltrims are positive just before WOT, the PCM will try to add fuel. This will lead to inconsistent fueling. So, need to work on the part throttle and a good range would be 0% to -5%. I am sure that the Predator will does not allow tuning of part throttle ltrims. Since you are stock internals, the MAF table would be the place to start.
Positive trims means adding of fuel
The part throttle ltrims need to be zero or slightly negative. This will allow the WOT ltrims to be locked at zero. If the ltrims are positive just before WOT, the PCM will try to add fuel. This will lead to inconsistent fueling. So, need to work on the part throttle and a good range would be 0% to -5%. I am sure that the Predator will does not allow tuning of part throttle ltrims. Since you are stock internals, the MAF table would be the place to start.
most people tune th evehicle to be 0 or slightly negative...but remember..on any given day...in closed loop..your car will automatically adjust your trims to be at 0...so even if they are slightly negative...they might swing positive because we cannot control mother nature.... positive and negative doesnt mean you are lean or rich....it means your computer has adjusted your mixture leaner or richer to keep a stoich ratio... It is a constantly adjusting factor to maintain 14.63:1 Air Fuel.
When you go WOT you usually meet the requirements of PE mode(usually Throttle position and MAP based..
at this time...whatever # is in your PE table or your MAF table directly dictates what the fueling does....Exactly.....henceforth the table PE EQ ratio vs RPM
meaning if that area is tuned wrong then your mixture will be wrong....Fuel trims always lock to 0 in open loop.
10-05-2005, 01:04 AM
#4
If my ltrims are positive, the ltrims would be positive at WOT. Once I got the ltrims negative then the ltrims at WOT would lock at 0. The problem with the ltrims being positive at WOT, is each time you go WOT, it could be a different value. That is why you want the ltrims to be negative so this issue will never be a problem.
10-05-2005, 06:18 AM
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Blacker is correct...Positive L-Trims, at WOT, will add fuel on top of what is determined by the other tables...Negative L-Trims will always be 0 at WOT because the computer already knows the car is running rich and therefore does not need to add fuel as a safety precaution...
S-Trims will always go between positive and negative, that is the way the system is designed to hold Stoch. Air ratio...The L-trims are simply the long term averaged value that the computer uses to keep the S-trms bouncing back and forth between positive and negative evenly...
Peace...Gman
S-Trims will always go between positive and negative, that is the way the system is designed to hold Stoch. Air ratio...The L-trims are simply the long term averaged value that the computer uses to keep the S-trms bouncing back and forth between positive and negative evenly...
Peace...Gman
10-05-2005, 09:10 AM
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Thanks guys. So my short term trims should still bounce around at wot? Well mine dont they lock at 0. What would cause this if they should always bounce around?
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10-05-2005, 09:57 AM
#8
Originally Posted by DevonsZ
Thanks guys. So my short term trims should still bounce around at wot? Well mine dont they lock at 0. What would cause this if they should always bounce around?
so I would guess that you are not entering open loop if they are still changing at WOT
10-05-2005, 01:33 PM
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Originally Posted by Gman2002Z06
Blacker is correct...Positive L-Trims, at WOT, will add fuel on top of what is determined by the other tables...Negative L-Trims will always be 0 at WOT because the computer already knows the car is running rich and therefore does not need to add fuel as a safety precaution...
S-Trims will always go between positive and negative, that is the way the system is designed to hold Stoch. Air ratio...The L-trims are simply the long term averaged value that the computer uses to keep the S-trms bouncing back and forth between positive and negative evenly...
Peace...Gman
S-Trims will always go between positive and negative, that is the way the system is designed to hold Stoch. Air ratio...The L-trims are simply the long term averaged value that the computer uses to keep the S-trms bouncing back and forth between positive and negative evenly...
Peace...Gman
Gman, your logic is right but your reasoning is backwards. Negative L-trims before open loop (WOT) will go to zero because the computer is subtracting fuel right before going WOT. It is a safety feature to keep from going lean, or even close to going lean. The computer will not subtract fuel at WOT (open loop).
Now, if you have a positive Ltrim in open loop it will not drop to zero. I have seen this many times while scanning. This is the reason most guys tune it so the L-trims are slightly negative (I shoot for -2 myself).
10-05-2005, 01:40 PM
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Originally Posted by soundengineer
as far as I know the trims always lock at 0 when you enter PE...
most people tune th evehicle to be 0 or slightly negative...but remember..on any given day...in closed loop..your car will automatically adjust your trims to be at 0...so even if they are slightly negative...they might swing positive because we cannot control mother nature.... positive and negative doesnt mean you are lean or rich....it means your computer has adjusted your mixture leaner or richer to keep a stoich ratio... It is a constantly adjusting factor to maintain 14.63:1 Air Fuel.
When you go WOT you usually meet the requirements of PE mode(usually Throttle position and MAP based..
at this time...whatever # is in your PE table or your MAF table directly dictates what the fueling does....Exactly.....henceforth the table PE EQ ratio vs RPM
meaning if that area is tuned wrong then your mixture will be wrong....Fuel trims always lock to 0 in open loop.
most people tune th evehicle to be 0 or slightly negative...but remember..on any given day...in closed loop..your car will automatically adjust your trims to be at 0...so even if they are slightly negative...they might swing positive because we cannot control mother nature.... positive and negative doesnt mean you are lean or rich....it means your computer has adjusted your mixture leaner or richer to keep a stoich ratio... It is a constantly adjusting factor to maintain 14.63:1 Air Fuel.
When you go WOT you usually meet the requirements of PE mode(usually Throttle position and MAP based..
at this time...whatever # is in your PE table or your MAF table directly dictates what the fueling does....Exactly.....henceforth the table PE EQ ratio vs RPM
meaning if that area is tuned wrong then your mixture will be wrong....Fuel trims always lock to 0 in open loop.
Scott, I agree that the Ltrims lock at WOT, but I don't agree that they lock at 0. If my L-trims are positive before going WOT they lock at that value (say 5 for example).
Now the short trims do lock at 0 when at WOT, regardless of where they were beforehand. I think of it as short term trims adjusting for minute to minute differences, long term trims adjusting for day to day or week to week differences.
10-05-2005, 02:15 PM
#12
If your short trims Lock to 0 at WOT then by nature of the beast your Ltrims would never deviate from 0
If you have trims at WOT then it means you gained them from somewhere...which means you were in closed loop at some point in those cells...you can not get L Trims From Open Loop operation...and 99% of teh time WOT is Open loop..
anything that is past your PE vs TPS table is PE especially if you have entered PE ok mode(meaning your PE enable has been met)
If you have trims at WOT then it means you gained them from somewhere...which means you were in closed loop at some point in those cells...you can not get L Trims From Open Loop operation...and 99% of teh time WOT is Open loop..
anything that is past your PE vs TPS table is PE especially if you have entered PE ok mode(meaning your PE enable has been met)
10-05-2005, 03:47 PM
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That is not correct...Short term trims always go to zero at WOT...They are being ignored, so the computer sets them to zero...The Long term trims at WOT, will be some value based on the averages prior to WOT...Positive L-trims average, then you get pos. L-trims at WOT...But the S-trims still go to zero at WOT...
I checked an old log of mine that showed I had +3.1, and +2.4 as my L-trims at WOT, but the S-trims show zero the entire time I was at WOT...
Peace...Gman
I checked an old log of mine that showed I had +3.1, and +2.4 as my L-trims at WOT, but the S-trims show zero the entire time I was at WOT...
Peace...Gman
10-05-2005, 06:58 PM
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bowtieman81...My logic is not backwards...If you have positive L-trims showing at WOT, then the computer is adding extra fuel...When you have neg. L-trims while cruising, then L-trims are always zero at WOT...No additional fuel is being added...
Peace...Gman
Peace...Gman