Fuel trim & Timing
11-17-2003, 03:14 PM
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Fuel trim & Timing I have my timing set @ 28 on Edit, on the scan tool I use, it always shows 28.
I added a dual exhaust and went from a SY3500 to a SY4000 and now show 26 at the most. I only show .5 knock retard when I hit it but that goes away (0).
This is a stock internal bolt on car, my LT fuel trim show 8.0 to 8.5 or so at full throttle, I have no codes. Anyone know where my timing went? Someone else is helping w/ edit as I'm just learning. Car is a 98 Z28
JD
I added a dual exhaust and went from a SY3500 to a SY4000 and now show 26 at the most. I only show .5 knock retard when I hit it but that goes away (0).
This is a stock internal bolt on car, my LT fuel trim show 8.0 to 8.5 or so at full throttle, I have no codes. Anyone know where my timing went? Someone else is helping w/ edit as I'm just learning. Car is a 98 Z28
JD
Last edited by JASON; 11-17-2003 at 03:20 PM.
11-17-2003, 03:27 PM
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If you are pulling more air past the MAF, it will see it as
higher load and pull timing back. A looser converter and
catback might both push in this direction. But seeing
those LTFTs at full throttle means you are probably
lean going by MAF output and no telling what the real
WOT mixture is at upper RPM. You should do some more
data logging and be sure you haven't got more KR than
you think.
Timing should never "always show 28". It should run up
with RPM. On my '02 I see 20 down low and don't get
over 28 until it gets past 5500RPM. At WOT, anyway;
lot of variation with load (vacuum) around town.
higher load and pull timing back. A looser converter and
catback might both push in this direction. But seeing
those LTFTs at full throttle means you are probably
lean going by MAF output and no telling what the real
WOT mixture is at upper RPM. You should do some more
data logging and be sure you haven't got more KR than
you think.
Timing should never "always show 28". It should run up
with RPM. On my '02 I see 20 down low and don't get
over 28 until it gets past 5500RPM. At WOT, anyway;
lot of variation with load (vacuum) around town.
11-17-2003, 04:21 PM
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The air fuel @ WOT was set on a dyno at 12.8, so I know the car is not lean at full throttle. Also I have a true ram air thats been on the car, but the timing went away w/ the true dual and converter. Yes timing is set @ 28 wot.
11-17-2003, 06:05 PM
#4
First you need to tune the L-terms back to 0.Then see where the timing is.If it still shows 26 degree's then the MA meter is probly reading a higher load or more airflow due to the mods.Go to the octain table and adjust those tables to 28 degree's of timing.
11-17-2003, 08:53 PM
#5
Originally Posted by JASON
I have my timing set @ 28 on Edit, on the scan tool I use, it always shows 28.
I added a dual exhaust and went from a SY3500 to a SY4000 and now show 26 at the most. I only show .5 knock retard when I hit it but that goes away (0).
This is a stock internal bolt on car, my LT fuel trim show 8.0 to 8.5 or so at full throttle, I have no codes. Anyone know where my timing went? Someone else is helping w/ edit as I'm just learning. Car is a 98 Z28
JD
I added a dual exhaust and went from a SY3500 to a SY4000 and now show 26 at the most. I only show .5 knock retard when I hit it but that goes away (0).
This is a stock internal bolt on car, my LT fuel trim show 8.0 to 8.5 or so at full throttle, I have no codes. Anyone know where my timing went? Someone else is helping w/ edit as I'm just learning. Car is a 98 Z28
JD
From EFILive.com Forum post by GMPX :
"There appears to be alot of myths and confusion about the High and Low Octane tables in the LS1 PCM.
Well, hold onto your hats, we here at EFILive have been torturing our poor LS1's with junk fuel getting to the bottom of what really happens...
The PCM will ALWAYS try to run with the High Octane Table values, however if there is a MAF or Knock DTC set, it defaults to the Low Octane Table only.
But with a vehicle that has neither of those faults set it actually does a 'blend' of the two tables, it does not totally switch between one or the other.
In an upcoming release of EFILive there will be a new PID that will show you what percentage of the High Octane table values are being used (I'll refer to it as the Octane Multiplier).
Say for example the High Octane table has a value of 20 degrees, the same load point on the Low octane table has 10 degrees, and your octane multiplier is set at 50%, the final timing value would be 15degrees, if the octane multiplier is set to 75% it would result in 17.5 degrees, etc.
So what changes the Octane Multiplier value?, I have personally logged this on my car so I have seen it first hand. Basically any sustained amount of knock above about 2 or 3 degrees causes the Octane Multiplier to head towards 0%. It is a constantly changing value, it does NOT get reset to 100% when you fill up with fuel, the only thing that will bring it back to 100% and keep it there is minimal knock activity.
This has been tested on my own 2000 Commodore and emarkay's Camaro.
The PID will be supported for most LS1 powered cars/trucks.
On that note, if anybody has a BIN file or LS1 Edit file from a 2003 & 2004 Truck and 2004 C5, please PM me." - GMPX
FWIW. I bumped the related Timing thread here on LS1Tech, also.
joel
Last edited by binksz06; 11-17-2003 at 09:03 PM.
11-17-2003, 10:29 PM
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Joel, explain this please:
If his LTFTs are + 8 and such, and he is widebanding at 12.8afr, How is that possible? And why is it so necessary to get the LTFTs to 0 if his WB is reading 12.8?
By your pasting the Octane tables, are you saying his car is likely stuck in the multiplier? Makes sense!
If his LTFTs are + 8 and such, and he is widebanding at 12.8afr, How is that possible? And why is it so necessary to get the LTFTs to 0 if his WB is reading 12.8?
By your pasting the Octane tables, are you saying his car is likely stuck in the multiplier? Makes sense!
11-18-2003, 11:35 AM
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The jacked up LTFTs represent the PCM's best guess
at making mixture right, applied forward to WOT. From
the looks of things the guess is not bad; however, as
LTFTs vary so does the influence -and- you lock in
different ones depending on which cell you step off from.
So, a pedal mash from idle can get you a pretty different
WOT mixture from a slow roll-on from part throttle, same
car, same day, makes that last inch of tweaking nigh
impossible.
If a car is 8 points lean, there is probably a lot of
throttle transient knock (transients break closed loop
temporarily, exposing lean natural mixture) and the
transient knock counts could be driving him down the
octane table slope even if cruise & WOT are cool.
at making mixture right, applied forward to WOT. From
the looks of things the guess is not bad; however, as
LTFTs vary so does the influence -and- you lock in
different ones depending on which cell you step off from.
So, a pedal mash from idle can get you a pretty different
WOT mixture from a slow roll-on from part throttle, same
car, same day, makes that last inch of tweaking nigh
impossible.
If a car is 8 points lean, there is probably a lot of
throttle transient knock (transients break closed loop
temporarily, exposing lean natural mixture) and the
transient knock counts could be driving him down the
octane table slope even if cruise & WOT are cool.
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11-18-2003, 12:52 PM
#9
Joel, explain this please:
If his LTFTs are + 8 and such, and he is widebanding at 12.8afr, How is that possible? And why is it so necessary to get the LTFTs to 0 if his WB is reading 12.8?
**** -> Seems like his LTFTs were probably negative when he had the Dyno. But, since the addition of the Duals went positive. Guess the duals increased through flow and thus fueling needed to increase. I doubt WOT AFR is still 12.8 since the positive LTFTs are being added at WOT. Added to prevent Lean condition at WOT. Want 0 ->(-) LTFTS so that fueling is consistent. Positive fuel trims can be added ( LTFT from last cell visited before WOT) ....thus inaccurate final AFR .
By your pasting the Octane tables, are you saying his car is likely stuck in the multiplier? Makes sense!
*****-> Yup. I was always frustrated with the fact that I couldn't see where the timing values were coming from. The above, and the thread, pretty much explain it.
Hope this makes sense.
joel
If his LTFTs are + 8 and such, and he is widebanding at 12.8afr, How is that possible? And why is it so necessary to get the LTFTs to 0 if his WB is reading 12.8?
**** -> Seems like his LTFTs were probably negative when he had the Dyno. But, since the addition of the Duals went positive. Guess the duals increased through flow and thus fueling needed to increase. I doubt WOT AFR is still 12.8 since the positive LTFTs are being added at WOT. Added to prevent Lean condition at WOT. Want 0 ->(-) LTFTS so that fueling is consistent. Positive fuel trims can be added ( LTFT from last cell visited before WOT) ....thus inaccurate final AFR .
By your pasting the Octane tables, are you saying his car is likely stuck in the multiplier? Makes sense!
*****-> Yup. I was always frustrated with the fact that I couldn't see where the timing values were coming from. The above, and the thread, pretty much explain it.
Hope this makes sense.
joel
