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Old 04-19-2005, 08:36 AM   #1
fmowry
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Default short term fuel trim ?

I just installed a bunch of stuff in my Forester XT:

FP green
Perrin modded injectors
Perring turbo inlet
Walbro FP
catless TBE
ECUtek flash (mailorder from Kingpin)

I have a Scanmaster SM3 which shows fuel trims among other things. In notice that while cruising, my short term fuel is in the 11-14 but will drop in the 4-10 range and at idle it is at 25. While this could be an issue with the reflash, would something else show a 25 trim at idle? I'm assuming it is lean and trying to add fuel based on my LM-1 output. I didn't go into boost because of the large short term trims. I wanted to make sure there are no leaks (exhaust/boost/fluid) before I get on it.

Could it be an exhaust leak or pre turbo leak somewhere? Or is it most likely the reflash. Clark did say that if I saw short or long term fuel trims outside of the 10 to -10 range, he would reflash. I want to make sure there isn't something else going on before I send the ECU back.

Thanks,
Frank
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Old 04-19-2005, 10:50 AM   #2
MustGoFast
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short term trims fluctuate a lot based on driving conditions (although rarely to the max setting 25)... check the long term trim if it's outside of the 10 then send it back its definatelly the flash. The issue may be that w/ the modded injectors and a shipped out flash they are trying to tune for an unknown fuel flow rate.. the modded injectors are great but w/ as inconsistent as the flow seems to be in the ones I've seen I don't know how someone could "ship" a tune on them well.
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Old 04-19-2005, 12:53 PM   #3
jetskizero
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<disclaimer> This may be internet rumor, so take it FWIW </disclaimer>

Isn't 25 the max # of trim (i.e., indicating that the short term can't correct any more). If that's correct then the short term is outside the "normal" range of fluctuation and you should adjust the fueling accordingly (in your case through the reflash).
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Old 04-19-2005, 10:16 PM   #4
Kingpin
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Frank, If the trim is 25 at idle then I need to adjust the mapping in the ECU. Send me an email with the trims at idle, and 1000 rpm increments up to 5000 at a rest. Then trims at cruise. I need long and short trims. Then I can adjust it for you. Of course for no cost.

I have been sick this week but I should be back tomorrow so email me or give me a ring.

Cya

Clark
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Old 04-20-2005, 08:54 AM   #5
fmowry
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Clark,
I'm waiting on a new Palm so I can log with the SM3. My old one was too old. Short term fuel trim seems OK (under 10) driving around town. Just at idle and decel when it jumps to 25. Long term is at 6. Does this store in the ECU each time I drive the car, or reset to 0 after I turn the car off?

I haven't gotten into boost much. What knock correction do I want to remain under again? Positive knock correction = bad, negative = good, right?

Thanks,
Frank
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Old 04-21-2005, 12:09 AM   #6
Kingpin
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Decel is ok to read 25. ST and LT should be less then 10 -+. Positive 6 means that the ECU is adding in fuel at 6%. Probably the intake or I just missed the target in the mapping. I can add in fuel to get the trims closer.

On knock correction you should see 5-8's. This means that the ECU is adding 8 degrees over the base map. Thats good. If you see 0 or 1 or 2 then you encountered some knock and the ecu is not advancing to max potential. This is ok as the ECU is doing its job, but it does tell me the tune is a bit hot. If its maxed out all the time then there is more room for advance.

Cya

Clark
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Old 12-04-2005, 10:10 PM   #7
PatentGuy
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I full understand if Clark does not wish to tell, but I would greatly appreciate hearing what some of the other values displayed on the Scanmaster should be for a properly tuned car. I'm thinking of things like advance, etc. This way I could know when I've changed the car too much and need a custom tune. Just an idea, maybe a bad one!
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Old 12-04-2005, 10:38 PM   #8
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nice service clark
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Old 12-04-2005, 11:34 PM   #9
richde
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Quote:
Originally Posted by Kingpin
Decel is ok to read 25. ST and LT should be less then 10 -+. Positive 6 means that the ECU is adding in fuel at 6%. Probably the intake or I just missed the target in the mapping. I can add in fuel to get the trims closer.

On knock correction you should see 5-8's. This means that the ECU is adding 8 degrees over the base map. Thats good. If you see 0 or 1 or 2 then you encountered some knock and the ecu is not advancing to max potential. This is ok as the ECU is doing its job, but it does tell me the tune is a bit hot. If its maxed out all the time then there is more room for advance.

Cya

Clark
8 is the most you'll see on KC and 5 is the lowest number you want? (@WOT, of course)
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Old 12-05-2005, 01:12 PM   #10
ride5000
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Quote:
Originally Posted by richde
8 is the most you'll see on KC and 5 is the lowest number you want? (@WOT, of course)
that depends on the range of authority the tuner has programmed into the map.
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Old 12-05-2005, 01:48 PM   #11
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Quote:
Originally Posted by ride5000
that depends on the range of authority the tuner has programmed into the map.
And what the base timing map is.
You could run 18 in the base and 3 in the advance to end up with 21.
In this case the IA would be 3.
Or you could run 21 in the base and 0 in the advance to end up with 21.
In this case the IA would be 0

But both maps run the same total advance.

TMS
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Old 12-05-2005, 02:22 PM   #12
richde
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Quote:
Originally Posted by TheMadScientist
And what the base timing map is.
You could run 18 in the base and 3 in the advance to end up with 21.
In this case the IA would be 3.
Or you could run 21 in the base and 0 in the advance to end up with 21.
In this case the IA would be 0

But both maps run the same total advance.

TMS
So.........is the actual advance, the Ignition Timing in the Tari logger for example, the sum of the preprogrammed base number plus the KC?
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Old 12-05-2005, 05:19 PM   #13
TheMadScientist
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Quote:
Originally Posted by richde
So.........is the actual advance, the Ignition Timing in the Tari logger for example, the sum of the preprogrammed base number plus the KC?
I am not 100% positive on how the tari logger displays the #'s. But I "think" it displays total advance. I got a second I think from a friend, so odds are yes.

Simply yes that is how the timming advance works. There are other factors that effect timing though. For the 2004 Sti, Cobb Pro tuner has 9 ignition maps then add the IAM into it. Some of those maps are "learned" and others are programed. So how the timing is computed is still somewhat of a mystery.

TMS

Last edited by TheMadScientist; 12-05-2005 at 05:34 PM.
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