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Old 01-22-2005, 11:55 PM   #1
stevepius
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Default Looking for LTFT and STFT advice

Here is my current situation. I just hooked up my scantool and let the car warm up to operating temperature. At that point the LTFT was about -6.5 and STFT was abot 8.5. My question is, since they are going in opposite directions, one adding and one subtracting, how do I compensate for that when trying to tune? I figured they would both either be positive or negative so I'm kinda confused. Any advice on this would be great as this is my first attempt at dealing with fuel trims.
*sidenote - if anyone uses the scanmaster 3 and WRXd software on a PC palm emulator did you have the problem of it only logging for a few seconds because the "Pause" box checked itself? For me I kept trying to log and the box would uncheck itself for a few seconds and then recheck itself and stop. If anyone has had this issue and resolved it let me know how.

Thanks everyone.
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Old 01-23-2005, 02:39 AM   #2
mick_the_ginge
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Long term fueling is a course correction while short term is a fine correction. You can sometimes see it in action. Reset the ECU and watch it, first thing is that STFT goes almost fully +-, then the ecu applies some LTFT correction. Then the STFT continues to do quick corrections until finally it settles. Anything within +- 7 LTFT is fine in my books.

If you do want to get is closer to 0 then you need to remove fuel using your EM at that load point. The ecu is trying to remove fuel using the LTFT, so should you. If you have larger injectors keep the LTFT negative, your idle will be better.
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Old 01-23-2005, 09:24 AM   #3
stevepius
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I do have larger injectors, I have 785s but my cold start is horrendous. I already have 500,750,1000 rpms set at -1.5 and I think that is way too rich but with LTFT being -6.5 it seems like that is an OK setting. The idle oscilates greatly. Like dropping R's and then reving itself again. Also, my car knocks at cold start. I know that may sound odd, but when I cold start my check engine light flashes for a few seconds. I have check engine light, P0171 System Too Lean (Bank 1). It says the symptoms can be You will more than likely not notice any drivability problems, although there may be symptoms such as a lack of power, detonation (spark knock), and/or a hesitation/surge on acceleration. I know I need new spark plugs but could that be causing my knock? On my scantool it says no knock correction but like I said the check engine light flashes. Any further info would be greatly appreciated. Thanks.
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Old 01-23-2005, 11:10 AM   #4
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How many times does the check engine light flash when ya start the car? Are you using a utec? The check engine light will normally flash at startup more then normal with the utec to designate the map that's chosen. Ie-map 5=5 flashes. Also, usually the idle is above 1000rpm during cold start, so ya might wanna adjust fueling up there(1000-2000rpm) depending on what ya see. From what I've seen with my car, cold start will never be perfect.....

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Old 01-23-2005, 06:50 PM   #5
stevepius
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I have a utec and it flashes more than 2 times and I am on map2. I know cold start wont be perfect but mine is the worst I've seen. It goes from 2500rpms to 500rpms for a few minutes. I'm just unsure how I should ajust when LT and ST are going in opposite directions.
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Old 01-23-2005, 07:00 PM   #6
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You adjust according to the lt, not the st. With the example above, the st should eventually get close to 0 and the lt would go to something between -6.5 and 0. Removing more fuel would push the lt closer to 0. -6.5 isn't bad though, so I'd question why the idle is bad. I dunno the answer, but with the fuel trims that close to 0 it really doesn't seem like the problem is the fuel trim. Maybe it's your o2 sensor, the idle air control solenoid or something else? This is just my understanding of what sounds like's goin on though, and I'm no expert.

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Old 01-23-2005, 10:11 PM   #7
mick_the_ginge
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If it's just a cold start issue try using the UTEC's coolant compensation. ADD FUEL until it gets to about 60f. System too lean code should not happen when it's cold as the ecu does not use the O2 sensor when the car is cold. Try making it a little richer when it is cold then normal when it warm.

Just a suggestion.
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Old 01-24-2005, 12:21 AM   #8
stevepius
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How can I access the coolant compensation? I have heard that suggestion before but never understood it.
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Old 01-24-2005, 11:32 AM   #9
mick_the_ginge
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Tuner Constants in the UTEC menus.

To make the whole map rich when you are cold you will need to add some constant MAF mod to the whole fuel map. Then turn on the coolant correction and put the same contant value but negative in the fuel compensation. A little strange but it works.

In effect under the coolant point the correction is not applied. After the coolant correctoin point the correction is applied.

You may want to contact TurboXS as they created a special firmware version that had a very indepth temperature compensation table. It was never offically released.
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Old 01-24-2005, 09:30 PM   #10
stevepius
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What do you mean by make a MAF mod? I talked to turboxs and they said that due to having UR injectors they sometimes act funny and I may not be able to fix my issue. I'd like to look into the coolant idea further, but I'm not sure what you mean by MAF mod.
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Old 01-25-2005, 09:57 AM   #11
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if you don't know what a maf mod is, read the utec manual about 1000 more times.
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Old 01-25-2005, 11:37 AM   #12
mick_the_ginge
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UR injectors, no idea how they act. They maybe talking about the different dead times that most aftremarket injectors have over stock.

MAF modification (MAF mod) is what you are doing the the fueling table. Even in open loop fueling mode the fueling in the table is a MAF modification. The actual background OLF UTEC map is MAF based..

Like I said earlier, +-7 is fine in my books. My car is at about -7 in the summer and +7 in the winter.
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Old 01-25-2005, 12:22 PM   #13
stevepius
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Thanks for the replies. I am wondering if the bad cold starts are due to a sensor malfunction because as I was driving on the freeway today out of nowhere my CEL started to flash and the car started to shake. I didn't have any odd A/F readings on my scantool though, but I'm wondering if something is going bad. Either that or my spark plugs are horribly misfiring because they are so dirty but I'm picking them up today and hopefully getting them replaced. It was scary none the less.
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