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Ltft show rich but wideband and stft show otherwise. by Tweeder
Started on: 09-03-2014 01:07 AM
Replies: 4 (243 views)
Last post by: Tweeder on 09-05-2014 01:03 AM
Tweeder
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Report this Post09-03-2014 01:07 AM Click Here to See the Profile for TweederSend a Private Message to TweederEdit/Delete MessageReply w/QuoteDirect Link to This Post
Not sure what's going on and my tuner is having no luck keeping this thing stable. It will run good with a new tune then it will go rich again. The stft are from -3 to +3 cruising around and will occasionally go richer on decel. The ltft go between -13 and -21 but will lean up on decel as the stft richer up by roughly the same. The wideband is in the 14's most of the time but will head towards the 11's under accel and in the 12's in decel. This has been this way since I got the motor and now I'm running sd headers, gen v with a 3.5 pulley. I've tested for leaks and nothing shows up and my vacuum is in the low 20's.

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Report this Post09-04-2014 12:20 AM Click Here to See the Profile for TweederSend a Private Message to TweederEdit/Delete MessageReply w/QuoteDirect Link to This Post
Anyone, can't seem to get it out of closed loop as well.

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Report this Post09-04-2014 03:53 AM Click Here to See the Profile for army_greywolfClick Here to Email army_greywolfSend a Private Message to army_greywolfEdit/Delete MessageReply w/QuoteDirect Link to This Post
Okay, a couple basics for you.

First and foremost check for vacuum leaks. Second, what are you tuning? Is it OBDII?

I am going to assume by your use of long term and short term fuel trims that your tuning an obdII computer. Or he is rather.

You want to build a base tune by disabling deceleration fuel cutoff, set your cat overtemp protection temperature to 240 degrees and turn off long term fuel trims (also by setting the temperature to 240) Likewise, EGR needs to be disabled. Now your all set to tune from short term fuel trims only.

But wait, there's more. If you are using NON STOCK fuel injectors you need the flow rates set and the injector pulse adder table fileld out for that particular injector, if your in doubt leave it alone. minimum pulse adder should remain factory on 3800sc motors.

Now assuming you have everything set up, your going to do the VE tune first. Basically you will set MAF takeover above the maximum rpm of the engine. You really shouldnt have to make adjustments to the maf table at all because it isn't a cartridge style maf, although I've noticed some SC cars with ported blowers require a 10% upward adjustment in flow rate correction. Anyways, every time you log your looking to cover as many cells as much as possible with emphasis on the cruise cells. Cruise at a variety of speeds up and down hills and through towns, only a few full throttle blasts are really required...that sort of thing is easy enough to adjust with a wideband anyways. All initial adjustments are HALVED. Why? Well if you missed anything, and by making a 50% of scale adjustment you will know if that adjustment has actual correlation to the next log. Adjustments are not entirely linear. Often by adjusting fueling you increase or reduce engine loads, it shifts the load cells around and your tune isn't what it's supposed to be. A good tune is built from three logs, half way, 75% adjustment and a longer log for fine tuning that you will set exactly as it prescribes. Things you need to remember. Tuning is based on alot of factors, don't do a log one day when it's 70 degrees out and relog an adjustment when its 95. It's not going to be a good tune. Try to get the first two logs and retuning done in the same 3 hours or so. The drive it for a few days and do an extended log for your tuner should be done in a situation that shows how you intend to drive the car most of the time. I can record 96 hours of log on the hptuners pro, so I generally leave it with the customer over a weekend so he can log the car in situation for me.

Also, to answer your topic question specifically. LTFT is an adjustment, it's called "long term" for a reason. I'm not sure exactly how many cell hits and how much time it takes to influence but it's a long term percentile correction the ecm had to take to achieve stoich from commanded. short term covers everything from the evap opening to atmospheric changes, temperature changes, fuel quality, all the environmental factors in tuning. It takes only a few counts to change the correction, I believe the ecm will step down(or up) injector pw in percentile increments in a particular cell until it achieves stoich. It happens quickly because most switching o2 sensors are pretty quick, up to and over 60 lean/rich events per minute, tahts why they are called narrowband and why you shouldnt try tuning with one.

Prior to tuning a performance engine, plugs should always be gapped as perfectly as possible, fuel quality assured and injectors matched as closely as possible in flow rate. Siemens are NOTORIOUS for being as much as 8% off, thankfully most modern computers can be hard tuned for individual injector skew.

If it's an HP tuners log you can send it to me to look at. Tuner Pro as well.
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Tweeder
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Report this Post09-04-2014 08:33 AM Click Here to See the Profile for TweederSend a Private Message to TweederEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by army_greywolf:

Okay, a couple basics for you.

First and foremost check for vacuum leaks. Second, what are you tuning? Is it OBDII?

I am going to assume by your use of long term and short term fuel trims that your tuning an obdII computer. Or he is rather.

You want to build a base tune by disabling deceleration fuel cutoff, set your cat overtemp protection temperature to 240 degrees and turn off long term fuel trims (also by setting the temperature to 240) Likewise, EGR needs to be disabled. Now your all set to tune from short term fuel trims only.

But wait, there's more. If you are using NON STOCK fuel injectors you need the flow rates set and the injector pulse adder table fileld out for that particular injector, if your in doubt leave it alone. minimum pulse adder should remain factory on 3800sc motors.

Now assuming you have everything set up, your going to do the VE tune first. Basically you will set MAF takeover above the maximum rpm of the engine. You really shouldnt have to make adjustments to the maf table at all because it isn't a cartridge style maf, although I've noticed some SC cars with ported blowers require a 10% upward adjustment in flow rate correction. Anyways, every time you log your looking to cover as many cells as much as possible with emphasis on the cruise cells. Cruise at a variety of speeds up and down hills and through towns, only a few full throttle blasts are really required...that sort of thing is easy enough to adjust with a wideband anyways. All initial adjustments are HALVED. Why? Well if you missed anything, and by making a 50% of scale adjustment you will know if that adjustment has actual correlation to the next log. Adjustments are not entirely linear. Often by adjusting fueling you increase or reduce engine loads, it shifts the load cells around and your tune isn't what it's supposed to be. A good tune is built from three logs, half way, 75% adjustment and a longer log for fine tuning that you will set exactly as it prescribes. Things you need to remember. Tuning is based on alot of factors, don't do a log one day when it's 70 degrees out and relog an adjustment when its 95. It's not going to be a good tune. Try to get the first two logs and retuning done in the same 3 hours or so. The drive it for a few days and do an extended log for your tuner should be done in a situation that shows how you intend to drive the car most of the time. I can record 96 hours of log on the hptuners pro, so I generally leave it with the customer over a weekend so he can log the car in situation for me.

Also, to answer your topic question specifically. LTFT is an adjustment, it's called "long term" for a reason. I'm not sure exactly how many cell hits and how much time it takes to influence but it's a long term percentile correction the ecm had to take to achieve stoich from commanded. short term covers everything from the evap opening to atmospheric changes, temperature changes, fuel quality, all the environmental factors in tuning. It takes only a few counts to change the correction, I believe the ecm will step down(or up) injector pw in percentile increments in a particular cell until it achieves stoich. It happens quickly because most switching o2 sensors are pretty quick, up to and over 60 lean/rich events per minute, tahts why they are called narrowband and why you shouldnt try tuning with one.

Prior to tuning a performance engine, plugs should always be gapped as perfectly as possible, fuel quality assured and injectors matched as closely as possible in flow rate. Siemens are NOTORIOUS for being as much as 8% off, thankfully most modern computers can be hard tuned for individual injector skew.

If it's an HP tuners log you can send it to me to look at. Tuner Pro as well.


I don't believe I have a vacuum leak, it has all new vacuum lines and my vacuum is in the 20's. Yeah it's obdII. Even In open loop, it was running rich, he had the fuelling within a couple percent then my o2 went bunk is I bough a new one as well as a new maf. The next log, it went back upwards of -20 for ltft's again. So we went sd, trying for open loop but the bugger is stuck in closed loop. I see the o2 switching so I assume it's got normal readings, just waiting on a response from the tuner on that.

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86 SE Convertible 3800sc 4t65e HD.

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Tweeder
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Report this Post09-05-2014 01:03 AM Click Here to See the Profile for TweederSend a Private Message to TweederEdit/Delete MessageReply w/QuoteDirect Link to This Post
No matter what, he gets the fuelling spot on and then a couple drives later, it's back to being extremely rich again. This morning going to work, it was rich like normal, 12 hrs later and on my way home the ltft's were -7ish and the stft's were -3 to +3 and were balancing each other out. An hour later I seen ltft's in the 30's at idle. This is all in closed loop, but going down the long hill in town I drop it down into second to keep the speed rather than ride the breaks and when it's like that, it goes into open loop. I hit the throttle and it's back in closed and back and forth. This has more mood swings than the wife.

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