Can an aftermarket tune be over ridden by the stock tune?
02-02-2012, 01:42 PM
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Can an aftermarket tune be over ridden by the stock tune?
If you pay to get a tune, is it possible that the ECU can revert back to the stock tune completely on its own without you doing anything to it?
02-02-2012, 03:13 PM
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This is valid for the older (2002 and older ECU's, i'm not familar enough with the newer ECU's, so it maybe different, but I'm assuming it's more or less the same).
Some settings would stay altered...such as Spark timing and fuel injection pulse timing(when the fuel squirts, not how much).
The "learning" nature of stock ECU's when running in close loop mode, will adjust 4 parameters...and you can't really do much about it.
The ECU will adjust fuel quantity to adjust for overly rich or lean (as sensed by the 02 sensor). This is done anytime you are in closed loop mode (anything below about 75% or 80% of TPS value or 75% or 80% of engine load). There is a "Short Term" fuel trim(STFT) and a "Long Term" fuel trim(LTFT). The STFT is only allowed to adjust fuel about 10-15%. If the O2 readings indicate that 10-15% fuel increase/decrease isn't enough, it adds or subtracts 5% from the LTFT...and the process starts over. If you're still rich or lean, it adds or subtracts another 5%. repeat as needed. The STFT fuel trim does not affect stored fuel quantity for FULL LOAD (over 75%-80%). LTFT does affect fueling in Open Loop Mode.
So Let's give you a real world example. Your tuner adds way too much fuel @ part throttle. He does something stupid like increase all injector timing 45% and lets the ECU figure out the part throttle settings. The A/F Ratio may be great at Full Throttle(Open Loop), but you're running hella rich at part throttle(closed loop). The ECU does it's hokey-pokey with the STFT and LTFT. You end up at -7% STFT and -15% LTFT. When you next go to Wide Open throttle, you'll be running 15% less fuel than you were originally tuned for. That's why you really need to get a ECU TUNER who can map not only the FULL THROTTLE/MAX POWER settings, but also the part throttle settings.
The other ECU Setting that adjusts is ignition timing for detonation/knock. If detonation(knock) is sensed, the ECU it will retard ignition timing. There is a Short Term Ignition Trim(STIT) and Long Term Ignition Trim(LTIT), just like with fuel. If you get knock @ part throttle due to bad gas, or poor tuning, the ECU will eventually retard your ignition timing down. Just like with fuel trim, the STIT values don't affect full throttle(Open Loop) but the LTIT does.
Now, both LTFT and LTIT have "max" values. If either goes over the "Max Adjustment" as set by the factory, your ECU will go into "LIMP" mode, and you'll get a Check Engine Light. In the older ECU's I think it was 40 or 45%..so it's fairly dramatic. But I've seen a car go into LIMP mode due to the LTFT and LTIT.
Because of the above, this is why it's important to ask the right questions of anyone you hire to "tune" your car. What are they doing. EXACTLY. Are they going to install a RRFPR(Rising Rate Fuel Pressure Regulator) and let that deal with the extra fueling? Or are they actually going to alter the fuel/ignition maps. If they are altering the ignition maps...are they doing ALL the maps? Or just OPEN LOOP(full throttle). Are they using a WIDE BAND o2 sensor/ Where are they plugging it in? If they slip it up the tail pipe they are going to be about half a second behind the engine in trying to tune/adjust. How good is their Wide Band o2 sensor monitor? How often does it update/take readings? If it's only recording/sensing once a second..and they are doing it from the tailpipe, you're not going to get a very accurate tune/map. It might be "good enough"...plenty of shops do it that way and they survive and have customers. But if it was my money, I'd be looking for better, or doing it myself.
I also STRONGLY RECOMMEND if you're running a "tuned" car (modified ecu, turbo/supercharger), getting an ODB-II cable, software and a cheap laptop. It gives you the ability to monitor sensors..and ECU Settings like STFT/LTFT/STIT/LTIT and it gives you the ability to read Check Engine codes and reset them, so you can get out of LIMP mode. It will also allow you to "data log" runs, so you can see if you've got problems anywhere with any of the fuel/ignition timing, or if knock/detonation is detected..etc. I used mine on a regular basis back when i had the Alpine turbo setup and Alpine Supercharger setup. I could data log the engine's performance/settings and then show them to Alpine so they could adjust the tuning of the ECU piggyback module they used. ODB-II isn't perfect. It's really a slow interface. The more data you request/monitor, the slower the refresh rate. So if you're requesting 25 sensors, each one will get updated about every 2 seconds. Not ideal. If you select say 2-4 sensors, then you can get updates every second to half a second. If you're worried about any one particular setting, you can just select that one sensor/setting and get updates about 4 times a second. Now, while 4 times a second sounds awesome, in terms of engines spinning 6000+ RPM, that's horribly slow. Thing about it. 6000RPM = 3000 spark events per minute. divide by 4 cylinders = 750 individual ignition events per minute PER CYLINDER. or roughly 12.5 per second PER CYLINDER. You're only monitoring 4 of them per second. The ECU is fast...ODB-II is slow. That's why you usually want to monitor STFT and STIT as your regular monitoring, and then switch it up to say LTFT and LTIT just as a verification. BTW, it's fairly worthless to try to monitor o2 sensor readings or even using an A/F gauge..the O2 sensor values are read by the ECU between 60-200 times PER SECOND (it needs to monitor each individual ignition pulse, just before and just after)..so any reading you record is going to be off WHAT Cylinder? Also, stock o2 sensors have a very narrow range. They only monitor about 1.5% (.75 either side of 14.7%)..so If you go rich..you have no idea how rich, ditto with lean. So why bother to have a gauge telling you the reading or a ODB-II reading that's only 4 readings per second over 1.5% range out of 60-200 measurements. Get a WIDE BAND o2 sensor and a monitor to go with it, not a gauge.
Some settings would stay altered...such as Spark timing and fuel injection pulse timing(when the fuel squirts, not how much).
The "learning" nature of stock ECU's when running in close loop mode, will adjust 4 parameters...and you can't really do much about it.
The ECU will adjust fuel quantity to adjust for overly rich or lean (as sensed by the 02 sensor). This is done anytime you are in closed loop mode (anything below about 75% or 80% of TPS value or 75% or 80% of engine load). There is a "Short Term" fuel trim(STFT) and a "Long Term" fuel trim(LTFT). The STFT is only allowed to adjust fuel about 10-15%. If the O2 readings indicate that 10-15% fuel increase/decrease isn't enough, it adds or subtracts 5% from the LTFT...and the process starts over. If you're still rich or lean, it adds or subtracts another 5%. repeat as needed. The STFT fuel trim does not affect stored fuel quantity for FULL LOAD (over 75%-80%). LTFT does affect fueling in Open Loop Mode.
So Let's give you a real world example. Your tuner adds way too much fuel @ part throttle. He does something stupid like increase all injector timing 45% and lets the ECU figure out the part throttle settings. The A/F Ratio may be great at Full Throttle(Open Loop), but you're running hella rich at part throttle(closed loop). The ECU does it's hokey-pokey with the STFT and LTFT. You end up at -7% STFT and -15% LTFT. When you next go to Wide Open throttle, you'll be running 15% less fuel than you were originally tuned for. That's why you really need to get a ECU TUNER who can map not only the FULL THROTTLE/MAX POWER settings, but also the part throttle settings.
The other ECU Setting that adjusts is ignition timing for detonation/knock. If detonation(knock) is sensed, the ECU it will retard ignition timing. There is a Short Term Ignition Trim(STIT) and Long Term Ignition Trim(LTIT), just like with fuel. If you get knock @ part throttle due to bad gas, or poor tuning, the ECU will eventually retard your ignition timing down. Just like with fuel trim, the STIT values don't affect full throttle(Open Loop) but the LTIT does.
Now, both LTFT and LTIT have "max" values. If either goes over the "Max Adjustment" as set by the factory, your ECU will go into "LIMP" mode, and you'll get a Check Engine Light. In the older ECU's I think it was 40 or 45%..so it's fairly dramatic. But I've seen a car go into LIMP mode due to the LTFT and LTIT.
Because of the above, this is why it's important to ask the right questions of anyone you hire to "tune" your car. What are they doing. EXACTLY. Are they going to install a RRFPR(Rising Rate Fuel Pressure Regulator) and let that deal with the extra fueling? Or are they actually going to alter the fuel/ignition maps. If they are altering the ignition maps...are they doing ALL the maps? Or just OPEN LOOP(full throttle). Are they using a WIDE BAND o2 sensor/ Where are they plugging it in? If they slip it up the tail pipe they are going to be about half a second behind the engine in trying to tune/adjust. How good is their Wide Band o2 sensor monitor? How often does it update/take readings? If it's only recording/sensing once a second..and they are doing it from the tailpipe, you're not going to get a very accurate tune/map. It might be "good enough"...plenty of shops do it that way and they survive and have customers. But if it was my money, I'd be looking for better, or doing it myself.
I also STRONGLY RECOMMEND if you're running a "tuned" car (modified ecu, turbo/supercharger), getting an ODB-II cable, software and a cheap laptop. It gives you the ability to monitor sensors..and ECU Settings like STFT/LTFT/STIT/LTIT and it gives you the ability to read Check Engine codes and reset them, so you can get out of LIMP mode. It will also allow you to "data log" runs, so you can see if you've got problems anywhere with any of the fuel/ignition timing, or if knock/detonation is detected..etc. I used mine on a regular basis back when i had the Alpine turbo setup and Alpine Supercharger setup. I could data log the engine's performance/settings and then show them to Alpine so they could adjust the tuning of the ECU piggyback module they used. ODB-II isn't perfect. It's really a slow interface. The more data you request/monitor, the slower the refresh rate. So if you're requesting 25 sensors, each one will get updated about every 2 seconds. Not ideal. If you select say 2-4 sensors, then you can get updates every second to half a second. If you're worried about any one particular setting, you can just select that one sensor/setting and get updates about 4 times a second. Now, while 4 times a second sounds awesome, in terms of engines spinning 6000+ RPM, that's horribly slow. Thing about it. 6000RPM = 3000 spark events per minute. divide by 4 cylinders = 750 individual ignition events per minute PER CYLINDER. or roughly 12.5 per second PER CYLINDER. You're only monitoring 4 of them per second. The ECU is fast...ODB-II is slow. That's why you usually want to monitor STFT and STIT as your regular monitoring, and then switch it up to say LTFT and LTIT just as a verification. BTW, it's fairly worthless to try to monitor o2 sensor readings or even using an A/F gauge..the O2 sensor values are read by the ECU between 60-200 times PER SECOND (it needs to monitor each individual ignition pulse, just before and just after)..so any reading you record is going to be off WHAT Cylinder? Also, stock o2 sensors have a very narrow range. They only monitor about 1.5% (.75 either side of 14.7%)..so If you go rich..you have no idea how rich, ditto with lean. So why bother to have a gauge telling you the reading or a ODB-II reading that's only 4 readings per second over 1.5% range out of 60-200 measurements. Get a WIDE BAND o2 sensor and a monitor to go with it, not a gauge.
02-02-2012, 05:49 PM
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I'm not all that familiar with tuning Asian cars but am with Fords. There is no way the learned closed loop fuel tables are what the ECU uses at WOT.
02-03-2012, 12:11 AM
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The 4 TRIMS (ignition and Fuel, long and short) are adjustments to the tables/maps/values. Short term only works on Closed Loop tables/maps/values, Long Term works on BOTH Closed and Open Loop tables/maps/values
This comes direct from FORD Tech document
The fuel system monitor is an on-board strategy designed to monitor the fuel control system. The fuel control system uses fuel trim tables stored in the powertrain control module (PCM) keep alive memory (KAM) to compensate for the variability that occurs in fuel system components due to normal wear and aging. Fuel trim tables are based on engine RPM and engine load. During closed-loop fuel control, the fuel trim strategy learns the corrections needed to correct a biased rich or lean fuel system. The correction is stored in the fuel trim tables. The fuel trim has 2 means of adapting: long term fuel trim and a short term fuel trim. Long term fuel trim relies on the fuel trim tables and short term fuel trim refers to the desired air/fuel ratio parameter called LAMBSE. LAMBSE is calculated by the PCM from the heated oxygen sensor (HO2S) inputs and helps maintain a 14.7:1 air/fuel ratio during closed-loop operation. Short term fuel trim and long term fuel trim work together. If the HO2S indicates the engine is running rich, the PCM corrects the rich condition by moving the short term fuel trim into the negative range, less fuel to correct for a rich combustion. If after a certain amount of time the short term fuel trim is still compensating for a rich condition, the PCM learns this and moves the long term fuel trim into the negative range to compensate and allow the short term fuel trim to return to a value near 0%. Inputs from the engine coolant temperature (ECT) or cylinder head temperature (CHT), intake air temperature (IAT), mass air flow (MAF) sensors are required to activate the fuel trim system, which in turn activates the fuel system monitor. Once activated, the fuel system monitor looks for the fuel trim tables to reach the adaptive clip (adaptive limit) and LAMBSE to exceed a calibrated limit.
Short Term Fuel Trim
If the oxygen sensors are warmed up and the PCM determines that the engine can operate near stoichiometric air/fuel ratio (14.7:1 for gasoline), the PCM enters closed loop fuel control mode. Since an oxygen sensor can only indicate rich or lean, the fuel control strategy continuously adjusts the desired air/fuel ratio between rich and lean causing the oxygen sensor to switch around the stoichiometric point. If the time between rich and lean switches are the same, then the system is actually operating at stoichiometric. The desired air/fuel control parameter is called short term fuel trim (SHRTFT1 and 2) where stoichiometric is represented by 0%. Richer (more fuel) is represented by a positive number and leaner (less fuel) is represented by a negative number. Normal operating range for short term fuel trim is +/- 25%. Some calibrations have time between switches and short term fuel trim excursions that are not equal. These unequal excursions are used to run the system slightly lean or rich of stoichiometric. This practice is referred to as using bias. For example, the fuel system can be biased slightly rich during closed loop fuel to help reduce oxides of nitrogen (NOx).
Long Term Fuel Trim
While the engine is operating in closed loop fuel control, the short term fuel trim corrections are learned by the PCM as long term fuel trim (LONGFT1 and 2) corrections. These corrections are stored in the keep alive memory (KAM) fuel trim tables. Fuel trim tables are based on engine speed and load and by bank for engines with 2 heated oxygen sensor (HO2S) forward of the catalyst. Learning the corrections in KAM improves both open loop and closed loop air/fuel ratio control. Advantages include:
Short term fuel trim does not have to generate new corrections each time the engine goes into closed loop.
Long term fuel trim corrections can be used both while in open loop and closed loop modes.
Long term fuel trim is represented as a percentage, similar to the short term fuel trim, however it is not a single parameter. A separate long term fuel trim value is used for each RPM/load point of engine operation. Long term fuel trim corrections may change depending on the operating conditions of the engine (RPM and load), ambient air temperature, and fuel quality (% alcohol, oxygenates). When viewing the LONGFT1/2 PID(s), the values may change a great deal as the engine is operated at different RPM and load points. The LONGFT1/2 PID(s) display the long term fuel trim correction that is currently being used at that RPM/load point.
Short Term Fuel Trim
If the oxygen sensors are warmed up and the PCM determines that the engine can operate near stoichiometric air/fuel ratio (14.7:1 for gasoline), the PCM enters closed loop fuel control mode. Since an oxygen sensor can only indicate rich or lean, the fuel control strategy continuously adjusts the desired air/fuel ratio between rich and lean causing the oxygen sensor to switch around the stoichiometric point. If the time between rich and lean switches are the same, then the system is actually operating at stoichiometric. The desired air/fuel control parameter is called short term fuel trim (SHRTFT1 and 2) where stoichiometric is represented by 0%. Richer (more fuel) is represented by a positive number and leaner (less fuel) is represented by a negative number. Normal operating range for short term fuel trim is +/- 25%. Some calibrations have time between switches and short term fuel trim excursions that are not equal. These unequal excursions are used to run the system slightly lean or rich of stoichiometric. This practice is referred to as using bias. For example, the fuel system can be biased slightly rich during closed loop fuel to help reduce oxides of nitrogen (NOx).
Long Term Fuel Trim
While the engine is operating in closed loop fuel control, the short term fuel trim corrections are learned by the PCM as long term fuel trim (LONGFT1 and 2) corrections. These corrections are stored in the keep alive memory (KAM) fuel trim tables. Fuel trim tables are based on engine speed and load and by bank for engines with 2 heated oxygen sensor (HO2S) forward of the catalyst. Learning the corrections in KAM improves both open loop and closed loop air/fuel ratio control. Advantages include:
Short term fuel trim does not have to generate new corrections each time the engine goes into closed loop.
Long term fuel trim corrections can be used both while in open loop and closed loop modes.
Long term fuel trim is represented as a percentage, similar to the short term fuel trim, however it is not a single parameter. A separate long term fuel trim value is used for each RPM/load point of engine operation. Long term fuel trim corrections may change depending on the operating conditions of the engine (RPM and load), ambient air temperature, and fuel quality (% alcohol, oxygenates). When viewing the LONGFT1/2 PID(s), the values may change a great deal as the engine is operated at different RPM and load points. The LONGFT1/2 PID(s) display the long term fuel trim correction that is currently being used at that RPM/load point.
02-03-2012, 07:23 AM
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What vehicle is that for? It says can be used. Source for the article? I have never seen it used and it is as foolish as some say the timing tables are adaptable.
You can't use a narrow band O2 sensor to read open loop fuel trims. So why would they use it to adjust the stock fuel table?
You can't use a narrow band O2 sensor to read open loop fuel trims. So why would they use it to adjust the stock fuel table?
02-03-2012, 01:30 PM
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RR-
You really need to do more reading on how ECU's work, and how they use the readings from the various sensors to make their adjustments. It's way beyond the scope of a simple thread in a forum. I can recommend a couple of books for you if you are interested.
Here's a detailed explanation on how narrow band and wide band O2 sensors work
http://www.enginebasics.com/EFI%20Tu...%20Basics.html
This particular FORD excerpt comes form the Ford Technical Manual for the Ford Edge.
Regarding your question on why Narrow Band 02 sensors from the factory vs Wide Band. That's a long story, but it boils down to cost, and service life.
In a perfect engine/ECU system, it would be ideal to have one wide band o2 sensor about 3" off each exhaust port, and have an ECU that is able to know that if you are running 12.5(rich), that it has the power/ability to calculate the value/figure out that it needs to EXACTLY take out 3.87% of fuel to get that cylinder at the perfect 14.7 A/F ratio. (Rather than just adding an pre-programed value of 1% 5% or 10%, etc.) As far as I know, no factory/stock ECU does this calculation. We may get there as emissions requirements and fuel economy requirements get tougher and tougher. But right now, Cars don't NEED this setup to run/perform properly. they may in the future.
Here's also a quick article on how to tune. This by no means exhaustive.
http://www.enginebasics.com/EFI%20Tu...%20tuning.html
You really need to do more reading on how ECU's work, and how they use the readings from the various sensors to make their adjustments. It's way beyond the scope of a simple thread in a forum. I can recommend a couple of books for you if you are interested.
Here's a detailed explanation on how narrow band and wide band O2 sensors work
http://www.enginebasics.com/EFI%20Tu...%20Basics.html
This particular FORD excerpt comes form the Ford Technical Manual for the Ford Edge.
Regarding your question on why Narrow Band 02 sensors from the factory vs Wide Band. That's a long story, but it boils down to cost, and service life.
In a perfect engine/ECU system, it would be ideal to have one wide band o2 sensor about 3" off each exhaust port, and have an ECU that is able to know that if you are running 12.5(rich), that it has the power/ability to calculate the value/figure out that it needs to EXACTLY take out 3.87% of fuel to get that cylinder at the perfect 14.7 A/F ratio. (Rather than just adding an pre-programed value of 1% 5% or 10%, etc.) As far as I know, no factory/stock ECU does this calculation. We may get there as emissions requirements and fuel economy requirements get tougher and tougher. But right now, Cars don't NEED this setup to run/perform properly. they may in the future.
Here's also a quick article on how to tune. This by no means exhaustive.
http://www.enginebasics.com/EFI%20Tu...%20tuning.html
02-03-2012, 02:03 PM
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I've had been tuning with SCT software for 10 years.
I've posted a question on the forum over there and will post back if I get an answer.
I've posted a question on the forum over there and will post back if I get an answer.