obd outputs and how to read them?
Discussion
I have a Lotus Evora -V6 3.5 supercharged and have decided to play with an obd reader.
Table below shows a random snapshot of an obd output from the Evora
Column 1 shows Fuel trim bank 1 sensor 1(%)
Column 2 shows Fuel trim bank 1 sensor 2(%)
Column 3 shows Fuel trim bank 2 sensor 1(%)
4.329999924 685 0.78125
4.28000021 674 -2.34375
4.28000021 687 0
4.28000021 686 0.78125
4.28000021 680 -2.34375
4.190000057 670 -0.78125
4.329999924 682 -0.78125
4.190000057 674 -0.78125
4.329999924 689 -0.78125
4.239999771 671 -2.34375
4.329999924 671 0
4.28000021 668 -0.78125
4.28000021 683 0
5.050000191 685 -0.78125
7.300000191 1183 2.34375
12.28999996 1695 -0.78125
12.57999992 2195 -3.125
13.32999992 2281 -7.8125
13.32999992 2313 -10.15625
14.71000004 2359 -2.34375
15.82999992 2557 0.78125
18.11000061 2807 1.5625
17.97999954 2955 -2.34375
18.11000061 2972 2.34375
18.11000061 2977 3.90625
18.23999977 2980 3.125
3.49000001 1779 0
4.46999979 645 0.78125
3.720000029 645 -0.78125
3.819999933 735 -3.125
5.78000021 861 -0.78125
6.349999905 853 0
6.75 846 -1.5625
7.070000172 867 0.78125
6.989999771 868 3.90625
7.070000172 868 7.03125
7.070000172 875 7.03125
7.070000172 877 9.375
40.38999939 1388 0
6.590000153 4027 0
Anyone know and care to explain what it all means?
What is the column 1 and 2 figures showing?
What is the column 3 figures showing in relation to column 1 and/or 2?
Where can I find info as to how to read obd outputs?
So answering my own questions with my guesses
Column 1, pre cat sensor and short term fuel trim?
Column 2, post cat sensor and long term fuel trim?
Column 3, same as 1 but on the other bank of the V6?
% figures +% is running towards lean and - figures is running towards rich? - not actually lean or rich but trending towards one or the other.
What the limits are I have no idea but plus or minus 25% rich or lean?
These figures come from a cold engine, so I'm not readin anything into them yet, just trying to understand what they mean.
For example these figures bank to bank seem relatively equal and may be correct?
7.070000172 868 7.03125
7.070000172 875 7.03125
7.070000172 877 9.375
whereas these may show a difference bank to bank, indicating a sensor not yet reading correctly (not up to temp)?
4.329999924 685 0.78125
4.28000021 674 -2.34375
4.28000021 687 0
4.28000021 686 0.78125
4.28000021 680 -2.34375
4.190000057 670 -0.78125
4.329999924 682 -0.78125
4.190000057 674 -0.78125
Any ideas, anyone?
Ta in advance.
Table below shows a random snapshot of an obd output from the Evora
Column 1 shows Fuel trim bank 1 sensor 1(%)
Column 2 shows Fuel trim bank 1 sensor 2(%)
Column 3 shows Fuel trim bank 2 sensor 1(%)
4.329999924 685 0.78125
4.28000021 674 -2.34375
4.28000021 687 0
4.28000021 686 0.78125
4.28000021 680 -2.34375
4.190000057 670 -0.78125
4.329999924 682 -0.78125
4.190000057 674 -0.78125
4.329999924 689 -0.78125
4.239999771 671 -2.34375
4.329999924 671 0
4.28000021 668 -0.78125
4.28000021 683 0
5.050000191 685 -0.78125
7.300000191 1183 2.34375
12.28999996 1695 -0.78125
12.57999992 2195 -3.125
13.32999992 2281 -7.8125
13.32999992 2313 -10.15625
14.71000004 2359 -2.34375
15.82999992 2557 0.78125
18.11000061 2807 1.5625
17.97999954 2955 -2.34375
18.11000061 2972 2.34375
18.11000061 2977 3.90625
18.23999977 2980 3.125
3.49000001 1779 0
4.46999979 645 0.78125
3.720000029 645 -0.78125
3.819999933 735 -3.125
5.78000021 861 -0.78125
6.349999905 853 0
6.75 846 -1.5625
7.070000172 867 0.78125
6.989999771 868 3.90625
7.070000172 868 7.03125
7.070000172 875 7.03125
7.070000172 877 9.375
40.38999939 1388 0
6.590000153 4027 0
Anyone know and care to explain what it all means?
What is the column 1 and 2 figures showing?
What is the column 3 figures showing in relation to column 1 and/or 2?
Where can I find info as to how to read obd outputs?
So answering my own questions with my guesses
Column 1, pre cat sensor and short term fuel trim?
Column 2, post cat sensor and long term fuel trim?
Column 3, same as 1 but on the other bank of the V6?
% figures +% is running towards lean and - figures is running towards rich? - not actually lean or rich but trending towards one or the other.
What the limits are I have no idea but plus or minus 25% rich or lean?
These figures come from a cold engine, so I'm not readin anything into them yet, just trying to understand what they mean.
For example these figures bank to bank seem relatively equal and may be correct?
7.070000172 868 7.03125
7.070000172 875 7.03125
7.070000172 877 9.375
whereas these may show a difference bank to bank, indicating a sensor not yet reading correctly (not up to temp)?
4.329999924 685 0.78125
4.28000021 674 -2.34375
4.28000021 687 0
4.28000021 686 0.78125
4.28000021 680 -2.34375
4.190000057 670 -0.78125
4.329999924 682 -0.78125
4.190000057 674 -0.78125
Any ideas, anyone?
Ta in advance.
The formatting in your post is all wrong, and I can't be bothered to comment on your actual results, but here's a basic explanation.
Fuel trim is the adjustment your ECU makes to the fueling. If we forget you have a V6 and say you have a straight 4, you'll generally have 2 lambda sensors. One before the cat, and one after the cat. The one before the cat would be bank 1 sensor 1, and the one after the cat would be bank 1 sensor 2. When your car gets up to a proper operating temperatue, the ECU will switch into something called closed loop mode. This means the fueling is controlled purely by the lambda sensors. It is no good trying to decipher short term fuel trims and lambda sensor readings with a cold engine. When your car runs at lambda 1 (14.7 to 1 air to fuel ratio (AFR)) the lambda sensor reads this from the exhaust fumes, tells the car it's running a good AFR and the car will keep adding the same amount of fuel.
Except the car doesn't work like this. What happens is the ECU keeps trying to add fuel. The lambda sensor reads this, and when it reaches a certain parameter it'll tell the ECU to add less fuel. So the ECU adds less fuel and when it reaches the other end of the scale, the lambda sensor tells the ECU to add more fuel. This keeps happening constantly at cruise (partially open throttle) about once a second. Because the voltage the lambda sensor gives out varies between abour 0.2v and 0.8v, this averages out at 0.5v, which is lambda 1.
Now, onto fuel trim. Fuel trim is the adjustment your ECU makes to the fueling. You have long term fuel trim and short term fuel trim. Short term fuel trim is what the ECU is doing whilst you're reading it. If you graph and lambda sensor output, and the short term fuel trim, the waveforms would be mirror images of each other.
Long term fuel trim is the clever bit. As your engine wears, and the car adjusts to your driving style, it adjusts the fueling constantly over time. Think of it like a carbouretted engine. As the engine gets older, you keep having to adjust the fuel adjustment screw, usually one way to keep the emissions right. So everytime the car goes into closed loop, it starts off at this value which the ECU has calculated over time.
Long term fuel trim is measured as + or - percentage. + means more fuel is being added (the exhaust gases are lean, which could be an indicator of air leaks, or failing MAF or MAP sensors) and - meants fuel is being taken away (the engine is running rich, perhaps the coilpack is failing.) Up to 10% either way is okay, anything above 10 will usually bring on a MIL (malfuntion indicator lamp, or engine management light) and will require fixing.
The problem with long term fuel trim is, that when you clear the emissions related data on a car, or disconnect the battery, it'll reset the fuel trim to 0. This is fine when the engine is in good order, but if the car has something wrong which was giving a high fuel trim reading, it can make the car run like a bag of crap when it's started up again. A classic example is the Mercedes A class. The MAF sensor is built into the ECU and they tend to fail. This is counteracted by the long term fuel trim, but when it's reset, the car starts running lean, rendering the car almost undriveable. Unfortunately, a new one is in the thousands of pounds, which can make changing the battery a costly mistake.
Post cat lambda sensors don't really do a lot. All they really do is tell the ECU the cat is working fine.
When you look at V and flat engined cars, the layout of sensors is up to the manufacturer. What you'll probably find is you have one cat which both exhaust manifolds go into. B1S1 is on the manifold of one bank and B2S1 is on the manifold of the other bank. B1S2 is the post cat sensor.
It's a relatively basic explanation but it might help you decipher your results.
Fuel trim is the adjustment your ECU makes to the fueling. If we forget you have a V6 and say you have a straight 4, you'll generally have 2 lambda sensors. One before the cat, and one after the cat. The one before the cat would be bank 1 sensor 1, and the one after the cat would be bank 1 sensor 2. When your car gets up to a proper operating temperatue, the ECU will switch into something called closed loop mode. This means the fueling is controlled purely by the lambda sensors. It is no good trying to decipher short term fuel trims and lambda sensor readings with a cold engine. When your car runs at lambda 1 (14.7 to 1 air to fuel ratio (AFR)) the lambda sensor reads this from the exhaust fumes, tells the car it's running a good AFR and the car will keep adding the same amount of fuel.
Except the car doesn't work like this. What happens is the ECU keeps trying to add fuel. The lambda sensor reads this, and when it reaches a certain parameter it'll tell the ECU to add less fuel. So the ECU adds less fuel and when it reaches the other end of the scale, the lambda sensor tells the ECU to add more fuel. This keeps happening constantly at cruise (partially open throttle) about once a second. Because the voltage the lambda sensor gives out varies between abour 0.2v and 0.8v, this averages out at 0.5v, which is lambda 1.
Now, onto fuel trim. Fuel trim is the adjustment your ECU makes to the fueling. You have long term fuel trim and short term fuel trim. Short term fuel trim is what the ECU is doing whilst you're reading it. If you graph and lambda sensor output, and the short term fuel trim, the waveforms would be mirror images of each other.
Long term fuel trim is the clever bit. As your engine wears, and the car adjusts to your driving style, it adjusts the fueling constantly over time. Think of it like a carbouretted engine. As the engine gets older, you keep having to adjust the fuel adjustment screw, usually one way to keep the emissions right. So everytime the car goes into closed loop, it starts off at this value which the ECU has calculated over time.
Long term fuel trim is measured as + or - percentage. + means more fuel is being added (the exhaust gases are lean, which could be an indicator of air leaks, or failing MAF or MAP sensors) and - meants fuel is being taken away (the engine is running rich, perhaps the coilpack is failing.) Up to 10% either way is okay, anything above 10 will usually bring on a MIL (malfuntion indicator lamp, or engine management light) and will require fixing.
The problem with long term fuel trim is, that when you clear the emissions related data on a car, or disconnect the battery, it'll reset the fuel trim to 0. This is fine when the engine is in good order, but if the car has something wrong which was giving a high fuel trim reading, it can make the car run like a bag of crap when it's started up again. A classic example is the Mercedes A class. The MAF sensor is built into the ECU and they tend to fail. This is counteracted by the long term fuel trim, but when it's reset, the car starts running lean, rendering the car almost undriveable. Unfortunately, a new one is in the thousands of pounds, which can make changing the battery a costly mistake.
Post cat lambda sensors don't really do a lot. All they really do is tell the ECU the cat is working fine.
When you look at V and flat engined cars, the layout of sensors is up to the manufacturer. What you'll probably find is you have one cat which both exhaust manifolds go into. B1S1 is on the manifold of one bank and B2S1 is on the manifold of the other bank. B1S2 is the post cat sensor.
It's a relatively basic explanation but it might help you decipher your results.
Upatdawn said:
ill ask here.....lol
how is that my Mondeo Tdci trip can show 65mpg but the real brim-brim vs mileage figure is only 54mpg, id expect much closer given its all computers and sensors......
The algorithm estimates the amount of fuel used in each injection cycle, the system doesn't have a flow meter to tell it the exact volume of fuel passing through either the pump/injector/fuel system etc.how is that my Mondeo Tdci trip can show 65mpg but the real brim-brim vs mileage figure is only 54mpg, id expect much closer given its all computers and sensors......
So it uses the pressure or more specifically the delta pressure, this is run through a calculation with the area of each injector and the pulse duration.
These area's are not 100% accurate, the timing is not 100% accurate, also they are affected by temperature (no temperature sensor in the injector
) and as above they wear over time.This is then used with the vehicle distance travelled, calculated from wheel speed and integrated (integral error), wheel speed can be upset by different tyres, tyre pressures, vehicle load, etc.
All adding error into the system.
This error integrates over time, the longer you leave it, the more progressively worse it gets.
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