nonickatall
Full Access Member
So I would start logically.
The fuel system works as follows.
You accelerate and the throttle opens.
The engine sucks in more air and therefor oxygen, this is measured by the MAF. Based on this measured value, the engine control calculates the corresponding injection quantity with the help of other parameters, e.g. the engine temperature.
The point of the whole thing is to inject so much fuel, that all fuel molecules can react with all oxygen molecules and produce optimal combustion.
But since this is never really possible because, for example, the amount of oxygen at sea level is greater than in the mountains and on a dry winter day it is greater than on a humid summer day, the o2 sensors measures the residual oxygen content in the exhaust gas.
Based on this values, the motor control adjusts and tries to reach lamda 1. In order for this system to function, it is essential that the intake line between the cylinders and the MAF is airtight.
For example, if your vehicle is drawing incorrect air, the MAF measures less air than actually reaches the engine.
Therefore, the very first step is to check whether you have a false air problem. It only makes sense to check this with a smoke test.
A false air problem can arise, among other things, from a defective intake area between the throttle valve and MAF, but also from a leaky oil cap or even an oil dipstick seal, but also from the intake manifold seals or a defective evap system. The hose between the PCV and the intake manifold may also be defective.
If it's not a false air problem, it could be a sensor problem and of course the MAF, the o2 sensors and the temperature sensor are suspect.
Since your engine doesn't show that it is much too hot or much too cold, the sensor for the coolant temperature gauge and the ecm are the same, and the o2 sensors have been changed, then of course the MAF remains.
Of course, it can also be the case that the amount of fuel injected is not correct because, for example, the fuel pressure is too low.
Since it mainly happens at full throttle, this can also be a cause if, for example, the fuel filter is tight and too little fuel reaches the engine at full throttle, which can also lead to the engine running too lean.
Not all of our vehicles were equipped with a fuel filter. I don't know what it's like with yours. You can measure the fuel pressure with a pressure gauge. In order to be able to measure this properly at full throttle, you would have to place a pressure gauge so, that you can observe it through the windshield when you accelerate at full throttle.
Fazit:
First do a smoke test., them check fuel pressure also at full throttle, while driving, clean MAF, if all does not help, swap MAF.
A defective cat has other symptoms...
The fuel system works as follows.
You accelerate and the throttle opens.
The engine sucks in more air and therefor oxygen, this is measured by the MAF. Based on this measured value, the engine control calculates the corresponding injection quantity with the help of other parameters, e.g. the engine temperature.
The point of the whole thing is to inject so much fuel, that all fuel molecules can react with all oxygen molecules and produce optimal combustion.
But since this is never really possible because, for example, the amount of oxygen at sea level is greater than in the mountains and on a dry winter day it is greater than on a humid summer day, the o2 sensors measures the residual oxygen content in the exhaust gas.
Based on this values, the motor control adjusts and tries to reach lamda 1. In order for this system to function, it is essential that the intake line between the cylinders and the MAF is airtight.
For example, if your vehicle is drawing incorrect air, the MAF measures less air than actually reaches the engine.
Therefore, the very first step is to check whether you have a false air problem. It only makes sense to check this with a smoke test.
A false air problem can arise, among other things, from a defective intake area between the throttle valve and MAF, but also from a leaky oil cap or even an oil dipstick seal, but also from the intake manifold seals or a defective evap system. The hose between the PCV and the intake manifold may also be defective.
If it's not a false air problem, it could be a sensor problem and of course the MAF, the o2 sensors and the temperature sensor are suspect.
Since your engine doesn't show that it is much too hot or much too cold, the sensor for the coolant temperature gauge and the ecm are the same, and the o2 sensors have been changed, then of course the MAF remains.
Of course, it can also be the case that the amount of fuel injected is not correct because, for example, the fuel pressure is too low.
Since it mainly happens at full throttle, this can also be a cause if, for example, the fuel filter is tight and too little fuel reaches the engine at full throttle, which can also lead to the engine running too lean.
Not all of our vehicles were equipped with a fuel filter. I don't know what it's like with yours. You can measure the fuel pressure with a pressure gauge. In order to be able to measure this properly at full throttle, you would have to place a pressure gauge so, that you can observe it through the windshield when you accelerate at full throttle.
Fazit:
First do a smoke test., them check fuel pressure also at full throttle, while driving, clean MAF, if all does not help, swap MAF.
A defective cat has other symptoms...
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