With a catalytic converter, the concentrations look like this:
Obviously in the small range around the shaded part, the emissions are very low. So, the trick to passing smog is a) to get the air fuel ration in that region, and b) to understand why it isn't in that region (assuming you are not passing).
Verify you have no vacuum leaks causing air to enter the engine when it shouldn't be. Since you have replaced most components, this makes sense.Causes of rich running can include:
- Bad plugs
- Mis set AFM
- Excessive fuel pressure
- Bad coolant sensor (the ECU senses the temp and richens the mix when the car is cold), or bad wiring between the coolant sensor and the ECU
- Bad air temp sensor in the AFM (the ECU richens the mix when the air is cold, because cold air is denser, so it takes more gas to maintain the 14.72:1 air fuel ratio
Causes of lean running can include:
- vacuum leaks (oil cap, valve cover, dip stick seal, breather hose between the throttle body and the valve cover (basically almost inaccessible), throttle body bellows leaks, manifold leaks, etc)
- Mis Set AFM
- Low fuel pressure
- Leaky valves
If your car is not passing smog, the first thing to check is the basic operation of the sensor. You can do this with a meter, or you can make or buy a little LED display. If you put a meter on the signal line (while it is hooked up and the car is running), the meter should sort of wobble around, never quite settling on any voltage (put the meter on a 1 volt, or 2 volt scale). If this is happening, and the car is still not passing smog, then the cat is probably not working.
If the O2 sensor output is pegged at 1 volt, then either the car is running very rich, or the sensor is not hooked up to anything (this is common on Euro cars..the sensor is there for appearances and isn't actually doing anything).
If the sensor output is at zero, then it is either not operational, or the car is running very lean. On Motronic cars, as I recall, the ECU will default to 0.5 volts if the O2 sensor is bad, so if the output is not zero, but is lower than about .6 volts and is not changing, then the sensor is probably bad.
Because your car should have an 80°C/176°F thermostat in it and the thermostat should open fully at any temp above 176°F and allow coolant to flow out to the radiator, that never seeing 12:00 on the gauge is fine, better, that it actually reaching 12:00.socalM5 wrote:Another quick question ever since I purchased the car a couple years ago my temperature gauge on the cluster never goes past 11 o'clock on my car. its not getting up to normal operating temperature should I say 12 o'clock. Would that cause it to run rich meaning the cts is telling the motor to burn more fuel?
It could be, and it's close enough a new cat would probably get it to pass, but I doubt it. New cats usually have just amazing numbers, but even good ones don't stay that way. Charles (Karl Grau) recently had troubles with his M5, but eventually got it to pass. Not guaranteeing anything, but check his post and the next few. Also, again, was your cat hot when you took it in? If it wasn't, that alone is enough to make it fail. It doesn't work until it's hot.socalM5 wrote:I will have to check the o2 sensor reading and the coolant temp sensor tomorrow. Do you think the cat could be bad?
]I just went through this with my M5 and I'm pretty confident that replacing the CTS made the difference although looking at the OPs numbers he could still have a failing cat.tschultz wrote: I'd verify your CTS is good and not causing it to run too rich and overheat the cat.
