52 votes
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What does a water-like drip coming out of the exhaust of the car signify?

It signifies that the car is running absolutely correct. Here is the reason why: A gasoline (petrol) molecule is made up as such: C8H18 (or 8 Carbon atoms and 18 Hydrogen atoms) Energy is obtained ...
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52 votes
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What is the point of the exhaust?

Safety, comfort, noise and space are the things that come to mind. Safety Exhaust gasses are hot as hell. Hot enough that we put heat shields all over the exhaust line. In engines, we are actively ...
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45 votes

What is the point of the exhaust?

Well, we can have a pipe going out the front of a car as in this design here: or its heavier predecessor: Arguably, the aerodynamic properties are not optimal in both, but here is a similar approach ...
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20 votes
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What could cause high HC and CO, but low NO and CO2 in a smog test

The supplied gas values suggest a rich run condition and possibly a non-functional catalyst. Using a mixture calculator for the supplied gas values shows that the mixture is 6.4% rich. CO elevated ...
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14 votes

What is the point of the exhaust?

Several things; Exhaust coming out the front is dangerous. If the fumes are ingested into the cab the driver may be harmed. Normally a car is driven forward. If the exhaust is coming out the back ...
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13 votes
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Why are VW recalling their cars to remove a defeat device?

The recall is not to remove the cheating logic; it is to actually make the engines meet emissions requirements so they do not violate the law any more. From Autoblog's initial article on the scandal: ...
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13 votes
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How does raw fuel damage the catalytic converter?

A catalyst is a chemical that contributes in a chemical reaction but remains unchanged after the whole reaction is complete. In a catalytic converter platinum is the catalyst that converts unburned ...
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11 votes
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How are diesel engines better for the environment than gasoline?

They aren't better for the environment But efficiency is often confused with emissions. The average person would think that because diesel engines are more efficient and burn less fuel, they must be ...
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10 votes
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Why don't all diesel engines have throttle plates?

tl dr: By adding a throttle plate, it creates the vacuum needed to draw in gasses from an EGR valve. Since diesel engines are designed to run lean, they don't need throttle plates to run. They ...
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9 votes

What does a water-like drip coming out of the exhaust of the car signify?

Every gallon of fuel your vehicle burns produces a gallon of water out of the exhaust. If the weather is cold you will see it as steam. If the rear of the exhaust system is still cold even in warm ...
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9 votes
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What is the "Activated Carbon Cannister"?

Gasoline is a pretty toxic liquid. And it evaporates pretty easily. The Carbon Cannister is a system to help keep toxic fumes from gasoline out of the environment. So here's how it works. You ...
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9 votes

What is the point of the exhaust?

The exhaust also creates a pressure differential, which can help scavenge exhaust gases from the chamber. So a properly tuned exhaust will therefore increase the fuel efficiency of the engine. Whilst ...
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8 votes
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Cheap vs Expensive Fuels

Gasoline is made in large batches. Each batch has a number of attributes that should be met; Octane, specific chemistry, volatility, contaminates, ethanol content, and others. The output is dependent ...
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7 votes

What effect will removing my EGR have?

As a vehicle technician for BMW I can assure that it is good for your engine to get rid of EGR. EGR systems are there to improve the exhaust gas quality and slightly win a few miles on a tank (in ...
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7 votes
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How to install a California oxygen sensor into a federal catalytic converter assembly?

Looking at the description of the California O2 sensor for your car, the only thing different on it (besides the internals) is the electrical plug. The wrench which you tighten it down with is 7/8", ...
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7 votes

How are diesel engines better for the environment than gasoline?

Locally worse, globally better Diesel exhaust versus gasoline: about 15-20 % less CO2 about 4-100 times the NOx (highly temperature dependent, mitigated by proper use of diesel exhaust fluid, ref ...
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7 votes
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Connecting to the Battery During Emissions Testing to Measure RPMs?

The voltage being a little low (13.75 is not low enough to be considered a problem in any case) is not going to affect their RPM reading - as it's the frequency of voltage variations that is measured ...
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7 votes

What is the point of the exhaust?

Adding to the excellent answers already given. An important point to note is that we need to have a catalytic converter somewhere in the exhaust a short exhaust will not have room to fit it. Then ...
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6 votes
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How is barometric pressure related to emissions testing?

The federal test procedures for vehicle emission certification(FTP) is run on a dynamometer. It starts with the vehicle at an exact temperature and barometric pressure and humidity. It is run in a lab ...
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6 votes

CO, NOx, HC plot with AFR Table

Combustion Chemistry from Princeton This isn't much of an answer but here is some data from a Princeton class related to Combustion Chemistry. You will see that the table you are looking for is ...
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6 votes

Why don't all diesel engines have throttle plates?

Anti Shudder Valve Not a direct answer, but one engine component that many people confuse with a throttle plate on a diesel engine is called an "anti shudder valve". This looks exactly like a ...
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5 votes

How to install a California oxygen sensor into a federal catalytic converter assembly?

Just to add to the other answer as I ran into this same issue, what kind of emissions do I have on my mitsubishi galant? I had this code: P0421 and I had to replace my O2 Sensor & the catalytic ...
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4 votes

What does a water-like drip coming out of the exhaust of the car signify?

The car has not been driving long. As the others have said, the water comes from the combustion of the fuel. When the exhaust system is cold, it cools the exhaust enough that the water can condense. ...
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4 votes
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Is a secondary air injection pump motor necessary?

Yes, it will probably be necessary to fix the problem in order to pass emissions requirements. The secondary air injection pump on the Beetle is apparently used to accelerate the transition from cold ...
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4 votes
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Exhaust on a replaced motor

With the check engine light on, the car is going to be running a fixed set of parameters from the Engine Control Module. For instance Fuel Pressure will be held at max pressure and timing and spark ...
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  • 3,097
4 votes

Why are VW recalling their cars to remove a defeat device?

The way I understand the issue, VW wanted to increase performance and fuel mileage. The easiest route was to allow the car to pollute more. This was not possible while meeting the stringent emission ...
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4 votes
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Possible Fuel pump damage

The black powder was charcoal from the evaporative fuel filter/canister. This filters evaporated fuel from your fuel tank. When your fuel tank gets warmer and the gasses expand above the fuel line ...
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4 votes
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Formula to calculate emission rates

I think you miss-understand how OBD tells that your car is passing emissions. All the car does is make sure that the emissions control systems are functioning and then it hopes that what is coming ...
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  • 15.9k
4 votes

EFI engine car failed Emission test?

Before suspecting a bad O2 sensor... You need to be sure that the replacement MAF is suitable for your car. You mention the replacement MAF is a 5-pin and not a 4-pin like the one originally on the ...
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4 votes

How to calculate fuel consumption and CO2 emission on flex fuel cars using OBDII data?

"Flex Fuel" isn't an issue (I assume you mean E85 and similar) if you use injector duty cycle as the basis of your calculations. Total injector "on" time gives you fuel consumption, regardless of the ...
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