shortyboy

ok,i just noticed this today.i started up the car,let it idle for a little bit and when i walked past the exhaust i got wet by something.i went back and check the exhaust,it was spitting what looks to me as unburned gas or something like that.its spitting all over the place.this has to be the reason why im not getting good gas mileage.well,i told my dad and he held a napkit near the exhaust while i reved it,it sput a complete back wet circle onto the napkin.it smells like gas alright,our oil level is fine,but what could be causing this?bad spark plug?or vaccum leak?please help.thanx in advance.

mpw

It's probably water.

Mighty Shilling

specially if it's a cold day. condensation bein pushed out. mine does it too.

Yabo

yeah, i would imagine its water. the gas smell is probably coming from the exhaust fumes running over the water as it goes out. if it were gas, once the pipes are warmed up it woudl probably be disasterous, which i am guessing youve driven it, so you would have already ahd that problem

joseph mitro

mine does the same thing, but my question is - how does condensation ever get built up in there to begin with?

Oddjob

Water is a byproduct of the chemical reaction of burning gasoline (in oxygen).

I forget the Carbon Hydrogen chain for Octane, but when it reacts with oxygen, the results are water (H20) and Carbon Dioxide (CO2). But of course the reaction isnt always complete and you end up with a lot of Carbon Monoxide (CO) along with various other molecules.

When the car is warm and the exhaust is heated up, the water escapes in vapor form. But on a cold day or when the car is just started up and the exhaust is cold, the water vapor will condense and youll get water dripping out of the tail pipe.

Someone with a more recent organic chemistry background can throw the stoich equation out here.

Joe944

Yep a lot of cars have water coming from the exhuast on a cold startup. Not sure if it's coincidence but I always see this from a lot of v8's, like camaro's, mustangs, etc.

Charlotte944

Close, but no cigar.

You are partially correct in that SOME water is fromed during combustion, but the primary by-products of gasoline compustion are NitrousOxides (NOX), un-burned HydroCarbons (HC), CarbonMonoxide (CO), and some other trace gasses.

The liquid that you are seeing at the exhaust is from water condensation in the exhaust system, particularly in the muffler and CAT. Raw un-burned gasoline in the exhaust would make a very loud noise, once.

This water is formed in the CAT along with a considerable amount of CarbonDiOxide (CO2). Basically, the media in the CAT breaks up all the "bad" gasses and lets the "pieces" re-combine to form water and CO2.

If you are experiencing poor gas mileage, my first recommendation is to have the exhaust gases checked at your local emissions testing station. If the test results show high levels of HC, then the engine is running rich. If you see high levels of NOx, the engine is running hot and lean.

Another option is to take a reading from the O2 sensor while the engine is running. For an early car ('83 to '85.0) you need to install a 'T' jumper between the O2 sensor plug and the DME plug at the center line of the fire wall. Standard male and female "Bullet" style connectors will fit the stock O2 sensor plugs.

For later cars you can 'back-probe" the O2 sensor plug. The black wire is the O2 sensor lead.

Connect a Digital Volt meter to a good ground and the O2 sensor lead (either back-probe, or 'T' jumper). Set the meter to read the 2 volts DC scale. Start the engine and let it warm up (fans cylcle on and then off.).

At idle the O2 sensor voltage should vary or dither across 0.5 volts DC. If the voltage does not vary, chances are the O2 sensor is bad. A good replacement is the Bosch 13913 3-wire heated sensor. Cost is about $40.00 at Pep Boys and the like.

If you replace the sensor, use a crimp on butt splice for the sensor lead. You can solder the heater leads, but the sensor lead is used to supply a reference atomsphere to the sensor. If you solder the sensor lead you can seal the insulation to the wires which will disable the sensor.

As with any performance related issue always check plugs, wires, vacuum lines, fuel pressure, and so forth.

One final thought: I had a real nasty idle problem and some horrible mileage with my '87. I checked the O2 sensor, plugs, wires, cap, rotor, timing, fuel pressure, vacuum lines, compression, etc., and found nothing amiss. On a hunch I checked the Fuel Quality Switch on the DME. Turned out the switch was "off" by one click. Turning the switch fully counter-clockwise (the "stock setting for the US) fixed the problem.

Boricua944

feel like i'm back in chemistry lol. thats pretty much what cars are a bunch of chemistry

James86-951

Everything involves chemistry. One of my old Chemistry professors used to say,"Better living through Chemistry." He was an odd sort.

Oddjob

">Close, but no cigar."

Well, luckily I don’t smoke cigars.

>"You are partially correct in that SOME water is fromed during combustion, but the primary by-products of gasoline compustion are NitrousOxides (NOX), un-burned HydroCarbons (HC), CarbonMonoxide (CO), and some other trace gasses."

The main reaction for octane in air is:

C8H18 + 12.5O2 + 47N2 --> 8CO2 + 9H20 + 47N2

Those are the primary byproducts. Because of incomplete combustion and various additives, there are some secondary products which include CO, H2, O2, unburned hydro carbon chains CnHn, and traces of aldehydes, alcohols, ketones, phenols, acids, NOx, and carbon.

All the clean air acts and emissions laws and regulations limit the amount of pollutants (mainly the hydro carbons, carbon monoxide, and the nitrogen oxides) to certain levels as a % of the total emissions. So the only numbers you ever see measured from emissions testing are the pollutants and possibly CO2 (because of greenhouse concerns). NOx are quite toxic and measured in PPM (parts per million) so they are far from a primary byproduct. The largest % of total emissions are N2, CO2, H2O, O2.

>"This water is formed in the CAT along with a considerable amount of CarbonDiOxide (CO2). Basically, the media in the CAT breaks up all the "bad" gasses and lets the "pieces" re-combine to form water and CO2."

Platinum/rhodium catalytic converters reduce the NOx emissions and cause some Oxygen to form free radicals and combine with CO to form CO2, but do not create the majority of CO2 or H2O in the exhaust. And its not uncommon for a car running a proper A/F mixture to pass some state emissions testing with the cat removed.

My track car with no cat and no muffler shoots out more water on start up than my street cars, because there are no obstacles (cat or muffler) to collect/pool the water and keep it from going out the tail pipe.

Mighty Shilling

HAHAHA! my mom says that about drugs! she's a nurse, and says that mocking all of the coke-heads or whatever they get in the ER.

Tom M'Guinn

My car does this too. When it is cold and running rich, it will spit out specs of black gas-smelling soot-soaked water--all over the garage floor. I'm always happy to see that it is black. When it turns clear and starts to flow like a leaking faucet, it means your head gasket is most likely leaking. Been there, done that.

I don't have a clue about chemistry, or who is entitled to cigars, but I note that my car pumps out quite a bit of this stuff even though I have no CAT.