running rich in cold start

[seanhawn]

I own a 04 hyundai accent with 133,000 kms on it. I recently been burning through a lot of gas. Got no codes and no CEL. When I start the car in morning after sitting over nite, the exhaust smells really rich. Know some people say this is normal, but I don't think that getting 350km out of a 45L tank is good. What could cause this?
Once the car is warm the exhaust smells like exhaust. What should I check. Got fairly new plugs, new spark plugs, air filter, oil change.


Thanks for any help.

 

[abycat]

Is the cat plugged?

 

[oggb]

Could have a lazy O2 sensor.

 

[dparm]

Sounds normal to me. Gas mileage always tanks in the winter because the car has to run a high-idle for much longer.

 

[Dakota1820]

I agree cars run rich when cold . And the gas mileage isn't ever as good in the winter either. It is probably fine.

 

[AdRock]

Originally Posted By: dparm
Sounds normal to me. Gas mileage always tanks in the winter because the car has to run a high-idle for much longer.


I agree, and since it takes a little longer to warm up it's running in open loop longer. Also, the colder the air the more dense it is. The more dense it is the more fuel needs to be added to keep the ratio right. I know that my cars have always lost a little mpg during the winter.

As said above it could also be a lazy O2 sensor. But combine a lazy sensor with the other factors I mentioned and they can add up. Yoou could have someone watch the O2 with a handheld scanner to see if it's being lazy or not, but the caost for that might be the same as just replacing the sensor to begin with.

 

[seanhawn]

Don't know if the CAT is clogged, A little back I was getting a rotten egg smell out of the exhaust for a different problem. Since that problem was fixed the smell has gone. Guess I can still faintly smell it though.
If it started to smell and now the smell is gone, should I still replace the CAT?
Can't test the CAT can you?
If I am not getting a CEL and/or codes could the )2 still be a problem?
Going back to last winter I was getting at least 400 km in the winter time when it was colder than this now. Agree that gas milage does go down but not by this much. In the summer time last year I was getting 450 to 500km in city.
Know if I could hook it up to a per second scanner I could see what is happening but dont have one and would cost me 160$ at most shops.

Thanks

 

[Dakota1820]

Hold on you say your only getting what about 18 mpg right? Sorry I'm American we are to slow for the km l stuff

does it have any black smoke? You should be getting better mileage than that. No engine lights though? Try cleaning your throttle body and iac try a tune up it shouldnt cost much and maybe a fuel filter and then you know you got all that out of the way . And it doesn't hurt to change that stuff and clean it once in awhile anyway. Id do that and see where your at o and make sure your Thermostat isn't sticking open. My Saturn when I bought it was getting 22 mpg and I changed what I just mentioned and i am not getting 32 in pretty much all town driving. Big increase . Other than that maybe the vent canister when my aunts 00 elantra started doing what your saying your Hyundai is doing it was the vent canister and it wouldnt take more than 20cents of gas before clicking off . Took like 30 mins to fill up.

 

[seanhawn]

the fuel filter was done just over a year ago, spark plugs are brand new, the IAC was cleaning along with the throttle body, with seafoam, the thermostat is working as the car heats up as quick as always, the car takes gas no problem, pcv was cleaned, new air filter. how can you tell if the CAT should be replaced beside the rattling after everything is burnt out. The car has power some days or even some runs and other days or a few starts later the same day there is not much power. What could cause that? CAT? O2? fuel injector. I am getting around 200 psi in each cylinder for compression test.

 

[Quest]

When was the last time you have your thermostat serviced/replaced? Are you getting heat soon enough ? (alternatively, are you losing heat while cruising down the hiway?)

I'd go with thermostat first before I focus on IAC, o2 sensor, etc.


Q.

 

[JimPghPA]

When you run an engine rich you wash the oil off of the cylinder walls. This ages the engine very fast. You could wear an engine out in less than one year if you ran it rich enough and long enough.

I would throw a bottle of RedLine SL-1 in the tank. It cleans your entire fuel system including all the things that control flow of the fuel, and it also provides upper cylinder lube. After you run a tank of fuel with one bottle of RedLine SL-1 then continue to use it at the recomended dose of one bottle per 80 gallons. You will require a means of measuring, something like a 100 mL graduated cylinder works well. If a dirty fuel system was the problem you should see improvement after the first tank of gas, and then get to maximum improvement after you use up enough gas to use two more bottles of RedLine SL-1 at the recomended dose.

 

[seanhawn]

But what would cause the exhaust to be rich right at starting the car when cold. Even with I new thermostat, it will still be cold from start. A leaking injector? Can a failing O2 not trip the CEL or code but still tell the car it need a lot of gas? Like I said, once the car is warm, the rich smell is not longer there. I believe that is where I am losing the most fuel.

I am sure there is a lot of stuff I can replace to get better gas milage, like buy new wires, coil pack, CAT, IAC, MAP, TPS, O2 sensor, but which would I start with? Guess there is no way of really knowing what I need other then to spend the money and replace it.

 

[Dakota1820]

Doubt its the cat if it was clogged it wouldn't have power at all and would over heat and the cat would glow red. If throttle response and idle are good it isn't tps or iac. Doubt its a map and 02 sensor should throw a code I've never seen one not. [censored] a lot of engines code throw the o2 with the actual problem code. Maybe a fuel injector. When it doesnt have power does it fun rough or anything?

 

[seanhawn]

not really, maybe a little different then usual. Cant be much if I'm not that sure. Sometimes have good throttle response. Takes off when you put your foot a little down. Other times you put your foot down the same and the engine sounds loader but don't really go anywhere fast. It's an intermittent problem. Car does run a little better when the car is cooler then hotter, but not really cold or runs like [censored] too.

 

[Dakota1820]

Check you cat after you drove it see if it is glowing red. Other than that maybe a fuel injector or regulator. It's hard to say with out seeing it

 

[Colt45ws]

The computer is going to dump a ton of fuel in the engine at cold start to get it going. Think if it as the choke on a carburated car except instead of cutting air its just dumping in a ton of fuel to get you that instant start we all know and love. Then it will keep dumping in fuel trying to get it hot, until the O2 starts working. Ive started my car when it was 10F out and seen a cloud of black smoke blow out when it fired. Normal.

 

[JimPghPA]

Many O2 sensors have a resistive heater. If this vehicle has one like that and the resistive heater was burned out that might be the cause of the problem because the O2 sensor is taking way too long to get hot enough without a working heater in the o2 sensor.

 

[Colt45ws]

That should set a code if that were the case. A code exists for heater failure and another one if the O2s take too long to begin switching.

 

[Bladecutter]

Several systems come into play when a vehicle is started cold to determine how much fuel gets used in open loop mode:

Coolant Temp Sensor
Air Temp Sensor
O2 Sensor

Now, typically, the O2 sensor is ignored until it gets up to temp, and starts responding a certain way to electrical inputs. If the sensor is getting weak to the point that this takes longer than normal, but still passes its ECU testing, then it takes longer to get out of Open Loop mode, causing you to burn more fuel than needed over a longer period of time.

If either the Coolant Temp Sensor or Air Temp Sensor is getting lazy, then your ECU might think that its way colder than it actually is, so keeps the car burning more fuel over your whole drive.

If you can, get a scan tool, and watch the readings all three sensors give during your morning commute. If the readings look normal, then you need to go in a different direction. If one sensor seems to be giving bogus information, replace that one first.

Next up after these sensors would be ignition system. Coil(s), wires, plugs. If they are weak, then not all the fuel will get burned, causing you to waste gas.

BC.

 

[dailydriver]

Their is also the Catalyst Operating Temperature setting/program in the PCM which heavily enrichens the mixture when cold in order to 'light off' the catcon(s) up to their optimum operating temp(s).

But I cannot see what would change to cause that program's mixture to all of a sudden go MUCH more rich to the point of Sean noticing a radical difference in exhaust smell.