arielb1

I've got a 94 V6 4X4 with 108K miles. Sometime awhile ago, the exhaust started to really stink. I cant even leave my back window without the kids screaming at me to roll up all the windows. The fumes makes me feel ill if exposed for a short time.

It is a real drag. What can it be? Can it be my O2 sensors both front and back? These have never been replaced and I just passed smog. I live in California. I never understood the meaninng of rich and lean so I dont know what to look for. No fluid coming out of exhaust pipe..just really offending odor. No smoke either.

thanks all....need the education and help

Elton

sounds like its time for a new cat

arielb1

If the cat was bad, would I still pass smog? When does the O2 sensors need changing?

thanks again Chief.

Elton

when you get a cel or really crappy gas mileage are a few ways to tell

arielb1

Well, thanks again. I dont have a CEL and my gas is pretty good. Do cats typically go bad at 100K miles? If I recall correctly, it started at 75Kmiles. Thats for taking the time to help me. I appreciate it...Nice to learn.

Elton

you could take it off and look at it to check

arielb1

Okay, at least now I have something to do my research on. I didnt realize I can take it off to check it. thanks for the advise. At least it may not be the O2 sensor.

thanks again Elton...many thanks

Anyone else, feel free to chime in.

95RunnerSR5

when you take it off, look through the engine side and hold it up toward a light source. you should be able to see all the light through the honeycomb

arielb1

hmm...I assume the engine side is the pipe closest to the engine. If it is bad, I also assume it will be dark inside? Gosh, I dont mean to sound ignorant. I will hold it up and have the flashlight on the other end of the pipe and I should see light...if not, then I should assume it is bad....correct?

thanks 95RunnerRS

Ganoid

you may want to try something as simple as a different brand or grade of gas. Is it more of a rotten egg smell or just a really toxic vapor smell like you would smell out of an old 70's V8?

The rotten egg smell can some times be cured with different gas but that old 70's V8 toxic smell is usually a sign of a rich condition.

Rich and Lean conditions are a measure of the fuel to air ratio. Your engine needs X amount of air and Y amount of fuel to run properly. If you get too much fuel for the amount of air your are consuming then your engine usually cant burn it all completely and you end up with a toxic raw fuel smell out the tail pipe. A lean condition (not enough fuel) will usually result and higher operating temps and pinging or knocking as its some times called along with a lack of power.

The Rich/lean conditions are controlled by the engine ECU (computer) constantly changing the amount of fuel injected to keep up with us the driver who is constantly changing the amount of air the engine ingests by way of the throttle valve (aka the skinny pedal). there are several way that the ECU keeps tabs on the amount of air ingested like...
1) "Throttle position sensor" (TPS sensor) Tells the ECU what the position of the throttle is (or what your right foot is doing in this case).
2) Air Flow Meter (AFM) tells the ECU approximately how much air is being ingested.
3)Oxygen sensor (O2) tells the ECU what the condition of the exhaust gases are. If there is too much raw unburned fuel the ECU will see that and reduce the fuel input if it see's too much oxygen then it will increase the fuel input.

The ECU takes all this information and applies it to a set of tables in its little brain and comes up with an idea of how long and how often the fuel injectors need to open and allow fuel in. Usually it does a pretty good job if all the sensors are working.

there are a few things that the ECU will not see like fuel pressure. If the fuel pressure drops too low then the fuel wont be sprayed in properly when the injectors open and it wont mist or atomize very well (it needs to mix with the air as much as possible) so it will go largely un-burned. A clogged fuel filter can cause a drop in fuel pressure in some cases. Poor ignition systems in need of repair can also cause fuel to be expelled out the tail pipe in a raw form due to their lack of ability to ignite it. The engine often times cannot detect a bad Cat but with two O2 sensors it should since that is the whole idea behind two sensors one fore and one aft of the cat to analyze the before and after condition of the gases.

The job of the catalytic converter (aka Cat) is to help burn up any unburned gases sent through the system. The Cat is made to be a catalyst it basically gets hot due to exhaust heat then it actually causes the un-spent gases to burn in a sort of chemical reaction (exotic metals are used in cat assembly) as they travel through. One sure fire way to test a cat with out removing it is to run the truck on the road driving for 20 min or so to get everything up to normal operating temps. Then get underneath and shoot an infrared non-contact thermometer at the inlet pipe and then the outlet pipe of the cat. As strange as it is to believe the outlet pipe (tail pipe side) of the cat should be much hotter than the inlet side (motor side) because the cat is actually heating up the exhaust gases and burning off the extra fuel. A bad cat will clog up and make the Inlet (motor side) very hot because its causing all the hot gases to back up in the system and not allowing anything out very quickly. Some times a rotten egg smell can develop due to a stinky reaction between the additives in the particular brand of fuel and the catalyst in the cat not getting along.

If I remember correctly (and I may not) the last time I checked my cat it was around 200* on the input (motor) side and over 400* on the output (tail pipe) side., This will vary considerably but you get the general idea.

I hope this helps a little in your diagnosis of things. I'm sure some one will chime in here to point out something I said wrong in typical message board fashion. But thats the basic idea of how things should work..... Sean



Edit.. to check it with a flash light you need the cat completely out of the vehicle. It will be very dirty and dark on both sides (its part of the exhaust pipe after all) but there is a very fine honeycomb inside and thats the part you need to see through. Its pretty tough on a used cat to see through unless you have ideal conditions like holding it up to the sunlight to look through and even then I don't think a factory cat un-bolts in such a fashion that you can see straight through as it usually has a section of bent pipe on one end. Even with a new cat the honey comb is very fine and runs the length of the cat so you can only see through about an inch of area at a time you need to move your eyes and light source all around. If your cat is really shot it will have a nice coating of what looks like Tar on the engine side then its a no brainer.

traben27

I'm not even going to say anything about this subject, but that was THE BEST response to a question I have ever seen on yotatech. Good job.