View Full Version : Cause to bad catalytic converter
I purchased my first BMW 328i (1998) last Friday and just as I started to enjoy it, the check engine light came on. Now the car ran great, but I decided to bring it into the dealership where I bought it, because they provided a 30-day warranty. So after waiting for 5 hours I'm told they can't read the BMW code (They sell bmws yet they dont have the proper diagnostic tool, which is innexpensive enough for me to buy.) and have to loan me a car so they can send mine to the actual BMW dealership for diagnostics. I bet they're paying $$$ a lot for this.
So to make this story shorter, they finally find out my catalytic converter has to be replaced. I know a little bit about cars and this is suppose to realy last the life of the car. Usually its a cause of some other fault. My only guess is, my friend the locksmith who does keys for this dealership on occasion knows they only have one fuel area (regular gas) which is bad for the car.
So my question is, what could cause this part to go out? What should I go looking for when I get my car back or is it the low octane gas they fueled the car with and purhaps I'll be fine (I did put octane booster into the car soon as I realized they may have used regular gas).
PJBIMMER
03-15-2008, 10:37 PM
Its possible that the previous owner failed to change the o2 sensors, which makes the engine run rich, If the exhaust has a bad smell like rotten eggs, then the cat is bad.
What's funny is when the check engine light came on, there wasn't a funny smell and the car ran perfectly. I figured it was just a bad quality gas warning or they left something loose. I was very surprised to hear the BMW shop was replacing the part.
If they know this is likely a cause from another problem, I wonder why they're not doing anything else to the car.
pife999
03-16-2008, 06:59 AM
When your catalytic converter goes bad it doesn't have to smell funny. The people who think that the almighty 02 sensor fixes every problem or ruins the exhaust and the catalytic converter are unknowing lost souls that should not suggest "fixes" or possible problems. If your cat. went bad the performance of your car would suffer greatly. When a cat. goes bad part of the ceramic internals of it fall apart and block your exhaust gases. This causes bad throttle response among other very noticeable things. It doesn't sounds to me as if your catalytic converter went bad as you said your car was running great. The cat can go bad for numerous reasons. Most of them that i have replaced have been due to overheating and from hard hits or jars caused by rough driving on rough roads. aka car bottoming out. Hope this helps.
~Pife~
pife999
03-16-2008, 07:04 AM
When your catalytic converter goes bad it doesn't have to smell funny. The people who think that the almighty 02 sensor fixes every problem or ruins the exhaust and the catalytic converter are unknowing lost souls that should not suggest "fixes" or possible problems. If your cat. went bad the performance of your car would suffer greatly. When a cat. goes bad part of the ceramic internals of it fall apart and block your exhaust gases. This causes bad throttle response among other very noticeable things. It doesn't sounds to me as if your catalytic converter went bad as you said your car was running great. The cat can go bad for numerous reasons. Most of them that i have replaced have been due to overheating and from hard hits or jars caused by rough driving on rough roads. aka car bottoming out. Hope this helps.
~Pife~
But then what causes the overheating?
My main concern is the dealership diagnosed the issues. I was only told "they're replacing the catalytic converter. I'm worried theyre fixing the symptom of something else.
Probably have about 3 weeks left on warranty. I want everything that could be wrong fixed b4 then :-) So purhaps I'm not going to take it easy on the car for a week, check everything daily.
E36 Phantom
03-16-2008, 07:33 PM
Xeek,
Leaded gas will quickly destroy a cat, but cheap gas shouldn't affect it terribly.
Also, since your warranty is almost up, you know the drill. Dealers will just slap a bandaid on it to get rid of you. Warranty expires, a month down the road your brand new cats are destroyed. Instead of the dealer doing free work on the real source and never seeing you again, you now must come back and drop coin for the repairs.
It sounds like Pife is pretty knowledgeable in this area, so I'll just let him diagnose it, as he probably knows of a lot of causes I wouldn't have imagined.
The check engine light came on after about 60 miles of driving (before I brought it to the dealer). So when I get the car back, I'll be sure to drive it that far (Of course, I'll enjoy every mile). Since everything ran fine, I can only guess Lamda sensor (O2), less the previous owner was dumb and drove on 87 octane for a long while and the extra unburnt fuel screwed the cat. (I'll be sure to also ask specificly what was wrong with the cat, meltdown, broken pieces inside, clogged.)
We'l have to continue this later when I get the car. I hate buying "THE" car I wanted and only getting to drive it for a day. They stuck me with a 07 Malibu. EW.
Dealership fixed the issues. New catlytic converter and also they replaced the O2 sensor. They weren't screwing me as I thought. Theyre wanting to refund the car and get me a car that wont start with these problems. Theyre afraid there maybe another underlying issue. They replaced the o2 sensor just to be safe, but now theyre rethinking.
So they wanted to refund the car and I am considering just taking the car anyway because it was exactly what I wanted. I need some advice on diagnosing the issues that caused the catalytic converter to fail, what can I check?
pife999
03-20-2008, 02:36 AM
It's ten years old...I would expect to change items like that. I have on my truck that is also ten years old. The over heating is sometimes caused by running the piss out of a old car that hasn't been ran like that in years. The Cat builds up with carbon among other byproducts of gasoline and then someone gets in the car and runs a lot of super heated gases through the exhaust and it's like magic the damn thing fails and there you have it. I drive a 93 bimmer and I wouldn't trade it for anything but another bimmer. Hope this helps. I am glad to see a dealership helping you out.
Theyre not realy helping. Theyre suppose to help me find another car, but the cars sell before they can call me back and do anything to reserve it. I'm just an inch away from taking the car i bought, it twas perfect cept for that catalytic converter.. I read more about causes, but for everyone's benefit:
#1 Bad Oxygen Sensor, this makes the engine run rich, extra gas in the catlytic converter overheats it and breaks down the materials inside.
#2 Bad Ignition coild (easily replaced) not letting the spark plug ignite properly which makes one of the cylinders misfire I think or just not burn the fuel properly and again gas gets into the catlyst.
#3 Oil or Antifreeze gets in the catalytic converter. Doubt its my problem or the car would proably run like crap.
#4 Bad spark plugs or wires (again easily replaced and tested.) Again gas in the catalytic converter.
#5 Road damage, hitting the catalytic converter (bottoming out as someone above said) potholes, offroad driving.
Thanks for all the help, finally got a complete list put together.
zachiepie
03-21-2008, 11:40 AM
Try banging on the cat converter with your hand. If it rattles, theres a pretty good chance its bad. I guess that would be the ceramic stuff falling off the insides...
Well no, it's already determined it's bad. It's finding the underlying cause that's the fun part we're talking about :-)
zachiepie
03-21-2008, 05:25 PM
Oh, sorry, I just got done working a 24 hour shift and I must have skipped ahead...
northstardragon
11-08-2008, 10:34 PM
Hi everyone. I am currently experiencing the same issues with my cat; This is the 4th time for the same issue.
Xeek, did you ever fix the problem with your cat? And if so, what was the underlying cause? I'm driving on eggshells here!
diptenkrom
11-09-2008, 10:02 AM
the actual cause of the rotten egg smell is directly from the o2 sensors themselves. they cause the car to run rich which leads to elevated levels of hydrogen sulfide. it is not the cat that is smelling.
check out this site:
http://www.aa1car.com/library/converter.htm
if you didn't smell it before, then you were not running rich. maybe running lean??? not sure, but the problem may be fixed if they replaced the o2 sensors.
i actually replaced my sensor and the smell went away, power got better and the
Franky goes
11-10-2008, 08:58 PM
I would go with no.1 on your list myself.
A code will not always trigger the 'Check engine' dash light. You will need a code reader to know what's going on with your engine. I fell off my chair when I read the codes on my car when I first got the tool. I had 4 different codes, including O2 sensor but no dash light. (Yes the dash light works)
I suspect this is what happened with your car. It was probably running with codes when you bought it. With some time on the meter it eventually triggered the dash light. But the problem could have been there for some time.
Not replacing an O2 sensor is a false economy in my experience. You lose 10-15% gas mileage and you damage the cat. Not good.
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