Catalytic converter replacement - Cause
 

For the last month, every once in a while, my car will "hiccup" while I'm driving. There is clunk and a little jerk. During these hiccups, the check engine light will go on. Sometimes it turns off imediately, other times it will stay on for a few days and then go off.

So I took my car to the dealership today and this is what they told me: I need to replace 1 of my 2 cats @ a price of $1,515.

I was reading through other posts on the subject and found this:

"I need to caution you that cats will fail on 540i due to occasional misfire under heavy load. This generally occurs on M62 when the rearmost spark plugs and primary leads slowly become submerged in oil when the valve cover seals and gaskets seep or they leak & fail from a plugged engine ventilation system.

Replacing the cats without addressing root cause (oil leak) will result in another failure."

I have also been hearing a slight whirring sound coming from the engine, and I was told that it could be the PCV valve - positive crankcase ventilation.

Should I have the techs at Bob Smith investigate that? Could I have a ventilation problem as described above that made the cat go bad?

Any advice or information is welcome. Thanks!

Based on the information you found, it wouldn't hurt to have those items reviewed... sounds like that may have caused your cat failure...

Also, have you researched the price of a "generic" cat? I'm not sure if BMWs are proprietary in some way, but if you can find a generic one that will work, my guess is you'll save at least half on parts....

Apparently Bosal makes a generic cat for your car... about $350...

http://www.******************.com/ap...997&modelid=54

Aren't cats covered under the 8 year/80,000 mile EPA requirement? Click here. Excerpt:

There are three specified major emission control components, covered for the first 8 years or 80,000 miles of vehicle use on 1995 and newer vehicles:

Catalytic converters.
The electronic emissions control unit or computer (ECU).
The onboard emissions diagnostic device or computer (OBD).

Yup, but he has a 97, so that won't help him. It expired in 2005.

Good search job. I see you found my post about the "primary root cause" for cat failure. Engine misfire for any other reason or fuel delivery system malfunction can cause cats to burn up. What more can I say...

If you search some more, you'll find my threads that caution 540i owners about crankcase ventilation problems. Tech Tips shows repair methods, but a thorough fix involves removal of the intake manifold to ream out vent piping. The rear cover diaphram valve clogging or failing is generally only symptomatic. Positive pressure cause the oil seals to fart and make a buzzing/whirring sound. This can really screw up your motor seals and gaskets.

Thanks for the replies.
I had a Master Tech at Bob Smith BMW check everything, and he said there were no oil leaks and that the PCV valve was OK etc.
The dealership's price of $1,515 more than I want to pay, so I think I will buy another OEM cat and have it installed at an indie shop. My service advisor at Bob Smith warned me against using non OEM cats, and I like having the OE BMW stuff on my car anyway (except for the brake pads).

Is there any negative effects on the car from driving around with a bad cat? I haven't noticed any decrease in mpg etc. Thanks.

Hope that check wasn't done based upon my expressed concern. Ventilation problems can be diagnosed by removing the dipstick and checking for pressure with your finger. The whole ventilation system can be rebuilt by a reputable dealer for $500. What the heck did you get for $1500??

Your service advisor at Bob Smith is a smart guy. If you choose non-OEM cats, he will not be able to profit. He is milking you dry with his recomendations.

I would advise you to purchase a set of used cats from some M5 gearhead that put race cats on. The going rate on ebay and elsewhere is $400, but you need to confirm the reason they removed them. Plan B is aftermarket and plan C is overpriced OEM. Search for posts about good aftermarket units...do not just buy anything or service engine lights and failed tests can result.

You can not run a car on bad cats for long. Once they quit working, they begin to clog. At some point, the backpressure will destroy your cylinder heads and a $8K motor replacement will be needed.

Coelacanth,

How many miles do you have on your 97? I threw a check engine light last year and took it into the dealer. They gave me the same diagnosis and of course wished to sodomize me with two new cat banks. The problem was the 02 sensors.

I found direct OEM (Bosch) 02 sensors, replaced them, and have not had a issue since. 02 sensors are often overlooked as maintenance items. I stress they are something that need to be changed. My 97 Arctic had 79K on it when I changed them.

Food for thought.

One other thing. The cat problem is apparent with these vehicles. The previous owner of my vehicle had both cat's replaced with MAGNAFLOW Catalytic Converters. They are high-flow, and a fraction of the price. Again, no issues at all with these.

I understand and appreciate sticking to OEM parts. But I also think that there comes a point when something works just as well and is 80% less cost to do, then it should be entertained at least.

Good luck either way.

will aftermarket cats throw cel codes? im getting the code for cat converters but they were replaced about 2 months ago. thanks

Did you replace the 02 Sensors as well? Is this the first you are getting the CEL since you replaced the Cats?

The most important thing to aftermarket cats is having them placed exactly where the OEM cats were placed. This is so the pre and post 02 sensors get the proper reading.

The codes more than likely are saying that your post sensors are sensing that your cats are not working properly when there could be a strong possibility it is just a worn or old sensor that is not as sensitive as it should be.

so should i buy 4 new o2 sensors? what should i do then? i was told that the aftermarket carts that were put in are alot smaller than the oem ones. but the shop that put it in said that it should be just like stock. so i dunno what to do. thanks again

Well I think you need another professional opinion before you go and buy anything more. Find out what the CEL exactly said. Where did it come from? How many miles are on your vehicle and have the sensors ever been changed?

If you do need the sensors, Autozone, yes Autozone sells the exact same BOSCH sensors with direct plug in end for a fraction of the price. (same BOSCH part number). fyi.

Very good point. Do not try alternative or generic O2 sensors. They need to be specifically calibrated to maintain proper fuel mixture and no thrown codes. If Auto Zone sells exact replacements for cheaper, go for it. I concur that O2 sensors can throw these codes. The DME computer can not tell the difference between defective O2 sensors and defective Catalytic converters. It only extrapolates and guesses based upon fore and aft O2 sensor outputs. If the O2 sensor is bad, the DME trouble code diagnosis can be bad as well.

The dealers aren't much better at determining root cause components in this regard.

Thanks for the input. I had them check the ventilation system because I started hearing a howling sound coming from the engine a few months ago and got advice here on the Fest that it could be the PCV valve.

Here's my car:
1997 540i-6
120K miles
Dealer says that the cat on bank 1-4 may have been replaced before. I thought that $1,515 was a bit steep as well, but Calabasas is a pretty affluent area, and people around here just say yes to whatever their service advisors tell them. Each labor unit at Bob Smith is $120...outrageous.

Is there a way that I could tell if it's the cat or O2 sensors that are bad?
I think I'll end up taking your ebay advice, getting a new cat and having GT International, an indie shop in Los Angeles that I've heard good things about, install it.
http://cgi.ebay.com/1997-98-BMW-540i...QQcmdZViewItem
$503 shipped for new OEM cat is all I could find. I hear it's about an hour job. So I guess I'm looking at about $600.

When I told my service advisor that I'd have the cat fixed elsewhere, she said, "Oh I was talking to the tech and he thinks that you probably found someone else to do the job for about half as much as we charge". I looks like it'll be less than half. =)

DOH! I just realized that the ebay cat is not legal in California. Bavarian Autosport has cats for $409.95, but the ones that are legal in Cali are $929.95 each.

I guess it's time to start cruising BMW boards to try to find someone in Cali who replaced theirs with an aftermarket cat.

Here's some additional information, not sure if it's helpful.
My car is originally an Oklahoma car, not a California car.

After reading more posts, I think I may go the Magnaflow route. If I do buy Magnaflow cats, do I need to buy them 2 spots for the O2 sensors? I read that the 540i has a 2.25" inlet, but the only dual O2 sensor Magnaflow cats that I could find only come in 1.75" and 2" inlet (Part #53064). The Magnaflow parts finder suggests a 2" inlet cat with no O2 sensor holes (Part 53004).

From the Magnaflow website:
"The 53000 Series universal is a small footprint round body universal for use with small displacement engines or as a front converter in dual converter systems."

Are they all weld in or are there bolt ons?

While I'm at it, I think I'll get a stealth downturn tip Magnaflow exhaust. :D

You won't need to worry about the 02 Sensor bungs because they are not in the cat on your existing system. Look at this pic: See how they are in front and behind? (pre #7 sensor and post #8 sensor) You won't be touching those or the distance between them. You will only be cutting out the old cat and welding in new cats.

Another thing, be sure in getting the OBII compliant cats Magnaflow has. Since your vehicle is OBII compliant.

Before and after:

Ahhh OK makes sense. Thanks for the info.
I was getting all riled about this. Now I'm having a lot of fun thinking about getting cheap cats and a magnaflow exhaust.:thumbup: