Buying a '92 BMW 535, worried about failing emissions

Hello,
I'm in the market for a used car and today I looked at a very nice '92 BMW 535. However, when the owner showed me the papers from the last
safety inspection I noticed the car was very close to failing emissions. It had a HC reading of 98 PPM, with max allowed being 100 it was only *two* PPM below the limit. I compared this to the reading a year before which was only 6 PPM. IOW, it had gotten 16 times worse between the inspections. The CO went from 0.1 to 0.3 (max allowed 0.5%) during this time also.
I'm worried that if I buy this car, it's going to fail emissions next time. However, I managed to get the price down to $3300 from $4000, so I'm really tempted to buy it. The question is, what is failing and how much will it cost? High HC means the engine is running rich and has nothing to do with the cat? The problem would more likely be a non-working oxygen sensor, right?
Thanks,
Ulf
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Ulf wrote:

How many miles on it? It might need a new catalytic converter pretty soon. My '95 525i w/187K has been close to the limit for a couple years now.
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JimV wrote:

About 120K miles.
Another thing, when the car was parked with the engine running and I hit the gas the revs dropped a little and it hesitated before revving up. Not sure if that's significant.
Ulf
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Often that goes along with a bad cat: the plugged cat throws off the vacuum, which affects spark advance and other engine controls. 120K and 12 years is certainly in the range of when a cat can/will fail.
Floyd
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fbloogyudsr wrote:

My 318ti did that (the apply accelerator->slowdown->accelerate REALLY SLOWLY sequence) just before the cat failed (could hear bits of it rattling around at 3000RPM) on the A1M at the weekend. Only had 70K on it, too >:(.
If you hear a rattling that seems to come from underneath the car when you start it or at any point when you rev up slowly, insist on an exhaust inspection.
Regards
Peter.
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HC, or hydrocarbons, are the result of unburnt fuel, the catalyst will have little affect on this measurement as its more likely attributed to an ignition or compression problem, it could be related to an incorrect mixture, however the CO levels would suffer as a result. anything below 100 is a reasonable figure, the limit here in the UK is actually 200 for HC's. i would guess a new set of spark plugs and maybe leads will improve that figure by a good margin. the catalyst will only deal with carbon monoxide levels (CO). it is actually designed to convert these gasses into carbon dioxide. regards. Steve.
wrote

years
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Sorry, Steve, but you are wrong, wrong, wrong. 3-way catalytic converters "burn" three sets of combustion by-products: CO, NOx, and HC. Googling "3-way catalyst" gives multiple explanations, here is one: http://www.sanken.osaka-u.ac.jp/~nky15/e_function/e_catal.html
Floyd
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fbloogyudsr wrote:

Would a broken cat affect the fuel/air ratio? Assuming it was running rich, which I think it was, would a non-working oxygen sensor be more likely to be the problem? Called BMW today, $1800 is the price of a new cat. Called both a scrap yard dealing with BMWs and a couple of part stores and non of them had anything. One person said the cat was the same part as the headers, but there must be aftermarket cats that would fit, right?

Ulf
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call a muffler shop a generic CAT should be about 300 bucks installed some cars have a pair of cats on the headers then a 3rd after the down pipes merge... (like a Nissan maxima) you could go with an aftermarket made for the BMW http://www.cheapexhaust.com/bmw-535-converter.html <no i don't work for cheapexhaust, they just turned up on a Google search to give you a starting place> O2 sensors are relatively easy to install given the engine is cool & you can get the car in a position where you can crawl under it park it parallel over a dry ditch for instance
wrote

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What John said.
Since a common failure mode of catalytic converters is to become plugged, it can affect the airflow and hence manifold vacuum, which affects fuel-air mix. Most modern engine controllers are less sensitive to this than older vacuum-based controls, but it still affects things. I have experienced this first-hand on my Ford E350-based motorhome with fuel- injected engine (even though it had electronic controls).
One thing about catalytic converters you should consider before using a generic one (of course, you can buy 6 $300 converters for the price of an OEM one - are you sure that's not the installed price BTW?) is that the guys writing columns in Roundel say that non-oem ones are trash and have caused problems.
I have to agree that a $75 oxygen sensor is way cheaper to try first if you're shot-gunning solutions. Personally, I'd take it to an independent shop and have them put it on their analyzer for $100 for an hour before spending any kind of money on parts.
Floyd
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fbloogyudsr wrote:

I assume the price they gave me was if I were to buy one over the counter. Could driving with a plugged cat damage the engine in any way, or will it only affect fuel economy and power? I must admit, I really like this car. Full service history, inspection II done a year ago for $1000 at a BMW dealer, fully equipped, manual, cloth seats, original rims, not lowered, and owned by a father of a little girl. I've sent the seller an e-mail saying I'll buy it for $2700, so hopefully we can agree on a price around $3000, otherwise I'll probably buy it for $3300.
Thanks for your help.

Ulf
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Ulf wrote:

It usually doesn't *damage* the engine too much. Increases fuel economy almost infinitely (you use *no* gas) as well as reducing engine power by the same amount (to 'zero', to be precise). The downside is, you have to walk home when the *engine won't run*! -- C.R. Krieger (Been there; done that)
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C.R. Krieger wrote:

LOL. I wouldn't let it go that far... Besides, I do have two cars (well, three until I can unload my E30 on some poor sucker...) so if one's out of commission I'll use the other one to get parts. :-) Yeah, this means I did buy the 535! Got the price down to $3000 just as I wanted, and insurance is a reasonable $500/year.

Ulf
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Well, I don't think it's the cat anymore. The engine misfires at idle, so I'll check the plugs, wires, and distributer next week. Also found some more stuff to look at on this page:
http://www.bmwe34.net/e34main/trouble/hunting_idle.htm
Anyway, took a few pictures this weekend. Here are three of them for those who are interested:
http://members.roadfly.com/ulf/535_1.jpg
http://members.roadfly.com/ulf/535_2.jpg
http://members.roadfly.com/ulf/535_3.jpg
I must say, the 535 E34 is a lot of car for little money (so far..).
Ulf
Ulf wrote:

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wrote

point taken, however most cars built for the UK market dont use 3 way catalysts, and besides if the HC levels were too high i wouldnt be looking at the catalyst.... as mentioned, and i'm sure you already know, HC is the result of unburnt fuel.....so therefore, with this in mind why would you be looking at the catalyst if this figure was too high. a "3 way" catalyst may well be able to deal with these gasses and reduce them, but this does not rectify an engine problem causing these high HC levels to be present in the first place.. Steve.

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And you guys over in Europe wonder why your air stinks so bad. 3-Way cats have been required in the US since about 1990. The fact of the matter is, at stoichiometric fuel-air mix (where best fuel economy is) there is almost always some un-burned fuel due to poor combustion chamber mixing.
Floyd
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Not so - a leaner mixture will give better economy at cruise.
--
*Why do we say something is out of whack? What is a whack? *

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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In wrote

I was under the impression that all cats no matter what final market the car is sold in would be 3 way - saves manufacturing costs idf they only order/fit one type of cat, let alone having different engine tuning.
Jason
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Yeah, actually, since EU changed their emission standards about 10 years ago to essentially match the US's, most cars sold in both markets have almost-identical emission control systems. So anon's original statement (that UK cars don't have 3-ways) was incorrect. I didn't catch that in my original post.
Floyd
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Call the people at timevalve.com. They don't list anything on their website, but I would think they would have it so a call might yeild a good quality cat at a good price.
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