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Catalytic Converters

Started by Jeff Wilk, September 23, 2012, 08:21:10 PM

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Jeff Wilk

How about a good discussion about these catalytic converters.....

1. How do you determine if they are blocked?
2. How do you tell if still effective?
3. Any downside to removing and replacing with straight pipe?
4. Can a car that came with one pass inspection with it removed?

My car with a cat is a '75 Eldorado and i have it registered as a non historic car in NJ which requires it to pass emissions tests as well.

Just wondering what it really does and how to tell what its still doing.

Jeff
"Impossible Only Describes The Degree Of Difficulty" 

Southern New Jersey

1959 Cadillac Fleetwood Sixty Special
1975 Eldorado Convertible (#12 made)
1933 Phaeton Chevrolet - "Baby Cadillac"
1933 Master Sedan Chevrolet - "Baby Cadillac"

SOLD
1976 Cadillac Mirage (factory authorized Pick-Up)
1958 Cadillac Sixty-Special
1958 Cadillac Sixty-Special
1958 Cadillac Sedan
1958 Cadillac Coupe Deville

waterzap

Not sure about the historic registration, but why would you not want to register it as a historic vehicle?

My 76 Seville and 78 Eldorado both have straight pipes. Bought them that way so I dont know how they would have felt with the cats. On the other hand, from what I have read the cats in those days werent too good. You can probably get a bit of money for that cat, and maybe put a new high flow cat on.
Leesburg, AL

936CD69

Most cat con cars that have to pass emissions have both a visual and tailpipe sniffer test, which would mean your car would fail both without it. GM was basically forced by EPA regs to equip all their cars with cats starting in 75. They simply could not make them pass without them. My new 74 Caprice with a 400 small block had one, while a friends caprice conv't 454 didn't. Your car's cat con is filled with beads of platinum and palladium, which catalyzes unburned hydrocarbons and carbon monoxide into water and oxygen. They stunk to hi heaven because of the sulphur content in the fuel also produced sulphur dioxide. later pre  81 cats had  mesh converter guts with the catalyst bonded to the mesh. 81 and later cars had 3way cats to control oxides of nitrogen as well, earlier cars used only EGR for that.

As long as the owner only used unleaded fuel, they rarely plugged. Some early cars needed the beads changed at a certain mileage, most did not. Your 75 would gets points off for an incorrect exhaust at a Grand National as well.
Craig Brillhart CLC# 26217
1993 Sedan deVille Spring Edition Carmine Red White Top-SOLD!
1993 Sedan deVille Spring Edition Triple Black
CLCMRC Benefactor #302

EAM 17806

The 76 Cadillac Sevilles and the 78 Eldorados both came from the factory with cats on them so how is it those two cars get pass car inspections; are they outside the USA?  EAM
Ev Marabian

1976 Cadillac Coupe DeVille, 1989 Chevrolet Caprice Classic, 1990 Pontiac Bonneville and 1996 Buick Skylark

936CD69

One more point that just occured to me. I had a new 77 Delta 88 coupe with a 403, and was disappointed in the performance. The "common wisdom" of the hi perf guys at the time was get rid of the cat con. I talked a friend who had been a GM dealer mechanic since the early fifties in taking mine off and replaced with a "test pipe. What a miserable running car...and he couldn't make it run right. So we put the cat back on, reset everything to factory spec and it ran great. Later i put a 3.42 rear end instead of the 2.41 and she would scat!
Craig Brillhart CLC# 26217
1993 Sedan deVille Spring Edition Carmine Red White Top-SOLD!
1993 Sedan deVille Spring Edition Triple Black
CLCMRC Benefactor #302

waterzap

How about the current hi flow cats? Anyone have any experience with them?
And what about oils with high ZDDP? Which are good for the engine, but apparently can clog cats?
Leesburg, AL

Jeff Wilk

Great discussion going here.  I don't register the car as Historic because then I have to have historic insurance that limits driving in NJ to very very low mileage for club or similar purposes ONLY.  I like to take the car out once and awhile and have Hagerty Insurance that allows for very occasional driving aside from parades and club use.  Put these two together and in NJ that means NORMAL plates and registration and unfortunately Emissions Testing............

Car is passing inspection as I take it to a local repair shop that also has a NJ Emissions Testing Certificate.  He can really lean the carb out for the inspection which is something that would not happen at a State Center where they are not allowed to adjust your car.

Jeff
"Impossible Only Describes The Degree Of Difficulty" 

Southern New Jersey

1959 Cadillac Fleetwood Sixty Special
1975 Eldorado Convertible (#12 made)
1933 Phaeton Chevrolet - "Baby Cadillac"
1933 Master Sedan Chevrolet - "Baby Cadillac"

SOLD
1976 Cadillac Mirage (factory authorized Pick-Up)
1958 Cadillac Sixty-Special
1958 Cadillac Sixty-Special
1958 Cadillac Sedan
1958 Cadillac Coupe Deville

TJ Hopland

On newer cars the way they test cats for flow is by removing the o2 sensor and installing a gauge to check the exhaust pressure.    Since the old stuff did not have o2 sensors or a speck in the service manuals this would not likely do much good.  The later honeycomb cats you can just look through them and see if they are plugged.  The pellet ones are more difficult to tell.  One clue is to put a gloved hand over the tail pipe at idle.  A good system will have fairly distinct pluses to it.  A plugged cat will be smoother.   Its pretty easy to tell the difference if you have done it before or if you have a similar car to compare to.   Same goes for temp readings, the plugged one will be running much hotter before the cat but those were not published numbers so without something to compare to its hard to know if yours is normal or not. 

I have seen cats plugged from running rich.  That was real common on the 80's Oldsmobile V8's when the choke quit working and I just had it happen on a 93 Ford that had a bad sensor.   

The pellet style like your cad has were not known to be free flowing and they are among the most valuable to recyclers.  I have not looked lately but at one time you could get $150 for one.  Again I have not looked but I bet you could buy a new one for that so it would be just be the labor to fit it to your car.    I would consider swapping it out for a newer one.  The new ones flow much better than the old ones did even when they were new so you could gain a little mpg and power from the deal.   Just be sure you get one that is approved so it will still pass testing. 

My cars are all registered as normal cars too.  Just too many limitations on the historical registrations and no benefit other than saving me $40 per year.   I too like to drive my cars if I feel like it.   
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

curly

Quote from: Jeff Wilk on September 23, 2012, 08:21:10 PM
How about a good discussion about these catalytic converters.....

1. How do you determine if they are blocked?

Backpressure test is the best, but you can also check for blockage with a Vacuum Gauge on the intake side. Exhaust blockage will affect the engines ability to breathe, so a vacuum gauge connected to intake manifold vacuum and the engine held steady around 2500 rpm will show blockage. 
2. How do you tell if still effective?

On newer cars, the rear o2 sensor monitors cat efficency. On older cars, an exhaust gas analysis is really the only effective method to know if the cat is still working properly.

3. Any downside to removing and replacing with straight pipe?

It is illegal for a shop to do so, but a private owner can do it.  Mechanically, there is no harm to the engine/vehicle.  On newer cars that monitor the cat, the check engine light/service engine light will come on.

4. Can a car that came with one pass inspection with it removed?

Depends if the car undergoes a 'sniff' test or a visual inspection.  I'd be willing to bet a carb'd engine could not pass a sniff test without a cat unless the carb was properly adjusted and the engine was in good internal health.

My car with a cat is a '75 Eldorado and i have it registered as a non historic car in NJ which requires it to pass emissions tests as well.

Just wondering what it really does and how to tell what its still doing.

Jeff

T Lewis

62droptop

the pellet converters were heavy and poor flowing
our 76 caddy had one ,the car had fairly low miles at the time and dad removed it

it made a huge difference in performance and mileage

the big gm converters are worth a fortune at a recyclers

have heard stories of people in detroit area  to get theirs stolen while parked somewhere
come out and converter has been cut off

if you are really concerned about passing the test, get it sniffed before you remove it and again after  and check to see any difference

also ,if you lean out the mixture too much , you start producing waay too much Nox, which is caused from too much heat in the combustion chamber from the lean mixture
if left ,lean mix will burn valves and pistons
 




Barry

My 76 Bicentennial just does not seem to have the performance I remember from an earlier 76 convertible I had years ago, not to mention a 73 I had. My car has California Emissions on it. Any suggestions, or do they just tend to be sluggish ( 22,000 miles) ?
Barry Norman
1958 Biarritz
1961Biarritz
1976 Bicentennial
1976 Fleetwood Talisman
1961Continental Convertible

TJ Hopland

With everything working I don't notice much difference between my 73 and 75.  I have recently driven a 69 and even that was not dramatically different.  They all have a nice solid feel.  I do notice quite a difference if I have been driving my newer Dodge with the Hemi in it but a lot of that feel I think comes from the 5 speed transmission.  When I go back to the Cads I tend to let off waiting for the 3-4 or 4-5 shift which just does not happen when you only have 3 speeds. 

If you think its sluggish first thing would be to make sure everything is working properly.   When I work on cars that are getting to that age its pretty rare to see the timing components working properly, even 'low mileage' ones.   Vacuum advance is almost never working, even if the vacuum can is still working chances of the vacuum lines and various thermal valve switches still working is pretty slim.  Springs and weights are often stuck too.   With the timing basically fixed you will have really flat performance.   Its also fairly common to find carb issues that prevent the secondaries from working.  The mechanisms for the secondaries varied quite a bit over the years and models so you kinda have to take them case by case, there is not one thing that usually causes the problem.   Its all pretty easy and inexpensive stuff to deal with if you know or have some one that knows what they are doing.         
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

R Schroeder

In my 1978 repair manual for my Deville it shows that the pellets can be removed from the converter. I have been thinking about doing this to my car, and making a new plug for the converter.
There is 22,000 miles on the car right now, and it runs perfect.

Any thoughts ?
Roy

62droptop

i believe there is a standard  size frost plug that fits right in after you knock out the plug
i seem to remember fitting some years ago after i  had to replace some rotted ones working at the garage

Guidematic


GM used to sell a plug kit for these convertors, but not anymore.

The pellet type are quite restrictive and can really affect performance. I have a straight pipe on my '88 Eldo, and it runs very strong. The exhaust has a nice raspy note to it as well.

I used to remove the convertors on every car I bought as a matter of coarse. The differance in in some cases was quite remarkable. There was always a jump in performance and fuel economy.

Mike
1970 Fleetwood Brougham 68169
1985 Eldorado Coupe 6EL57
1988 Eldorado Biarritz 6EL57
1990 Brougham d'Elegance 6DW69
1994 Fleetwood Brougham 6DW69

bcroe

I can assure you the old pellet "one size fits all" cat are restrictive, esp on a big
block engine.  A stopwatch may be needed to put numbers to this.  If removing
the cat doesn't help, you have other issues as previously mentioned, and don't
forget the timing chain. 

If you must run a cat, get one of the newer monolithic units, which meet the
spirit and the letter of the law.  They are much smaller, and much less restrictive;
you may notice the exhaust is louder. 

My 77 Olds 403 is licensed because it travels coast to coast; collector cars are only
allowed a few miles from home in IL.  No emissions testing for it here.  With nothing
but good duals & a switch pitch trans, the 4150 lb and a 2.41:1 axle managed to do
91 mph in the 1/4 mile.  No need for a 3.42 on this high mileage cruiser.  Bruce Roe

Aaron Hudacky

I would take the car and have the sniffer test done to verify if not just the cat, but the complete emissions system is working properly.  If the car fails, that doesn't guarantee the cat is bad; the many vacuum lines often create high NOX problems when they crack and cause the engine to run lean, as well as clogged/failed EGR valves, leaky carb gaskets and bad ported vacuum switches.   Depending on the state, a punched out leaded fuel restrictor in the fuel filler tube can cause your car to fail emissions, although if your car exhibits this it likely has had the cat destroyed by leaded fuel or the cat was already removed. 

The originality concern seems like it could be a real problem if you are showing a car without a cat, and finding a NOS cat seems like it could be a big challenge.  I'm not aware of a reproduction that looks anything like the original.  My 79 deVille didn't have a cat when I bought it because the previous owner was a retired Navy PB4-Y pilot who liked leaded fuel from his radial engine experience, and he punched out the fuel restrictor to use leaded fuel which ruined the cat and made my car a gross polluter when I brought it to CA from FL in 2005.  I had a universal cat installed along with everything I mentioned above, and it has passed CA emissions without a single problem since.   If your 75 fails smog, I'd go after everything before the cat, and if you have to replace it with an aftermarket part, at least you can be certain that registering it won't be a problem ad that it is running relatively well.  My 79 hasn't become any slower since getting the emissions system squared away, and it idles much better because it is actually running properly. 

Regarding your ZDDP concern, I don't use ZDDP and there has been no deterioration in performance or major mechanical failures in the 9 years I've had the car.  The engine has 150k and has never been rebuilt.  However, if you did use ZDDP, I don't think it would ruin the cat.  ZDDP was present in the 70's when the original cats appeared and they didn't fail from zinc; I think removal of zinc was to prevent problems with newer ULEV certified vehicles and more stringent EPA requirements for new cars in general. 
1970 Eldorado
1978 Coupe deVille
1979 Coupe deVille
2008 Subaru STI

Guidematic


I have had nothing but good experiences from convertor removal. To me adding a convertor is detrimetal, not beneficial. It's like adding a more restrictive exhaust system and saying the car performs better.

The only car that I can agree with making sure the entire exhaust system is stock to be sure the car runs correctly are the '70's Cadillacs with EFI.

Mike
1970 Fleetwood Brougham 68169
1985 Eldorado Coupe 6EL57
1988 Eldorado Biarritz 6EL57
1990 Brougham d'Elegance 6DW69
1994 Fleetwood Brougham 6DW69

R Schroeder

I'm pretty well leaning towards removing my pellets from mine. I can make a plug on the lathe that will fit in there. That's no problem.
Fun to see if it makes a difference in the way the car preforms. Does pretty well now.
Roy

62droptop

the new style converters are not really restrictive if sized correctly
all the new high power cars have them and they do alright

just the first generation pellet ones sucked royal hiney