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Pre Cats

Marv02

Well-known member
Joined
May 4, 2010
Messages
472
Location
California City Ca
Corvette
1986 C-4 Corvette
How can you tell if your pre cats are bad.
After installing the new motor The pre cats are both smoking.
The Right side cat smoked before the motor swap but now both of them are smoking.
White smoke comming off the outside body of the cats under the heat sheilds.
I tryed to run the motor to burn off what every making them smoke no luck so far.
The smoking starts after the cats get hot it seams like when it get up top temp to light off for smog thats when they start smoking.
Also notice the motor runs a little ruff when they come up to temp.
The water temp is normal and the oil temp is normal.
I tryed to use some engine cleaner on the cats then wash them off but still smoking.
I don't smell like oil or coolent just white smoke.
Any Ideas or are the cats gone bad on me.
 
You don't need precats for anything. I'd remove them and replace them with the head pipes off a car w/o precats. You don't need precats for the smog check.

I'm going to bet the smoke is from fluid which dripped into them during the work you were doing.
 
I was thinking the samething but it not burnning off yet I just worried I don't want the car end up a fire ball.

I was also thinking about get a new non pre cat Y pipe and a new 3 way cat for it.

Money Money and more Money.


I just want take the car for a drive it been on jack stands now going on 4 months.



You don't need precats for anything. I'd remove them and replace them with the head pipes off a car w/o precats. You don't need precats for the smog check.

I'm going to bet the smoke is from fluid which dripped into them during the work you were doing.
 
One more stupid Question If I don't need Pre cats why can't I use full lenght Headers And get by Smog.

If The Headers have all the smog hook ups I don't get Ca smog laws.


QUOTE=Hib Halverson;1045222]You don't need precats for anything. I'd remove them and replace them with the head pipes off a car w/o precats. You don't need precats for the smog check.

I'm going to bet the smoke is from fluid which dripped into them during the work you were doing.[/QUOTE]
 
I was thinking the samething but it not burnning off yet I just worried I don't want the car end up a fire ball.

If you're worried about fire, I'd do my best to ascertain exactly what's dripping on the precats
I was also thinking about get a new non pre cat Y pipe and a new 3 way cat for it.
Good idea. Those precats probably eat up 5-7 hp.
Money Money and more Money.
I feel you pain, dude.:W
One more stupid Question If I don't need Pre cats why can't I use full lenght Headers And get by Smog.
That's not a stupid question. The answer is headers are specifically illegal on cars built after 1975 unless they have a CARB EO number. In practice, a lot of smog stations will let them go as long as the AIR system is functional, the main cat is installed and the car passes the tailpipe test, but sometimes a station will fail a car for headers.
 
I mite take the gamble and get a set of long tubes headers a 3 way cat and cross my fingers.

If you're worried about fire, I'd do my best to ascertain exactly what's dripping on the precatsGood idea. Those precats probably eat up 5-7 hp.I feel you pain, dude.:WThat's not a stupid question. The answer is headers are specifically illegal on cars built after 1975 unless they have a CARB EO number. In practice, a lot of smog stations will let them go as long as the AIR system is functional, the main cat is installed and the car passes the tailpipe test, but sometimes a station will fail a car for headers.
 
And what others are saying on the other fourms is If raw fuel got down inside the converter this will clog them and make them smoke like what happening now.

I had all kind of issues get the new motor to run I sure raw fuel got the the converters.
 
up Date I going to get new Y pipe keep the sock Manifolds.

Best bang for the bucks.
 
Found the cause

I took the car off it jack stands it been on for the last 3 months now.
Rolled the car outside and wacthed the smoke issue in sun light The smoke is beeing cause by the injector tube on Number 7 cylinder is leaking some kind of fluid The tube is cracked.
The car go's in reverse fine but slips bad going foward plus is leaking trans fuild.
So the car back in the garage back on jack stands again.
I mite tomarrow pull the exhaust back off and pull the trany again.
This time send the trans out to get rebuilt.
Take the Exhaust manifold to work get it welded and try to find out what fluid is coming out of the air injector tube.
 
if a rich mix gets run thru the precats that will over heat them pretty quick and burn them out. Basically plug them from the exccess fuel. I had a P/U with a carb that was having problems running way rich, and the cat actually got RED hot...scared the crap outta me when I looked under the car. There used to be grass fires in the early days of cats that were started this way. Rich mix and the cat goes crazy hot. At first they will run red hot then die from over heating.The insides melt and clog the passages.

Loose 'em. A new front Y pipe solves this problem. They make bigger tubes also.
Load the car on a trailer, take it to a performance shop and tell them you need this big new front Y pipe fitted for the track. No law against modifying a car for offroad use.....remove precats, install a BIG Midstream Test pipe with flanges where the main cat lives.. None of the smog techs know to look for pre-cats on 80's vettes...as long as they see that main-cat and the air pipe going to it.
Had mine done in Oxnard.

If the precats are plugged, it will be slow to rev, sluggish and eventually heat up too much. No power, some misfiring. when it gets serious the motor won;t rev and will spit and backfire while trying. Basically it will be gutless. I had one plug up where the first symptom was sluggish performance and a very short time later it was so clogged that the car could not run past 25 mph....barely got it to a muffler shop.

To Test for plugged Cats....

If you can pull your O2 sensor out, remove it, run the engine and feel the exhaust thats escaping from the O2 bung hole....the FSM says just a couple PSI...any more than that and the cat is plugged. Some compression testers have an adaptor to screw in and test the exhaust back pressure. The other way is to see how much blows back from the Cats air supply pipe. Pull the check valve off and see how much blows back.
 

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