Let me give you some background info before you answer the question.

This is for a 1998 Chevy Blazer S10 with 4.3L V-6 2-wheel drive and 4-door model belonging to by girlfriend who in the original owner and it now has 200,000 miles on it.

A few days ago she started it up and heard what I would call a "rattling" sound coming from approximately the underside/middle of the vehicle. To me I was guessing it was a rusted muffler or other exhaust component to include perhaps a bracket that rusted out. I took a broom stick while it was running a pushed on the muffler, exhaust pipe, and the catalytic converter slightly from the drivers side while laying on the ground. The "rattle" seemed to stop whenever I applied slight pressure. I really could not discern exactly the source of the sound so I told the girlfriend to take it to a couple of places so they could put it on a lift to find the source of the noise. She did this and both places told her it was the CAT. Apparently, it was said that the CAT is just old and most likely some of the ceramic honeycomb inside deteriorated and pieces of the honeycomb are rattling inside the CAT. My girlfriend likes to describe the sound more like the sound of "marbles" or "rocks" rattling in a can while the vehicle is idling. She doesn't hear it when she is driving it at speed. Assuming the two shops are correct then the CAT needs to be replaced. So my questions are:

1. Does this sound like a correct analysis from the shops? I should have stated the vehicle otherwise runs fine and there is no loss of power although the girlfriend says that over the last two years her gas mileage dropped from about 16 mpg to around 12 mpg. The mpg didn't drop over night.

2. How hard is it for a weekend garage warrior to change out the CAT with the use of a couple of ramps and typical moderate-level mechanic tools? Is this a knuckle buster or is it as simple as unbolting the old one and putting in the new one. The assumption here is that I would not be purchasing a "generic" CAT but a direct fit CAT.

Thanks in advance for any enlightenment you can provide here...

 

if it is bolted then unbolt ,if it is welded use a sawsall comes off esy did both my cats recently then either clamp on or get welded on .. since my pipes were fairly new i just cut the cats off but thats your call can have it all done in a few hours that includes taking a break or 2 ,I used after markets
and everything is fine alot cheaper than the others

 

For the 1998 Blazer with the V-6 does anyone know if the CAT came with mounting/stabilizer tabs that are spot welded to the frame to hold it steady?...or does it only have the flanges on either side?

 

my 4door 98 has flanges on both side, its fairly simple to do (with the right tools). however, for the price of getting it replaced vs cursing on your back in a driveway, you're better off just getting a mechanic to do it. i found mine online for cheep and paid for an hour labor, total about 200 bucks

 

Direct fit is the way to go. Unbolting the flanges is a real challenge due to rusty threads. It will most likely require acetylene/oxygen to get them hot enough, and maybe they'll come loose... maybe. Without heat, forget it, I wouldn't attempt the job without a torch. Might have to blow the studs out and use bolts and nuts. It can be done, but be prepared for a battle

 

The vehicle has always been in Florida away from the snow and salt. I'm hoping it doesn't kill me.

 

The cheap route is to get a universal replacement cat and unless you have a welder, have a shop install it. Universal cats are about $100; installation probably $50 - $100. These cats only last about 2 yrs at best.

The best route is to get a direct replacement cat which includes the Y pipe and if a '98 had a pre-cat, this in included as well. Price is higher though, around $250 plus install if you are unable to DYI. As Captain stated above, the flange bolts are going to be difficult. Heat and also air tools are usually required, along with replacement exhaust manifolds studs that will likely break / twist....so add a few more $$ for some of these...there are total of six. And then either the two tor three flange bolts at the muffler. If a shop installs, then expect to pay around $350 - $400.

There's the information; up to you.

 

Apparently, what I saw in pictures of a new CAT are the hangers that plug into the rubber isolators not mounting tabs that weld to the frame. Didn't know that as I've never worked on any exhaust component of any vehicle. Anyway, now that I understand what these are it looks like you just wiggle the hangers out of the rubber isolators.

 

I wanted to close this thread by thanking everyone for giving me input on my question of difficulty changing out the CAT. I did end up changing out the CAT myself.

I took the advice I received about spraying down the flange bolts with liquid wrench. I sprayed the bolts several times while the CAT was hot then again the night before removing the bolts while the bolts were cold. I also sprayed the O2 sensor.

All bolts apparently are pressed into the flange from the muffler and also the flange of the old CAT to the exhaust manifold. The nuts were all very easy to remove and took perhaps ten minutes to get all six off. Also the bolts are pressed into the flanges it was very easy to push the muffler back to get the CAT disconnected easily. While you can reuse the bolts that are pressed in the muffler side flange the bolts on the manifold side are pressed into the old CAT so you can't easily reuse them. Also, the O2 sensor easily came out using a borrowed O2 sensor socket.

The most difficulty I had was with the rubber insulator hangers. These insulators are heavy duty in that they are reinforced with steel belts. Even though I sprayed the hangers with WD40 I wasn't able to get enough leverage from under the car to squeeze them off. In the end I just took a screwdriver and forced them off without regard for being able to reuse them. At $6 per rubber insulator it wasn't worth the aggravation of spending the time and effort to save them. If they were made totally of rubber without the steel belts they'd probably be flexible enough to get off without damage.

The CAT went in easily and the flange bolts were torqued to spec as was the O2 sensor. Again, I had to supply new bolts/nuts for the flange on the manifold side. There is really a lot of room under there with this particular vehicle so it never was a knuckle buster. Taking out one of the hanger brackets was necessary to easily remove the length of the CAT out but the hanger bracket was very easy to remove and only took two minutes.

In the end this was a very worthwhile job to do for a weekend garage warrior. The total cost of the job breaks down as:

$178 MagnaFlow direct fit CAT (delivered cost)
$12 two (2) rubber reinforced insulator hangers from O'Reillys
$6 three (3) each of stainless steel bolts, nuts, lock washers
COST was $196

Keep in mind the old OEM CAT containing platinum, paladium and rhodium will be sold to a recycler with a quoted price of $110. Shipping will be $11 so the net is $99.

TOTAL COST $196 - $99 (recycle) = $97

The $97 compares to the best quote the girlfriend got from calling a number of places was $346. Consider, they probably would have kept the old CAT to recycle for themselves then that is $346 + $99 = $445

Was it worth doing for her? $97 her cost plus some of my time versus $445 to have someone else do it....you make the call....

 

Three - Four years ago I had a mobile mechanic which (I knew x 2) had much better mechanic skills than his welding.
This SUV has been in storage 2 1/2 yrs. of recent. The Cat probably has 6 K miles or 9 month's of drive time , thus far. The Cat still looks new. Concerned about / Confused about earlier post relating Generic Cat vs Name Brand Cat life expectancy ? My experience . . .
1. Adv Auto or Auto Zone Generic ( for my 95 Gmc Jimmy ) Catalytic
convertor purchased
2. My mobile mechanic poor weld Cat to Muffler joint
3. Mobi mechanic U bolted front of Cat to extension pipe to Exhaust
Y pipe

~ 6.27.14 Failed Yearly Inspection -- due to exhaust leak -- U Bolted area

~ 6.29.14 Midas Muffler repaired and welded new joint pipe bet. Cat and Y pipe.
Cleaned up remaining path welding . . .
Midas Muffler-- caught 'em on a Sat. morning - was complete by 4 pm.
$126.00
Pleased with midas muffler work ! passed inspection . . . !