muffler ?? cat. ?? help !

[surfnobc2]

I have a 98 4.3 145k blazer

Runs like a champ .. cleanest blazer you’ve ever seen

New intake manifold
Super clean maf
Great tranny

Got some rattling coming from the muffler I can actually see the muffler rattling itself.

But I think I hear another rattling too. The infamous Catalitic converter!!

The blazer bogs sometimes for about 1-2 seconds and shifts hard sometimes from 2nd-3rd

My question is could the muffler be causing some bogging .. or would that be the cat ..

You can see the muffler on the bottom rattling in and out and its black on that part of it ..


I just hate the light sound it makes from 2nd to 3rd it feels like it struggles a little and it also shifts good from 3rd to 4th and it hops back into third sometimes.. feels like I get no power …

In more details .. when shifting great it idels better.. at about 550 which could be low..
Not sure ..

Ive had the tranny checked its super clean as well …

Help ?

Thanks in advance

[Chris Stewart]

Does the Check Engine light come on?

You can have a bad cat. converter but the rest of the car be just fine. You might need to check the fuel pressure, low fuel pressure is a pretty common problem...here's where,




Have you replaced the spark plugs and spark plug wires lately?

[MT-2500]

On the cat make sure it is not a heat shield rattle.
A rattle inside cat is lose stuff in it.
May or not cause restriction.
Black exhaust or muffler indicates a rich system.
If system is running rich it will plug cat.

A good fast check on exhaust back pressure or restricted cat is a vacuum gauge.
Check vacuum at idle and at 2K rpm.
If vacuum drops when speeding uop to 2K -2.5K rpm's the exhaust is restricted.
Post back vacuum readings.
MT

[surfnobc2]

ok sooo ... could just be heat shield rattling not sure i dont think i feel any restriction ... it does loose rpms sometimes while driving ... and a lot of times when it does this its been raining .... i could have a bad cap, rotor, plugs, or wires or somthin ..... good idea... i dont have any way of checking these other than taking it to a shop ... soooo tomorrow ill take it down ill see whats up

[MT-2500]

Good Luck and let us know how it goes.
MT

[surfnobc2]

ok so i got some Seafoam filled up put a bottle of it in the tank and what do ya know .. runs great..

ive heard some rattling but no restriction at all ..

it took about 4 seconds to start this morning though dont know why .. never happend before but hasent done it again ...

anyways ive posted some more in another thread ..

thanks for all the help on this one !

best site around !