peeeot Posted October 26, 2006 Report Share Posted October 26, 2006 I've been toying with the idea of replacing my cat lately. Most of the time I've had the car I get a rattle coming from the cat (as far as I can tell, about 90% sure) when I first accelerate, when the tranny shifts into overdrive, or any other time the engine is under load at rpms at about 2k or less. I can also hear it more often than not at idle in drive. I've hesitated to replace it because I know those things fail for a reason and there are a lot of people with much higher mileage cars that don't have rattling cats. So I want to make sure that if I put a new one in there it won't break down prematurely. Anyhow, recently I put new spark plug wires on the car and suddenly the rattling happens less often and less audibly. I tried to get some people at a shop to hear it while driving around them a little but they didn't hear anything (figures). It's usually very easy to hear. If I get under the car and knock on it, of course the whole exhaust around the cat vibrates too but I do hear an extra sound that I'm pretty sure shouldn't be there. I've been thinking about getting the Magnaflow direct fit converter, part no. 23480. I can get one for $63 shipped. Do ya'll think I need to get a new one? Quote Link to comment Share on other sites More sharing options...
97loudcut Posted October 26, 2006 Report Share Posted October 26, 2006 get the magnaflow hi flow cat from summit for $50 Quote Link to comment Share on other sites More sharing options...
intern8tion9l Posted October 26, 2006 Report Share Posted October 26, 2006 hi flow is the shit. or just remove it completely if you can get away with it Quote Link to comment Share on other sites More sharing options...
Euro Posted October 26, 2006 Report Share Posted October 26, 2006 ive heard that there isn't really THAT much of a big deal between the high flow and regular cats. BUt i could be wrong. But if the cat is rattling/making noise, then the baffles ahve probably blown out, and it'll probably need to be replaced soon Quote Link to comment Share on other sites More sharing options...
sclary18 Posted October 26, 2006 Report Share Posted October 26, 2006 well, it isnt true that they dont go bad on thier own.. they actually can just blow out or clog without anything causing it, it is just more likely for an engine problem to blow it out. What I would do, is hook it up to a scanner, and test all the sensors first.. Then what you want to do is a fuel pressure test. If everything is all good just replace the cat and test everything again. That actually happened to my car.. I replaced my cat, and about 4 months later it started rattling. I tested everything and it was fine, so i put a new cat on, tested again.. and its been running great since... Quote Link to comment Share on other sites More sharing options...
Euro Posted October 26, 2006 Report Share Posted October 26, 2006 good point Quote Link to comment Share on other sites More sharing options...
peeeot Posted October 26, 2006 Author Report Share Posted October 26, 2006 I don't think I have access to the kind of scanner you're talking about, sclary18. All I can do is check for trouble codes. The only indication of a problem to me is that last time I checked I had a manifold vacuum reading of 18 inches Hg. I posted about this and the only response I got said it should be more like 21-23 or so. Every modern fuel-injected car I've ever tested for manifold vacuum gets around 22 except mine. Even my 1959 thunderbird does 21. Anyhow, I haven't tested it again since I replaced the spark plug wires. If that vacuum reading has gone up then I will have no fears about replacing the cat. So I guess I should check that pretty soon. Quote Link to comment Share on other sites More sharing options...
sclary18 Posted October 26, 2006 Report Share Posted October 26, 2006 yeah, the scanner i used hooks up through the same plug under the dash, but it also has a datastream option that reads the computer as well.. Quote Link to comment Share on other sites More sharing options...
intern8tion9l Posted October 27, 2006 Report Share Posted October 27, 2006 ive heard that there isn't really THAT much of a big deal between the high flow and regular cats. BUt i could be wrong. i'm sure it varies from motor to motor, but my friend put one on his 4.0 jeep and the difference was def noticeable Quote Link to comment Share on other sites More sharing options...
peeeot Posted October 28, 2006 Author Report Share Posted October 28, 2006 I checked my vacuum at the trans. vacuum modulator port. Initially it was just under 19 inches, but as the car ran for a while it dropped to just above 15. This was idling in park with 2, maybe 3 bars on the engine temp. gauge at around 700-800 rpms. Even though the engine wasn't fully warmed up, I feel like that reading is waay lower than it ought to be. Did I pick a bad port to take the reading from, or do I have a problem? I want this taken care of before replacing the cat. Quote Link to comment Share on other sites More sharing options...
Euro Posted October 28, 2006 Report Share Posted October 28, 2006 you might've.. where else could you check? Quote Link to comment Share on other sites More sharing options...
peeeot Posted October 28, 2006 Author Report Share Posted October 28, 2006 I also tried checking it at the line that goes into the vacuum tank under the fender. It read a steady 18 inches there. I still think that's too low. Quote Link to comment Share on other sites More sharing options...
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