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Need advice/help

1K views 17 replies 5 participants last post by  TaylorF25 
#1 ·
To start off I posted this originally in the wrong tread spot (oops). Alright ladies and gentlemen, I'm reaching out to you for your opinions and some assistance. This is regarding my 03 3.8 v6 So last week my car threw a SES (CEL) with the dreaded P04020 "catalyst convertor efficiency below threshold bank 1" So I started going down the checklist of what could cause it. My local exhaust shop found cracks in both my exhaust manifolds, which we all know is common on the 99-04's. He convinced me to let him reweld both of them instead of replacing them. Well my CEL light has stayed off but my passenger upstream catalytic convertor is rattling and needs to be replaced. Now here's my questions: should I just replace my exhaust manifolds or will the rewelded ones be stronger and last longer? Also as far as replacing the cats go, I found a bunch of options online. I've decided to just replace the whole Y pipe with all four convertors all attached to it. A company called eastern catalytic makes a direct fit replacement for about $480 shipped to my door. I also saw that flowmaster and I believe magnaflow makes direct fit replacements for around $500-$550. With that being said does anyone have any experience with any of these? I figure while I'm doing it I might as well replace the four O2 sensors and possibly the exhaust manifolds while I'm at it. I also plan on running some fuel injection cleaner (stp or similar) through my next tank of gas just to clean everything out before replacing everything. I want to make sure it wasn't a fuel injector problem causing the cat to go bad. Anyways I'm just trying to get opinions before buying any parts. Thanks everyone in advance!! -Taylor
 
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#3 ·
As a welder I can tell you replace them. Especially on those exhaust manifolds, I considered doing the same when I had my 04 mustang but if you weld it there's always the potential of the heat warping the flange. I'm assuming that's where your crack was at the flange. Its where most of them crack. Where it meets up to your block.
 
#4 ·
Thanks for the response! There were cracks there and also at the bottoms where they bolt to the y pipe. It was bizarre to see as many cracks in them as they had. Now what do you recommend replacing them with? Stainless? I wanted to go stock replacement at first but they would run me about $600 for the set of them. I'm now leaning toward the Flowmaster direct fit Y pipe replacement for my cat converters.
 
#5 ·
Someone may correct me if I'm wrong but I know exhaust leaks are a common issue with the 99-04 mustang, it's just the way the 3.8 and 3.9 was made. I don't think any new manifold you'd put in would correct it( I may be wrong). I've heard ceramic ones might but I really don't know much about it. I would just go through your local parts store, (O Reilly's, Autozone, NAPA) or perhaps online AmericanMuscle.com or ebay. All good places to look
 
#6 ·
Partially correct, the problem with the 99-04 V6 is 1) the AC drip is right above the passenger side exhaust manifold which causes constant heating and cooling and eventually causes it to crack (happened to me) and 2) the log manifolds for the car just suck completely and the weld at the flange is crappy. If you replace them with aftermarket manifolds or with the 94-98 headder style manifolds it will fix the leak, my only suggestion after that is to make sure you re-direct the AC drip away from the exhaust. Also, if you use the 94-98 headder style manifolds the flange on them is about 1/4in or so wider than the stock log style that cam on the 99-04

I have a pair of the headder style manifolds off the 94-98 that I'm waiting on enough money to have my exhaust completely re-done to put them in. I got them from a pull-a-part junk yard for about $40. They bolt straight up to the block but just the slight different in the flange.
 
#7 ·
What would the process be to change where the AC drips from? I've heard good things about Dorman exhaust manifolds off of rock auto. I figure that I should replace them since I'm already changing out the whole Y pipe. I'm planning on using new studs and nuts when I replace the manifolds also.
 
#8 ·
The only thing I can figure right now is just find some rubber tubing thats close in size, a clamp and an elbow and just direct it where you want it to go, I haven't done it yet, but it will be done before I get my exhaust redone with tax returns
 
#15 ·
+1000

Seems pretty straight forward, anyone have any advice on headers or exhaust manifolds?
Personally, if you are going to get shorties anyway, save yourself about $110 and go to your local pull-a-part and try to find the exhaust manifolds off a 94-98 V6. They have the same 3.8 block as the 99-04 V6 so the those will bolt straight up to the block ( i know because i've had them bolted up to the block before i found out...) but the flange size is slightly larger than the 99-04 stock mani, however, since you are putting in a new system anyway, it wont be to big of a deal.
 
#11 ·
Yeah thanks for bringing that up, I plan on soaking them for a few hours before taking them off. What brand manifolds or headers did you go with? I'm pretty sure that I'm going with the direct fit flowmaster Y pipe. Now I just need new manifolds or headers and the new hardware.
 
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