I have seen a ton of folks talk of the evil buzzing or ticking hiss from their engine bay... flex pipe failure. Mine finally started to go out, so I figured I'd have a go at repairing it.

First thing to do is be sure the flex pipe is the actual problem, and not some other issue like a gasket leak. To do this I use a sort of homebrew stethoscope: 4-5ft of flexible tubing (1/4" id should be fine). Stick one end in your ear and poke the other around the flex pipe, listening for the hiss/tick. I could do this because i could hear the leak a bit at cold idle. If your's does not yet, you may need to keep driving it until it begins to.

Tools needed:
-Mig/gassless welder w/ necessary accessories (gloves, mask etc.)
-Breaker bar (I have a 18"x3/8 for my 3/8 sockets)
-Socket wrench
-15mm long socket (manifold to DP bolts)
-14mm long socket (DP to catback bolts)
-O2 sensor wrench (optional)
-Sawzall w/ 6+" metal blade
-Angle grinder
-Penetrant oil
-Coarse Sand paper or wire wheel for rust removal
-Jack, wheel chocks, stands
-Beer (optional... well maybe. I call it a tool more than a material)
-(Anything else? IDK I'm not done with the project yet)

Materials/ Parts needed:
-Flex pipe (See below)
-Steel round bar stock (1/4"+ dia)
-Replacement gaskets (3-bolt manifold to DP and 2-bolt DP to catback)

---Flex Pipe Selection---
The flex section of the stock LSJ pipe appears to be 2.5" while the rest of the pipe is 2.75". 4" lenght is the shortest I could find. I got mine off ebay. There are a few versions out there. Ones with inner braiding is probably not a good idea because of how our engines squeese the flex pipe. This would cause a sort of "Bunghole effect" of the braid, choaking off the exhaust. I purchased one with and inner "interlock" section, then proceded to remove the interlock because it was very inflexible. It may have broke in eventually and been fine, but I heard of the aftermarket downpipes requiring solid engine mounts or suffer exhaust failures... most likely because they used these very inflexible (but strong) flex pipe sections. so I may or may not regret my decision later to remove it..



Now to the Meat. Sorry about the Cell pix but that's what I had onhand.

1) Hose down the 5 nuts with penetrant to make them easier to get off. 3 are accessable from the engine bay, other 2 under the vehicle. Allow some time to soak.... I didn't wait, which may be why I needed the breaker bar to get em loose.

2) Jack up the front of the car and get it secure. I like to have someone else on the premesis to be able to get help if it somehow falls. Then unbolt the pipe and remove it. The O2 sensor may be removed from the pipe. I just traced the wires back and disconnected it.. leaving the sensor attached.

3)The steel bar stock is needed temporarily to keep the manifold-side flange in the correct position while you cut out the old flex section. Give it a bit of a bend so it will clear the bigger new flex pipe, then weld it on; One end to the side of the flange and the other to the pipe on the other side of the flex. (I didn't get a pic of just this, see the other pics)

4)Cut out the flex section with the Sawzall. On the flange side I cut as close to the flange as possibe, then close to the flex on the other side.


5)Grind any remaining pipe flat on the flange section. Measure and mark the pipe for a second cut. Be careful; if you cut way too much off you're kinda screwed. Cut less, then you can grind down to a good fit for the new flex.


That's all for tonight. More to go in the morning.

 

What happened next?

 

Or if you have less than 80k miles and since cobalts haven't been around for 8 years. Take it to a dealer and have the whole thing replaced for free. The flex pipe is part of the cat and there is a law warranting cats for 8 years or 80k miles on ALL new cats sold.


Oh and a "long socket" is called a deepwell btw.

 

That federal law only covers states with Inspection and Maintenance programs. Keep this in mind if you live in a state without inspections, such as Iowa for instance.

 

what if you have a header on ur car think they will warranty it still.. i highly doubt it but curious

 

Sorry about abandoning the thread. The weld was going well enough for the terrible welder I am (they were likely not leaky but looked awful), but then when I was nearly finished I blew through the pipe and couldn't do a good enough job to close it up. It still whistled like crazy on the car because of it, but it fit up well enough.

For a more compitent welder, I think this is a perfectly viable repair option. I just couldn't bear not atleast trying, since it only cost $30 for the flex pipe. After the repair failure I picked up a ZZP pipe (which the cat seems to be going, so I'm now replacing it too)

For the record I did bring it to the dealership first, but got the usual runaround of "we find nothing wrong with the cat itself"