That crack WILL affect performance AND gas mileage in pretty much every case. Aftermarket will have problems if you buy crappy parts, will not pass emissions if you buy crappy parts. Sensors are as easy as scissors and tape and a little piece of wire (of course soldering would be better though). But since you already have a new one on there...

Make sure you do the reset process properly (nothing can be on and it needs to sit for a while and then driving it, i dont remember exactly but there is a right way to do it so make sure you do it that way) or it can idle badly like that, but it might just take time driving around until it sets itself properly. Steam or smoke the first time I have heard is normal, you could have cleaned it first to help get the oils and what not are on it from the factor ect but it is not a big deal as long as it does not continue happening. Probably just take the sticker off before it melts or something haha

Welding should less than $50, people out here do it for like $20 really quick, but it is a very temporary fix and will cause it to be worse than before in short time (usually anyway) so you are much better off replacing it.

 

u should be able to get a manifold from a junkyard for cheap. why halfass it and try to repair it. just dump the shyt and get it replaced. youll thank yourself and if you got some tools its not too much of a tedious task.

 

I went with the best non-OEM replacement exhaust manifold / catalytic converter option available (Dorman 674-439 Exhaust Manifold), and not some $80 knockoff on eBay. The idle seems to be much better this morning. I'm hoping it's simply part of the re-learning process. When I reset the ECU, nothing was turned on... no stereo, no headlights, no brakes being depressed. Hopefully I'm good to go now. It drives much better.

 

if its doing good then it should be ok. youll truely find out when its time for you to go for emissions testing..

 

I have the same issue on my 97 Del Sol. Bought it off Craigslist and found that not only was the header cracked, but the guy who owned it before me had the header welded. I'm pretty sure that the header had been cracked, and then previous owner had it welded to pass emissions. The emissions were done about 11 months before I bought it so the weld didn't last a year, and is really bad now.

The reviews of people not passing emissions are usually from those that bought a test-fit straight pipe. A straight pipe is not a Catalytic converter so whatever gas goes into the pipe will come out the tail end. These are illegal in all states, and are ticketable. I also bought the dorman replacement and have read good reviews of that from amazon.

I will install mine this weekend, and post on my results on Monday. Good luck with your car, and if you see this update post back and let me know how it's running a few months later.

 

97 - Civic - d16y7 - 200k - cracked exhaust manifold = bad MPG. FIXED , thank god ! Now I get 42mpg average. I got a cheapo Chinese header and full EK exhaust with the header off eBay for $185 with a test pipe. That didn't do it. I got the Magnaflow 22628 cat for $92 and a new distributor for $72 and now most always get right over 40 mpg using Regular unleaded. Alcohol gas is junk and will not give us good mpg. Try the Denso Iridium spark plugs.

 

Any updates on the Dorman manifold / catalytic converter?

I am considering buying one and wanted to see if you are still happy with it.