I used seafoam in my intake manifold and afterwards the check engine light came on. I got rid of the light by disconnecting the battery but I think that a lot of the smoke and bad elements got into my cat converter. It also seems like my car is getting noticeabley worse gas mileage. Is my sensor bad or my cat. converter? They have never been changed on my car befor and it's got 111,000 miles on it. Also my magnaflow exhaust is noticeably louder after i used seafoam( I think it's kind of cool but the gas mileage isn't).

 

Run another half canof that seafoam through there, and the other half in the fuel. Pull the plugs to see how they are burning.

 

shouldI havea full tank of gas when I add the seafoam to it? or does that not matter

 

One can treats 8-25 gallons, I am pretty sure most civic tanks hold what, about 9-10 gal. I put 7.5 filled mine up, and added about half a can. and ran the other half through my vacume hoses. I pulled my sensor prior to the job though, it might just be the sensor head, got some funk on it and now it's not reading right, not sure.

I can't see why it would be the cat, they usualy don't just go bad like that.

 

I had the same experience, I didn't notice the mileage difference but my CEL came on also after running seafoam. I'm really curious as to what CEL code was stored on yours. Mine was code 67 (catalytic). When I put the seafoam thru the fuel pressure regulator's vacuum hose, I saw smoke coming from under the engine in the vicinity of the catalytic. The code is recurring, after reseting. I'm guessing the seafoam burned right thru a weak spot in the catalytic and now the oxygen levels are way off due to the leak. I've resigned myself to replacing the cat this spring, but this maybe a warning to other high milage folks considering using seafoam. It may cost you a catalytic (not cheap).

A brief consideration, There are EPA mandated warranties on catalytics not sure what year you have, but check it out, it may still be under warranty. Im thinking its something like 10 years.

****sorry for no pm reply, i accidentally deleted it.****

 

I kind of want to get one of those magnaflow cat. converter's anyway. I know it's not much of a hp increase but the one on there now is pretty old and rusted with the heat shield ripped off.

Also I added a little more to the intake manifold figured it couldn't hurt any more. Also my car is due for an oil change that I'm going to do myself. Should I add some seafoam befor I change it, run it a couple hundred miles first. Or do it when I get new oil and a new oil filter put in?

 

If I pulled the sensor out and wiped it off do you think that would help? Just the one around the converter right?

 

Beware if you use the maganflow, or any hi-flow cat, you may not pass emissions.

There should be two o2 sensors, one before and one after the catalytic.

 

Is it possible to poke a hole thru the middle of the cat to restore airflow?