99 Civic EX PO420 and PO303 301 300 304 codes
 

hey my 99 Honda Civic EX is throwing these codes and we think it's a clogged catalytic converter it bogs when I try to press the gas it don't get no power it goes slow up hills is there any way somebody could help me trouble shoot fix this maybe an oxygen sensor or change the catalytic converter I'm pretty good with cars and directions any help would be much appreciated.also a mechanic said it might be the ignition coil but I'm not for sure I bought a new one I know how to change it.I had to change the radiator because there was a leak on the very top seam so I did that and bled the system. New plugs

does yours have dual cats or just the single mid cat? if you have just the single mid cat you can just remove it to check it. will be visibly clogged or you could do a short very loud test in the street to see if its driving normally again.

Just the single cat. It won't rev past 4000rpms and I have to press gas pedal all the way down to get up to speed 60 80 mph. But the cat flanges are really rusted . Is cataclean really worth buying for cat clogged?

wont rev past 4k do you have any other codes besides the ones you posted? not reving past 4k could be a result of p0420 or another problem. they do have sort of a limp mode with these cars. i know if it sees a critical vtech fault it wont let you go above 4k until the codes are cleared. and no magic fluids wont help your cat. your only options for a clogged cats is removal or replacement. ebay 99 civic test pipe will get you a delete pipe for as cheap as 30 bucks. the cheap 50 dollar ebay headers work well enough but the rear o2 sensor will have to be moved up front. most of the cheap header rear o2 sensor placement is wrong so the wires will have to be extend and placed on the optional cylinder one header port. removing the cat entirely will give you a check engine light but the car will run fine but the exhaust might smell different. rusty flanges in that area are pretty common.

also if the test pipe fixes the problem you can buy a universal cat and cut the flanges off the test pipe and have them welded to the universal cat instead of spending 150 for a stock oem cat. saves a couple bucks.

well I have cash that I've been saving and I want to get this Civic backup to par. then I thought about putting maybe a turbo kid on it or something like that you know I want to add horsepower to it once I get the engine problems solved.I do see a lot of exhaust manifold and catalytic converter and exhaust kits on eBay and Auto part websites are they actually worth buying the cheaper parts from like rock auto places like that.I can put the exhaust manifold to catalytic converter the O2 sensors all everything that you discussed in the previous reply I can do I just need a little bit of guidance but no it's not throwing any other codes besides the PO420 all the random misfires in the cylinders and the 1399 misfire code. if you had the money would you just buy the new exhaust manifold header the muffler the kid the catalytic converter the pipes all or what would you do

ill tell you what i did and where it got me on my d16y8 and what information ive come up with. the d16 without serious engine work will constantly be a dog off the line. a turbo setup will definitely give you a boost in the higher rpms tho. an engine swap can be done in roughly the same cost range as a turbo kit if you keep your budget in mind. ebay turbo kits are generally junk and best used as a short interim stepping stone but most of the kit is junk and a waste of money if you can jump straight to a real kit but either way its expensive. your looking at 3k range for a base starter kit thats actually worth it including upgrading the fuel and a tune. my 00 ex the exhaust was shot so at first to keep it on the road i bought one of those ebay headers and bolted it to the stock exhaust. i noticed a slight increase. i wanted a nice exhaust system anyway so i saved some cash and bought the skunk2 alpha headers and bought a tanabe medallion cat back. my state requires at minimum a visual so i wanted to keep a cat in the exhaust. there's isnt a bolt in performance cat that matches the diameter of the sk2 headers and the cat back so i bought a universal magnaflow cat and a cheap invidia test pipe and used the test pipe to make my own catted mid pipe. i did notice a slight further increase but honestly the good brand parts are expensive for only a slight increase. but honestly its my dd and the downtime for a turbo install just isn't worth it. ive decided to spend my time on my motorcycle anyway so im probably selling my civic.

My man do u think I had dual cats or just the single mid on my 99 Honda ex automatic were talking about? Is the a way to determine?

I definitely think it's a clogged catalytic converter though my man I'm going to send you some pictures of the actual exhaust system it only has the one single mid-cat on it but it could have very well maybe had the dual cats I'm not for sure that's what I need to know I'm going to try to figure that out maybe you could help me

single cat is just the mid pipe cat. dual cat there will be a cat before the mid pipe cat thats actually part of the exhaust manifold/header. if you pop your hood and look straight down if you just see pipes and maybe a heat shield then its single cat. if you see a canister right under the 4 pipes you have dual cats.