Hello, hoping someone has some insight and can point me in the right direction here.

Have a 2000 Civic with just over 300,000 on it. Just replaced the head gasket and had the check engine light come on after. I assumed/hoped the computer just needed a reset. I removed the battery cable for 15 minutes and cleared the code. It was good for about an hour/60 miles then the light came back on. Read the code and it came up as P0420 (replace catalytic converter).

Is this just a coincidence that this happened immediately after the head gasket change or is it related? Is this even actually the cat that's the problem, or possibly something else throwing this code up?

Other note: Something tells me this is factoring in, but I'm not experienced enough to understand how: It's now starting differently as well. It used to start up instantly, now there's a slight hesitation and takes a little longer to crank. With a slight high pitched metallic sounding whine to it (if that makes sense?) while cranking. It seems to be getting plenty of spark so I'm lead to believe something else is causing this.



Thanks for any help,

 

Update

After further driving Civic is still getting hot. Cause seems to be coolant loss as after another 100 miles and waiting for things to cool down a bit I added about a half gallon of distilled water into the system. At least some of the loss seems to be from the cap of the overflow reservoir which doesn't seem to be airtight even by design.

Checking hoses: top hose to rad is hot. But return hose to block is significantly cooler. Maybe only from ambient heat from the engine after going for a 100 miles.

Tried throwing a cat converter cleaner treatment in the gas tank. Ran it for about 60 miles then reset the computer. Check engine light (assuming p0420 again) came on again though after about 20 miles.

Is there the possibility that a failing cat was the cause of problems from the start? That the increased back pressure from exhaust caused overpressure and eventually caused the head gasket leak as well?

Any help appreciated,

 

In a round about way... yes. The clogged/reduced flow cat causes increased engine temperatures... which causes a blown head gasket. You will continue to overheat and ultimately lift the head and blow head gaskets as long as you have a cat problem. If you are pushing water out of the top of your overflow bottle, you are generating excessive coolant system pressures, which overpowers the radiator cap as well. Once the engine is cold, remove the cap. This will relieve any excess cooling system pressure... top off any missing fluid and then re-install the cap. Feel the upper radiator hose. It should be soft and you can feel fluid inside moving as you squeeze it. Now, crank the engine. Wait about fifteen seconds and then squeeze the upper radiator hose. If it feels stiff... like under excessive pressure... you have a blown head gasket again.

 

Okay next question: which type of cat converter do I have? I seem to find two very different looking parts when I look them up. One inline running to the tale pipe, and one that connects directly to the exhaust manifold.

 

cat on manifold.

 

Thanks again.

Any recommendations on a good cat? My definition of good: cheap & works. My definition of works: let's the engine do what an engine should do. I have no emissions standards that I will need to pass and have no intention of ever selling this car.

 

if you have NO emission testing to register the car, I would never do this, not in a million years because I love the environment and want clean air. But since I wouldnt do it, that doesnt mean you cant. Take off the cat and bash it with a pipe, gut that thing like a fish. I would NEVER do that. And see how the car runs

 

Bro I need help on this code also, did a head job (no diddy….) I changed the cat twice now and I’m still getting that damn code

 

I've had a similar situation with the exact engine in the picture. The cats been known to get clogged. In my case the root cause was bad valve seals.
-You can gut the cat without removing it, by removing the shrouds, and disconnecting the downpipe under the oil pan. Use a small pry bar or chisel and chunk it out bit by bit. It will get messy so wear a mask and goggles. Can be done with the O2 sensor still in but BE CAREFUL. Ensure the rest of the exhaust is free.
-Did you ensure the bleed valve on the thermostat was at the very top?
-Did you bleed the cooling system?
-Once you blow a head gasket you need to service the entire engine head (valve seals, check valve condition and seating), and check your injector spray pattern. As an aside when those engines overheat the water pump also suffers, and the timing cover warps.
-Check the coolant port on the intake manifold and those tiny hoses near your injectors. They may leak only when hot.
-As for the metallic noise, did you time the engine correctly? Did you mess with the distributor position? Did you check the water pump pulley for play? (They have friction type bushings so severe overheat will damage them)
-Double check the pcv as well, because they're only suppoed to handle pressure from one side.
-Change your radiator cap (eapecially if the relief valve is jingling) and ensure the pressure is correct (1.1 kg/cm3 or 108 kpa)
Not sure if that all helps but good luck to ya!