civic7th

Hi there… I could really use some help. My 2003 Civic EX broke down and long story short, I found the issue was the 12V power wire of an ignition coil was shorting to ground (sensor ground to be specific). So I fix that, replaced the ignition coil fuse and the car started right up. I was really happy to have my car fixed! Well… happiness quickly went away when I took it for a drive. Upon acceleration the car would severely hesitate and misfire and sounds like exhaust was coming from the front of the car. Check engine light came on and I got misfire codes for all 4 cylinders (P0300, P03001, P03002, P03003, P03004). There are no other error codes being generated. Troubleshooting things I’ve tried:

- With the car idling, I lifted each ignition coil one by one to see if any one coil didn’t have an effect on idling. They all did.
- I tried disconnecting the EGR valve to see if the car drove better. It didn’t. Disconnecting the EGR wiring harness had no effect at all.
- I tried disconnecting O2 sensor wire, but this had no effect on the car either (but did through the 02 sensor code).
- I tried disconnecting the cam shaft sensor (not crank shaft sensor) and this did make the idle a little worse. But had no effect on the misfire.
- I tried disconnecting the crank shaft sensor and this didn’t make a difference. Wonder if this is the problem.

So here’s the interesting thing. There is exhaust coming from the spring loaded exhaust joint the connects exhaust manifold to the catalytic converter pipe. So I’m wondering if the catalytic converter went bad when I broke down and the back pressure is causing the misfire. Is there a way to test the catalytic converter without buying a new one? I live in California and they are pretty expensive to replace.

Any other ideas or thoughts? Any guidance will really be appreciated. thanks.

Also, I should mention that the car starts and idles perfectly. It’s only a problem when I rev up the engine or accelerate.

ezone

Disconnect it so the exhaust is just an open pipe from the engine. If it runs ok again then the cat is bad....BUT that might not be the only issue:

You could smack the pipes behind the cat with your palm and see if they jingle/rattle like there's loose stuff in the pipes and resonator and muffler. (IF the cat broke apart the broken chunks can travel through the pipes to clog up wherever they lodge downstream.)

Wankenstein

Try the same drop (ilde) test by removing fuel injector harness one at a time.
Check mechanical timing..maybe the timing belt jumped a tooth/teeth. How many miles on the timing belt?
Try resetting ECU..will clear codes but may not help with hesitation issue. Sometimes by doing so only one (or possibly none) of the p030x codes will return which can help narrow down the issue.

civic7th

Thanks for the replies. I disconnected the gasket/flange that’s between the exhaust manifold and the catalytic converter. It worked! No misfires and the car accelerated normally. It of course, was super loud.

So now I’m debating if I should buy a bolt on Walker catalytic converter (on amazon for 350) or just have the local muffler shop weld one on. The OEM one is 650, which is a bit much for a car that has 230k miles on it.

Thanks so much.

Wankenstein

Does a 7th gen EX have a cat-back exhaust similar to a 6th gen? In OP's situation is the primary or secondary sensor readings causing the misfire codes?

NDNV

I would look at a possible cracked exhaust manifold which is common among these engines apparently.


Why no P0420 code if cat is bad? I wouldn't rush out to buy a cat before doing some more troubleshooting just yet.

ezone

First you (or the exhaust shop) need to check the rear of the cat to see if it broke apart and sent chunks of substrate downstream into the pipes and muffler.
If you replace the bad cat but don't remove the clog downstream.....that's like replacing a kitchen sink because it's backed up but not removing the clog in the pipe below.


Also...if you are in California, you MUST use a C.A.R.B. approved cat. It's a higher quality cat with a better warranty as well.

Make sure the problem that caused the cat to fail is truly fixed. Even a brand new cat can be ruined in just a minute if the engine runs bad enough.

No code does not mean no problems.

It must have no other conflicting fault codes AND it has to be driven through multiple drive cycles before the PCM can judge the catalyst efficiency as good or bad.

If the car can't be driven long enough to complete a couple good drive cycles or has certain other fault codes, the cat monitor will not run---therefore no code.


HTH

civic7th

Hi everyone, just wanted to give everyone an update and conclusion. Hopefully this will help someone out in the future. So I decided to order an Walter CARB catalytic converter from Amazon (it was only $347 and gotta love the free 2 day shipping). When I pulled off the old catalytic converter I found it was completely destroyed. Chunks of the honeycomb and a lot of fine powder came out of the front of the pipe. But lucky no chunks came out of the back part of the pipe (side that goes to the exhaust). So it appears only the front of the cat got damaged from a misfire that occurred when my ignition wire shorted out. Also, when I removed the 02 sensor from the cat I could see chunks of broken honeycomb – cat was definitely toast. Car is running perfectly now that I have the new cat in. Thanks for all the comments on this forum – it really helped.

I was also wondering why there was no cat error code, but I’m guessing ezone was correct that I couldn’t drive the car long enough for the bad cat to be detected.

So that’s it. Thanks again.