P0420 P0430 codes and car won't start

[pyroguy]

So I finished a 4th of July parade, shut the car down and it wouldn't start again. I had a friend run a code checker to see if I had any codes and P0420 and P0430 came up. They're catalytic converter related so I pulled a cat and it looks great. Has anyone experienced anything like this in the past, what was wrong, and how did you fix it?

[zz430camaro]

Check the basics, fuel, spark

[pyroguy]

Fuel pressure at 62 during cranking, plugs appear to still have spark and don't look bad.

[christianchevell]

I would be checking to see if anything melted down by headers on the O2 harnesses...

[pyroguy]

Originally Posted by christianchevell

I would be checking to see if anything melted down by headers on the O2 harnesses...

That's my next step, to see if my O2 extenders melted, but they're hard to get at right now.

[PepeLePew]

This could be an issue with having the downstream O2 sensors still enabled while running long tube headers. My tuner says he turns off the rear O2 sensors when he tunes a car with long tubes regardless of whether it has cats because the heat source is too far away from the sensors and will eventually cause the CEL to come on.

[Reichler]

Originally Posted by PepeLePew

This could be an issue with having the downstream O2 sensors still enabled while running long tube headers. My tuner says he turns off the rear O2 sensors when he tunes a car with long tubes regardless of whether it has cats because the heat source is too far away from the sensors and will eventually cause the CEL to come on.

Rear 02’s have nothing to do with how the car runs as they have no input to the ECU. His issue is something else if it won’t start.

[PepeLePew]

Originally Posted by Reichler

Rear 02’s have nothing to do with how the car runs as they have no input to the ECU. His issue is something else if it won’t start.

Great point, you are right that rear O2s going bad won't affect the car being able to start. I missed that in my initial read.

Pyro - I am curious if you have any other trouble codes popping up. Also, what happens when you try to start it? Does it crank at all? Or does it fire up and stall out? Or just nothing?

I had a stupid thing happen when I installed my headers and cam earlier this year and forgot to tie back the main harness on the passenger side. It drove fine for 500 miles until I took on a long drive and had a bunch of codes pop up. When I got under the hood, I noticed that my harness was barely touching the number 8 header tube and when I unwrapped it, I had burned through about 14 wires. 23 splices later and some new heat wrap and all was better.

[CamaroFred]

Originally Posted by Reichler

Rear 02’s have nothing to do with how the car runs as they have no input to the ECU. His issue is something else if it won’t start.

Of course they are read by the ECU, why else would they be installed and wired? They can be read through the OBDII port.
They aren't used to adjust anything though, you are right about that. They are there to monitor the efficiency of the converters.

None of the O2 sensors should prevent the car from running though.
I don't think you are chasing the real problem.
Maybe someone stuffed potatoes into your exhaust.

Have you tried to start it without the cat(s) installed?

[pyroguy]

Originally Posted by PepeLePew

Great point, you are right that rear O2s going bad won't affect the car being able to start. I missed that in my initial read.

Pyro - I am curious if you have any other trouble codes popping up. Also, what happens when you try to start it? Does it crank at all? Or does it fire up and stall out? Or just nothing?

I had a stupid thing happen when I installed my headers and cam earlier this year and forgot to tie back the main harness on the passenger side. It drove fine for 500 miles until I took on a long drive and had a bunch of codes pop up. When I got under the hood, I noticed that my harness was barely touching the number 8 header tube and when I unwrapped it, I had burned through about 14 wires. 23 splices later and some new heat wrap and all was better.

It tries to start and won’t. It “started” once and stayed at about 250 rpms but wasn’t doing what it should obviously. It popped a couple times, but never really did much.

As for the wires, I wasn’t the one who did the cam swap. A reputable shop in my area did the cam swap and that’s where I’m going to take the car this weekend.

Originally Posted by CamaroFred

Of course they are read by the ECU, why else would they be installed and wired? They can be read through the OBDII port.
They aren't used to adjust anything though, you are right about that. They are there to monitor the efficiency of the converters.

None of the O2 sensors should prevent the car from running though.
I don't think you are chasing the real problem.
Maybe someone stuffed potatoes into your exhaust.

Have you tried to start it without the cat(s) installed?

I haven’t tried to start the car without the cats, but I did pull one of them and it looks as nice as the day I installed them with the headers.

[PepeLePew]

I am puzzled by the car not running. Kind of indicates melted cats. But you don't have the heat from boost that would suggest your cats would melt and clog up.

If you tried to start it without the cats and it ran, it would indicate that your cats melted. If I remember correctly, the Kooks HFCs have the full honeycomb internals making it hard to see through them. Melting can occur anywhere within the cat making them look fine from appearance but still be damaged.

It might be worth a shot to try to start it up without the cats on if you are brave enough. If there were something else causing it not to run (like a MAF sensor) you'd have other codes stored. If you don't want to risk damage and take it to the shop, that is certainly reasonable though.

[go_go_gadget88]

I would pop the cats off and see if it fires up. Easy way to tell if that's your culprit

[Reichler]

Originally Posted by CamaroFred

Of course they are read by the ECU, why else would they be installed and wired? They can be read through the OBDII port.
They aren't used to adjust anything though, you are right about that. They are there to monitor the efficiency of the converters.

That's why I used the word "input". The are read by the ECU, and that's it. Fueling and spark are not affected by what the downstream 02's read.


OP -
Are you able to get a hold of a code reader to see if there are any "pending" codes? I've always suggested to people who begin to mod their car to buy a good code reader that can monitor some data. It can be a lifesaver in pinpointing what's going on.

[pyroguy]

Originally Posted by Reichler

That's why I used the word "input". The are read by the ECU, and that's it. Fueling and spark are not affected by what the downstream 02's read.


OP -
Are you able to get a hold of a code reader to see if there are any "pending" codes? I've always suggested to people who begin to mod their car to buy a good code reader that can monitor some data. It can be a lifesaver in pinpointing what's going on.

I borrowed a code reader from a friend and the only codes that came up were about the two codes in the title. Now I can't imagine that I melted the cats based off of what I was doing. If so then Kooks cats are garbage, which I know they aren't, or the tuner who has tuned many of these cars with this cam has messed something up with his tune. Other than firing it up without the cats I don't know much else to do. The car is going to go back to the tuner this weekend.