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'99 Chevy P/U K1500 5.7 OBS 73K miles

 

The other day my truck started running like it was on four cylinders and the check engine light started flashing. I managed to make it home (2 miles at about 50mph with one stop sign). The PCM indicated a random misfire code as well as misfire codes for cylinders #2 and #8. Turns out the distributor cap had a crack in it. Cap, rotor and plug wires were replaced 12 months ago. I put on a new cap and rotor, cleared the codes, and life was good. For about a week.

 

I am now getting a P0430 code, which indicates catalyst system efficiency below threshold, right bank. The truck seems to run fine, and when I reset the code, it comes back 3-4 days later when the engine is hot. The first P0430 code didn't appear until about a week after I replaced the distributor cap.

 

I've been told that a misfire can clog the catalytic converters. Do you think the bad cap issue I had fried the right side cat? It would make sense since both misfiring cylinders (#2 and #8) are on the right side and that is the side now throwing the P0430 code.

 

If I have to replace the one cat, should I replace both? Should I include new O2 sensors?

 

:thumbs:

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it is a possiblity, but most likely it is just the o2 sensor, since raw fuel was being dumped into the exhuast system it got into the cat the cat burned the fuel cuase excessive heat which would damage the o2 sensor. i would first look at the cat and see if you can see any heat disscoloration if not replace the o2 see if so then replace both.

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No aftermarket cats, but there are definitely two of them (OEM), with two upstream O2 sensors, and two downstream O2 sensors.

 

Replacing the O2 sensors one at a time might help narrow down the problem. It's hard to say what is going on by using the scanner. The voltages seem to keep changing on all of them, and the readings all seem to be fairly similar. At anywhere from $60-$100 per sensor I'd rather see if I can find a way to pinpoint the offending part.

 

I don't see any discoloration on any of the exhaust parts.

 

I've read in some other posts that the P0420/P0430 is more likely a cat than an O2 sensor due to the lack of a P0131-P0151 code. A bad O2 sensor will activate both codes (although not always). A bad cat will activate one code (although not always). Does this sound familiar to anyone? It makes sense to me but I'm obviously no expert.

 

Thanks for the responses. Every piece of info. helps narrow it down.

 

:thumbs:

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it is a cat converter problem for sure. take it from me ase master tech, toyota master diagnostic tech. also if you live in CA it might still be under emisions waranty, a bad o2 sensor would set a code for itself. the miss fire you had caused to much fuel to enter the cat and it got to hot .melt down!

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Thanks for the responses.

 

My warranty book says 8/80K for Federal emissions and 7/70K for California emissions. Lucky for me, my truck has California emissions and 73K miles. If it weren't for bad luck, I wouldn't have any at all.

 

I found an exact replacement part at discountconverter.com. It has both converters and both pipes from the manifolds to the muffler for $425 shipped. It's a one piece, bolt-in replacement. Does anyone have any experience with this seller and its parts? It sounds like a good deal. The one cat on my Suburban cost $400.

 

:thumbs:

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Do you have aftermarket cats on your truck?  If not, there is only 1 cat.  Check the O2 sensor first.

 

 

 

 

 

Most (If not all) of the '96 to '99 Old-Body-Style trucks with the 5.7-350 and 7.4-454 had dual cats.

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My warranty book says 8/80K for Federal emission

 

cool, so you dont have to pay for the cat out of pocket. Yaaaay :thumbs:

 

 

 

 

 

Yeah, but it has California emissions which has a 7/70K warranty. In the warranty book where it lists the covered components it shows the catalytic converter with a single asterisk, followed by a double asterisk. The single denotes the California warranty, and the double denotes the Federal warranty. Which leads me to conclude if the vehicle has California emissions the cat is covered by the 7/70K warranty.

 

I'll stop by the stealership today and double check just to be sure. It would be nice if they would cover it.

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Thanks for the responses.

 

My warranty book says 8/80K for Federal emissions and 7/70K for California emissions.  Lucky for me, my truck has California emissions and 73K miles.  If it weren't for bad luck, I wouldn't have any at all.

 

I found an exact replacement part at discountconverter.com.  It has both converters and both pipes from the manifolds to the muffler for $425 shipped.  It's a one piece, bolt-in replacement.  Does anyone have any experience with this seller and its parts?  It sounds like a good deal.  The one cat on my Suburban cost $400.

 

:thumbs:

 

 

 

 

 

this should help you. federal emissions over rules california so you are still covered for the cat. plus when you take it in "do not" tell them about the cap and rotor problem or they will denie your claim since it was cuased by somthing else.

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Thanks for the tip on the exhaust leak. I'll definitely double check to make sure. But, since it was so close to the misfire issue I had it makes sense that the two problems are related. I haven't heard or seen anything that would make me think there is an exhaust leak.

 

I stopped by the stealership today and they confirmed that the catalytic converter is covered under the 8/80 warranty, which means my luck is better than I thought. Once I rule out the exhaust leak I'll wait for the code to appear again then take it in to have them look at it.

 

On the bright side, the cat is probably the most expensive thing it could be and it's probably the only thing that's covered under warranty.

 

:thumbs:

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