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Discussion Starter #1
What could cause my catalytic converter to overheat after a block or 2? It's not clogged, I'm told by a muffler man (there's plenty of exhaust air pressure coming out of the tail pipe). It vapor locks, too and won't start back up til it cools off- 30-40 minutes. The distributor cap's ok; new dist. rotor; new plugs; plug wires look fine; new fuel filter and gas cap. And it passed inspection yesterday! (And then left me stranded!) If the list of possibilities is too long, what kind of situation might be the prob? Not enough oxygen mixture?...If the original timing was off, could it cause this kind of thing?
 

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Biru O' Kudasai
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The cat (or the muffler) is clogged, although it is not completely blocked but allowing a bit of flow and causes the heat to build all the way back up into the engine from the excess back pressure thus the "vapor lock" condition. If the muffler shop would pull the O2 sensor and install the back pressure gauge this would confirm the condition.

Troy
 

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Discussion Starter #3
So how do I find out what's causing it to clog? And does this mean I'll have to replace to cat.? (As far as you can tell)
Thanks for responding, too.
 

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Biru O' Kudasai
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I think it does mean you will need to replace it. Sometimes the additives in fuel can cause the honeycomb to sulfate up or rust scale can restrict the flow. But first I would try pulling the muffler off to inspect that and eliminate that if it is part of the problem.

Troy
 

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Consider also the gas mix being out of whack. The catalytic converter evidently is working "overtime" so, if it isn't clogged, the fuel/air mixture might be wrong. A quick start to for this kind of trouble is looking at the spark plugs. If they're fouled or wet or showing any other anormality that could be a sign of where the problem might be.
 

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KA24DET
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Definitely clogging of the ceramic honeycombing in the catalytic converter. Your car just passed an inspection, so I would just remedy this by punching holes in the catalytic converter with a long chisel (I used a screwdriver) and a hammer. In fact, I just hollowed out the entire cat.
 

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Discussion Starter #8
Won't that make it really loud and/or smoke? (Just punch the hole straight thru the bottom, or what?)
 

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I'm sure the guy would've done something to fix the problem sometime in the last 5 years.
 

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But...but...but...but...
Alrighty then.
 

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Im having the same problem with my 99 Frontier 3.3 liter V6
Just had both cats and both exhaust manifolds replaced. and within two weeks it started acting up again. Both cats were red hot and lost all power. barely made it home

Got a OBD reader to check for faults and i have a knock sensor fault.
No check engine light is on. Any ideas???
 

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NF Mod/Nissan Master Tech
2006 Pathfinder LE, 2003 Frontier SVE
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The knock sensor is likely the result of the problem, not the cause. It could be dumping fuel, so I would check the fuel pressure. Sometimes on the VG engines, the vacuum hose to the fuel pressure regulator, which is on the back side of the engine, splits and falls off, which cause the fuel pressure to be run at full pump pressure, creating a rich condition. In the future, you're best to post your problem in the Frontier section, rather than tag onto a six year old thread in the Altima/Stanza section.
 
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