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Your truck needs to be driven, not idled. Proper operating temp helps to ensure all is functioning as designed. W/ a 2.5 I4, you'll at least only have one primary cat to replace if it is indeed bad.
 

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Everyone else has the answer. How about an option- 3 miles one way, after the truck is fixed, leave the truck at home and ride a bicycle to work, you'll be there in 15-20 minutes. On an electric assist bike you'll be there in 10. That distance is walkable in 45 minutes or less. The truck stays healthy and you get healthier. Winner-winner!
 

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Discussion Starter #23
Update, went back to dealer told them I don't want diagnostic, just pull the damn cat, sure enough the primary cat spewed its guts into the secondary cat so both need replaced they said primary cat is covered but not secondary because previous owner for some reason moved O2 sensor port from back to front of cat?, my argument against this is it makes no difference where the damn O2 port is located the primary cat took out the secondary cat both should be covered under warranty, I will be going back Thursday for replacement. Not going to argue with dealer just going to make my case with Nissan, for the time being I'm out 1,000,00 bucks.
 

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Update, went back to dealer told them I don't want diagnostic, just pull the damn cat, sure enough the primary cat spewed its guts into the secondary cat so both need replaced they said primary cat is covered but not secondary because previous owner for some reason moved O2 sensor port from back to front of cat?, my argument against this is it makes no difference where the damn O2 port is located the primary cat took out the secondary cat both should be covered under warranty, I will be going back Thursday for replacement. Not going to argue with dealer just going to make my case with Nissan, for the time being I'm out 1,000,00 bucks.
Do you have the old parts? Maybe the secondary cat went out first, which prompted the prior owner to move the sensor.
I wonder what was run through the fuel system to ruin cats at 50K?
 

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Update, went back to dealer told them I don't want diagnostic, just pull the damn cat, sure enough the primary cat spewed its guts into the secondary cat so both need replaced they said primary cat is covered but not secondary because previous owner for some reason moved O2 sensor port from back to front of cat?, my argument against this is it makes no difference where the damn O2 port is located the primary cat took out the secondary cat both should be covered under warranty, I will be going back Thursday for replacement. Not going to argue with dealer just going to make my case with Nissan, for the time being I'm out 1,000,00 bucks.
the secondary cats that sensor is before it. Take a picture for us.
 

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Discussion Starter #26
I'm thinking I should verify engine serial # matches VIN # …. something is fishy here.
 

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If it's any consolation, at least you got the expensive cat replaced under warranty. Hopefully they put in a Nissan part, and not an aftermarket.
 

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Just noticed you have a 2.5 not a 4.0. but I think it still would be the same.
 

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Update, went back to dealer told them I don't want diagnostic, just pull the damn cat, sure enough the primary cat spewed its guts into the secondary cat so both need replaced they said primary cat is covered but not secondary because previous owner for some reason moved O2 sensor port from back to front of cat?, my argument against this is it makes no difference where the damn O2 port is located the primary cat took out the secondary cat both should be covered under warranty, I will be going back Thursday for replacement. Not going to argue with dealer just going to make my case with Nissan, for the time being I'm out 1,000,00 bucks.
First off, they wasted your time with the idle relearn step. There are two O2 sensors, upstream of the cat and downstream. They work in tandem to see if the cat is working. I can't imagine moving a sensor port and expecting it to work properly. The secondary cat is unmonitored, meaning the O2 sensors play no role in its function. If anything, you should have been denied warranty on the primary cat. Does not make sense.
 

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Discussion Starter #32
Update, just picked up my truck she is running like new! after two new cats. The attached photos show the mods to secondary cat.
cat1.jpg
 

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Idling can help with warmup but, make sure your taking longer drives from time to time and don’t be afraid to accelerate once you’re warmed up. Glad you got it fixed!
 

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So now, once every 2 weeks (2 weeks) you take her out on a Saturday morning with a fresh cup of coffee in the console and you drive her 50 miles...Take the wife with you, pick a new restaurant and go get breakfast. This will get the truck to op temps. At least once stomp the gas pedal and run her from 1rst gear to overdrive with about 4k shifts....

They need to be run to live long occasionally !!

(had the same problem till recently...Now I work from home...We go on 2.5 mile beer runs and I always manual shift her to operating temp. A can of seafoam a month is also in my rotation.)
 

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So now, once every 2 weeks (2 weeks) you take her out on a Saturday morning with a fresh cup of coffee in the console and you drive her 50 miles...Take the wife with you, pick a new restaurant and go get breakfast. This will get the truck to op temps. At least once stomp the gas pedal and run her from 1rst gear to overdrive with about 4k shifts....

They need to be run to live long occasionally !!

(had the same problem till recently...Now I work from home...We go on 2.5 mile beer runs and I always manual shift her to operating temp. A can of seafoam a month is also in my rotation.)
+1 on this

Gas engines have a maximum thermal efficiency of 20-35% in most cases. A carbureted engine leaning towards 20% and something like a Direct injected Mazda Skyactiv engine learning towards 35%. Our trucks with port fuel injection are somewhere in between. Thermal efficiency just means of the energy supplied to the engine (gasoline) how much of that energy is making its way out the crankshaft as mechanical energy. In all gas engines the majority of the energy from the fuel is lost as waste heat (out the exhaust and through the cylinder walls, into the cooling system, than out to the environment) some of the fuel is just not burned, mostly because it condensed back to liquid before ignition.

So when are our engines at their most thermally efficient? When they are warmed up and at the point which they are producing peak torque, which for the 4.0L V6 is 4000RPM.

So what happens when I take short trips and never get above 2000RPM? The fuel sprayed into the intake ports by your fuel injectors is condensing back into a liquid before ignition... fuel ignites as a vapor not a liquid. This results in your engine dumping a much larger percentage of your fuel unburned, out the exhaust. Also you are losing efficiency in another way as well... Your engine is a big air pump, at low throttle your engine only has a small slit to breathe through and has to work harder just to rotate itself against the restriction.
 

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Sorry, just a little clarification on the last post.... do not confuse thermal efficiency with fuel efficiency. You are consuming less fuel at a low rpm vs a higher rpm. Your engine is just burning a higher percentage of the fuel at the higher rpm.

this relates more to why things go wrong when we don’t run the engine through its power band. The byproducts of incomplete combustion are unburned fuel that ruins catalytic converters and can get into the oil. Incomplete combustion also produces harmful emissions and carbon. The carbon fouls plugs which leads to even less fuel being burned because of weakened ignition. Carbon gets into the oil and cylinder head and can cause sludge. This is why it’s a good idea to get up to temperature and to use your power band. (Not advertising you should go full send off of every green light)
 

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Update, just picked up my truck she is running like new! after two new cats. The attached photos show the mods to secondary cat.
Glad you got it sorted out! I'd go with the suggestions to take 'er to the freeway once a week or so and stomp on the "go" pedal to get those cylinder head and exhaust temps up.

When I go on "positioning" drives, I take the cars on a 20-mile round-trip that has a steep uphill on-ramp as the turn-around point. The on-ramp is a good 1/4 mile long and probably an 8-10% incline.
 

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Update, just picked up my truck she is running like new! after two new cats. The attached photos show the mods to secondary cat. View attachment 319024
Thanks for the pictures. But the mystery in my mind still exists. Why would anyone move an O2 sensor port? If it were for emissions, it would have been covered under warranty so there is a record somewhere with a dealer. In which case your secondary cat cost should have been covered by warranty. Alternatively, the previous owner may have move the port for performance reasons. This does not make sense.
 

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With the thermal efficience talk, maybe short commute, city street drivers would want to consider keeping the transmission from reaching the highest gears. Take the auto trans. truck out of overdrive. City streets limited to 2nd or 3rd for manuals. Let those revs rev a bit higher to generate some heat.

For my job, the company has me in a 2019 Chev Equinox (hate it for several reasons). That car does everything it can to get to 6th gear before 30mph, then it just chudders down the road, vibrating the whole time as it lugs along on city streets. I'll routinely downshift it to 4th or 5th, depending on the speed limit, to let the engine spin and smooth out the ride.
 
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