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Discussion Starter #1
I’ve been having idle/power under throttle issues with my 04 Murano. Replaced several things relating to a P0300 CEL and issue still continues. The CEL does shut off at times but recently starts blinking when attempting to drive the car, while having an odd loss of power under the gas pedal (yes, I know blinking CEL means a bad misfire).

Would extremely hot exhaust tips conclude a clogged catalytic converter? I’m basically trying to figure out/test if the cat is the definite issue, without really spending any more money on this thing. Any ideas on testing/concluding a bad cat? If so, what would be my best option to go about a car that is worth next to nothing.



Please note: this is NOT my daily driver and has been basically parked for months now, has a ton of miles (263K), but has been re-registered recently... so getting a few additional miles out of her for the next year would be great.
 

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Loosen the bolts remove it and then give it a firm shake. If it rattles a lot inside its done.

Your misfire can be due to a cracked exhaust manifold which is known to happen to these engines.
 

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I’ve been having idle/power under throttle issues with my 04 Murano. Replaced several things relating to a P0300 CEL and issue still continues. The CEL does shut off at times but recently starts blinking when attempting to drive the car, while having an odd loss of power under the gas pedal (yes, I know blinking CEL means a bad misfire).

Would extremely hot exhaust tips conclude a clogged catalytic converter? I’m basically trying to figure out/test if the cat is the definite issue, without really spending any more money on this thing. Any ideas on testing/concluding a bad cat? If so, what would be my best option to go about a car that is worth next to nothing.

Please note: this is NOT my daily driver and has been basically parked for months now, has a ton of miles (263K), but has been re-registered recently... so getting a few additional miles out of her for the next year would be great.
Which cylinders are misfiring? How many miles have you driven the car with the MIL flashing?
 

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Discussion Starter #4 (Edited)
Which cylinders are misfiring? How many miles have you driven the car with the MIL flashing?
It’s a P0300 - so that’s a random misfire. Spark plugs and coil packs have all been replaced, same with the fuel pump. I drove in it only a few miles. At times it runs fine and other times it starts flashing.. although no other noticeable issues are happening with the car other than the same lack of power I explained (doesnt sputter like if it had a bad spark plug or anything).

Cam/crank sensors have also been replaced but ran worse than on the stock sensors, so I put the stock sensors back in.
 

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Discussion Starter #5 (Edited)
Loosen the bolts remove it and then give it a firm shake. If it rattles a lot inside its done.

Your misfire can be due to a cracked exhaust manifold which is known to happen to these engines.
I can try but that may be an issue. I brought this car from Chicago, so the nuts and bolts are so rusted underneath, everything looks like one piece. I may try to get under there and start removing them but I’m fairly positive that something will snap. Also, which cat should I look into? I assume it’s not the one right underneath the car but either the front or rear exhaust section running near the firewall?

If I did get it apart, I’d probably gut the damn thing at this point. Not sure how much work goes into taking it apart on your own within a garage... any ideas(?)
 

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You can first leak test your exhaust manifold using a shop vac or leaf blower. Look at youtube. But you need to remove the heat shields on both front and rear exhaust manifold. Then spray soapy water on the manifold and see if it bubbles. However, sometimes the crack only shows up when its really hot. Still, testing this way will at least tell you if there are obvious leak already.

There is not really that much to remove from below. You will need an electric impact wrench to make things easier. HF 40 bucks works great. And deep wall sockets and extensions. Heat shields, the o2 sensors connections and you need a floor jack to catch the exhaust pipe. Get the service manual and see if its doable for you.
 

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It’s a P0300 - so that’s a random misfire. Spark plugs and coil packs have all been replaced, same with the fuel pump. I drove in it only a few miles. At times it runs fine and other times it starts flashing.. although no other noticeable issues are happening with the car other than the same lack of power I explained (doesnt sputter like if it had a bad spark plug or anything).

Cam/crank sensors have also been replaced but ran worse than on the stock sensors, so I put the stock sensors back in.
The title of the DTC may be a random misfire, but you can be sure that the ECM is logging which cylinders are misfiring. Check the misfire monitors with your scan tool. If they're all on one bank then that's a clue. Have you checked for a bad vacuum leak (a common cause of random misfires)? How do your fuel trims look on live data?

To answer your question specifically, the least-invasive way to check for a clogged cat or exhaust obstruction is to check engine vacuum. All you need is a vacuum gauge to hook up to one of the hoses coming off the intake manifold.
 

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Discussion Starter #8
Quick question... I took the nuts off the exhaust at the 3rd cat underneath the car but I am having a hard time separating the pipes. Do the studs after that cat stay in place and the pipe slides off?... or do the studs need to come out as well?

Not sure if they’re welded in ‘studs’ or just ‘bolts’ that go through the holes?



Believe it or not, all of the nuts are coming off very easily with some PB.
 

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You also need to disconnect the Y pipe from both CATs before you can disconnect it at the back end.
 

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Discussion Starter #11
You also need to disconnect the Y pipe from both CATs before you can disconnect it at the back end.
Y-pipe has been disconnected. Everything was going smoothly except one of the upper bolts on the front cat stripped and now I’m kinda out of luck. Not sure if I should keep going at this point.
 

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Quick question... I took the nuts off the exhaust at the 3rd cat underneath the car but I am having a hard time separating the pipes. Do the studs after that cat stay in place and the pipe slides off?... or do the studs need to come out as well?

Not sure if they’re welded in ‘studs’ or just ‘bolts’ that go through the holes?



Believe it or not, all of the nuts are coming off very easily with some PB.
I believe they are screwed-in studs. They stay. The nuts are on the resonator side. I replaced the 3rd cat section not long ago. I couldn't remove the nuts the usual way so I just cut them off. Here are a couple of pics.
51639

51640
 

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Discussion Starter #13
Okay, I got the nuts off but can’t seem to separate the two pipes. I assume those stud can stay in place as long as the nuts came off. I’ll try to put some muscle into it unless you have any additional ideas.
 

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Post some pics of the trouble area. You are there already. Just remove the rear CAT and shake it.

It helps to put a floor jack underneath to pull out the whole y pipe off the bolt at back - level sorta.
 

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Discussion Starter #15
Post some pics of the trouble area. You are there already. Just remove the rear CAT and shake it.

It helps to put a floor jack underneath to pull out the whole y pipe off the bolt at back - level sorta.
Here are a couple of pics of the third cat (front Y-pipe is removed).


Jack stands are in place and the nuts are off but the pipes won’t separate at the gasket. Not sure if it’s just the rust or do the bolts need to come out? I can’t seem to turn or punch them out.
 

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Okay, I got the nuts off but can’t seem to separate the two pipes. I assume those stud can stay in place as long as the nuts came off. I’ll try to put some muscle into it unless you have any additional ideas.
You can't easily remove the studs even though they are screwed-on. But I don't understand exactly what the problem is. Are the two pipe flanges so rusted that they are bond together, or is there not enough wiggle room for you to slide it forward and off from the resonator pipe? Once you remove the bolts/nuts in the front, there should be enough room to slide it forward. Plus, the Y pipe should give you some flexibility.

There is a sliding/hanging pin in the middle between the cat. and the "Y". You can put some grease on it so you can slide it forward more easily.

EDIT after seeing your pictures: Yours look different than mine. Yours look like they are actually bolts rather than studs. The new part I put in also has bolts. So can't you just break them loose and turn them out?
 

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Put your floor jack under the y pipe then try to level it (front not dipping down) tap the 2 bolts with a mallet or wood and hammer. Or hit the flange with hammer to shock the rust off. When it breaks off its bond, you just simply slide your floor jack little by little to maneuver it out of there. You should also support the rear part of the exhaust pipe after the flange.
 

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Discussion Starter #18
I ended up putting a nut in the studs and hitting it with a sledgehammer. I finally got the pipe out. There are pieces of the cat flying out of the Y-pipe side.... I’ll just clean everything out completely.

 

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Discussion Starter #19
So now that this is done, I assume it wouldn’t be a bad idea to attempt removing the Bank 1 ( firewall side) cat. The other front (Bank 2) cat I managed to strip one bolt, so I don’t think that’ll be coming out. Otherwise, everything would have came out smoothly.
 

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Discussion Starter #20
Anyone know how I can get the firewall cat down? It’s definitely clogged... with a melted ball of catalyst internals just floating around inside. I can see it but I’m not sure if I can get the stuff out without removing the cat(?) Either way..

Y-pipe is off, O2 unplugged and the two 14mm bolts facing up have been unbolted. The top two nuts seem close to impossible to get a wrench (14mm?) up there, let alone have room to turn it. That heat shield is definitely in the way. Any ideas? I can’t remove the passenger side wheel because my car is up on ramps.
 
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