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Discussion Starter #21
hey well listen to this, i ran the computer check and read the error codes online and one of them was a crankshaft position sensor, changed that and the rear motor mount and i tell you it was the best 120$ i have spent ever. the car feels like a brand new car and actually has alot of power all of a sudden, this is after motor mounts, premium gas, thicker oil change, engine restore can, air filter change, and oil filter change. the car runs twice as better as before and it the smoke seems to be reducing! im sure this wont fix my problem but i think its it perfect drivable condition. not only that, but the check engine light went away!!
 

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Good shot. Yeah that $120 sounds like it was well worth it. It's always good when we can fix/prevent grave problems. So I can't remeber, I know your car was having the smoking issue, but was it consuming excessive amounts of oil? If so sis that fix it? You might not be able to tell till a couple of days though huh
 

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Discussion Starter #23
yes its still burning oil and smoking, but nothing close to how it was a few days ago. we will just have to wait and see what happens, untill then im going to drive it all day haha
 

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OOOO Ok your fuct. What I was getting at is that if you did buy a new precat it would eat most of the oil.......but your motor sounds like it eats SO much oil that nothing can be done. My car eats 1 quart per 500 miles, which is shitty but do-able and I got 186k on it so I'm good.

Are u good enough to drop in a new motor? cheapest one I found was 3grand...and that was putting it in myself.

ALWAYS have a used car inspected.
 

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That car might have been using oil since the precat went out at 60k for all you know. You just bought it right? I'd just keep a real close eye on your oil.

Also, there is a butterfly screw issue you might want to address while you're tinkering with it.
 

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in this condition how much do you think the car is worth? for a fair sale on craigslist. its 126k miles. pretty clean body and interior.
I just bought a 2002 with bad motor, ran while burning oil resulting in throwing a rod. $1000, rest of car looks brand new, 111k. The guy who bought it paid $3500 knowing the car was burning oil, he had the car for less than 30 days.
 

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This problem may not be limited to the 2.5. I have a 2004 3.5 and it has slowly been loosing engine power (torque) over the last few months, and fuel mileage too. After filling my gas tank last night with Petro-91, suddenly the engine stopped accelerating at high (2750-3000) RPMs. I noticed this as I was trying to get on the highway, the car would struggle to get to 100km/hr. If i tried to floor the gas pedal, no acceleration and the heat shields rattled like crazy!

After reading some articles, I guessed that it was the Cat Converter or the Throttle Position Sensor. This morning I noticed immense heat from outside the passanger side while parked, so I assumed it was an exauhst blockage.

My summer savings later, and now the problem is fixed. They replaced all 3 converters and the car runs great, for now. What is causing the pre-cat failures? Bad gas? Engine decay? Bad seals? It looks like the inside of the pre-cat was melted, one of them was actually loose inside its case. One of them had visiable damage from debris, probably since it was clogged.
 

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This problem may not be limited to the 2.5. I have a 2004 3.5 and it has slowly been loosing engine power (torque) over the last few months, and fuel mileage too. After filling my gas tank last night with Petro-91, suddenly the engine stopped accelerating at high (2750-3000) RPMs. I noticed this as I was trying to get on the highway, the car would struggle to get to 100km/hr. If i tried to floor the gas pedal, no acceleration and the heat shields rattled like crazy!

After reading some articles, I guessed that it was the Cat Converter or the Throttle Position Sensor. This morning I noticed immense heat from outside the passanger side while parked, so I assumed it was an exauhst blockage.

My summer savings later, and now the problem is fixed. They replaced all 3 converters and the car runs great, for now. What is causing the pre-cat failures? Bad gas? Engine decay? Bad seals? It looks like the inside of the pre-cat was melted, one of them was actually loose inside its case. One of them had visiable damage from debris, probably since it was clogged.
It sure seems like driving habits play a big part from what I've read (i.e. the sporty Sentra se-r's having tons of issues with low mileage.) I have always babied my car and I just pulled my precat yesterday and it was in really good shape (2003 altima w/ 80k miles).
 

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I am starting to think the cat converters are overheating because of the high octane fuel. I thought maybe my cylinders were leaking fuel or oil but theyre not. Someone warned me about using premium fuel. Looks like they were right.

Im getting close to 600 km on a tank, 60% highway, since i replaced my cats MT, 91 oct. Thats pretty good. Conclusion, performance engine with mediocore exauhst, thats the altima.
 

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Putting premium in your car is in no way going to cause the precat to break up. It was a design flaw in the early altima years.
 

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Wow, r u serious, thats weak...

Next time ill do it myself , but the parts are still super expensive. Dealer wanted 900 each precat.. i guess the muffler shop gave me a good deal.

Anyway, is there anything to slow down the damage to the precat. Is there no aftermarket fix? The dealer made it sound like 135km is great for the cat. Also, how do u know if its failing again? A gradual loss of power? Theres gotta be a better way...
 

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$900 for each precat is ridiculously stupid.

as far as i know the only way to prolong it is to keep your rpms down and don't floor it and that'll keep them from getting too hot and cause them to go bad after time again. and as for failing i think the only sign is massive oil consumption. i don't think there's really any way of telling that its happening right now unless every so often you take off the precat and check to see that its still in one piece and that you can shine a light through it.
 

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Wow, r u serious, thats weak...

Next time ill do it myself , but the parts are still super expensive. Dealer wanted 900 each precat.. i guess the muffler shop gave me a good deal.

Anyway, is there anything to slow down the damage to the precat. Is there no aftermarket fix? The dealer made it sound like 135km is great for the cat. Also, how do u know if its failing again? A gradual loss of power? Theres gotta be a better way...
If you don't have to worry about emissions test where you live you can get aftermarket headers that don't have a precat on them.
 

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My therory is the top bung on the primary O2 sensor was fuse welded in place, via some induction method. The heat cycles, bad fitment and or replacing the O2 sensor cause a leak or crack. This lets extra air in the system boosting the surface temp on the substrate right by the bung. This dust then gets sucked back into the motor due the overlap on the cams. eating the o-rings and head gasket.

Now you have think at 3000rpm the internal temp of the gasses is around 800 to 1000 degrease. Higher if you are running it harder. With the presence of added O2 unburnt fuel and or the oxidizing effect of oxygen causes the substrate to turn to dust. This dust is silica, iridium, platimum, and few other rare earth metals. All of which are harder than the Nicolite/Iron sleeve in the block. can you say sandpaper.

When replacing head gasket I took my precat off and smashed it out. It seams to work good. with a 2" spacer I fab'ed for the Bottom O2 Sensor.
O' I welded the leaking top bung. Now no more exhaust leak.

GET RID OF THE PRECAT. It is eating your motor as we speak. If you car is under 80k miles have Nissan REPLACE THE MOTOR FREE OF CHARGE! GET THE HEADER.
If you removed the precat.. wouldn't you end up with a SES light on all the time? Is there a way to trick the computer and bypass the O2?
 

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o2 spacer

If you removed the precat.. wouldn't you end up with a SES light on all the time? Is there a way to trick the computer and bypass the O2?
Nope, if the last/bottom o2 sensor is reading cleaner air from top o2 you don't get the P0420 CEL. o2 spacer is great trick w/ header mod or no pre cat. The car still has a main cat that is mid car, but the sensors only read from the pre-cat that is in between them.
 

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Sorry for dredging up a necro thread but I just went through all this and thought I'd post my experience. 06' Altima, head gasket blew, I let it set for a year and when i got the time thought I'd replace the head but the engine wouldn't turn over because the pistons had rusted. At this point I decided the cheapest route was to replace the engine with a Japanese import, got it up and running but wouldn't rev over 3K. Borrowed an infrared thermometer and measured the top of the pre-cat, it was 500, bottom was 250. Pulled it off and it was fully clogged and partially disintegrated. Replaced it with an aftermarket one and things got worse, lol, car wouldn't rev above 2K. So I pulled the pipe off the pre-cat, ran it open, fired up the car and after mashing the pedal the car went right up to 6K. Today I pulled the rest of the pipe off with the main cat, turned it upside down and poured out the pre-cat, tried to run water through it but its still clogged. I plan to hollow it out, see if I can get through emissions and hope the engine light doesn't come on. I've now spent more fixing the car than its worth. I think the original problem was the pre-cat caused the head gasket to blow and after disintegrating it clogged up the rest of the exhaust. I bought the car @ 110K miles and the guy said he'd done the head gasket and had receipt to prove it. I drove it for another 10K before it started drinking water, he either got ripped off or they never fixed the original problem, a clogged pre-cat. If you have one of these older Altimas I think the thing to do is run the car with an aftermarket header and put the pre-cat on when its time for emissions.
 
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