# 04 Altima 2.5SL bucking at 70mph on occasion



## jon04alt (Jun 21, 2010)

On long trips more than 50 miles, my Altima with 130k miles will suddenly buck when going at a constant 70mph or so. A month ago, I switched from 87 to 89 octane and the problem went away until now. My check engine light went on this weekend, and stayed on for a day, but turned off. 

This weekend, the car actually stauled when I got towards the top of a 6 mile mountain road. I was able to restart the car again and drive no problem.

Today, I noticed that the car sounded funny when idling. When revving it to around 2500rpm, it sounded like a light rattle, possibly knocking. I drove the car softly for about 3 miles home, and then the engine sounded fine when idling or revving.

The crank shaft position sensor had to be replaced about 9 months ago. Is my MAF a possible culprit?


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## chimmike (Oct 17, 2002)

Did you find out what the code was?

I'm wondering if you have a loose connection on the fuel pump wiring or something, or maybe a loose connection on the MAF wiring.


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## jon04alt (Jun 21, 2010)

chimmike said:


> Did you find out what the code was?


I just got the codes using the gas pedal technique. It spit out 0335 and 0420 repeatedly.

0335=CKP (crankshaft position) Sensor 
0420=THREE WAY CATALYST FUNCTION

Seeing as I had the CKP replaced earlier this year, I wonder if it's not the root cause. 0420 has these possible causes listed in the service manual:

●Three way catalyst (Manifold) does not oper- 
ate properly. 
●Three way catalyst (Manifold) does not have 
enough oxygen storage capacity. 
●Three way catalyst (Manifold) 
●Exhaust tube 
●Intake air leaks 
●Fuel injector 
●Fuel injector leaks 
●Spark plug 
●Improper ignition timing


Should I resort to taking it to the dealer? Should I replace the CKP myself as a short term fix?


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## chimmike (Oct 17, 2002)

eithe an o2 sensor issue or an exhaust leak around the exhaust manifold. Maybe precat breakup?


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## jon04alt (Jun 21, 2010)

chimmike said:


> eithe an o2 sensor issue or an exhaust leak around the exhaust manifold. Maybe precat breakup?


How do I diagnose a precat breakup issue? I've read a little about it, but I'm not sure if I'm losing oil considering it's in normal range and it's been about 3000 miles since I changed it.


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