# erratic check engine light



## wannab-si (Mar 26, 2005)

first off i would like to say hello as a newbe. I just purchased a 1995 altima that has some issues. 

to start off, it has an erratic check engine light. this problem seems to be throttle dependent which would lead me to think its a MAF problem(let of the gas and its gone, step on it and its back). when hooked a snap-on scanner up it listed problems with the air intake temp sensor, primary ignition signal fault, and the secondary o2 was sticking on its readings. i replaced the second o2 and the problem is still there. all readings from the distributor/coil and AIT are within specs. if i clear the codes it still has the problem with no codes. i have cleaned off the grounds. the CEL is not allways there. im kinda lost right now so any help would be great


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## Asleep (Jan 19, 2003)

are there any other running problems? does the engine stumble on or off load? does it idle funny? does it hesitate at all?


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## wannab-si (Mar 26, 2005)

car runs great. compression is fine....leakdown is fine. i just drove the car over 800mi and got close to 31mpg the whole time. it does idle a little rough,(jumps around 50-70rpms @idle) but the car does have 212,*** mi on it.


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## Asleep (Jan 19, 2003)

im thinking bad wiring... like a loose ground wire or something to that effect. im not a wiring genius though - that and bodywork are my two weakpoints...  maybe KA24Tech could shed some light. hes my backup guy.


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## wannab-si (Mar 26, 2005)

update on the CEL problem. i took the metal guard off (under valve cover, covers timming chain) because of the chain hitting it. i herd it was a good idea to take this off from a number of people because this guard breaks and can clog the oil pickup.....and the noise was pissing me off. my CEL problem is gone and there are no codes or timming errors. the two codes i was pulling were related to knock and timming. plugs look good and timming is correct.

now my question is, how sensitive are nissan knock sensors? could the chain hitting the guard be interpreted as knock by the computer causing timming to be pulled and the CEL to come?


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## KA24Tech (Feb 2, 2004)

I agree that it is a battery connection or engine ground issue for those codes to pop up. The knock sensor code can occur if the piezo element intercepts anything remotely like a detonation moment. The sensor is shock sensitive but also is effected by the voltage and ground circuit for it's sensitivity. I would pull it off to clean the mount and to test the sensor with an ohmmeter it should measure between 500k and 620k ohms. Then apply an antiseize compound to the bolt and reinstall the sensor torqueing the bolt to between 15 and 20 ft.-lb.. I don't remember the early OBD II being that sophisticated that it would pull timing with a knock signal.

Troy


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## wannab-si (Mar 26, 2005)

ive gone thru and cleaned all connectors...there was a lot of road salt/dirt in most of the important ones. its gone two days without codes or the check engine light so im assuming the problem is gone. 

thanks for the help....


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