95 240SX 2.4L manual trans O2 sensor questions...

[EW]

110K on body. Don't know on engine. Computer and injectors are supposed to be factory. THERE ARE CURRENTLY NO CHECK ENGINE LIGHTS. Exhaust smells like there is no cat. It has a hot shot header with front O2 sensor. It has an intermediate pipe that came from another 240. It has a bung with dead O2 installed after the cat. It is not wired to anything. There is a socket on the car main harness directly across from the O2 that runs down the transmssion. I guessed it is for an O2 but the former owner says that this car only has one O2 (in the header). Car parts stores do not carry an after cat O2 in stock. Some show it as special order. Nissan dealer said special order. What is the truth? Did this car only have one O2 sensor from the factory? Is the socket on the car harness used when you have an auto trans? Is the cat just bad? Help before I drop $100+ on a sensor for no reason. How can I determine if the computer is reading/adjusting fuel properly? This car stinks and I want it "to smell alot like flowers".

[s13sr20chris]

i think the 95 had a rear o2. the ecm only uses the rear o2 to see that the cat is working. it is not used for any fuel control at all. that means the car will not run any different if you get the rear o2 working.

[EW]

So, the socket will accept the O2 but it is not doing anything so I don't need to fix it.When you replace the cat, won't what seems to be a rich condition damage the cat or is it a non issue? High flow metal catalyst cats are not free. I want this thing as clean as possible and to pass emissions w/o issues.

[NISTECH]

As Chris said the rear O2 has no effect on fuel control. It is only used for Cat effeciency monitering. It basically is designed to let you know when the cat took a dump.

If you want this car to run as claen and as effecient as possible you need to focus your diagnosis on the front O2 once the car is warmed to operating temp. During cold start up and any other time you also need to look at MAF operation, Coolant temp functionality and accuracy. Crank angle sensor signal, Basic ignition component condition such as cap, rotor, wires, and plugs.Check and set basic ignition timing to spec. Other fuel system components too look at are fuel filter, leak down check on injectors, compression of cylinders. These are just to name a few things to look at for proper 4 stroke engine efficiency.

[EW]

I drove the car 11 miles today. At around 10 miles or so the check engine light came back on. This time, it showed P0335 Crank position sensor, P0136 O2 malfunction bank 1 sensor 2, and P0325 Knock sensor 1 circuit malfunction bank 1 or 1 sensor.I do not know where the knock sensor is or what the error really means.Can I read the sensors with a meter while the car is running? If so, what should each sensor read?

<---Watching two 95 240sx manuals on ebay.

[NISTECH]

You wont see the knock or crank sensor on a scanner, only the rear O2 [B1 sen 2] The knock sensor Is located on the block just below the intake manifold, real hard to see. And your aware of the crank sensor right?

[EW]

Thank you for your help.Yes, I know where the crank position sensor is located but I don't know if it is good or bad. I don't want to take it to the dealer but I don't want to throw parts at it either. I guess I'll wait until I can get my hands on a manual to attempt to troubleshoot. I washed and clayed it today. It had been sitting for a while and was pretty dirty.

[NISTECH]

Ask and you shall receive

[NISTECH]

circuit

[NISTECH]

diag procedure

[NISTECH]

And finally component inspection

[EW]

WOW! Thanks. I guess if the sensor is good then I have a misfire condition. I haven't looked at the cap, rotor, or plugs yet.

[NISTECH]

no as that code is not for misfire, it is only for the integrity of the CKP circuit. A misfire would come up as P0300 - P0304.

[s13sr20chris]

yeah, that 95 ecm is not smart enough to fail the ckp for operating incorrectly or even a misfire. it can only check open and short circuits(for that particular code anyway). that does not, however, rule out the sensor itself or the ecm.

[EW]

I bought the Chilton manual at half price books for $5.98. I know they usually suck because they are generic, but the one for the 240 does not look that bad. I won the nissan manual on ebay today so hopefully I'll have it in a week or so.