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running rich in bank one?

6 December 2004
clifton park ny
over the weekend my 99 nsx popped a check engine light. i havent driven it since before today when i went right up to my buddies shop. with the light still on he hooked up the scanner and it said that bank 1 was running rich. it suggested checking the o2 sensors. we did so as to the instructions and the o2 sensor gauge on the scanner fluctuated between .15 and .85 at 3k. it did so kind of slow compared to other cars i have seen on the scanner and did not mention which sensor in bank one we were measuring. the scanner also mentioned lists of other alternatives to the o2 sensor that could be wrong w/ the car. btw, i have in the last month had the thermostat replace because the car was running cool. does anyone have any suggestions before i waste all his time chasing down these random diagnosis? :confused:
Pull the plugs on that bank and see what you have, keep track of position.

The engine will run rich if it thinks it is cold.

Swap O2 sensors and see if the problem moves or remains the same.

should i swap the sensors from bank 1 to 2 or the two sensors on bank one? are all of the sensors the same? btw. the code we pulled ended in 172
Pull the plugs first and see if you really do have a problem. It is easiest, quick and should be obvious.

O2 sensors are all the same, just the length of the wire is different. Take one that is known to be functioning correctly and swap. If you get the same result: you probably are running rich.

The O2 closest to the engine (as seen from the exhaust leaving the block POV) is the one that tells the ECU how to modify the fuel delivery. The sensor farthest from the engine block informs the ECU on how well the emissions are doing.

I don't have the codes for an OBDII around me, so I don't know which specific O2 sensor is complaining. It sounds like the trailing O2, but I dunno.

First question is did this start just after work was done?

Is your temp gauge reading properly now and the car is warming up quickly and running at a steady temp?

These answers may tell a few things.

no, the work was done @ 2 months ago. the car warms up quickly and once the gauge is at operating temp it stays right there. turned the check engine light off and erased the codes, the light hasn't come back on yet. the other thing the scanner told us to do was to check the purge valve. i dont know if these are related symptoms but 1 out of 10-15 times i start the car it cranks an exceptionally long time. i also noticed that my fathers car seems to have more low end punch than mine, i would have never noticed except i drive his every now and then back to back(2004).
I would check the purge valve as recommended. I suspect the CEL may come back after two "trips". If not, it may take a while to re-appear.

Regardless I think I would put a bottle of Techron fuel injector cleaner(they market it as "ProGard" now). Could make a world of difference if the injectors are dirty. If it returns, check the code again. Then look at 02 sensors.

The fuel injector cleaner is inexpensive and you will know within a 1/2 tank of fuel if it helped, probably less.

thanks for the advice! i will do the injector cleanor tomorrow. will have to wait till' monday to perform thorough checks. i have driven the car as much as possible and the cel does not come back on. i have also noticed that the car seems as quick, if not quicker, under 3/4 throttle than under full. it does not bogg, spit or sputter or what have you, but only noticed after driving a new nsx back to back :confused:
Every scanner has a differant sample rate, so the speed that the O2 vlotage changes (called 'counts') indicates very little. I know it is not the same as mine (Snap-On) because mine reads both banks, primary and secondary, IOW all four at once. If his only reads one, it will be primary and if you had a secondary failure- thats a differant code. The quickest way to eliminate everything about the fuel system (except injectors) i.e. fuel pressure, purge control, etc, is to see if the front bank (coded) and the rear bank (not coded) have the same counts. Also, any quality scanner should also show O2 trim, short term (STCounts) and long term (LTCounts) and comparing these for front and rear will also seperate an O2 sensor problem from a fuel system or emmissions sytem component issue. (Trim indicates the pattern, or frequency of the counts cycle)

I love when you guys talk dirty :biggrin:
thanks nsx tech. he does have a snap on scanner and he just didnt have enough time the other day to check everything with 2 customers sitting there. i was just hoping that it was as easy as replacing an o2 sensor. next week we will go through all possibilities. i have been driving it for the past couple days and still no cel. why the delay :confused: