CaliforniaDream

iTrader: (1)

Hi guys.

I got an oil change at EZ lube (I know, I know...never again) and after it my car started running ultra-rich, as in 33% reduced fuel efficiency. I've gone through 2 tanks of gas in less than 400 miles of driving. Normally I will hit 300miles/tank.

Engine idle has been rough lately. I did notice some abnormal (ie moreso than usual) early-morning mist/smoke from the exhaust.

I took it in to a local shop today and the tech indicated that the o2 sensors are shot (the front for sure, the rear 2 probably to follow shortly if not done already) and need to replaced.
He quoted $1,600 to replace all 4 of them. ~$1,050 for parts and 4hrs of labor lol? The o2 sensors are $135-150 each online, coolant sensor is around $25-30.

Note that I have not had a CEL. I did however request a copy of the service sheet from the shop, and this is what it shows:

"Notes: CAR IS RUNNING RICH ALL THE TIME.
DIAGNOSTIC TROUBLE CODE P0118 - COOLANT TEMPERATURE SENSOR CIRCUIT SIGNAL IS HIGH
SNAP-ON MODUS ANALYZER SHOWS OXYGEN SENSORS NOT SWITCHING"



Anyway... my question:
Do you think it would be advisable to replace the front o2 sensors myself, then see if the A/F ratio corrects itself and I get back to my original mpg levels?
What could the coolant temperature sensor do that would affect A/F ratio? Is it worth replacing? For $30 I think so.

davidv

iTrader: (2)

"Running rich" means what? 10:1? 15:1? And where we talking about? 2,000 or 6,800 RPM? I would want to see some definitive test results before throwing money at a problem which does not exist.

CaliforniaDream

iTrader: (1)

I dunno, you tell me! The only solid data I have is that the last two tanks of gas have taken me less than 200 miles each. I'm pretty sure you would agree there is a problem here.

The only time the ratio spiked into the lean side, that I saw, was when the tech punched the gas while it was hooked up to the machine. At idle and various pedal thrusts up to probably 5-5.5k rpm it was rich. I don't know what a bad or good AF ratio is, and from what I was able to see the graphing on their reader didn't have any numbers indicated.

Would the stealership be able to run diagnostics to get graph-type info you are referencing? Think they'd charge me to look at it? The tech was telling me that the AF ratio should be up/down constantly to keep it stabilized throughout the rev cycle, which it clearly wasn't from what I could see.

mistanismo

iTrader: (1)

What kind of oil did they put in your car and are you SURE it was what you asked for? Start there.

davidv

iTrader: (2)

Nissan is OK but...

Any performance shop doing dyno runs can give you a air:fuel graph. This may be a better place to start.

CaliforniaDream

iTrader: (1)

They should have filled with castrol synthetic, which is what I had in there before. I have no way of verifying this except the invoice, which may be notated incorrectly anyway.

Thanks. I will ask around and see if I can find one locally.

I just find this whole transformation rather abrupt and disconcertingly in step with the timing of my oil change. My mileage had been consistent up until 2 weeks ago and then it just took a dump right around the same time I took the car in.


Anyone know how, outside of individually switching them/resetting the ECU, if there is a way to check which of my Sensors is toast?

OrleanZ33

Im somewhat puzzled on how this mechanic diagnosed that it needs 4 new o2 sensors when a p0118 engine coolant temp sensor code comes up. I have never seen multiple o2 sensors fail at the same time...

Engine coolant temperature (ECT) affects how the engine operates in all conditions. If the sensor is inoperative it will assume the coolant temp is -40f and/or to hot (but the hot part doesnt concern your problem) and not come out of open loop operation so it will dump fuel thinking the engine is still not at operating temperature/cold. Symptoms can include poor/rough idle, hesitation on acceleration, stalling etc,...

I would advise checking to see if theres a open in the wire if not its probably faulty internaly and needs replacing. If I were you I would try not to drive the vehicle much more until you get the issue resolved before your cats are toast and/or your 02 sensors become toast too from running pig rich if there not already. Additionaly, im pretty sure the graph you were looking at wasnt A/F ratio but actually Short Term or Long Term fuel trim indicated by for exmaple -5.6 indicating fuel being pulled or +5.6 indicating fuel being added. You dont need to get on a dyno just for th sole purpose of A/F ratio's for your problem all the information a technician needs is accessable from there diagnostic equipment he has available to him to figure out the problem.

CaliforniaDream

iTrader: (1)

Thanks for the post. I am now trying to find a reputable shop where I can get the job done right, or at least diagnosed properly so I can fix it myself.

Myfirst06350Z

iTrader: (72)

I got your message. Yea 02 sensors do not all fail at the same time. If your ECU thinks the motor is still cold the Fuel ratios will be off. I would say to replace the sensor first and see what happens. But it def sounds like a wiring/sensor issue. If you can bring it down to the shop we can connect it to our computers and see if we can see something off on the operating temp or something.

Bryan

Zazz93

iTrader: (2)

It sounds as though the car is stuck in the closed loop and running incorrect mixtures as if the car is warming up. I would change that sensor first (ECT). Also, 4 hours to change the four other sensors seems excessive. The two rear sensors can't take more than 20 mins each on a rack and the two uppers no more 30 mins each (and thats being generous).

Back to the ETC sensor... its the one at the rear of the motor and the factory service manaul says replace that one first with that code.