Cleaning carbon from O2 Sensors

[tfvesquire]

Hi all. I posted a thread for my 98 Q45 that kept surging and stalling after throwing the code for the drivers bank rear downstream O2 sensor. I replaced just that sensor and the code stopped popping up, but the car continues to hesitate and sometimes stall after running perfectly without any codes. I have recleaned the MAF, IAC, TB and ran some additional Deep Creep thru the brake booster line. For the most part, the car will run great and have smooth, steady acceleration with full power, then all of the sudden, the idle will drop at a stop light almost to zero, the TCS and Slip lights will flash on and it will run rough/rich. There is no singling out when this will occur. cold temps versus hot day. I've ran fuel injector cleaners in with no long term cure.

At this point, the only thing I can point to is the other three O2 sensors that must have carbon on them when I did the initial SeaFoam intake soak. My guess is that when those sensors are cold, they are not feeding any mis-information about the air/fuel ratio to the computer. Then, after they "heat up" after driving a few miles or for a period of time, they cannot correctly measure the exhaust fumes because they are dirty and that must be causing the unpredicted idle issues. Am I wrong about this?

My real question is I heard you can soak the O2 sensors in straight gas and that is supposed to help clean them especially if they have an abnormal amount of crap caked/burned on them. I guess I could also use carb cleaner. Has anyone on the site done this to get a few more miles out of their sensors? should I just bite the bullet and purchase a set of the remaining three sensors and be done with this? I am willing to rent the "free" O2 sensor socket and remove the original sensors and try and clean them up especially since I would have to order the NTK or Walker sensors that are not available locally. Only the Bosch are available thru the local parts store.

Any help or assistance from someone knowledgable about this issue would be greatly appreciated.

Thanks and have a fun and safe July 4th holiday.

Ted

[elwesso]

I really don't think the o2 sensors are causing stalling and whatnot.. The o2 sensors don't really have that big of an impact on how the car runs at idle or WOT. Try running the car without the o2 sensors plugged in, overall it will run OK. If you're going to mess with taking the o2 sensors out, you'd be best off replacing them with new in my opinion, especially if they're all original. o2 sensors have a useful life of about 60-100k miles, so if they have more than that on them then you shouldn't waste any additional time if you're not going to replace them.

So when the car stalls, you don't get any codes? Seems kind of strange. Honestly what you're describing sounds kind of like a MAF failure, and cleaning won't always fix it, in fact it rarely makes any difference unless the connection is bad in the connector.

After reading your other thread, I really do not think the problem lies in the o2 sensors. I think like paranoidjack mentioned in that thread, you should pick up a used MAF and see what that does. I have a spare MAF on the shelf for my Q (at one point I had 2), and I've replaced my MAF once.

The problem with MAF failures is that 95% of the time they'll work OK, but since they're such an integral part of how the engine runs that even a small "blip" will be very noticeable. In other words, just because you unplug the MAF and the car stalls, that does not necessarily mean that it's working properly...

[tfvesquire]

I really don't think the o2 sensors are causing stalling and whatnot.. The o2 sensors don't really have that big of an impact on how the car runs at idle or WOT. Try running the car without the o2 sensors plugged in, overall it will run OK. If you're going to mess with taking the o2 sensors out, you'd be best off replacing them with new in my opinion, especially if they're all original. o2 sensors have a useful life of about 60-100k miles, so if they have more than that on them then you shouldn't waste any additional time if you're not going to replace them.

So when the car stalls, you don't get any codes? Seems kind of strange. Honestly what you're describing sounds kind of like a MAF failure, and cleaning won't always fix it, in fact it rarely makes any difference unless the connection is bad in the connector.

After reading your other thread, I really do not think the problem lies in the o2 sensors. I think like paranoidjack mentioned in that thread, you should pick up a used MAF and see what that does. I have a spare MAF on the shelf for my Q (at one point I had 2), and I've replaced my MAF once.

The problem with MAF failures is that 95% of the time they'll work OK, but since they're such an integral part of how the engine runs that even a small "blip" will be very noticeable. In other words, just because you unplug the MAF and the car stalls, that does not necessarily mean that it's working properly...

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Thanks for the response and info. The current O2 sensors have about 40-50K on them so they are close to the end of their life, but in my opinion, should still give me 20-25K more miles. The reason I point primarily towards the O2 sensors is because the car ran and idled just fine until I decided to do some preventive maintenance and run a can of Sea Foam thru the brake booster. After that, I started having all the above stated issues including the P0140 (rear downstream O2 sensor) code. I replaced that sensor and the code went away. I took a good look at the old sensor and it had a lot of carbon on it which lead me to suggest removing and cleaning the other three sensors and see whether that does anything. I have to disagree with you though about the O2 sensors not playing any role in the idling and running of the engine because it is my understanding that is exactly waht they are designed to do -- help measure the amount of air and fuel the engine requires to run efficiently. By unplugging the sensors I would be defeating their intended purpose.

I thought about the MAF going bad and I may still have to find a replacement. I already checked and cleaned the MAF connector and wire harness. I am just not one of those car owners who just starts replacing parts when the solution could very well be a simple cleaning. Plus, if the MAF was bad or going bad, I cannot understand why the car would run like a million $$ for 1/2 my trip and then run like sh*t out of nowhere. If any of these O2 sensors cannot read the exhaust mixture properly because I dislodged a ton of carbon and soot onto them, then I am willing to take 20 mins and remove them, soak them and reinstall them to at the very least rule them out as the culprit. Like I said on my original post, when I performed the SeaFoam intake cleaning, I got a lot of carbon loose which Im assuming was deposited throughout the entire exhaust system, including the sensors.

As far as cleaning them, I read about people soaking them in gas or carb cleaner to clean them. I also read about people using a torch to burn off any deposits that are causing them to malfunction. I just want to use the least harmful method. That was the main urpose of my post.

I am going to grab an O2 sensor socket from NAPA after work and pull and clean the ones I have and post the result back after putting some miles on them.

Thanks,

Ted

[tfvesquire]

Ok, I ended up buying one their sensors for $10 because they now claim they dn rent them, but due the design of the socket I could not access the upstream sensors (pre-cat). to remove them. I will have to get one that is similar to a line wrench design to remove those. I did remove the passenger downstream sensor. Almost identical to the drivers rear sensor, there was a lot of carbon covering the outer jacket and air holes plus the inner part as well. I used carb cleaner to clean it out and reinstalled it. When I started it up, the car started to fluctuate the idle again, just like it did before. Went really low like 500 and swung up and down a few times. I gave it some gas and it soon idled steady again. Drove it around the block and it had smooth acceleration and idle again. Will put some more miles on it tomorrow and post some results back -- I may even drive into work if it is going to rain because I was going to drive my convertible in.

Whoever designed the upstream sensors to be located that close to the pre-cat pipe ought to get a beating. There is literally no room in there for removal. I remember I pulled the passenger upstream sensor out using a 7/8" open end wrench when I supposedly bought a set of OEM sensors for my Q, but the wiring harnesses were too short so I reinstalled it. I didn't touch the drivers side at that time, but just by looking at them under the car, the drivers side is definitely a tighter fit for some reason.

Anyway, enjoying a glass a wine and heading to bed.

[elwesso]

Honestly in the debate of MAF vs o2 sensors, it's all guesswork until you can confirm the diagnosis by reading voltages. If you can get some sort of code reader that allows you to read sensor voltages, you can drive around and look at critical sensors, and then if it acts up it should be easy to tell which sensor is acting up.

The o2 sensors primary function is to monitor A/F mixture for cruising to optimize MPG. At idle and WOT they don't do a whole lot, mainly because they can't respond fast enough at WOT and idle doesn't really matter that much since the engine is using so little fuel. I would say they have even less effect at idle than at WOT. The MAF is the primary sensor that determines A/F ratio, the o2 sensors are there to fine tuning.

When MAF start to fail, they almost always will operate 95% normal and then screw up the other 5%.. Why MAF failures for inexperienced mechanics are very hard to diagnose (especially on OBDI Q), because they're so intermittent that it becomes hard to replicate.

[OwnerCS]

To Wes' point, I have purchased a few used MAFs from Qs and 4th gan Maximas in junk yards to keep as spares.
I always test drive a used MAF a couple of weeks before I decide to keep it as I found a couple that started failing after driving for a couple of days. The average cost has been $35 for a used MAF. The yards where I go give a 90 day $ credit warranty. Also, I've seen some reasonably decent looking 4th gen Maximas in junk yards with MAFs (after testing) that would not allow the engine to idle without stalling. It was sad to find a decent looking 4th gen Maxima in the junk yard with a failed MAF that I knew contributed to somebody's frustration to let the car be sold for salvage.

Last year (December 11), I found a lady (appeared to be 8 months expecting single mom) trying to sell a 98 I30 on Craigslist not far from my home. She said something was wrong with the car as it would stall at stoplights. A mechanic told her it would take over $500 to repair the car. She was selling the I30 as she had no for money repairs. It was classic MAF failure. I felt bad for her so I gave her one of my spares (that fixed the car stalling problem) and wished her a happy holiday season. She took the car off of the market the next day.

[zul8tr]

OwnerCS that was a nice gesture especially at X mass time and she couldn't afford repairs. I do stuff like that for neighbors and unknowns. Ex. Met a guy and his little 6 year old (taking apart the shelves Ha) at Home Depot that was buying polyester resin and cloth. He was spending alot of time reading the label so I knew he was not familiar with the stuff. I asked him what he was repairing and he said a hole in the roof of his vehicle. I told him I amd very familiar with that stuff and can fix that for you free, just buy the resin as I have non left just the cloth and other incidentals and meet me at my house. Next day he shows up with the puller/cab for an 18 wheeler and the hole was in the roof of the cab 15 feet off the ground Yips!. So I got my ladder and fixed the hole wished him a nice day. He is a long distance hauler, nice guy heard from him a few times on the road. Always good to help others.