cats and O2 sensors

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288
Location
Timonium, MD
99 v6 3.2 Isuzu Rodeo. can't believe I forgot that. I use maybe a qt every 3000. Not as much as many that have this engine on this vehicle. The code that was pulled lead me to the cat, but in some cases it was the rear O2 sensor. In stead of just throwing parts at it one at a time, I found a sweet deal on ebay and replaced it all. Good call about the plugs, I will pull a few and look at them. They are fairly new ( a little over a year old with 11,000 miles on them) hopefully they still look good. I'm thinking what happened to this side of the exhaust system took place over many years and miles. I'm nervous, because I dont want to have to do this again in a few years. Since this side of the exhaust was noticeably more nasty and the one that threw the codes, does this mean the majority of the oil is being burned on that bank of cylinders? thanks, marc
 
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3,094
Location
Metro Detroit
quote:
Originally posted by marcre: Since this side of the exhaust was noticeably more nasty and the one that threw the codes, does this mean the majority of the oil is being burned on that bank of cylinders?
I don't think so. Again, just judging from the O2 sensor, it looks like rich-mixture fouling, not oil fouling. Also, if you were burning oil on that side, I'd expect to see it on the pre-cat sensor, too. The more I think about it, the more I think it might have just been a bad cat.
 

marcre

Thread starter
Messages
288
Location
Timonium, MD
thanks for the replies. I've got a new problem I reset the CEL today by unplugging the battery. Instantly the CEL came back on. P0134 --> no activity sensor 1 passenger side. How can this be, the sensor is newish. The guy at AutoZone said I need to do 40 start/stop cycles, but I thought the battery trick would do. The thing is, if unplugging the battery won't do it, why would the other code not come back? I am not sure if this P0134 was present before the work anyway. My original code was P0420. That one is not present. Thanks, marc
 

marcre

Thread starter
Messages
288
Location
Timonium, MD
I am not sure yet, I just had the work done last night. The CEL is still on, so I am at a loss as what is going on. It's saying the one sensor has no activity. I tried to get under there and see if it was plugged in all the way, but it was too hot, maybe tomorrow. Mileage was pretty bad, so hopefully it will go up. marc
 

marcre

Thread starter
Messages
288
Location
Timonium, MD
quote:
Originally posted by warrior pilot: Switch the sensor to the other side if not too much trouble. See if the code reflects this .
I was thinking about that. I am going to see if it loose tomorrow and if not maybe I'll throw one of my extra sensors in there. It's kind of tough to get at though. marc
 
Messages
651
Location
Iowa
The most likey explanation for the excess carbon is that bank of cylinders was operating in open loop condition. i.e. a rich condition where the computer does not use the input from the O2 sensor to determine fuel ratio. This extra fuel cause your cat on that side to run hotter and possibly plug. As for your current problem. Clear all the codes with a scan tool and see what happens. If you have an immediate code I would guess either you don't have a good connection or the sensor is just plain bad. btw, lots of info on this stuff. Just google it.
 
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3,435
Location
FL
marcre did you noticed a difference in the way your vehicle drives after replacing the exhaust? Did you replace it with factory exhaust or aftermarket? I know someone already asked about mileage but if there is something wrong do you mind repeating the answer to all of this after it is running correctly? Thanks and good luck figuring it all out. I agree with trying to swap it out and then see if it does it again. Also have you tried to reset it again? Sometimes computers are weird and might just need to be reset one more time? Thanks again
 

marcre

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Messages
288
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Timonium, MD
vehicle drives great. I used OEM stuff I got off of ebay. Less than 10,000 miles on all the stuff. about 82000 miles I am going to get under it tomorrow when the pipes are nice and cold and see if I can figure it out.
 
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1,027
Location
Wisconsin
I am not familiar with your vehicle...but changed out the "Y" pipe on my '96 3.8L windstar (due to rattling inside the converter). NO activity from a sensor would lead me to check the wiring. There are 4 leads. 2 for the heater, 2 for the sensor. This code is for the sensor, not the heater (there are other codes for the heater in each oxygen sensor). If the sensor was locked rich or lean, or switching too slow, then there would be a different code for each of those conditions, for each sensor, as well. Point being, the oxygen sensors are very well covered by the OBDII system....and will tell you specifically what the problem is. So that is why I would suggest verifying the wiring, connections. One thing to check is to make sure that the wiring has not come into contact with the exhaust system at any point. The oxygen sensor works by generating a voltage, from a chemical reaction. It will switch from a slightly lean, to a slightly rich condition....as a result of the computer making adjustments to the air/fuel mixture. The oxygen sensors before the catalytic converters are the ones used by the computer for engine control. From my understanding, the computer will use an average between the 2 banks to control both banks, so if there is a problem with one side, the averaging between the 2 banks might be the reason that one side had more carbon than the other. Closed loop operation is when the computer is using the input from the upstream sensors to control the air/fuel mixture. Open loop operation is when the computer is using preset data, and not the oxygen sensors. Open loop is for when the sensors have not been warmed up yet, or the computer knows that the data from them is bad. It does not take long at all for an engine to go from closed loop to open loop operation.....it just has to be running for a short while to warm up....but does NOT have to be fully warmed up (closed loop happens before the heater is throwing warm air). Clearing codes by disconnecting the battery, you have to disconnect the battery, and wait about 15 minutes before re-connecting it. Doing so will clear the codes, but also will clear the "driveability" information. So you may notice that the shift point (auto trans) and engine performance is not the best until the computer "relearns" this information. I just did a search on automotive forum....P0134 in the isuzu, rodeo/passport room, and got 1 thread, and it looks like your thread over there, out of 3151 posts. I have read "Rodeo's" posts, and he seams to know what he is talking about. From the lack of posts on this problem, I would think that this is not an indication of the oxygen sensors failing left and right, causing this code.
 

marcre

Thread starter
Messages
288
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Timonium, MD
Thanks for the post wiswind. I am starting to suspect the wiring. I am going to get under there, but it may take a few days as time is not on my side. rodeo's posts are awesome, he knows what he's talking about. Hopefully I'll know more soon, this is driving me nuts not being able to get this taken care of. marc
 
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1,151
Location
Clovis, CA
By the way, when I'm doing the work myself and saving all the dollars that I would have otherwise spent on someone's labor, I have no problems with buying brand new parts. As a matter of fact, if I'm doing the work myself, I'll even buy parts from the dealer if need be.
 

marcre

Thread starter
Messages
288
Location
Timonium, MD
quote:
Originally posted by GoldenRod: marcre: I think the computer is telling you the truth; in that the "newish" sensor has no activity, meaning.... no good.
quite possible. I may have to swap in one of the older ones that I know works. Hopefully that will do it. I just don't understand how a sensor with ~10,000 miles on it is bad. Although, the vehicle it came off of went through a lot. marc
 

marcre

Thread starter
Messages
288
Location
Timonium, MD
quote:
Originally posted by GoldenRod: By the way, when I'm doing the work myself and saving all the dollars that I would have otherwise spent on someone's labor, I have no problems with buying brand new parts. As a matter of fact, if I'm doing the work myself, I'll even buy parts from the dealer if need be.
The work I do is limited. I had all this put on at a muffler shop. I tried, but it is too cold out and the space on the underside was very tight. Also, the old exhaust was extremely corroded. The parts were OEM, but I got them off ebay from a vehicle that met an untimely death. The guy selling it bought the vehicle for the transmission and he sold off what he could, cheap. marc
 
Messages
1,027
Location
Wisconsin
If you can switch the sensor to another position, I would do that. While you have it off, really look over the wire harness for it. If the code stays the same, then I would suspect the wiring from the O2 sensor plug to the computer. If the problem moves with the sensor, you know the rest. I like the idea of keeping the same age / brand of oxygen sensor for both of the upstream sensors.....this way they both have the same switching charactoristics.....which will result in the best engine performance / economy. 10K vs new is not a big difference, but I would certainly stay with the same brand.....or maybe move the downstream sensors forward....and have the mis-match (if you end up having to do that) be the downstream sensors. The downstream sensors switch at a much slower rate, so speed is not as critical. So this would be a way to save some money, and still have a matched pair for the upstream sensors. The money you spent having the "Y" pipe changed was money well spent. My "Y" pipe change over on my '96 windstar was not fun. Laying on my back on the cold cement, having rust particles falling on me....etc. And I have a stainless exhaust....but still had the brackets, bolts, etc to deal with. There are a lot of little "challenges" that seem to come up with exhaust work.....and a good shop has the tools, and know-how to deal with them. And they have the "blue wrench" (aka torch) which in my hands would end up with my car, garage, and me burned up. When removing the sensors, treating the threads with some good penetrating oil a few hours ahead of time is a good idea. I would try to avoid getting the oil onto the part where the wires go into the sensor...or up onto the body of the sensor....as the chemical reaction that generates the voltage is a reaction between the air inside the exhaust pipe, and the air outside.....so you don't want to "smother" the sensor from the outside air. [ March 08, 2006, 11:33 PM: Message edited by: wiswind ]
 

marcre

Thread starter
Messages
288
Location
Timonium, MD
hello all, Today I had both catalytic converters replaced, the "Y" pipe and all four O2 sensors. I got a great deal on all that stuff on ebay. Anyway, on to my questions and ponderings. On Thanksging while driving home from doing the family thing, my CEL went on. It was P0420. Basically telling me my catalytic converter on my passenger side was not operating properly (either that or it could have been the (O2 sensor). Fastforward to today, I replaced it all. I asked to save the old O2's as they were probably still good, one is only a year old. One thing I noticed was that the O2 sensor from the passenger side located after the cat was covered in carbon. Compared to the other three, it was nasty. Here is the nasty sensory that was located after the cat on the passenger side (the bad cat).  - Here is the sensor from before the same cat. It is a little more nasty looking thatn the one on the other side.  - Here is a look at all four sensors (LF, LR, RF, RR)  - As you can tell, the one from the rear on the passenger side is filthy, the front from the same side is slightly more dirty compared to its counterpart on the other side. My questions are: Is it probable that it was just the O2 sensor? Is it likely that this is due to the oil burning issue? Is there anything else that this says to any of you? Is there anyway to test the sensors to see if they still work? I am sure the other three are fine, I am going to save them for a rainy day. My gas mileage has been bad for a while, does a bad cat or a bad O2 sensor play into that? My knowledge on this is limited, but I am going to assume that the cat was toast due to the look of the sensor. I am thinking it was clogged, I wish I would have asked to keep it. Thanks for all the info, marc
 
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