Terrible gas mileage: Bad plug wires or bad o2 sensor the culprit?
Disclaimer: Excuse my car lingo as I am by no means a mechanic or anything that would allow for me to sound educated when talking about a mechanical problem.
I have a 2000 dodge neon and just recently got a check engine light. It said that it was running too rich and that the o2 sensor was bad. I don’t remember the exact code but I know that it was the sensor that is right behind the block on the top of the exhaust. I changed the spark plugs out only to find that they were damp and black. So I know for sure that it is running rich. What started this whole venture was that fact that my car was getting about 15 miles per gallon when I know that it should be getting closer to 30mpg.
So my question is, is it more likely the o2 sensor that is causing my car to run too rich thus causing bad gas mileage or is is possible that the plug wires are bad and I’m not getting efficient spark and it it is running too rich? Thanks.
Things to be considered:
I’ve just changed the plugs out with new NGKs.
The air cleaner was checked and was clean(also recently replaced)
I drive very conservatively to drive to conserve my gas.
I believe the code was P0135 which indicated that the system was running too rich and the guy at autozone straight up told me that the code was saying that the o2 sensor was shot and needed to be replaced. So what I’m getting at is the o2 sensor being completely shot the culprit behind my car running too rich and consuming way too much gas?
As far as I know, the MAS is fine. I’ve never gotten a check engine light for it or anything. What do you recommend that I do?
It sounds like I just need to replace the o2 sensor and see if that fixes my problem. My dad just keeps telling me that he has never seen an o2 sensor cause what is happening with my car but everyhing that I have read online indicates otherwise. I think the computer is not giving proper fuel/air ratios because of the faulty o2 sensor, would this make sense?
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Filed under Gas Conservation FAQ by on Feb 22nd, 2011. Comment. 
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Comments on Terrible gas mileage: Bad plug wires or bad o2 sensor the culprit?
possibly your carburator needs a repair kit.This is usually not that expensive and well worth the effort to have a mechanic find,repair instead of you (I like you am by no means a mechanic,yet will dive into my vehicle to fix ,to save some $$$) “throwing good money after bad”.
best of luck
Since the first post refers to the “carburetor” in the first sentence, we can immediately ignore that post.
While it is possible that the spark plugs are in such rough shape, they caused the running-rich problem, it is unlikely. The plugs and wires would have very gradually become weaker until they reached this point and this would have been an ongoing issue for some time.
An oxygen sensor can fail much more quickly and immediately cause the running-rich problem. Since you already have the code for the oxygen sensor, I’d be more inclined to check that first.
What exact code did you get? There are something like 20 possible o2 related codes and only a few of them actually point to a o2 sensor problem, most of them are saying what the sensor is reading is not what the computer expects to see and in that case there is noting wrong with the sensor.
First thing I think of when someone says their mileage as gone down but everything seems to be running fine is a bad fuel pressure regulator. Another symptom of a regulator problem is hard starting sometimes. I dont know that car or engine at all so I cant tell you where the regulator is located or if its easy to test and or replace.
when you do a tune up you should change the cap rotor and wires.if the code shows oxy censor is failing then you should change it.it controls the amount of air fuel being delivered to carb
Bad plugs will set a misfire code and turn the CEL on. The 02 may be the problem but it could also be the MAF sensor. I would need to read the engine data with the factory scan tool and check out the 02 sensors voltages and switching time. Next I would read the MAF sensor voltages and grams/second. You can try cleaning the MAF sensor wires with brake cleaner, gently.
Spark plug wires would have set a code in the 300 range indicating a misfire. Your P0135 is most likely the sensor. Read more here:
http://www.obd-codes.com/p0135
Mm… Is that what you want? http://findsth.info/838/air-cleaner