I just had my exhaust manifold replaced (used part) along with the O2 sensor (aftermarket) and went for a 1200 mile trip. Halfway I decided to keep track of my gas mileage and was amazed to find that I was only getting 11 - 14 mpg. My truck has 140,000 miles, but I was getting 18 - 20 mpg before swapping out the manifold and fixing the O2 sensor.
Also, the performance appears to be getting more and more sluggish. It doesn't like hills and unfortunately for my truck, I climb several everyday to and from work.
The mechanic who replaced the exhaust manifold said my former O2 sensor had been snipped and that was why my exhaust manifold rusted out.
The mechanic who replaced the exhaust manifold said my former O2 sensor had been snipped and that was why my exhaust manifold rusted out.
What happened to my gas mileage?
I don't see why having a clipped oxygen sensor would make the exhaust manifold "rust out". It sounds like something major is disconnected or not working (like an oxygen sensor), but it doesn't make sense that your mileage would have been normal before, even with a bad sensor. How along ago did the mechanic do the work? I'd take it back to him.
I don't see why having a clipped oxygen sensor would make the exhaust manifold "rust out". It sounds like something major is disconnected or not working (like an oxygen sensor), but it doesn't make sense that your mileage would have been normal before, even with a bad sensor. How along ago did the mechanic do the work? I'd take it back to him.
I had the work done two months ago and noticed the decrease in gas mileage within a few days after; the sluggishness is becoming more obvious. I hesitate to take my truck back to this mechanic as this will be the 4th time I will be returning to have yet another issue corrected.
A new O2 sensor was installed with the used exhaust manifold. Do you think there is a problem with the new sensor that would cause the poor gas mileage and performance?
Thanks for your help Bror Jace. I checked that thread before I posted my problem. I suppose it could be brakes dragging.
I've had my truck for 5 years and I find it odd that immediately after having the O2 sensor and exhaust manifold replaced that I began experiencing bad gas mileage. My truck has been consistent on gas mileage and performance for the past 5 years regardless of weather and terrain.
I think I'll start with the sensor and work toward other options.
A new O2 sensor was installed with the used exhaust manifold. Do you think there is a problem with the new sensor that would cause the poor gas mileage and performance?
It sounds like the new sensor isn't working right, and that would certainly cause poor gas mileage. However, it sounds like the original oxygen sensor wasn't plugged in, or the wire on it was cut? That would similarly cause poor gas mileage, yet you were getting exactly what you should have been getting...about 20 mpg. I would expect, that if the new sensor was bad, and that was the only problem, you wouldn't really see a net change in how the truck ran, since the old sensor wasn't working either.
I'd say something else is screwed up, and it probably has something to do with the exhaust manifold change, because that's when you noticed the difference. Maybe a different mechanic is in order. Unfortunately, there are some bad ones out there who really give the good ones a bad name.
It sounds like the new sensor isn't working right, and that would certainly cause poor gas mileage. However, it sounds like the original oxygen sensor wasn't plugged in, or the wire on it was cut? That would similarly cause poor gas mileage, yet you were getting exactly what you should have been getting...about 20 mpg. I would expect, that if the new sensor was bad, and that was the only problem, you wouldn't really see a net change in how the truck ran, since the old sensor wasn't working either.
I'd say something else is screwed up, and it probably has something to do with the exhaust manifold change, because that's when you noticed the difference. Maybe a different mechanic is in order. Unfortunately, there are some bad ones out there who really give the good ones a bad name.
Unfortunately I am a magnet for bad mechanics. My last problem involved a different mechanic who replaced my clutch but not the throwout bearing. So on top of having poor gas mileage, my engine growls whenever the clutch is engaged. As a student I don't have a large bank account so I can't always attend to the problem when needed or afford to have a mechanic charge me for a diagnosis. This forum has been extremely helpful in troubleshooting problems and narrowing the possibilities.
I love my truck and want to keep it as long as I can.
The disconnected O2 sensor could have plugged the catalytic convertor, which would cause excessive heat and crack the manifold. Plus, a plugged cat would also cause poor fuel economy. I don't know for sure, but I would look into the cat next.
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1998 Nissan Frontier XE/2wd/5spd 1 owner, 264k miles
1985 Olds Cutlass, 350 Chevy, owned for 14 years
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Well I hauled my truck into a different mechanic for inspection. This time I took it to the local Subaru dealership, yeah it's not the local Nissan dealer, but the local Nissan dealer is part of the problem.
It seems that one of the bad mechanics from past problems (throwout bearing) removed the bulb from my "check engine" light two years ago, and since then a whole slew of problems has arisen. The bad gas mileage is just the tip of the iceberg. I'm looking at repair costs upward of $1900. I won't know the final tally until they've dismantled the transmission which has been growling for months. Apparently there are bearings that need to be replaced?
If anyone knows of any websites out there that sell inexpensive Nissan parts, I'd sure like to know.
Thanks for everyone's help on this matter. I'll let you know what they find in regards to the bad gas mileage.
It seems that one of the bad mechanics from past problems (throwout bearing) removed the bulb from my "check engine" light two years ago, and since then a whole slew of problems has arisen.
Yes, small claims would seem appropriate, however I don't have proof that the mechanic removed the bulb from the check engine mechanism.
I did find out the source of my gas mileage problems. The mechanic currently working on my transmission told me that the idle was set at 0 when it should have been set at 14 degrees. He reset it, drove it and found it to have much more power and less activity on the gas gauge. Again, the same mechanic who allegedly removed the bulb was most likely the one who set the idle innapropriately. I would love to seek compensation and will continue to figure out how to go about that.
Now I await the final bill for the transmission problem...
Yes, having timing THAT far off would probably have a negative effect on fuel mileage. :-/ It's usually not something you think to suggest..."make sure your timing isn't 14 degrees off"...but then again, I guess anything can happen out there. Thanks for posting a follow-up.
I must have missed that someone did work on the truck and might've messed up your timing. That certainly would have an adverse effect on your gas mileage.
The same thing happened to me and my '95 Civic. Had the head gasket replaced and got the car back ... down on power. I also keep meticulous track of my mileage and after 6 weeks it was down 12%.
Took the car and my records back to the shop and they found timing was retarded ... not sure how much. They adjusted it and even advance it a little. Power came back as did most of the mileage.
Bad Gas Mileage
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Thanks for posting a follow-up.
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