Yes, back again for help.

So, I'm back. Same car (91 Sentra 1.6L E). Rumors say it should get near 30-40 city/highway mileage... I am pulling 24, 26 at best. I have read all on getting better mileage, but I don't think it should be that low. I have changed the oil, filter, put in NGK spark plugs, wires are only a few years old, and bought one of those k&n highflow air filters. The only two ideas I have left that are causing my bad mileage is my oxygen filter and fuel injector. I am thinking of replacing the oxygen filter (can this be done on my own?) as well as clean the fuel injector manually.

So I have a few questions...

Where is my oxygen filter located?
Should it be replaced?
Where is my fuel injector located?
Can I remove and clean it on my own?

And also, any other affordable suggestions for better mileage? I am thinking of lightweight pulleys, any other advice?

Thank you all for your help... I'm new to the car scene, and I'm trying to learn as much as I can, and do as much as I can. Lack of money motivates this too... Anyways, thanks again. And sorry for reposting after a few months, I did all that was suggested, and found no result.

Edit: I do drive conservatively. I go through the gears, I shift when the RPM's rise above 2,500... So it's not bad driving habits. Slow acceleration, slow braking etc.

I assume you mean the oxygen sensor. Should run you about $60-$80 at a local parts store. Follow your exhaust pipe forward from your muffler and you should see a fat part of it that looks like woven metal towards the middle of your car. That's your catalytic converter. The oxygen sensor should be plugged into the pipe on it or near it, can't remember on 1.6's. If the sensor is bad, then replacing it would definitely make a difference in your mileage.

If you're not experiencing and misfiring or sluggishness, then the injectors are probably fine, but your MAF sensor might be going bad. It's in the intake tube right behind the airbox.

For other ways to improve mileage, see the Sentra ReadMe.

Your in luck, I had a 92 1.6L Sentra, and yes when my O2 sensor went bad, I was getting about 20-25mpg, as opposed to the 35-40 I got otherwise. The O2 sensor that you need to worry about is the one on the exhaust manifold (unless you live in California your car will only have one O2 sensor as well). When standing at the front of the car lookin at the engine, the piping that comes off the front of the engine is your exhaust manifold. On that is where your O2 sensor is, and it kind of looks like a big spark plug with a wire coming off it. Get the Bosch OEM replacement (it's one wire so it's only 30 bucks or so at Autozone.) You also will need a special socket, one that has a place for the wire from the top of the O2 sensor (about 5-10 bucks). Now mine was seized up to all hell, so I had to heat it with a propane torch for about 20 minutes till I was able to remove it. Once you get it out it is simply a matter of putting in the new one , and reconnecting the wires (don't worry, they just snap in).

For the injectors, most cleaners are junk and hurt them on our engine. For a new mechanic like yourself, I wouldn't tackle these just yet, and I doubt they are your problem. But a good test to check the flow is to put a long screwdriver on each injector, and put your ear to the other end, listening for the fuel and you can tell if it is sputtering or no fuel.

Good luck!

Jerod

Thank you for all your help. Today I replaced the oxygen sensor, bought one for $22 at AutoZone. I read a few times about it being near the catback underneath, including from fugiot... So I spent 20 minutes looking for it. Finally, I open my hood. And it is RIGHT THERE in front of me, angled perfectly, nothing blocking. Funny how that works... I'm going to record my mileage now. I don't think this one has ever been replaced actually, and its at 134,000 miles. It had the Nissan logo, so I'm assuming it was stock. I'll drive about 90 miles, fill it up at the same station, and see how much it took. Thanks again for all your help. Also, will replacing my pulleys with lightwight ones make any noticeable difference to anything?

Edit: I just read the above post carefully, noting the location... I learned the hard way, next time I'll pay attention lol.

Oh, one thing I forgot is this, you may want to reset your ECU so that your car will "relearn" the new O2 sensor faster. At least that is what I have been told in the past, could be just an old wives tale, but who knows :)

Oh, one thing I forgot is this, you may want to reset your ECU so that your car will "relearn" the new O2 sensor faster. At least that is what I have been told in the past, could be just an old wives tale, but who knows :)


How is that done?

unplug your negative cable and leave it off for about 20 min, then there is a procedure for resetting the idle and all that good stuff but idk if its the same for b15's as it is for b14 and earlier

unplug your negative cable and leave it off for about 20 min, then there is a procedure for resetting the idle and all that good stuff but idk if its the same for b15's as it is for b14 and earlier

I'm not sure if that works just unplugging the battery, I thought you had to do it from the ECU directly (under the dash where the center console is). The battery trick might work though, but I never heard of having to reset the idle. Either way, if none of this works, it should be good to go in a 100-200 miles or so.

something like insert the key and remove it 5 times very fast and then press and hold the gas till your SES light blinks, im sure theres a writeup somewhere im just too lazy to look right now

on that old of a sentra there is no corective learning on the ECM. It doesn't need to be reset. Feel free it disconnect your battery for 20 mins if you like :)

I think I may have another problem. I replaced the filter, and about 40 miles later, I started feeling some slugishness in my acceleration at times. I went to fill up my tank again (40 miles off of a full tank, I wanted to measure per gallon mileage.) So I filled up again, same station, and it put in 1.8 gallons. Which comes to about 22 mpg. So... Any ideas?

What filter was it that you replaced? Sounds like your not getting 100% combustion. This could be from any of the following.

Bad spark plugs
Bad distibutor
Bad/dirty injectors

What filter was it that you replaced? Sounds like your not getting 100% combustion. This could be from any of the following.

Bad spark plugs
Bad distibutor
Bad/dirty injectors


Sorry, I meant sensor. I replaced my oxygen sensor, and I have those problems that I said before. I never had them before. I replaced the spark plugs about 100-200 miles ago (NGK), cant be them. How can I diagnose the rest? I dont think its a coincidenco that I get this sluggish behavior after sensor replacement... I think it has something to do with it.

sounds to me like you should run the car for more than 40 miles before you make judgement on fuel mileage.
give it a tank or two then come back.
other than that, id say something went wrong with the o2 sensor install, or you got the wrong one or something. sounds kind of like your ecu is pulling timing.

sounds to me like you should run the car for more than 40 miles before you make judgement on fuel mileage.
give it a tank or two then come back.
other than that, id say something went wrong with the o2 sensor install, or you got the wrong one or something. sounds kind of like your ecu is pulling timing.


Well, I don't see what could have gone wrong with the install... One of the easiest things I've ever done. They gave me the right one, AutoZone made sure of that. What does it mean if it pulls timing?

the ECU senses something is wrong and goes into ohshit mode. it will retard timing up to 20 degrees in an attempt to save your engine from whatever it thinks is wrong.

that sounds to me like it, or else one of your other sensors is malfunctioning.
incomplete combustion is also called "missing" and you should be able to feel it when driving(rough idle, rough acceleration, excess vibration in the motor).

the ECU senses something is wrong and goes into ohshit mode. it will retard timing up to 20 degrees in an attempt to save your engine from whatever it thinks is wrong.

that sounds to me like it, or else one of your other sensors is malfunctioning.
incomplete combustion is also called "missing" and you should be able to feel it when driving(rough idle, rough acceleration, excess vibration in the motor).

Anything I can do on my own about this?

Yeah, it's got to be either the O2 sensor installation didn't go right, or your MAF sensor is bad too. It's a rare thing to have the MAF go out on you before the car is retired, but it happens.

Other than that, if you've replace the spark plugs and distributor, then the injectors are the only other thing I can come up with.