Was 37mpg, now 23mpg?!

[Spike]

Okay.. First tank of gas we used got us 168 miles (13 inch wheels, so x 1.07 = 179.76), 37mpg out of 4.9 gallons. Next tank we got around 36mpg.

Then.. next tank we got 24.7. (121 x 1.07 = 24.66 out of 5.25 gallons of gas).

This is from empty, as we have yet to fix the fuel gauge and were judging by *around* 30mpg. So of course we ran out of gas and thank goodness I keep a gallon of gas with me (as unsafe as it is, we're doing what we have to for now).

Next tank had 4.7 gallons and netted us 23mpg. Mostly highway, accelerating as slowly as possible for much of this (and not going over 57).

I know I need a tune-up and a few other things, but what could cause such a drastic change inside of a few days? Our rusty Maxima gets 24mpg..

All tanks were using the same roads, speeds, and gentle driving.

Thank you for any help!

~Spike

P.S.: Oh, and the normal idle since we've gotten the car is pretty high, about 1700-1900 rpm, even when warmed up (although in first and second gear, doesn't get over 3k rpm even at 60 very often). Any help on this would be awesome, too.

VVV This is the car I'm talking about.

[Basement_Modder]

Wheel bearings? Low oil? Bad calculator?

[TominMO]

VAF went bad or wire broken, putting it in "limp-Home" mode, which uses a lot of gas.

O2 sensor shot.

Small hole in gas tank.

Someone siphoning your gas at 2 AM.

I'd start with the tuneup and check the O2 sensor, since they are simple, straightforward fixes. Then check other things.

[Spike]

Is the o2 sensor fairly easy to replace? Every time I think 'Oh, I have money to go get that manual now!', something else pops up that defers my money..

Been trying to find a thread saying how to replace, but I must be missing it.

Any specific brand I should look into, or would a $19 Bosch from Advance be fine?

Sorry to ask so many questions, but I'm slowly ...slowly... learning.

~Spike

[FestYboy]

use a Denso unit and "rent" the tool from the store. you'll need PB Blast and someone with a torch to get it out.

[htchbck]

Denso, part number 234-1000... you will have to use a pair of pliers to crimp the new sensor to the old plug wire. From AZ its about $15. Or you can pay over $50 for the exact same sensor part #234-1010 that has the sensor wire on it already. If you know how to use a pair of pliers, just get the $15 one though

[TominMO]

+1 on the Denso unit, as Festyboy said. The Bosch has a different electrical range.

Some O2 sensors are a biotch to get out, others come out fairly easily. There is a special long socket for O2 sensors, which has a section cut out so you can remove/install it without cutting the wire. Put the socket and ratchet on it, turn a little to put tension on it; tap the socket with a hammer to set up vibration; hopefully it will then break loose. Also, if it resists you, you can try tightening it just a little, also to help break it loose.

If you don't want to pay for the special socket ($10?), you can just cut the old O2 sensor's wire and use a regular long socket.

And be sure to use anti-seize on the threads of the new sensor!

[Spike]

Interesting how the normal Denso is $13.99 locally, and the all-ready one is $29.99 locally.

Think they'd figure a set price for an item country-wide.

Is a torch 100% needed? If so, I'll need to just send it to a mechanic, as I don't really have anyone around here with tools.. or anything else.

~Spike

[jamesmc]

Don't forget the PB blaster, and give it plenty of time to work. I always used to not bother, because I thought it wasn't that necessary. Learned that one the hard way.

[navdoc101]

The Denso I got with connector on was $19.95, & came with a tube of anti-seize. Mine was very easy to remove . PBed it the day before & used a breaker bar on the ratchet. The old one was all clogged up. seems a little zipper now.

[WmWatt]

Third part question: Do you have to remove the heat sheild? Mine's rusted on. One of the bolt heads is rounded. Thanks.

[WmWatt]

Duplicate post deleted.

[FestYboy]

Is a torch 100% needed? If so, I'll need to just send it to a mechanic, as I don't really have anyone around here with tools.. or anything else.

~Spike

torch isn't TOTALY needed most of the time, but i'm af the BE PREPAIRED philosophy. a brazing torch can be used as well. if you're really in a pinch, you can alternate BP soaking and getting the manifold hot by runing the engine. you should get your hands on a LONG 3/8 ratchet no matter what. Titan makes one as well as EZ Red, and you may find one at a local tool dealer.

[Spike]

Thanks for all the help!

I'll be attempting this in a few days, as soon as I have enough cash to do it.

Here's my last, tiny question:

Does my not having a catalytic converter have any bearing on the o2 sensor? The car came without it, and there's just normal exhaust pipe welded in its place.

~Spike

[htchbck]

No, it won't affect anything with the O2 till you get to 1996 and up (OBDII) since those have a second sensor after the convertor that is for emissions purposes.