i know theres tons of threads out there about mpg, but i've read them all and i asked around my local mechs (norman from sidepex?) and the forums tell me 12mpg is kinda low but the mechs told me it's normal and 15-17mpg is really rare. my car's completely stock, it's been given a recent full tune up and had the idle turned down. i'm still getting 12mpg from a 11.6gal tank? i was thinking o2 sensor, how much would it cost to replace (minus labor)?

o2 sensor is $35 +/-



makes all the difference in mileage. my stock 91 is getting 22ish, which is better than expected

i'm getting around 18 or 19 in city. but it still stinks horribly rich.

yeah, smell has nothing to do with mpg https://www.nopistons.com/forums/pub...#>/biggrin.png

how can i check my o2 sensor? can i replace it myself with basic tools?

i get 17ish mpg city driving w/ an 88 n/a with full exhaust, intake, all emissions removed etc etc. with a/c and p/s still on it too. and the plugs are like 10k-ish miles old. on the highway ive come close to around 22-24mpg.



kevin.

hmm i need an alignment pretty bad too... actually, all new suspension if i were to bother.

Ive consistantly hit 20 or 21 combined on a stock 88 N/A, so it is possible. definately check your O2 sensor, and at 12 mpg, make sure u dont have a hole in your gas tank. Does it smoke on startup?

no smoking.



can the mpg have something to do with my brakes?

well, it would, but only if they were REALLY dragging, or you just like keeping the middle pedal depressed when driving. Unless one of the calipers is completely seized, i doubt ud take a 50% hit in fuel economy, and if one of them was seized or dragging, you'd be able to hear and feel it

that's probably not it then.



o2 sensor? how can i check?

turns out all my brakes are MAD dragging. i got the car lifted up and the wheels are hard as hell to turn. solutions?

to test the sensor you need an o-scope so just replace it if there is any doubt. to fix the dragging you need to rebuild your calipers and prolly do a full brake job. you can get rebuild o-ring kits from mazdatrix for something like 13 dollars a caliper....

well...i got it looked at by an rx-7 specialist. turns out it's my brake lines, i'm gunna get a stainless steel set. the guy didn't check my calipers but he said he was positive that it was the brake lines.

if all your wheels are hard to turn id sorta doubt it was the calipers too, probably a line restriction somewhere thats not letting fluid back to the reservoir.



kevin.

so...a stainless steel set probably wouldn't help the problem? my friend had the same problem on his 1st gen and the problem went away when he switched to ss lines.

when he said it was your brake lines, did he mean the 6 or so inches of rubber hose or the hard lines that route back to your engine bay? if it's the rubber ones then yes the ss lines will fix the problem because you are replacing what has failed....make sense?

yea what he said.



but to add a little bit too it. if putting the SS lines on doesn't fix it then it could get pricey. most of the time replacing the rubber lines (most people replace them with the braided lines) should fix the problem as they deteriorate internally and block themselves up.



you could try opening all the bleeders and doing a complete system drain of brake fluid too might help you out, you could do it when you put on the braided line.



kevin.

ok well yeah he meant the 6 or so inches. and i ordered corksport single rotor ss lines early this morning so that should fix the problem.



on one hand, it makes sense that the ss lines will fix the problem because this car's been sitting for a decade before i came along and bought it (a few coolant hoses were dried up and so are the tires). on the other hand, ALL four brake lines failing? of course, some brakes are worse than others but they're all dragging.

Well, it is possible for all 4 brake lines to be collapsed/pinched, but with the car sitting out for 10 years, I'd still check and make sure the pistons in the calipers aren't seized. If you have any doubts, just replace everything. I recently put new calipers, rotors, and pads on my GXL and truth be told, it wasn't very expensive. I got rebuilt front Bendix calipers for $38 apiece (lifetime warranty), $33 each for front Bendix rotors, and $35 for front Bendix pads. Rear calipers tend to be a lot more expensive, I think I paid $90 for my left rear when the parking brake seal blew. I got everything from Advanced Auto, because around here their service and prices are very good.



As far as the Oxygen Sensor issue, I also just replaced mine on the same car, and I think I paid $18 for a universal Bosch one from Advanced Auto, it definitely improved my mpg, considering that the one that was on there before wasn't hooked up - the wire was melted through. I get about 21mpg in mostly stop-and-go traffic, with some highway speeds in between. My car is an 86 GXL with a full RB exhaust, cone filter, and 255 wide tires in the back, so it's not too bad.

can i install the o2 sensor myself? anybody got pix?

oh yeah, lxk99, are you talking about this one?



http://www.partsamerica.com/ProductDetail....ype=291&ptset=A

oh yeah is my o2 sensor that thing plugging into the red square?



Attachment 20848



btw, i dont have any CELs going off....so wouldn't that mean my o2 sensor is doing fine? or wait...does that only apply to the s5's?

You can install an oxygen sensor by yourself, it's easier if u have an oxygen sensor wrench/socket with the cutout for the wire. CEL probably wouldn't happen, given that its an S4. My wire was probably melted through for months before I noticed it. And yes, that's the one. Mine is on my header, so it's actually under the car and there's no heatshield, and it took about 30 seconds to remove the old and install the new. Yours should still only take a few minutes, even what with crimping the new end on the wire (the stock connector won't work with a universal sensor, but its no big deal).



PS-yes that is where the sensor is located, in your pic.

ah so i have to do some splicing/crimping then eh. does the o2 sensor really explain my 12mpg though?



and also, do speed bleeders really help that much? i still dont understand the concept of bleeding so i'm hoping speed bleeders might prevent me from pumping air into the lines.

the o2 sensor could be part of the problem, but the dragging brakes are definitely something to look at, as well.



speed bleeders are Ok if you don't have someone to help. It allows you to do the job alone with much less chance of getting air in the lines. The basic concept of bleeding is super easy.



IM me at kyrmsegalore if you'd like help with anythign

double post

ok here's another question



it says here "Measure the pedal height (distance from the center of the brake pedal's upper surface to the firewall, behind the insulation). It should be 7.48-7.68 in. (190-195mm) for 1979-85 models, or 8.07-8.27 in. (205-210mm) for 1986-89 models."



i measured it in my car and it's about 6 in. now can that be my problem?

That probably has something to do with the stuck caliper/collapsed line issue. Either of these would cause the pedal to not return fully.

ohhh ok. i'll install the new ss lines next saturday and we'll see how that turns out.

one last question. how long does it take to install the new brake lines? i have 3 hours with the lift at my friend's shop.

Shouldn't take that long. Just make sure you take your time not to strip/break anything, and take your time bleeding the system. Make sure the master cylinder doesn't get empty, and make sure not to press the pedal fast, or you'll just end up with tiny bubbles of air instead of actually bleeding the system. Pump the pedal slow, take your time.