lately i've noticed that i've been getting worse and worse gas milage. no no, it's not because i'm driving harder. i'm pretty consistant with my driving habits. i've talked to someone and they said that i might have carbon build up on my valves which is causing me to have bad gas milage and loss of power. or maybe i have loss of power so i mash down on the gas harder which leads to bad gas milage. anyways, i was wondering if anyone could help me out? should i take it into the shop and have a pro check it out or try some of those store fuel treatment or carbon reducing blah blah blah stuff? you know, like STP or other stuff.... i would preffer to work on it myself and save money so if anyone might have an idea on why i'm having these problems please let me know. it would help me a bunch!

thanx

oh yeah, i drive a 93 gxe....auto <--- +(

 

There are numerous possibilities. I have been working on the same problem with my '91 SE auto and have made some progress.

First of all, you might want to consider a full tune up. This includes, fuel filter, air filter, plugs, wires, distributor cap, rotor, and PCV valve. While you are under the hood, check for vacuum leaks. Wiggle the hoses, visually inspect... These can be difficult to detect but a small one dramatically affect performance. Also, be sure that your tires are properly inflated.

Another thing to check is the various sensors that feed information to your ECU. These include the 02 sensor, knock sensor, coolant temp. sensor... I recommend at least a Chilton's manual to properly diagnose these. These procedures can also be easily found by searching the archives. Do the self diagnostics for your ECU, that will give you the most information.

These are just a few ideas off the top of my head. Obviously, there are many other factors that can influence fuel economy. I would advise searching the archives as there have been many intelligent responses to questions such as yours.

 

How about the cat? If that's clogged it can ruin your mpg.

 

Every 6 months I run a can of BG 44k to clean out fuel system, carbon, etc. I get it for $15 at www.extrememotorsports.com Also I started cleaning my battery terminals and all ground wires as I come across them doing other maintenance. I use a dremel grinding stone to remove paint and primer from ground points and a medium stainless steel wire wheel to clean all brackets, connectors and bolts. After a complete tune up and the BG 44k, cleaning grounds provided an additional 10% increase in MPG. This doesn't surprise me since so many members also got improvements using the hyper wires. The stock grounds are poor, they attach a ground wire to a painted or primered surface with a bolt and the bolt is the only ground path. I remove the paint and primer completely thus increasing the ground path by a factor of three or four. I have since added an electric dielectric grease to ptotect the cleaned surfaces from corrosion. Got a lifetime supply for $5 at Advanced Auto. Not only did it increase milage but performance is noticably better. I guess this is my version of the free hyper ground system. After cleaning the grounds the car just started running better and better over a period of several weeks. We are now getting 22 mpg in 100% in town rush hour traffic. We used to get a solid 20 mpg before. By the way the car is an automatic 97 I30. Used to get 30 mpg on trips doing 80 to 90 mph, haven't had a trip since doing grounds so I can't report on trip milage. I assume getting an increase in town would translate to an improvement in trip milage but to be sure I need to go on a trip. Hope this helps!

 

Funny you should mention this....my gas mileage has been consistently rising over the last couple of weeks...yes rising. This is after I cleaned my pop intake filter, emptied the car of unnecessary stuff to make it lighter and I am yet to clean my throttle body. I still have my 50lb sub box in though. I used to get 300-305 on a full tank, but as of today, I'm at 401 on the full tank and right at the top of the E mark. I drive about 1000miles a week (yes i get raped on gas ) so i need the best gas mileage i can get. I'm gonna have to do those grounding things you said. sounds like a really good improvement.

 

Does anyone know what the average gas milage should be on a 94 SE. I'm getting just about 250 miles to the tank. I've got a bad knock sensor, but I don't think it should be affecting my gas milage that much right??

 

1000 miles a week?! Damn man, you sluttin the hell outta yo ride! I am only getting about 300mi to my tank if Im lucky, but I havent given my car a tuneup since the summer. My VG would get 350-400 miles to the tank and I used to put 1000mi per week on that car too. So I been there... I put 70k on that car in less than 2.5 years.

 

so what would be considered decent gas mileage for these cars? my 97' SE 5 spd. used to get about 400 miles to a full tank. my 93' GXE auto gets about 320. is this ok? i know manual usually gets more and i noticed this right away when i purchased my 99' infiniti I30t. i was getting about 340 per tank. big difference from the maxima.

 

I get between 20 and 27 on my 89 SE 5 speed AND it needs a tune up. Changing the fuel filter makes a huge difference.

 

try fuel injetor cleaner... it might help also to drive below 2500 rpm

 

i'm not too sure about those injector cleaner thingys...from what i heard they might do more harm than good. I used em for a lil bit but didnt notice any improvement or anything. I now get 415 miles to a full tank which is a huge improvement after cleaning my tb on thursday. Need to get that grounding thingy done as soon as it gets warm again. Temps dropped from 60 yesterday to 20s today, so out of the question for now.

I'm currently at 186900miles and rising fast. By the end of the semester i should be at 199k or thereabouts.

 

I think part of it is that Nissan engines don't like winter gas. This is the 3rd winter I've owned my car, and the gas mileage consistently goes down for "no apparent reason" during the coldest months. My $0.02.

 

thanx a lot everyone. i checked the easiest part to check, my air filter, and sure enough it was blacker than my exhaust. there was a section that wasnt just covered in black gunk, but there was like a ball of gunk stuck to it which protruded out atleast 1 cm.
got to nissan too late to get a filter. was thinking of getting a K&N drop in filter from pepboys, but the guy at the dealership said they stopped carrying K&Ns because the oils on the filter ruin the air sensor or just make it not as accurate.
you guys have any other recommendations for air filters, such a the $50 blitz one or any other high performace ones for a decent price.

as soon as my midterms are over, imma try and find the fuel filter. and hopefully durring spring break, ill check out my other sensors such as my air, knock, blah blah blah sensors.

if you guys have done this before, it would be a great help if you could let me know where some of these things im looking for are. pictures are always a plus!

thanx

 

you guys have any other recommendations for air filters, such a the $50 blitz one or any other high performace ones for a decent price.

I decided to keep the stock airbox and use the AMSOIL 2 Stage Air Filter. It is an excellent filtration filter while maintaining excellent air flow. Normally these parameters are mutually exclusive but they did a fine piece of engineering. You wash the filter about once a year and re oil it. Because of the design of the stock box and air filter I figured I would not have oil migration problems in the MAF, I have had no problems in 18 months of use. Cost about $30 and there are AMSOIL Dealers on this forum that will sell to you at a discount.

As far as pitures to help, you have several choices, keyword search on this site, www.motorvate.com and Haynes Manual.

If the air filter was that bad you probably need plugs, pcv valve, fuel filter, oil filter and oil and definitely clean the throttle body.

 

Yo, I'm lucky if I get 250 to a tank these days on my 94SE. If I do, I'm sucking fumes. Knock sensor seems fine, cleaned the throttle body, clean air filter, frequent use of injector cleaner and use 94 octane only. 95% of my driving is in traffic though so that may just the way its gonna be.

 

you guys have any other recommendations for air filters, such a the $50 blitz one or any other high performace ones for a decent price


-I'm running with a blitz right now. I like its look and it seems to stay cleaner than my old K & N but honestly, its not like I can tell any difference in performance or mpg.

 

I've had good luck with my K&N, haven't notice much gas mileage increases but I can definetly feel more torque. You must change your fuel filter, mine gas mileage went up 20% and I had a friend who's car went up 4-5 MPG.