To start of I have a 90 maxima 4DSC, or se or whatever. it has the VG. I know there is a known issue with the injectors but i dont know what the tell tell signs are, or what the exact problem is. Do they just stick open and dump fuel in because i do have a bit of a rough idle but upper rpms there isnt really an issue. From idle to around 2 grand it'll a lil rough but not jerky. i just filled the tank though and im down to a quarter tank after about 160 miles, I thought these could get around 20/gallon ( i realize my 90 is old) I've read also there could be a problem with the gauge being up to 5 gallons off. Do i just wait for the dummy light to come on or what? Any insight would be appreciated.

 

Best way to tell you MPG is to fill up the car and clear your tripometer, then drive til its almost empty and fill up. Divide the number of gallons you put in by the number of miles on your tripometer.

As far as mileage, my 89 SE has a 5 speed and I get about 27-30mpg on the interstate (thats where I do most of my driving). Whens the last time the car was tuned up? You might want to check all the basics (plugs, wires, cap, rotor, O2 sensor, etc...) that can have an impact on your MPG.

Good Luck, Joe

 

i wouldnt be surprised if you have a couple injectors going bad

do all the tune up stuff if you havent recently. do you know how many miles your o2 sensor has on it? If it has 60k on it or youre not sure its probably worth it to just replace it to see how it helps your gas mileage. i was getting 200-250 mpt and just replaced mine and the gas mileage increase is amazing.

I have a couple injectors goin bad and my car runs like yours (a little rough and shaky in low rpms and idle, doesnt affect acceleration too much... goes away in hgiher rpms, and gets a little worse when warm). but start with cheaper stuff if you havent

 

Forgot about injectors....

Yep, mine does the same, slightly rough idle....You could also try to run some Chevron Techron thru it, people here swear by it. Also, are you running premium gas in it? My GXE did fine on lower octane gas, but my SE dosent like it at all...go figure.

My SE especially loves Shell V-Power, I can actually tell a difference in idle using it and other brands.

 

yeah that stuffs no joke, just started using it

 

can certain gas makeu get more gas mileage..most of my driving is in the city. its true about the o2 sensor, ur gas mileage will go up. but what big difference can it make if ur injectors are totally shot..what is this chevron stuff.. is it fuel injector cleaner?

 

I've had my car do better on certain gas brands than others..such as the shell v-power...I get close to 30 on the interstate.

If you injectors are totally shot, i.e. missing and running like crap..you might can take them out and have them sonic cleaned. The guy I bought my SE from did that. Basically they put the injectors in a cleaning solution and then have some device hit the solution with ultrasonic waves that supposedly knock out the deposits.

If the injectors are shot, i.e. checking the impedance and finding they are BAD, then you need to replace them. You can get them out of junkyards but you dont know what you are getting, or you can get them new from internetautomar, his prices are good compared to what I have seen.

The Chevron Techron is an additive they add to their gas, but they also sell it as a fuel injector cleaner additive you can add to your gas tank. They sell it at WalMart and Chevron Stations. Works great flor clogged injectors. I have also had good luck with Gumout Concentrated Fuel Injector Cleaner and about 5 gallons of Shell V-Power. Actually had a clogged injector unclog with that and it has run fine for quite some time since then.

 

I had the same issues when I bought my used 91 max. First I got about 200 miles a tank, which is pretty sh***y. I replaced the O2 sensor, now I am getting 250 miles a tank. Next is the fuel filter, fuel injectors, ~300 a tank, and now a new knock sensor, I am getting about 365 a tank. Don't forget to clean the MAF sensor, check air filter and run some chevron with techron fuel system treatment.

 

yeah i run premium, ill start with the o2 sensor and fuel filter and go from there. Probably could use a tune anyway. I just bought it thrusday so who know whats bee done. Ill keep you posted.

 

My gas milege got alot better after replacing my fuel filter

 

Have you checked your spark plug wires??? Open the hood at night and look if you can see a blue spark when the wires are close to each other.

has anyone tried the "Valvoline Fuel SYSTEM Cleaner"?? it comes in a gold box. I have used chevron injector cleaner, and havent seen much of a difference. I was getting ~~350 before and after.

 

i just bought that chevron brand cleaner.. just for kicks,my mileage is pretty good considering i use my ac 3-4 times a day..all city driving,,their was a site here for cleaning the egr valve(but the sites 4 ve's) i guess il have to clean my egr and take some pics..

 

what would you use to clean the maf with....i heard they dont respond well to cleaning?

 

good point..that sensor is really touchy. i would try using electronics cleaner,its a spray that dissolves

 

hmm could you maybe use an air compressor to force dirt and grunge away with air pressure....maybe a combo of air pressure and electronic parts cleaner? just curious. Just got new o2 sensor on car with new plugs, gas mileage was about 240 a tank...it seems a little better now, but maybe not as good as some others are saying. haven't ran a full tank on new plugs and o2 sensor yet....my car runs and idles fine and everything, except for my random car "humpin" and very random car dies(1-3x a week). Was also wondering if i should replace my knock sensor and harness? doesn't seem like its bad...but is it like an o2 sensor and goes bad after 60k?

 

please do..

 

lol.. all this stuff u guys are talking about i just had them replaced.. some of u might have seen a post earlier about maxima stalling and bucking a lot..

so i took my car to the mechanic, they diagnosed it to be an ignition problem.. so they replaced my ignition module(the thing under the distributor and rotor).
i paid CAD$320 then drove around and it dies, i took the car back and have them re-fix it. they thought it might be bad spark plugs, so they replaced my plugs, and it still dies..
i drove back and had them fix it again. then they thought it might be a fuel problem, so they replaced my fuel filter... they charged me CAD$20 for the fuel filter and no labour. then i drove and it died again!
i took it back and have them fix it yet another time, then they spent another afternoon and finally found out i had a cracked distributor cap, and the master power plug was rotten, so they replaced my distributor cap and rotor.. then it still dies, then they decided to replaced the spark plug wires as well.. and hell those wires are expensive. they called up lordco auto parts, they only had these NGK wires available that cost CAD$235, but i went with it anyways, and the car has been running fine so far for today..

here is a pic of my engine bay with the new wires, they're blue and they're expensive!
http://members.shaw.ca/sunny_cps/IMG_0075.JPG

as for the gas i use, i usually go with chevron 87 octane. 89 or 92 when i'm feeling rich.. but i feed my max nothing but chevron. sometimes i might add a bottle of octane booster. otherwise everything else is fine...

 

You need to find a different mechanic. All those things (except the fuel filter) can either be tested with a multimeter or by just looking at them. Either the mechanic is taking you for a fool that he can gouge, or he has no idea how to diagnose a problem.

 

Not true. All those things singularly can cause the problem he's talking about. SO it is very possible and likely that they found each, one at a time and determined that was the sole cause of the issue. If they replace it and start it p in the shop and its runnin fine they give it back. They will not however, sit and test every little thing they come across in the engine bay though unless they are just dead slow.

 

How much did all this cost you???
Most of the things that they did are easy fixes, so buying a Haynes Manual will help. And $235 for NGK wires...Next time ask me, I can get those for about half that price..

 

First, to check plug wires, try using a spray bottle of water to mist the plug wires before this test. This will enhance the light show. Also, when doing the above night testing make sure you don't touch anything hot or moving in the dark engine compartment. Easy to accidentally touch a fan or belt in the dark.
Second, Chevron makes two cleaners, the fuel injector cleaner and the engine deposit cleaner (it's called something else now, like intake valve cleaner). I didn't get much out of the injector cleaner, but the engine deposit cleaner REALLY worked. One of the few cleaners that really does something.