Curry

iTrader: (1)

I'll keep that in mind when shopping for plugs. Thanks.

UDel

If you are driving in New York City you are going to get horrible gas mileage no matter what. Four cylinders get bad fuel economy in the city. There was a thread a few months ago by someone with the same problem and he tried everything but the culprit was all the stop and go driving, poor roads, short trips, and car never having a chance to warm up to proper operating temp in New York City. On the weekend drive out of the city and try driving it mostly on the highway. I am sure your mileage will drastically go up, if it doesn't then you might have a problem.

Are your tires properly inflated? You may want to over inflate them. Are you using snow tires?

Remember that all that money your putting into your GS like new spark plugs, O2 sensors, servicing, alignments, replacing suspension parts just to try to improve mileage is going to cost you a ton more then you will ever get back in improved mileage. Unless your car needs these things or they are due to be replaced I would not bother spending all that money in hopes of just improving gas mileage a little because it is not worth it.

Curry

iTrader: (1)

Even with highway driving i'm getting about 11-12. The plugs do need changing. Alignment is also needed since most of the front end was in crappy shape. I ended up replacing everything with the front suspension. I highly doubt the o2's need replacing.

Tires are inflated to factory spec. No snow tires on the car.

UDel

If you are only getting 11 or 12 mpg on the highway then something is off and not working right. You should be in the 20's for steady highway driving. I was able to get 25-29mpg on a vacation trip that was all highway and with the GS430 loaded with suitcases.

jcat_350

1mpg could be the result of deciding to wear sneakers instead of boots every day for a week.


Curry, since you've already reverted back to stock wheels and cleaned out your trunk, these items should be next, in order:

-air filter
-clean maf
-clean TB
-lucas fuel system cleaner in your next tank
-spark plugs
-fuel filter
-diff fluid (yes, it does make a difference)
-o2's
-remove injectors and have them professionally cleaned/replaced




EDIT: just saw your most recent post where you say "plugs do need replacing". DUH. that'll definitely kill your mileage.

jcat_350

that's like saying I'm not going to spend the money on cleaning visits because I'll eventually have to go to the dentist to get dentures anyways.

Running with bad plugs makes the engine run RICH. Running too rich causes the engine to EAT piston rings. Running with bad injectors can cause the engine to run LEAN. Running too lean causes the engine to BLOW.

these cars REQUIRE regular maintenance to stay running as well as they do for as long as they do. Have you ever tried to comprehend how the self-learning ECU even works? All the tiny little variables it calculates? If airflow, fuel flow, ignition timing, or anything is even SLIGHTLY off, you're hurting the engine's performance.

Curry

iTrader: (1)

I didn't know about the diff fluid, thanks for the heads up on that.

Sorry what I meant was the plugs don't need replacing as in they have been in there forever. I recently did them but I wanted to pull them to double check them to see if anything was wrong with them. I did pull them a month ago and there was nothing wrong with them and they were gaped correctly.

jcat_350

how do you know they were gapped correctly? did you actually check the gap with a slide gauge? If so, this may be your problem. When installing plugs for these cars, you should NOT attempt to gap them.

I bet once you think about this, your mileage was OK until you checked the plugs (and i'm betting checked the gap with a slide gauge) and reinstalled...I'll be anxiously waiting your "Ah HAH!" momend

Curry

iTrader: (1)

When I put the new plugs in (as-is) the mileage was still crappy. I ended up pulling them, looking at them and putting them back. Took them out again a month later where i then I used the thin metal slide to check them. The plugs were bought from autozone. Denso's... I'll see if I can find the PN for you later.

jcat_350

were they platinum? iridium? Copper? I'm pretty sure the GS300 requires ONLY iridium plugs (please correct me if I'm wrong, anyone that knows for sure).

I remember when I was on the maxima boards back in the day, those cars called for copper plugs, and some guy tried NGK iridiums and it eventually ended up blowing his headgasket (through other contributing causes of course) but still.

Curry

iTrader: (1)

I honestly don't remember what I bought that day. I just told him 99 GS300 he looked it up and gave me plugs.

Curry

iTrader: (1)

Sparkplugs.com says NGK Iridiums BKR5EIX-11

UDel

Did you even read what I posted?

I said don't start replacing things just to try to get better fuel economy unless they NEED to be replaced as part of regular maintenance. What I was saying is if the part is working properly and not due to be replaced then it can be a waste of money to just start replacing a bunch of parts working properly in the hopes of better fuel economy. I never said not to maintain the car or if the plugs were bad to not bother replacing them. Try rereading the post if you did not comprehend it the first time because I never said what you are eluding to.

Some people spend a ton of money to try to get better fuel economy like cold air intakes, lighter aftermarket wheels, engine cleaning kits they see on infomercials, after market spark plugs, expensive batteries(I have heard people say certain batteries give them better fuel economy), etc when none of it needs to be replaced and all they do is put a bunch of money they will never get back from better fuel economy and most of that stuff won't help fuel economy anyways and that is what I was getting at. I never said not to replace things that are in need of replacing.