Bad Gas Mileage [Merged 9-6]

[99GST]

I am still getting some pretty bad gas mileage.

I am only getting about 19.7 mpg with mostly city driving shifting at 4k.
I have already replaced my front O2 sensor and am looking to replace the fuel filter.

I have a 99gst with about 55k miles on it. Should my fuel filter already be bad?

What else should I check or change? I have NKG plugs and Accel wires are on the way.

Thanks,
Nathan

 

[VTRICCO]

i was planning on doing the plugs and wires in the next few days because that was my first thought of what it would be just curious if it could be anything else potentially

 

[BoostedinSoFla]

Also you might wanna change your O2 sensor if you haven't changed that in a while.

 

[blkwidow]

It could be a few things. Change out the fuel filter. It also depends on your driving habbits too.

 

[95TalonOwner]

It could also be a clogged cat.

 

[forumboarder154]

Clogged air filter maybe. Just putting it out there. Mostly maintenance problems, how its modded, or how you drive it could cause it to have bad gas mileage .

 

[dyno_detour]

My 95 twin brother runs about 27 mpg highway and 18 in city. 108,XXX miles

Like stated before, change your spark plugs and wires.

Also,

Fuel Filter
Tire pressure
Air Filter


Good Luck

 

[Glliw]

yea you definitely have a problem. When was the last time your fuel filter was changed? I get 30mpg highway at 123k miles

 

[fwdturbobov1996]

Isnt the awd fuel tank smaller than the fwd?

 

[95TalonOwner]

Isnt the awd fuel tank smaller than the fwd?

Yes, by only about a gallon.

 

[VTRICCO]

well like i said in the begining Ive only had the car for a week now so i havent had a chance to get thru any of the routine maintinence yet but i appreciate everyones input

 

[vr4gasmtt]

My cars getting terrible gas mileage. I don't know if its the weather or the car.

I usually get around 280-300 per tank, but my last tank of gas only went to 200miles, and I'm babying my car like no other. I'm not sure whats wrong with the car too, what could it be? I think my rear shock is beginning to go out, it squeaks when I make a turn and does that little rumble noise.

Could the rear shock going out be the problem? Keep in mind that I'm not sure if it is the shock? How do I check if the shock is good or not?

Any type of advice would work,

thanks

 

[Ceddy]

Your shocks will have very little bearing on you gas mileage.
A more likely culprit is the front O2 sensor. Test that.

Push down on both rear sides of your car. If there is difference in force needed to move it, then most likely one of the shocks is bad.

 

[sag1441]

try checking the plugs, wires, fuel filter, o2 sensor, air filter. all those things (might be missing some others) could have an effect on fuel economy. you can do a jounce test for the shock, push down on the rear and let go, it should bounce up and settle back down, if it bounces up and down then its time for replacement

 

[Chuck_3]

First off I have a 99 GSX with 75,xxx miles on it. The only mods I have so far is a injen style intake, hard ucip with 1g bov. Less then 1000 miles ago I replaced the spark plugs (Stock NGK's gapped to .028), plug wires, and PCV. Lately I've been having horrible gas mileage, even before I replaced everything. I can't even push 200 miles on a full tank of premium (91 Octane). My average is 160-180 miles on a tank. I don't rod on it, even if I try to push it and baby it I can't even hit 200 miles on a tank. I think I'm somewhere around 13mpg. I occasionally get a rich smell but not too often. My last guess is a clogged fuel filter. I have a new one, I'm just waiting for work to slow down so I can do it here where my tools are. Any tips for the fuel filter? It looks like its gonna be a pain in the ass. Would I still get a rich smell with a fuel filter clogged? If its not the filter any other suggestions of what it could be? Any help would be appreciated, Thanks!

 

[Gromit]

First off I have a 99 GSX with 75,xxx miles on it. The only mods I have so far is a injen style intake, hard ucip with 1g bov. Less then 1000 miles ago I replaced the spark plugs (Stock NGK's gapped to .028), plug wires, and PCV. Lately I've been having horrible gas mileage, even before I replaced everything. I can't even push 200 miles on a full tank of premium (91 Octane). My average is 160-180 miles on a tank. I don't rod on it, even if I try to push it and baby it I can't even hit 200 miles on a tank. I think I'm somewhere around 13mpg. I occasionally get a rich smell but not too often. My last guess is a clogged fuel filter. I have a new one, I'm just waiting for work to slow down so I can do it here where my tools are. Any tips for the fuel filter? It looks like its gonna be a pain in the ass. Would I still get a rich smell with a fuel filter clogged? If its not the filter any other suggestions of what it could be? Any help would be appreciated, Thanks!

Classic signs of dead/failing O2 sensor. I think recommended replacement intervals are 60k miles. Do you have a logger? If so, look at your O2 voltage at idle/closed loop operation. You should see it cycling nicely between 0 - 0.9v. If it doesn't cycle or just spends most of the time on the low end it's either dying or dead. A dying O2 sensor will tend to read lean & cause the ECU to add more fuel which leads to your rich exhaust smell & bad gas mileage. OEM-identical Denso replacements can be found cheaply at www.sparkplugs.com

 

[v2ner]

http://dsmtuners.com/forums/showthread.php?t=242145&highlight=gas+smell

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[ChvyKc]

No fuel mods at all? I had the same problem with my 255HP and the stock fuel pressure regulator. I was around 12-15 mpg even on the interstate before I swapped it for a higher flowing one.

If you're still on the stock fuel set-up then I would say fuel filter or O2 sensor.

 

[Blueiii]

Also, an added FYI since you may ask shortly. It still can be the o2 sensor even if you're not throwing a CEL. The o2 sensor will progressively deteriorate and it may not be registered as dead (yet) but will impact gas mileage.

 

[andymoraitis]

Classic signs of dead/failing O2 sensor. I think recommended replacement intervals are 60k miles. Do you have a logger? If so, look at your O2 voltage at idle/closed loop operation. You should see it cycling nicely between 0 - 0.9v. If it doesn't cycle or just spends most of the time on the low end it's either dying or dead. A dying O2 sensor will tend to read lean & cause the ECU to add more fuel which leads to your rich exhaust smell & bad gas mileage. OEM-identical Denso replacements can be found cheaply at www.sparkplugs.com

Exactly!

Also, an added FYI since you may ask shortly. It still can be the o2 sensor even if you're not throwing a CEL. The o2 sensor will progressively deteriorate and it may not be registered as dead (yet) but will impact gas mileage.

Nicely said and very true.

 

[abaum565]

I experienced a similar problem also. It turned out to be one of my plugs. But a lot of people suggested a boost leak test, just to make sure.

 

[Chuck_3]

Classic signs of dead/failing O2 sensor. I think recommended replacement intervals are 60k miles. Do you have a logger? If so, look at your O2 voltage at idle/closed loop operation. You should see it cycling nicely between 0 - 0.9v. If it doesn't cycle or just spends most of the time on the low end it's either dying or dead. A dying O2 sensor will tend to read lean & cause the ECU to add more fuel which leads to your rich exhaust smell & bad gas mileage. OEM-identical Denso replacements can be found cheaply at www.sparkplugs.com

Thanks for the response! I do not have a logger, but I'm going to go ahead and get a new 02 sensor.

Also, an added FYI since you may ask shortly. It still can be the o2 sensor even if you're not throwing a CEL. The o2 sensor will progressively deteriorate and it may not be registered as dead (yet) but will impact gas mileage.

Thanks, I was wondering that since gromit said "failing" and I don't have any CEL's I figured it might not throw any if it was at the early stages of going bad.

Thanks again for the responses and help, I'll let you guys know how the new 02 goes.

 

[Chuck_3]

Well I went ahead and just had the 02 sensor delivered to my work from the Mitsubishi dealer instead of getting one online. I got lucky that it was slow enough towards the end of the day for me to install it at work. I filled up on my way home from work, hopefuly this does it. Thanks again.

 

[eboy0]

Keep us informed, i replaced my o2 sensor, yet i'm in the low 140's per tank...

 

[sureshot971]

Yes it could most definetly be the 02 sensor, both of mine went bad within a week and i was getting like 12 the the gallon. Replaced them and right back up to 20mpg.

 

[laserspeeddemon]

Well since the 02 was well covered I'll give you some other tips. Boost leaks, clogged cat-converters, bad timing, bad valve seals (falls under boost leaks) and worn piston rings will also cause bad fuel milage. Have fun!