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

 

[hellotbone]

Your second O2 sensor just tells the ECU if the cat is working or not, this would be the O2 right after your cat. The one upstream of the cat is the one that the engine relies on for information on fuel tuning. Have a look over this sensor.

 

[91BlackLaser]

The gas mileage in the laser is terrible. I installed a AFPR as I was told the 255lph pump was over-running the stock regulator. On a half a tank my son only managed 113kms (about 70miles). Why would it be soooooooo bad?

 

[erebusknight]

high rail pressure builds up high pressure right behind the injectors. This is why the injectors may be pissing more then neccessary(you want more fuel at higher loads). This is why fuel pressure goes up when there is no vacuum (technically more load on the engine). Mabye your son has a heavy foot. I know I do! Have a little chat with him about street racing. He may spill the beans (I think my parents just know Im a speed racer)

 

[No_Skillz]

Any tune/maintainence performed on the car? Is this before or after the FPR install?

 

[91BlackLaser]

Any tune/maintainence performed on the car? Is this before or after the FPR install?

After the AFPR. Car has been dyno tuned with an SAFC.

 

[91BlackLaser]

high rail pressure builds up high pressure right behind the injectors. This is why the injectors may be pissing more then neccessary(you want more fuel at higher loads). This is why fuel pressure goes up when there is no vacuum (technically more load on the engine). Mabye your son has a heavy foot. I know I do! Have a little chat with him about street racing. He may spill the beans (I think my parents just know Im a speed racer)

His foot is a bit heavy. Can't blame him, he went from 10psi to 19psi and he has been "testing it out". This tank has been driven under normal driving conditions as I told him to drive it normal so we can see what the car will get for mileage. So far it is very bad. What does everyone see for mileage?

 

[erebusknight]

Well I get about a little over 200mptank even when I goose it at the occasional stoplight. 19psi is kind of high dont you think? I heard that it aint too good for the factory turbo, much less a high mileage turbo

 

[91BlackLaser]

Well I get about a little over 200mptank even when I goose it at the occasional stoplight. 19psi is kind of high dont you think? I heard that it aint too good for the factory turbo, much less a high mileage turbo

I backed it off to about 16PSI already.

 

[PieEyedPiper]

Back it off to 15psi.
Check for boost leaks,
Make sure you're not venting, (bov)
Was the dyno tune before or after the AFPR?
I can squeeze ~300 if I have to out of a tank of gas, but oddly enough I only managed 220 last week. We drive weird creatures.

Also drive it like a granny!!

Let us know if anything helps

Edit: do as you will in regard to how much boost you want to run, I thought you were a 2g/T-25

 

[Tx97GSX]

Change out your Fuel Filter, Put new plugs in and spark plug wires. That should help you get improved gas mileage.

 

[Black91TSiAWD]

I dont know about everyone else, but I can get over 400 miles on a full tank in my talon. Granted I dont have any fuel mods and I drive alot of highway, but 140-ish miles on a full tank says somethings not right to me too.

Checked the o2 sensor? They can severely kill has mileage when they go out

 

[droppinbottom]

With normal in town driving i can barely squeeze 180 out of a tank. And I rarely get on it. Now for highway driving I can easily get over 250.

 

[gammey4]

The fuel pressure is raised to compensate for boost, if the regulator was installed and the fuel pressure was set to high it would allow to much fuel in. Put it back to factory specs and put a rotten egg under the gas pedal. I usually get 275 out of a tank, all stop and go.

 

[mr2turbo]

I can get a little over 300 on a tank If I only get on it a couple times. Make sure you do regular maintenance That's a huge factor in MPG

 

[turbo2g111]

Also, be careful not to call it miles/tank, but rather try and figure out miles/gallon. As we all know, our DSM gas guages suck. Mine will go from reading 1/2 to 3/4 tank depending on if I'm driving up hill or down. The miles/gallon is a much more important number.

 

[nightspeed87]

remember we have a return fuel system . well at least in the first gen dsms, i dont know about the 2nd gens, so sometimes you have more fuel in there then you think you do even though the needle sits on E. just pay attention to the gas light and whether it comes on, because on my 1st gen eclipse ive driven on it on E for pretty long distances and it never ran out of gas ( of course only because i didnt have money at the time to fill up) Also a255 pump will definitly push out more fuel especially without a tunable regulartor to back off on someof the fuel. but changing thge o2, getting a hiflow fuel filter, fuel injection system cleaned, andinjectors andregulartor flow tested and that should restore performance and mpg. And if not well hey you still got a fast car that im sure doesnt burn more than a v6 or v8 monster... but with the way gas prices are rising who knos how important mpg is really going to become...

oh and maybe try hacking your mass air flow sensor because i hear ppl do that for fuel cut maybe it wont make your car run as rich. I did it on mines but havent noticed fuel differences but car ran a little better . maybe worth the effort. Also full exhaust mods, underdrive pulleys , lighter flywheels, knN air filters anything that essentially make the engine gain power easier and or take from rotational mass or back pressure will give you more gas milage that i do know from experience. good luck on your quest for less gas station trips...

 

[toicy4ya]

Sup guys,

I’m consuming entirely too much gas. I currently live and do most of my driving in the city. Currently I’m consuming about 200 miles per tank which is roughly about 13 miles per gallon. Since initially having this problem I have given my car a complete tune up. I’ve changed the oil (Mobil1 10w-40) oil filter (Mobil1) fuel filter, air filter (K&N) pcv valve, spark plugs, wires and replaced the O2 sensor (denso oem) and I’m still having the same problem. I have a 99 GS automatic w/ a 2.4 engine, 18” rims with the correct tire pressure. I’m stumped! Any one has this problem or has any suggestions on what to look for to resolve it? It would be greatly appreciated.

Also, someone asked me whether I gapped the spark plugs correctly. I informed that that I had not because as I understand it they’re pre-gapped. Would this affect gas consumption?


Thanks

 

[DSM90AWD]

Also, someone asked me whether I gapped the spark plugs correctly. I informed that that I had not because as I understand it they’re pre-gapped. Would this affect gas consumption?

There is no such thing as "pre-gapped" plugs. The same model plug may be used for several different make/model/year car. The box does not know which of these you drive

Yes, fuel consumption would be affected

 

[toicy4ya]

BTW, whats the correct way to reset the ECU? I've read several ways,

1. unplug the negative battery cable for 5-10 minutes?

2. unplug the negative battery cable for 5-10 with the car idling and hit the brakes a couple of times. Then reconnect and let the car idle for a while?

3. unplug 10A fuse by fuse box located near the brake/gas pedals for 5-10 seconds?

Being that the car does not automatically give a signal or sign that it was done correctly, can someone please set the record straight on the correct way to do this without a datalogger?

 

[DSM90AWD]

#1.. though should not take that long to reset

 

[Nautica985]

1. unplug the negative battery cable for 5-10 minutes?

it only takes 15 seconds

 

[pooya]

Sup guys,

I’m consuming entirely too much gas. I currently live and do most of my driving in the city. Currently I’m consuming about 200 miles per tank which is roughly about 13 miles per gallon. Since initially having this problem I have given my car a complete tune up. I’ve changed the oil (Mobil1 10w-40) oil filter (Mobil1) fuel filter, air filter (K&N) pcv valve, spark plugs, wires and replaced the O2 sensor (denso oem) and I’m still having the same problem. I have a 99 GS automatic w/ a 2.4 engine, 18” rims with the correct tire pressure. I’m stumped! Any one has this problem or has any suggestions on what to look for to resolve it? It would be greatly appreciated.

Also, someone asked me whether I gapped the spark plugs correctly. I informed that that I had not because as I understand it they’re pre-gapped. Would this affect gas consumption?


Thanks

10-40 is kinda thick....I would suggest a synthetic 5-40 or 5-50

 

[kawboy]

You're actually getting about 11-12 miles per gallon

And wouldn't those tires affect gas mileage if you are doing a lot of city driving?

 

[WhtEclipse705]

There is no such thing as "pre-gapped" plugs. The same model plug may be used for several different make/model/year car. The box does not know which of these you drive

Yes, fuel consumption would be affected

Actually the some Iridium plugs from NGK are pregapped. now other plugs are different, thats when you really need to make sure gap is right..

 

[The_EE]

Dont forget 02 sensor. If its reading incorrectly, it will pump out too much fuel.