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

 

[mokkema]

Yes. What kind of BOV are you running? You want to get one that recirculates back into your intake. You DO NOT want to vent your BOV . Type in vent and BOV in the search feature and you will see a million reasons why.

hey i know venting is bad...believe me i know. my main question was whether it was bad in the fact that it wasted more gas ontop of running rich and losing performance.

 

[its_hey_ma]

I vent to the atmosphere and have no problems. None at all. And good gas milage. Are u venting correctly or did you just stick a loud blow off in place of your stock one and call it a day?

 

[chico904]

About how much MPG did you get?

 

[mokkema]

I vent to the atmosphere and have no problems. None at all. And good gas milage. Are u venting correctly or did you just stick a loud blow off in place of your stock one and call it a day?

honestly I don't know. I bought the car this way. its a blitz bov...and it sounds great...


but fvck it if the gas milage (which i DONT know yet...I'd have to go threw all my trips yesterday and today to find out) is gonna be this bad.

 

[boostedinaz]

A vented BOV will cause bad milage, but depending on how you drive it shouldn't kill a tank in one day. It sounds like a combination of things that may be your problem. When was the last time the O2 sensor was change?

 

[98DropTop]

venting=bad everything

what about venting using the blow through method w/ the MAF-T and the GM MAF sensor?

 

[CorvetteBoy]

As long as the Sensor is after the BOV, your good to go!

 

[bob123131]

Just got fmic and my gas mileage has always sucked like 18mpg but now its like 12. Do i prolly have boost leak or could this be explained by the large greddy front mount?

 

[HighPsi92GST]

did you do a leak test after the install?

 

[bob123131]

Yes but i couldnt find my good compressor and i only had a tiny one for like balls and stuff that only goes up to like 3 or 4 psi so i couldnt tell really.

 

[bob123131]

I felt around all couplers and stuff while some one rev'd it for me and couldnt feel anything.

 

[funguy]

weird, when i installed my fmic and pipes and all, i'm getting way better mileage. with lots of boosting too and venting.

i would check for leaks.

 

[Thomas91169]

definately leaks of some sort.

and since a FMIC usually lengthens lag, you can drive around under 0 boost usually(depending on turbo's) which is what saves gas. the less boost you can do, the better your economy will be. my buddy had a 56 trim and got excellent mileage(up to 350 a tank he says) but me on a evo16g can get maybe 250. and its all in how one drives.

 

[HighPsi92GST]

was it your first tank of gas since the install? People tend to run their cars harder after installing a new part to see how it works/feels !

 

[carl5463729]

I only get about 200 miles out of a full tank of gas. with a 16 gallon tank that's about 12.5 miles per gallon. My lifters are ticking, so would that be the cause of the bad gas mileage, or is it something else. I just bought it with 130,000 miles. it's a 90 GSX.

Thanks guys

 

[marcmsj]

lifter tick would have no effect on your gas mileage...

first thing to check when having bad gas mileage would be your O2 sensor. make sure it's in working order. if not, take it out and clean it (brake cleaner works great). that has been known to fix a dirty one.

 

[flytalon93]

When was the last time you had routine maintenance done, ie plugs, wires, etc?

 

[carl5463729]

Yeah, i just bought the car and am out of money right now, but i should be buying some plugs soon. I'll check the O2 sensor soon, but how do i know if it is good, and what else should i do.

Thanks guys

 

[leakyfaucet]

lifter tick would have no effect on your gas mileage...

Of course it does. If it's bad enough to get picked up by your knock sensor, the ECU will retard ignition timing, making for a much less efficient engine.

 

[marcmsj]

Of course it does. If it's bad enough to get picked up by your knock sensor, the ECU will retard ignition timing, making for a much less efficient engine.

yes, if it's bad enough it could come up as phantom knock, which would retard your timing... if anything though you'll be losing a bit of power, i don't see it making as a significant impact on gas mileage as he's reporting and i'm willing to bet it's due to something different.

 

[Kapok6]

Of course it does. If it's bad enough to get picked up by your knock sensor, the ECU will retard ignition timing, making for a much less efficient engine.

I am guessing that could be the problem with my car too. I have a 1992 AWD Talon and I only get like 150mpg if I am lucky. My lifters are really noisy. I suffer major power loss. I have been trying to figure out what the problem is for a year now. I recently got smart and spent $20 bucks on a datalogger and am reading a knock count of 43 before I even hit boost. There is no way I am detonating on stock boost (or before) with 93 octane. So my only conclusion is noisy lifters or a bad knock sensor, and since the ticking is loud, I am assuming it is phantom knock caused by lifters. I am going to test th knock sensor, and if it turns out fine, I will be replacing lifters. I think the lifters are a very logical explanation for your bad gas mileage, however, that could be caused by a # of diff things. Just my $.02 Thanks for the space.

-Ryan

 

[Dream On]

You might also try a new fuel filter if you don't know when the last one was changed. It can help increase your gas mileage. Good luck.

 

[athens14]

ok so i cleaned the throttle body yesterday, but when i was doing so the spring assemby that the accel cable connects to came apaprt. i cant figure out how to make it right. i put it back together but now it seems as almost if the tb was sticking, even after i cleaned it. how much does a whole new tb cost? could i get it from a junkyard or should i get used upgraded one? also i am running extremely rich according to the nose test. i can smell the fumes in my car, no help from the leaky dp though, but i get horrible gas mileage 189mi last tank. i need to figure this car out. also when i spin the turbine on my turbo, it makes kind of like a rattling sound, and doesnt spin that freely. is my turbo shot? this car is starting to dissappoint. any help would be appreciated.

 

[John99GSX]

Is the TB sticking open or staying shut? the spring could be to loose or to tight. Did you totally disassembled it, or just remove it and clean it? check the sprint for a line, maybe your lucky and someone had marked it before with whiteout or a marker. If so the sprint needs to be wound until they line up. Pick one up from the junkyard if you can not get it assembled correctly. follow the cleaning or seal replacement FAQ.

http://www.vfaq.com/mods/wayback/BradBauer/engine/tb.html

http://www.plymouthlaser.com/tbor.htm


For the turbo do you hear or feel it touching the housing? some play is ok but if it is rubbing anything that is bad. For a stock turbo it should spin a few turns when you spin it by your fingers.

running rich- have you changed plugs, wires and so on recently? maybe a boost leak causing extra fuel. we would need a lot better info to track that down. is the back of the car black, or putting out black smoke when you go WOT?

 

[athens14]

ok the throttle body is sticking shut, and yes i totally disassmbled it. my bad. and i can hear and feel touching the housing. im guessing thats pretty bad right? it spins a few times though but sounds like a ringing when i turn it. im pretty sure i have a mean boost leak somewhere but i cant figure out where. i have the sympotms of it. as for the fuel part, o have not changed the plugs or wires recently. i took then out and looked at them and they look fairly new. but when i pulled out one of them it was covered in oil. didtn know what to think so i put it back in. im pretty sure there is no smoke coming from the back of my car. im stuck on this.