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

 

[Disturbance]

So I thought that maybe when I got link that this problem would hopefully go away and it hasn't. On a full topped off tank of gas I get no more than 200 miles on a full tank of gas. According to my AFR gauge I don't run rich at all, I do run very rich under full boost but I didn't hit boost once this last tank of gas and got 170 miles and it was on "E" does anyone have any idea what's going on?

 

[faulkner]

have a wideband? or larger than stock injectors?

 

[Disturbance]

It's just a narrowband, but on link it's showing that its not running rich, and stock 450 injectors as far as I know

 

[faulkner]

hmm, maybe an o2 sensor. and tuning done? safc?

 

[redheadbov]

most common cause of bad mpg is leaking exhaust before or near the front 02,
make sure all your exhaust is leak free,
next make sure there are no vacuum leaks

 

[crash89]

How many gallons are you putting in when you're filling back up? 2g's have almost a 16 gallon tank. I thought I was having a similar issues a few years back. Turned out I was only using about half a tank of fuel but my gauge would read full to empty. Thats an issue with the sending unit. Try running the car until your dummy light comes on, thats what I did and the needle went WAY past E

 

[MJBean420]

Narrowbands are garbage/waste of time. Get a good wideband to get accurate AFR readings.

 

[Disturbance]

Vacuum is good, deleted all my emissions stuff and have great vacuum and no boost leaks at all, what's the best way to check for exhaust leaks? My gas gauge does seem to act weird, it stays above F until about 100 miles than drops to E within 70-80 miles. It seems like every time I fill it up I'm putting about 13-14 gallons in though. It doesn't have a dyno tune or been tuned by a professional, I have just kinda played with it myself. This has been an issue since I bought the car.

 

[91-GS]

Have you checked for fuel leaks? Check both lines, delivery (please correct me if it's called something different) and return.

 

[Breezio69]

I just had exhaust leaks all over my bay... fixed one and another would emerge. Look for black soot around the gaskets, on the head around the gasket, around the turbo to manifold, on the o2 manifold, and around the downpipe gasket. Another indicator is if you've got some white residue on those same areas.

Also, I could tell when my downpipe gasket went because the wastegate was sounding like it was open dump, a bad o2 gasket (that I currently have in the mail) will make the turbo sound like it's "fluttering" under boost. The manifold and turbo gasket will simulate a boost leak so you will have those symptoms if its bad... I lost 7psi for a week waiting for my 7cm ss gasket.

I had same symptoms of fuel loss with a bad o2. And my gauge does the same thing, ill be at full or around 7/8 of a tank for like 3-4 days then it only takes me a few more days to go through 3/4 tank. Seems like the gauge holds at full for a while then gets back to the real reading.

I'm getting a confirmed 25mpg average though, I set the trip every fill. Usually fill to 10 gal not a dollar amount and get 250-275 miles on it depending on if I get lead foot or not for that week.

 

[JosephMiranda]

To check for exhaust leaks inspect the whole exhaust pipe starting with your exhaust manifold youll be looking for any black suit around where a pipe meets another pipe or where your manifold bolts to the head. You may have to remove your heat shield. If you habe a friend stick a rag in the end of your exhaust tip causing a restriction you may actually be able to hear a leak when the car is on and you lay under it.

 

[DSM1G90]

2G's are hefty vehicles - almost 3000 LBS for a 2.0L to move around and along with running another axle ... in which all of this eats up fuel at a decent pace.

And 91/93 octane is such a dirty fuel with all of the additives that the fuel really isn't a hot and clean burning fuel ... and that's gonna be some mileage reduction as well.

Big thing is town driving - dumping the clutch, or tranny shifting with an automatic and mashing on the throttle soaks up SO much fuel. Just takes that much to get the mass moving forward until the weight and engine power can catch up to each other.

With my stock 1G turbo, in town I just barely can muster 21 mpg and that's being easy on the throttle and barely any boost, but get the thing on the freeway doing 80mph on cruise control engaged for a good hundred miles, I can get close to 30mpg.

 

[Bmxr152]

If you think 3000lbs is heavy try a galant vr4. Mine weighed in at 3456lbs. I get about 220 a tank and put just around 11 gallons in. I have a mix of city and highway with 5 to 6 wot sprints. I would say get a wideband and see Whats up with your air fuels.

 

[Spanky_DSM]

haha AKA baby evo, anyways im surprised at your gross weight. I always thought those things were lighter. Guess a colt/mirage is the way to go for the weight savings.

 

[FIBA M - EC17PSE]

As said already check if your o2 sensor upfront is cycling, I renewed both of mine and I now get about 300 sometimes a little more to a tank if I drive normal on the highway,

 

[Disturbance]

I'm averaging around 13 mpg city driving without getting on it or anything. My logs in link seem to show that my o2 is cycling fine. If it was an exhaust leak would it make this big of an impact? The only other strange thing it does is when it sits for awhile and I start it, it kind of bogs and idles low for 10 seconds than the idle kicks up and it seems to run fine.

 

[DSM1G90]

Mine weighed in at 3456lbs.

"Dang!" No wonder why the 4G63 VR4 came with a B16G and 510's to muster out 225HP from the factory ... to slug that extra weight around compared to the 1G's Turbo FWD coming in only at 2700 lbs.

Is "Disturbance", an automatic? Also, do you have a 195* T-stat installed, for if not, the ECU will make the thing run rich trying to get the block heated up to what it's programmed for best effiency....and that will kill mpg in a heartbeat.

 

[Disturbance]

It's a 5 speed, and I haven't checked out the T stat, ill take a look into that

 

[johnpaul17]

I have the ability to get better gas mileage if I keep my foot off the peddle and car out of boost, which rarely happens

 

[Wooley91TSI]

Currently getting 14 mpg in my 91 awd auto. 14b, 550's, 2g maf untuned. Car runs pig rich through the rev range until the temp gauge reads in the middle, then it leans out a bit and starts running 13-15:1 afrs at cruise, 10:1 at wot and 10-12:1 at idle for some reason.

AEM standalone running speed density going in this week so im not too concerned. just kinda curious what the problem might have be.

 

[dsmgst1996]

Your untuned on 550s and you have even stated you are pig rich . Rich Rich = more fuel Im supprised with no tune your even getting 14 mpg

 

[spyderdrifter]

So I'm finally sick of trying to figure this crap out. My car is averaging only 170 miles per full tank of fuel. I only use premium like normal. I have a new O2 sensor, but nothing has worked. Need ideas.....

 

[WES_393]

What about boost leaks, exhaust leaks, or alignment issues?

And have you verified that the new front O2 sensor is actually working? I've seen dozens that were bad right out of the box.

 

[spyderdrifter]

No leaks. Even realigned it a couple weeks ago. The o2 does work. Have verified that with my scanner. I do have sporadic smoke from my exhaust that to me looks white, but others think its a very light blue. Not burning coolant, but my oil level has gone down some.

 

[DSM1G90]

Even an engine being an oilburner can still give decent gas mileage if all is in order - like timing, A/F ratios, tires inflated at proper trim and the similar.

170 miles on the fill can looks like a rich running system. I hit double that on a fill, mainly due to freeway driving and get close to 27 MPG.

How's the PCV valve or system .. breathing normally or all choked up ?

-DSM