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

 

[spyderdrifter]

The past 2 fill ups I've done, I've kept the receipts to do such, but I forget to do it then loose the receipt. I'm about to pull the sender unit back out so I'll check it out for saturation.

 

[spyderdrifter]

Well, today I tested the resistance on my level sender unit and it seems to be fine. Pulled it out and put it in the full position which gave me 3 ohms, and empty gave me 115 ohms. Put the unit back in and it read 99-100 ohms which by my math gives about 3 gallons left in the tank at 6.6 ohms per gallon. I checked the resistance of the fuel gauge and it's at 88 ohms which is low. Should be 122 ohms. So I'm looking at it being the issue now. I finally filled up full though, 14.044 gallons. That's the most I've ever gotten into a DSM tank. But had 216.1 miles on the trip ODO. I reset it for this fill up so we'll see where I am when it's low again mileage wise. I kept the receipt this time and will track it fully. I ohm'd my injectors too since I do know there's trace fuel odor in my exhaust. They all read 2.9 ohms. Checked the injector connectors and cyl 1 & 2 are both at 44 ohms and 3 & 4 both read 79 ohms. Anyone know if that's right for the connectors?

 

[BogusSVO]

Check the temp sender to the ECU, when they fail, they tell the ECU that it is colder that what it really is, so the ECU dumps more fuel to compensate for the colder denser air.

IIRC, the DSM sensor fails to -70*

I see that you may have located one issue, but it will not hurt to check this one.

 

[spyderdrifter]

The temp sensor was brought up while talking to others as well and it's not more the 5 months old. Bought a new one since I broke the old one.

 

[iiNFAMOUSCHRiS]

ah, bookmarking this thread...i'll probably be needing this...i was getting 8MPG before I pulled the head off the car

 

[Hillala]

Now you have me thinking what type of milage I get and why... Granted you can litterally watch the fuel gauge drop when i'm balls deep on it but other then that I have no clue what i'm getting, never really care to think about it.

Even if the temp sensor is new i'd still check it to make sure and rule it out.

I highly doubt this is the reason for crappy milage on yours but who knows. About six years ago, mine had three out of four injectors that had a very slight leak. It didn't really effected the car in any way other than crappy milage.

Although if i'm not out of my mind there could be a lot of different reasons you're getting bad milage. Fuel, air filter, dead animal wedged up under your car somewhere creating drag. From what you said, you're getting around 15-16mpg? If your in it hard and often or the condition of the roads you drive on aren't the best, that sounds about normal to me. I live in an area with a ton of hills that kills my milage on both of the other cars I drive not just my dsm.

Dude, Chris... if you're getting 8mpg, I challenge you to a duel of crappy fuel milage, sir.

 

[iiNFAMOUSCHRiS]

Dude, Chris... if you're getting 8mpg, I challenge you to a duel of crappy fuel milage, sir.

that's without getting into boost very much, haha. but my car is torn apart right now waiting for me to get my new head put on, then replacing all the vacuum lines and checking for boost leaks and such, so i'm hoping for an improvement....haha, but im gonna do the stuff suggested in this thread though.

 

[Tyeler18]

No need to keep the receipt. Drive until you're at say 3/4 of a tank and fill back up full again. Then divide the amount of miles you went by the gallons of gas you put in. That's all there is to it, I do it at the pump with my phone every fill up

 

[Hillala]

That sir is how you do it.

Unless you're a lazy ass some of the time like I am and just push a button and your car tells you what your average is... then you realize you're not in your DSM because something broke again.

 

[962ndgen]

ah, bookmarking this thread...i'll probably be needing this...i was getting 8MPG before I pulled the head off the car

Sounds like a timing issue, what did you do while the head was off?

 

[iiNFAMOUSCHRiS]

the head is currently off, being replaced this week. it had a couple burned valves, also vacuum and boost leak... all being fixed now

 

[buhay6]

I'd check injectors and stock fpr, somethings giving out under boost. You've basically checked everything else.

 

[Benjyc32]

you could always pull your gauge face off and filling your tank up andthen outting your needle to the full mark and seeing what it does from there.

 

[spyderdrifter]

Well I checked all my parts again yesterday. The gauge reads empty with 262 miles on the trip ODO. Checked the tank and had 3 1/4 inches left with the level sender reading 81 ohms which leaves 34 ohms left from 115 ohms at empty. This equals 5 gal at 6.6 ohms per gal (or 1/4 tank). So I think it's safe to say my gauge needs to be replaced.

 

[Maroon98gst]

98 eclipse gst.... So I've been driving the car for about less then a month. I just got it, bought it in wi. Filled it up an was getting like 300miles out a full tank on way back. Got it back an now were only getting like 160 to a full tank. I put injector cleaner in, been running premium 92/93 octane. I thought it would help but it just seems like it gets worse, also needle likes to jump like it will drop a quarter tank in 16miles. Any ideas guys?

 

[callmesaj]

98 eclipse gst.... So I've been driving the car for about less then a month. I just got it, bought it in wi. Filled it up an was getting like 300miles out a full tank on way back. Got it back an now were only getting like 160 to a full tank. I put injector cleaner in, been running premium 92/93 octane. I thought it would help but it just seems like it gets worse, also needle likes to jump like it will drop a quarter tank in 16miles. Any ideas guys?

are you sure your actually running through the whole tank? Your float could just be bad. and do you have an adjustable fuel pressure regulator? are you running rich? i need more info bro!

 

[Insane20]

Like he said it could be a bad float or the float could be stuck. My ground was all rusty, so I relocated it to a cleaner location and my gauge work's fine now.

 

[Maroon98gst]

I'll have to check that thanks man... An no adjustable regulated the whole car is pretty stock

 

[Insane20]

Check all your lines for leaks if it turns out not to be the gauge. Also dose it have a cel?

 

[Maroon98gst]

No I do not have a fuel cell... Also I hit fuel cut any idea to what size injectors I should get

 

[Insane20]

I meant is the check engine light on. My advice is do a boost leak test, compression test, and all maintenance before we start talking about bigger injectors. Get it running perfect while its still stock so when you start modding all the bs of running issues is over.

 

[spyderdrifter]

Here's a link for the testing I did on my fuel sender unit and fuel gauge (post #1773)
http://www.dsmtuners.com/forums/newbie-forum/1415-bad-gas-mileage-merged-9-6-a-89.html#post153344858

It turned out that my fuel gauge was bad, and that I was getting the normal fuel mileage.

I have a picture somewhere that I'm looking for to post here for you that shows which spots to use to test your fuel gauge. Once I find it I'll post it for you.


EDIT: Here's a link to the posts with the picture to test your gauge.
http://www.dsmtuners.com/forums/mai...ry-fuel-gauge-not-accurate.html#post153350386

It also says AWD unit, but it worked out for my FWD.

 

[Maroon98gst]

Thanks, an no none of the lights are on. car runs fine only issues I'm having at the moment is clutch an fuel mileage.

 

[spyderdrifter]

What's your clutch issue?

 

[Maroon98gst]

http://www.dsmtuners.com/forums/newbie-forum/475134-got-worse-clutch-issues.html