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

 

[John99GSX]

TB- Are you able to open the TB with your hand? it should move fairly easy. You could have the spring thats winds around the arm too tight. You should be able to move the "rings" of the spring front to back what A little effort. When I get home I will count the "rings" and then respond here, that might get you close. You might want to check the TB and be sure you don't have any scrapes that the tb plate is sticking on. If you had it all the way apart and the plate out, maybe the seal is twisted up where the shaft goes.


If the turbo is scraping then you need to get it replaced. If its rubbing on the intake side then the metal is going to be pulling into the motor. Either way eventually your going to have a water or oil seal problem. I would not drive the car like that.


If a plug had oil on it then you could need to replace the seal on the valve cover (and the 4 for each spark plug well) or you could have oil coming up past the rings.

If you have a boost leak then you are counting air as it comes in, adding fuel for it, and then losing the air.
http://www.vfaq.com/mods/ICtester.html this is one way you can test for leaks.

You can cap off the turbo inlet, and the bov and apply pressure to the system (air compressor or air tank) at the intake manifold. a spray bottle and soapy water can make them easy to find. just look for the bubbles

 

[athens14]

when i disassembled the tb i didnt take the plate out. but it doesnt open very easily when the spring isnt on there. i gotta put some effort into it. i think i might just get a whole new tb. ill do a leakdown test probly sunday when my dad gets home, and im not driving it now. its in pieces in my garage.

 

[John99GSX]

TB- Without the spring or anything attached it should move very easily. Sounds like the shaft my be bent. New the TB is going to cost a bundle. You may want to check a few local salvage yards.

 

[ozzeran]

Hello guys, I have a 95 GST that when I bought it a year ago used to get 27-28mpg with just a kn replacement filter. Since then i added all the basic bolt ons and still managed to get 26-27mpg. I recently reverted my car back to stock and right after that I got 24mpg, and this last tank was 21mpg. I have since replaced my plugs, brand new air filter, coil pack, wires and fuel filter. Car seems a little down in power as well. I was curious what kind of checks I could do to the car? Car has 97k on it and I am sorta thinking about the o2 sensor but there is no CEL on at all. Also i have not performed a compression test either. Please any pointers greatly appreciated. This is a 5speed.

 

[oldman]

Hello guys, I have a 95 GST that when I bought it a year ago used to get 27-28mpg with just a kn replacement filter. Since then i added all the basic bolt ons and still managed to get 26-27mpg. I recently reverted my car back to stock and right after that I got 24mpg, and this last tank was 21mpg. I have since replaced my plugs, brand new air filter, coil pack, wires and fuel filter. Car seems a little down in power as well. I was curious what kind of checks I could do to the car? Car has 97k on it and I am sorta thinking about the o2 sensor but there is no CEL on at all. Also i have not performed a compression test either. Please any pointers greatly appreciated. This is a 5speed.

Did you touch any part of the intake tract when you return it to stock? If so, perform a boost leak test.

 

[ozzeran]

Did you touch any part of the intake tract when you return it to stock? If so, perform a boost leak test.

Yeah I have had the intake hoses off several times. Could be the problem, I need to make a boost leak detector. Problem is I dont have a boost gauge anymore to see what the intake manifold is seeing. I'll check that though and report back.

 

[oldman]

Yeah I have had the intake hoses off several times.

Do you mean the intake pipe before turbo? If so, it's not part of the intake tract. Intake tract goes from the turbo to intake vales and all vacuum hoses connected to it.

 

[ozzeran]

Do you mean the intake pipe before turbo? If so, it's not part of the intake tract. Intake tract goes from the turbo to intake vales and all vacuum hoses connected to it.

Yeah I had the upper i/c pipe upgraded along with a 1g bov on it, i took that off. I connected everything up very tight but that doesnt mean there isnt a hole somewhere in that tract. I also have fiddled replacing the lower with a hardpipe as well, now stock, so it has been handled a few times.

 

[midnght]

Get a gauge and hook it up while you are standing infront of the engine bay. "T" into the same area that you had one in before.

Make that boost leak tester.

Test it out.

Remove the "T"d in line and you are good to go.

 

[Defiant]

One tank doesn't mean anything. Give it at least five tanks to establish a trend.

 

[midnght]

Maybe even reset the car. And do as the oldman says.

 

[ozzeran]

Ok I performed the boost leak test this evening and here is what happened.

During the pressurizing of the pipes the bov would leak air out around 4psi and up. First of all is this normal? This is a stock 2g bov and stock 2g car btw. Most i could get the system up to was 12psi or so, but when i put my hand over the bov opening the system got up to 20psi. Either way the system wouldnt go above 12psi (guessing because of the stock bov) and it wouldnt stay there but for a second and leak its way down to 0. I hope i explained it ok, this is strange. Also i had my boost gauge hooked up to the intake manifold.

thanks

 

[oldman]

Damn 4 psi? WTF You should upgrade the bov asap but cap off the return tube for the sake of the pressure test so you can fix other leaks first if there are any.

 

[ozzeran]

Damn 4 psi? WTF You should upgrade the bov asap but cap off the return tube for the sake of the pressure test so you can fix other leaks first if there are any.

Does that 4psi indicate a malfunction with the BOV?

 

[oldman]

Does that 4psi indicate a malfunction with the BOV?

They're known to leak at 12psi and 4psi is just not good, it's normally one of the first mods for a 2G.

 

[ozzeran]

Ok well i'm glad i checked it then, so under boost its just being thrown back into the turbo and not the combustion process Looks like i'll be getting an upper i/c and 1g bov soon. I'll get that and then do another boost check.

Thanks

 

[asexton6969]

Why did you revert it back to stock...only to reupgrade it again...???

 

[ozzeran]

Why did you revert it back to stock...only to reupgrade it again...???

I get bored, problem of mine.

 

[carl5463729]

I am getting bad gas mileage. I get about 200 miles per tank. So far i have changed the spark plugs and yesterday the O2 sensor. I also used seafoam and i cleaned the trhottle body with carb cleaner. I have been watching my gas gauge and my milage doesn't seem to have gotten any better. I have a 90 eclipse GSX. Anything that helps would be appreciated. the car has 130,000 miles on it.

 

[DSM90AWD]

Check for boost leaks from the turbo to the TB and loose couplers from the MAS to the turbo.

May also want to change the fuel filter (if in unknown condition).

Have you checked your base timing and compression recently?

 

[carl5463729]

I was going to do the boost leak soon, i probably won't do the base timing, but how much would a good compression gauge be around. I will do my fuel filter soon because i don't know the last time it has been changed.

Thanks

 

[DSM90AWD]

I was going to do the boost leak soon, i probably won't do the base timing, but how much would a good compression gauge be around. I will do my fuel filter soon because i don't know the last time it has been changed

Compression testers are not very expensive. Can pick one up at any of the chain Auto Parts stores / Sears for ~$25.

If you're doing the fuel filter yourself make sure you have a set of metric flare wrenches to get at the lower fuel line fitting

 

[SoonToBeDSM06]

Harbor Freight has them for $15

 

[BergayaJS]

Make sure you're recirculating . I remember my friend who was not and got around that much too.

 

[toicy4ya]

Sup guys,

I know this question might be vague but here it goes anyway... What causes poor gas mileage on a eclipse (99 spyder gs automatic )? Tire pressure is fine, rims are stock 16". There are no air leaks in the exhaust, I checked it this weekend. I recently bought the car so I cant really tell if it had or needs a tune up but I plan on giving it one shortly. I've also noticed the slight smell of gas (fumes) coming from the rear of the car possibly the exhaust. Currently I get about 200 city miles on a full tank of gas, I know I should be getting much more than that. Any help would be greatly appreciated.


btw, i tried searching this topic but the search engine on this forum is really general.