Horrible Gas Milage, What can i do?

[99GsxMD]

I have read a lot of these topics to try to figure out how to get better gas milage because my car is getting terrible gas milage. I own a 99' eclipse gsx, with a few mods such as ic piping, greddy rs bov, and intake.. thats its. My milage is horrible and i am trying to figure out ways to help my milage. If you know of ways i can get better gas milage please let me know thanks.

 

[sprfunk]

How is your car running? Idle? I would do a boost leak test.

 

[Artago]

Boost leak test, Vac test, new O2 sensors, new catalytic converter, clean and replace air filter, new sparks plugs/wires and if all else fails.... get a bigger (late spooling) turbo. But most importantly of all, change your driving habits.

 

[99GsxMD]

How is your car running? Idle? I would do a boost leak test.

Well i bought it about 3 months ago... but it really runs well. At idle, it sounds fine, idle's just around 600-700... which is about normal. But at idle, i can smell gasoline from the exhaust. Where can i buy a boost leak tester so i dont have to make one?

 

[Artago]

Where can i buy a boost leak tester so i dont have to make one?

Took about 30 seconds to find using the search feature:
Boostpro.net : Products - Boost Leak Testers

If you smell gas from your exhaust at idle (when the car is warm) you probably have a dead (or dying) O2 sensor.
I got mine here:
Sparkplugs.com - Application Search Results

 

[99GsxMD]

Took about 30 seconds to find using the search feature:
Boostpro.net : Products - Boost Leak Testers

If you smell gas from your exhaust at idle (when the car is warm) you probably have a dead (or dying) O2 sensor.
I got mine here:
Sparkplugs.com - Application Search Results

Yeah the car does have 95000 miles on it so that could be the issue. Thanks man.

 

[Artago]

Yeah the car does have 95000 miles on it so that could be the issue. Thanks man.

No problem. Let me know if you have any other questions. Good luck. Tom.

 

[crimsondragon]

How bad is "bad?" Our cars do run on about 25 mph average. like 21ish for city miles and 30ish for highway. You said you bought it 3 months ago. Was it like this when you bought it? Have you done a full complete tune up since then? Check the fuel injection internals for anything worn or leaking. Change the fuel filter. Check the air filter and change if necessary. Check the plugs and plug wires. And also check the oxygen sensor as stated above.

 

[hahnsuper16g]

Is the car tuned with the mods you have on it? One of the first lessons i ever learned was when modding the car always get it tuned. My first mods ever were custom 3inch exaust, a blow off valve and an injen cold air intake. When i did this i had the same problem as you i could smell the gas and i think it was because the car was getting more air the computer automatically added more fuel but it was not tuned and so i ran as rich as donald trump. I later got a safc, a boost controller and had it tuned and it ran great. So if your boost leak tests net you with nothing it may be that you need to find out who last had the car and if it was ever properly tuned.

 

[crimsondragon]

Is the car tuned with the mods you have on it? One of the first lessons i ever learned was when modding the car always get it tuned. My first mods ever were custom 3inch exaust, a blow off valve and an injen cold air intake. When i did this i had the same problem as you i could smell the gas and i think it was because the car was getting more air the computer automatically added more fuel but it was not tuned and so i ran as rich as donald trump. I later got a safc, a boost controller and had it tuned and it ran great. So if your boost leak tests net you with nothing it may be that you need to find out who last had the car and if it was ever properly tuned.

The ECU naturally compensates for the extra air by adding extra fuel to get a stoic burn. I don't see how tuning could be the problem unless he is running mods that don't support each other like a 255 Walbro without an AFPR. Correct me if I'm wrong.

 

[firefightermdc]

^^you're right on that one..but it depends on what kind of gas mileage you're comparing this to...I personally don't get the 25mpg. I have done a full tune up on my car and it's bone stock except for the bcs mod, k&n filter and an aftermarket blowoff valve(it IS a vent to atmosphere, but my car runs better with this setup than it did with the stock one..?) anyways, I get around 19-24mpg driving almost all freeway

 

[allwheelTSI]

Just for reference, this doesn't sound like the symptoms of a boost leak. It can' hurt to do one, but it most definitely will not cause you to smell gas at an idle. The only way a boost leak will affect MPG is if its bad and you have to depress the accelerator more than normal because of power loss.

 

[99GsxMD]

How bad is "bad?" Our cars do run on about 25 mph average. like 21ish for city miles and 30ish for highway. You said you bought it 3 months ago. Was it like this when you bought it? Have you done a full complete tune up since then? Check the fuel injection internals for anything worn or leaking. Change the fuel filter. Check the air filter and change if necessary. Check the plugs and plug wires. And also check the oxygen sensor as stated above.

Its probably getting maybe 10 to 12 mpg.. i changed the wires and plugs... still running rich..

 

[V8notENUF]

it IS a vent to atmosphere, but my car runs better with this setup than it did with the stock one..?) anyways, I get around 19-24mpg driving almost all freeway

The reason it appears your car is running better is because you replaced the stock bov with an aftermarket, which gives you a couple psi more boost, especially with the bcs mod. When stock, the bcs and bov work together to control boost. You are still runnin rich, and the more you get into your mods the more exposed the runnin rich will be. I vented to atmosphere for close to 6 years, until finding this site about 4 months ago and learning my short falls. Try adding a set of 272 cams and running vented and see what it does!

 

[crimsondragon]

^^you're right on that one..but it depends on what kind of gas mileage you're comparing this to...I personally don't get the 25mpg. I have done a full tune up on my car and it's bone stock except for the bcs mod, k&n filter and an aftermarket blowoff valve(it IS a vent to atmosphere, but my car runs better with this setup than it did with the stock one..?) anyways, I get around 19-24mpg driving almost all freeway

I get an average of 21. But that's cause I floor it alot on the highway. If I was to drive it steadily and under 2k RPMs city-wise, easily 30 mph. Driving style affects gas mileage as well. Btw how is it you can run vented and not crappy? Do you have a blow thru setup? Sounds like you're running too lean.

Just for reference, this doesn't sound like the symptoms of a boost leak. It can' hurt to do one, but it most definitely will not cause you to smell gas at an idle. The only way a boost leak will affect MPG is if its bad and you have to depress the accelerator more than normal because of power loss.

To add on this, a boost leak would only cause you to run rich. If you have black smoke coming out the exhaust, it's signs of running rich. It might smell like gas as well. It would not cause you to have low gas mileage though. He mentions he smells gas near the exhaust. I would look at the fuel lines for signs of leakage.

 

[99GsxMD]

The reason it appears your car is running better is because you replaced the stock bov with an aftermarket, which gives you a couple psi more boost, especially with the bcs mod. When stock, the bcs and bov work together to control boost. You are still runnin rich, and the more you get into your mods the more exposed the runnin rich will be. I vented to atmosphere for close to 6 years, until finding this site about 4 months ago and learning my short falls. Try adding a set of 272 cams and running vented and see what it does!

That seems like to much to cause bad milage.. Adding cams... i doubt that would help... And what do you guys mean running vented... sorry i am trying to learn all this. Also my driving habits are good because i dont floor it to much, only if i really need to. Still running like crap.. and i dont think i am running lean because i have a air/fuel gauge and it has never said i was running lean. I dont know what to do at all to fix this. I got a boost leak checker on its way in and a new o2 sensor. I am going to see if either of these help.

 

[crimsondragon]

If you run vented without a blow thru MAFT setup, the car will run like shit. The OEM MAS is positioned before the BOV. If you vent, that's air being released into the atmosphere, air that has been monitored by the ECU so it knows how much fuel to put in for a stoic burn. But since there isn't that same amount of air that was calculated for the ratio, the car runs richer instead. Running richer fouls the plugs. Fouling the plugs leads to misses, shitty idle, and other things.

By the way you should update your profile. You claim to have an A/F gauge. What does it say your running? Stoic or rich?

Also just in case, here is the procedures for a proper boost leak test.

1. Disable your mbc.

2. Turn your motor to 30* ATDC to avoid valve overlap.

3. Start your test at the TB elbow and focus on area behind the TB first.

4. Spray soapy water at TB gasket, BISS, TB shaft on both sides, IM gasket, injector insulators, brake booster, afpr and all vacuum lines/connections.

5. Open your oil cap and listen for leaks. (PCV, valve seals/guide, rings)

5. Listen to your tailpipe for leaks. (EGR, valve overlap, jumped timing, bent/unseated valves)

6. Once all leaks are fixed, move the tester back to the turbo inlet.

7. Spray down the compressor cover (known leak), BOV return/flange (DO NOT TAP YOUR BOV LINE FOR YOUR MBC!!!), IC end tank/fins and all connections. Re- test.

8. Note that you will leak air into the crankcase through the turbo seal but do not panic, this is normal during a static pressure test as long as there are no shaft play.

The desired test result from the begining of the LICP (bypassing turbo) is around 20psi (on boost gauge) with the compressor set at 30psi, while taking no less than 30 seconds to bleed down to 0.

As a reference, my last test on my 500 mile new engine, I was able to pressurize the system to 25psi, bled down to about 16psi (my 1G bov) in about 30seconds, then took about 3 mins to 6psi and just kinda lingered there for a while. It's not easy to do but the point is it's possible. My next goal is 30psi After motor break in and Dodge modding my BOV. A boost leak test is one of most pita but important regular maintenace task, the key is patience and endurance, have fun.

Also some advice for changing the O2 sensor: pick up PB Blaster, oxygen sensor socket, torque wrench to fit socket, and a breaker bar.
Spray the sensor with lots and lots of PB Blaster. Knock on it gently to let it penetrate. Let it sit overnight. Proceed to go to town with it with a breaker bar. If this does not work, use a monkey wrench and/or torch it. Once you have it out, coat the new one with copper anti-seize. It should have came with the new sensor. Be careful not to touch the actual sensor head itself. Install it and twist by hand first. Then torque it down to 29 ft*lb. Connect it to the plug and you're done. Make sure to tuck the wire in the heat shield clips.

 

[FlyByNight]

Is the check engine light on? If the O2 sensor crapped out, it'll normally through a code. Or possible misfires at idle...

 

[99GsxMD]

Is the check engine light on? If the O2 sensor crapped out, it'll normally through a code. Or possible misfires at idle...

No the engine light isnt on...

 

[RayBan GST]

do a boost leak and change the spark plugs and the wires


good luck

 

[Artago]

No the engine light isnt on...

A dead O2 will throw a CEL code. A dying will not. You can test your O2's if you'd like (there are instruction on the forum somewhere on how to do this) but if you are going through that much hassle you might as well change it. If the car has never had it's O2 replaced and it's running rich, chances are the O2 is on it's way out.

My advice is, just buy a new front O2 and have it replaced (you can do it yourself but it's a b.i.t.c.h.)

PS: It never hurts to do a boost leak test.

 

[99GsxMD]

A dead O2 will throw a CEL code. A dying will not. You can test your O2's if you'd like (there are instruction on the forum somewhere on how to do this) but if you are going through that much hassle you might as well change it. If the car has never had it's O2 replaced and it's running rich, chances are the O2 is on it's way out.

My advice is, just buy a new front O2 and have it replaced (you can do it yourself but it's a b.i.t.c.h.)

PS: It never hurts to do a boost leak test.

Yeah i got a new o2 sensor on its way in and also a boost leak checker. So I will be doing both of those to see if it helps or not. Whats the best way to do a boost leak check?

 

[Artago]

Yeah i got a new o2 sensor on its way in and also a boost leak checker. So I will be doing both of those to see if it helps or not. Whats the best way to do a boost leak check?

I'm still trying to figure that out. In my case, my best guess would be to skip the turbo and check from the turbo outlet pipe and go backwards. I have a V-Trim which leaks via the shaft bearings so hooking up the boost leak tester to the turbo is useless for me. Also, you should have your motor at 30* ATDC otherwise the valve overlap will cause the pressure to leak via the valves (valve overlap) and out the exhaust. Once you have pressure in the system, the easiest thing to do it spray the heck out of everything with soapy water. If you see bubbles you've found a leak.