Enormous Fuel Consumption problem

[Prodigyman]

I have this problem with my 2G GSX. Bought the car few month back and was working on it and ever since I bought it, it was eating enormous amount of fuel.

Car 97 Eclipse GSX
~90K Miles


Here are mechanical mods and fixes I did to the car (the major ones)

New FB Big T28 Ported Turbo
All new exhaust gaskets (Turbo, O2 housing, DP)
All new Water and SBR Oil lines with new washers
New SBR Hybrid Connection 2.5” O2 Sensor housing
New O2 Sensor
New Secondary O2 Sensor
Custom Full Turbo Back Exhaust system (2.5” DP, 3” High Flow CAT, 3” Turbo back)
Brand new Spark plugs
Brand new Spark plug wires
Greedy Type S BOV (On stock pipes for now)
Injen Intake with K&N Filter
Fresh new coolant
Fresh Mobile 1 Synthetic Oil
Brand new power steering pump
And more but they are not connected with fuel consumption (brakes and such)

The problem is that I drive for 150-160 Miles and FULL tank of 50 liters (94 octane) is GONE! DRY and empty.

My mechanic told me I still have a small boost leak where stock SMIC connects with plastic upper pipe but I don’t think that should affect that. Plus I got a quite large FMIC and waiting on my stock bumper to arrive so I can install that with all custom IC pipes.

No check lights are on, on the dash and they are all connected too. My A/F gauge is not connected yet but my boost gauge is and it holds stock 12 PSI boost to redline @ WOT and spools up to full boost @ about 3200 – 3500 RPM.

Also I just did emissions and my carbon level was 55 out of 200 that is VERY good and I passed it with ease and I have NO fuel leaks at all. So where da hell all this gas goes? This is killing me especially with current gas prices we have. Any help or suggestions would be appreciated.

 

[LiquidOC]

quite frankly, check your driving style first.....if you're flooring it everywhere, you'll use a lot more gas than if you're drivng like a normal person. Other than that, realize that you upgraded the turbo, therefore it'll require more fuel, which in turn hurts gas mileage. You can have two of these three: Good Gas Mileage, Fast Car, Reliable Car. but not all three.

 

[Prodigyman]

I understand what you are saying but 150 miles full tank? That’s just insane for any car. Plys my car ate the same amount of gas when it had all stock components when I bought it. And I don’t drive like a grandma nor like a maniac. I drive this car normally and when I need speed boot it sometimes. I bet any V8 or V12 don’t eat that much gas and this car is a 4 cylinder and suppose to last at least 400 miles for a full tank not quarter of that.

My mechanic keeps on insisting that my boost leak causing this but I am having hard time to associating a boost leak with more fuel consumption, HP loss? Yes not fuel. And car still feels like its running very rich and don’t have much HP. More then when I got it but not quite as it suppose to even @ stock boost I am running it at.

 

[Fattie92]

boost leaks will kill your gas milage!

 

[gurrmanator]

I blew a turbo hose,It took me a full tank of gas to go 110 miles(2 inch cut in turbo hose).I could only boost about 3lbs and then the car would cut out

 

[Quasimondo]

My mechanic told me I still have a small boost leak where stock SMIC connects with plastic upper pipe but I don’t think that should affect that. Plus I got a quite large FMIC and waiting on my stock bumper to arrive so I can install that with all custom IC pipes.

Your question is answered right there. Intercooler leaks cause excessive fuel consumption because they force the turbo to spool faster than normal to maintain boost pressure. The increased spool means more air is passing through the MAS which makes the ecu dump more fuel into the mixture to compensate for what it thinks is lots and lots of air.

My mechanic keeps on insisting that my boost leak causing this but I am having hard time to associating a boost leak with more fuel consumption, HP loss? Yes not fuel. And car still feels like its running very rich and don’t have much HP. More then when I got it but not quite as it suppose to even @ stock boost I am running it at.

Have you done a compression check? Lost compression can reduce engine performance and economy.

 

[SaintcruGSX]

I was getting 5mpg when one of my injectors was leaking, but you've prolly already check those.

 

[Prodigyman]

Your question is answered right there. Intercooler leaks cause excessive fuel consumption because they force the turbo to spool faster than normal to maintain boost pressure. The increased spool means more air is passing through the MAS which makes the ecu dump more fuel into the mixture to compensate for what it thinks is lots and lots of air.



Have you done a compression check? Lost compression can reduce engine performance and economy.

Yes I have done compression check and its 185 across all 4 ciders which i think is pretty amazing for the age of the car and milage. I guess boost leak would explain it. But it still holds 12 PSI to the red line. (10 PSI in the first gear and rest is 12). That would explain why after all the mods it still eats all that gas. Also if its a small leak though how much just approximately HP loss would i have? Dramatic one or little? And That would explain turbo spooling to the full boost @ such high RPM (3500) for a T28.

 

[olmytsi]

So why are you still typing instead of fixing the leak?

 

[tstkl]

fix the leak, and what rpm/gear are you in when you are crusing at 25? 35? 45?

i try and stay below 3k rpms while accellerating, and under 2k when maintaining speed...shift like its a saturn and your trying to keep that light from coming on....you know the one im talking about...

 

[Fattie92]

im sure you have more then just that one "small" leak. Go make a boost leak tester and do it all yourself for free! JB weld the intercooler leak, then soap and water everything to find others.

also, just because your boosting 12psi to redline does not mean that you dont have leaks. That just means that... well your boosting 12psi to redline. You will still boost the same amout of air regardless of boost leaks (unless its one HUGE leak, but im sure that one would be easy to find!) ....lets just say if your boost controller is set at 15psi, and you have 5 boost leaks...youll still be pushing 15psi. But the turbo will be working harder to make that 15psi, thus sucking in more air and dumping more fuel. FIXING BOOST LEAKS IS THE BEST THING YOU CAN DO TO A TURBO CAR!!!