Regular or Premium fuel? [merged]

[Eclipse_98_RS]

Hi guys, my car is an all-stock RS, but I'm going to start doing some mods to it. Right now I just use regular unleaded gas, but when should I start going up in the octane? After intake/exhaust, or beyond that? I don't want to screw up my engine but I don't want to have to shell out more cash on fuel than I do now. I know, I'm a cheap bastage.

 

[Laser-man]

i know it will, but 93 gives me better gas milage.

 

[brokencpsd95tsi]

I always run 93 octane and octane boost every so often. It runs real good on that 104 octane boost.

 

[laserblue]

I thought that the ECU's in these cars is 'smart' and adjusts to things like driving habits and grade of fuel.... so, better gas means better performance, right?? Wrong?? Who knows about this?

 

[pneumo]

If you car has a knock sensor, then it's smart enough to know how to run on low octane. So far, only the turbo cars have knock sensors. (not sure about 2G) The ECU will cut timing and open the boost control solenoid sooner to reduce knock to safe levels. Of course, this will reduce power. Don't run cheap gas with a manual boost controller, the ECU won't have enough control to limit knock. As for the NA motors, just run what the manual reccomends. You won't get more power with higher octane unless the car is modded. Ironically, high octane gas has a lower BTU rating, which means that it actually has less energy than low octane gas, which means that it takes slightly more high octane gas to get the same energy as low octane gas. The power of high octane gas comes from better ignition timing, and being able to crank up the boost or use high compression pistons without causing detonation.

 

[SANiTaRiUM16]

it says to use 87 octane for all 1.8 SOHC engines and at least 91 octane for all 2.0 DOHC engines. So i run 93 all the time and haven't had a problem

 

[GoSpeedRacerGo]

Does Octane Booster really work? I heard that it barely helped at all.

 

[nine5raptor]

generally when you look at the bottle, it will say boosts octane 10 'points'...points can be anything they want it to be, their is no standard. I have heard many of them raise octane rating by about 1 at the recommended dosage.
higher octane means less heptane and less power per liter but because it is harder to burn, it is less likely to burn uncontrolled, thus less knock (uncontrolled burning)

 

[SLAMMED91]

'93 Talon TSI AWD. 16G, HKS EBC, intake, and exhaust. Auto Tranny.

I certainly didn't expect to get 30 mpg like my N/T Eclipse does, but this is not right.

I am getting like 13 mpg on my Talon! AND, this was during easy driving, only really putting the pedal down a couple times and running at stock PSI! (with the Boost Controller off)

I've heard the O2 sensors in DSMs go bad and I have not tried that yet so I probably will. Everything else seems normal so I am not really sure what the deal is on the gas mileage.

Suggestions please!

 

[OneBlackTalon]

you should check your o2 sensor first, i had the same problem and i got a new o2 sensor, fuel filter, plugs, and wires. One of those fixed the problem, not sure which one

 

[TSiAWD91]

Im having the same problem with the junk gas mileage,and I only have a few mods with a stock 13b@13-15#s and fuel sytem.Should both o2 sensors be replaced or only the one on the housing?Ive done the plugs and plan on doing everything else soon.

 

[miubhi856]

If your check engine light is not on, could it still be the O2 sensor. I'm a auto technition and every car I've ever worked on would through a engine coad. The gas mileage could also be caused by a pluged up cat! I just get my 91 GSX and it's getting 10-11 mpg around town plus I've got the famos idal surge. I've changed my plugs, fixed my wires (quick fix for now), EGR block off plate, BISS o-ring, and cleaned my throtle body (compleatly). I know there is a sensor called a TIP, TPI or something like that, that will cause idal surge but will it give you that bad of gas mileage? I'm stumped, PLEASE HELP!!!

 

[RedLineShifter]

Do ya just got to a Mitsu dealership to replace the O2 sensor? Im going up there later today to buy another clip for that little cover in the hatchback.. not staying in the hole like it should.

 

[Bigpav7]

i think you mean the TPS, throttle position sensor, its on the throttle body and turning it counterclockwise is sposed to lean out the mixture.
good luck

 

[Thebeast431]

I believe the 1G's only have one O2 sensor to worry about. I also get crappy mileage, but I am not worried about it. Its only $1.70/Gallon for 93 here. Dealer wanted $80 wholesale for one, but I found this place for really cheap, but not sure if you get just the sensor, and need to splice the wires, or not.

http://www.partznet.com./dsmpage3.html

Travis

 

[miubhi856]

No it's not the TPS. I just checked and it's called an ISC unit and not TIP or TPI, I don't know where I got that from. Could the ISC unit cause bad gas mileage? Check out myzero.com under engine then idal surge for what the ISC dose.

 

[doug]

Not sure about 1Gs, but 2Gs have a ground strap attached to the downpipe, that, if disconnected, hoses the O2 readings from the sensor and craps out the gas mileage. You could check to see if this ground strap is connected properly.

 

[SLAMMED91]

Let's give this a bump!

I haven't remedied my issue yet, I night try the O2 sensor (I would like to be sure before I spend $50 on one though.)

 

[TSiAWD91]

I know for a fact that my 91 has that ground strap on the DP,and mine isnt connected,its just flappin in the wind.I never thought of that as being a contributor of lousy gas mileage,but i guess im gonna have to fix that and see what happens.Thanks Doug!!

 

[laserturbo91]

id try some of that zemax junk you see on tv, you can pick it up at walmart. i had water in my gas (damn cheap gas station) and the zemax bottle said it got rid of water and cleaned out the injectors or something, well i put it in for the water, but it made the gas milage a hell of a lot better, i was getting the same around you fellows
cliff notes: zemax from walmart

 

[doug]

Originally posted by TSiAWD91
I know for a fact that my 91 has that ground strap on the DP,and mine isnt connected,its just flappin in the wind.I never thought of that as being a contributor of lousy gas mileage,but i guess im gonna have to fix that and see what happens.Thanks Doug!!

No problem-- if you do a search either here or at dsmtalk on "ground strap" you'll be reading for hours.

 

[SLAMMED91]

Well- $77 dolars later and I replaced the O2 sensor. It came out nicely (with the help of special socket.) Hopefully this will cure the gas mileage issue. I also put some NOS injector cleaner in (it was on sale! ) to be clean out the fuel system.

I didn't notice a big difference in drving it yet, not that I expected it to feel so much different.

I will let you guys know how this goes later!

 

[doug]

So do you have a ground strap on the downpipe or not?

 

[SLAMMED91]

I do NOT have a ground strap on my TSI. I believe that just the 90-91 DSM's had it setup that way.

 

[TSi92]

My 92 had that groundstrap as well. I had to ditch it because my custom dp didn't have where to bolt it on. And yes, gas mileage will suffer without that strap.

 

[SLAMMED91]

Well, this ground strap thing is interesting. How many other 92-94 Turbos have a ground strap? Mine is longer 4 wire connector with the plug on the end.

BTW- I already notice the gas gauge moving down only after 10 miles of driving.

Maybe I should expect NOT to remedy the gas mileage issue on the first try!

What next on this issue? Spening mad amounts of money when I don't know for sure what part is faulty is not what I wanted to do.

Could a clogged cat or muffler cause you to loose that many miles per gallon! I would thing you would notice a bit more hesitation and erratic behavior with the exhaust system plugged.

Thank you.