ECU reset gas mileage

[2.5T_/<ouki]

Start you off with a bit of info on the car.

S14 w/ RB25DET
- Rebuilt
- Greddy Intake Manifold
- Intake
- FMIC w/ HKS BoV (non recirc)
- Stock injectors / turbo @ 10psi

I granny drive my car and I'm only getting about 200 miles to a full tank of gas, so i decided to search around a few forums (including this one) about such situations and noticed everybody saying they reset their ECU and it makes a huge different in upping the overall gas mileage. This is not the case for me! My gas mileage has gone down by 30mgp; I'm not sure if this is a coincidence or there is something wrong with the engine and it's getting worse? Would an ECU reset do this type of thing?

Curious to know if you guys would point me in the right direction of where to begin when it comes to fuel management and overall fuel economy.


Things to check
- o2 sensor (purchased BNIB 300zx tt o2 about 5 months ago)
- MAF
- Coil pack

is there anything else i should be checking/looking for? What would cause me to have such horrible gas mileage? I know running the stock ECU isnt really helping, but i figure it should be more than 170-200 miles to a full tank of gas considering i GRANNY drive my car.

[Def]

Recirc your BOV and get a wideband to check your AFR. You should have one anyway on a modded turbo car.

[Sileighty_85]

Thats pretty bad
Clean MAF, Check Plug gaps, Timing, Boost/Vac Leaks.

I get about 18 City, and 26 Highway, My Wife gets about 21 city some how.

[cotbu]

clearing self learn, short and long term will cause worse gas millage if the problems aren't fixed. no brainer there.

[Kingtal0n]

Fuel economy: The not so final answer

Heres my quick list of things to do and check for maximum fuel economy;

1. Vehicle Weight. Take out the spare, take out the luggage, take out the toolbox, eject your passenger.
2. Wideband Oxygen sensor w/ Simulated Narrowband output. Trick your computer into thinking that 15.2 is really 14.7. Also monitor the A/F ratio to ensure it is correct for the driving situations!
3. Rolling resistance. Check your brakes for dragging, check your wheel bearings for resistance to turning, check your air pressure, check your alignment, anything that slows the car down eats fuel right?
4. Engine efficiency. Change your spark plugs, increase the power of the ignition (MSD DIS) and widen the plug gaps, if using a stand-alone, monitor EGT and Wideband to dial in the ignition timing for cruise situations. If using an OEM ecu, verify ignition timing as set by the factory, replace the knock sensor if possible with a brand new unit
5. Cleanliness is fuel economyness. Clean the air filter, clean the intake tract, clean any ducting that air needs to flow because dirt provides resistance to airflow and resistance to airflow means the engine needs to work harder to get the air.
6. Utilize the proper sized exhaust plumbing. If your engine < 300 horsepower and you own a 240sx, you should be using the OEM exhaust system for maximum fuel economy!


That should get you started

[Kingtal0n]

All about the ECU:

Why do we reset our ecu? What happens when we reset it? And why wouldnt it just go back the way it was before?

1. ECU reset clears the storaged {+/-} (12-18% maximum) values for cruise situations based on O2 sensor feedback.
Scenario:
you are cruising at 50MPH in fifth gear. The fuel map puts you at 13.6:1 air fuel ratio. The BLM(block learn multiplier) decides to pull 7% fuel to bring you back to the .1-1V swing point of the O2 sensor- that is, the point at which the narrowband flips from 1V (too rich) to .1V (too lean) happened to be 7% in that situation. The computer memorizes that value (7%) for that particular fuel cell array.

The point of this, is that the next day when you start your car and drive 50MPH again, the computer already knows that you needed 7% less fuel to hit that O2 feedback swing point. Its already there in the computer.

If you reset the computer, it just goes back to 0%, and when you go back to 50MPH, it will just pull that same 7% back out to bring you back where it was before.

When does this cause problems???
When the O2 sensor is bad or sluggish to respond, the computer is memorizing values that make no sense. You are cruising at 50MPH and the O2 sensor is saying (LEAN!! .1V!!) and your computer is adding fuel, and adding fuel, and adding more fuel, until it hits the maximum value (12-18%~) And it stays there forever because the O2 sensor is bad or sluggish (giving old information without regard to transient delay).

Get wideband, use it to simulate a narrowband. It will pay for itself.

[2.5T_/<ouki]

I've checked all this and everything came up good/clean. I'll double check everything just to be 100% sure.

Thanks for the input

[2.5T_/<ouki]

Originally Posted by Sileighty_85

Thats pretty bad
Clean MAF, Check Plug gaps, Timing, Boost/Vac Leaks.

I get about 18 City, and 26 Highway, My Wife gets about 21 city some how.

How many miles do you get to a full tank of gas?

[Sileighty_85]

Originally Posted by 2.5T_/<ouki

How many miles do you get to a full tank of gas?

I never really empty the tank I always refill at like 1/2 a tank, but I calculate my Tip OD with how much gas I put in the car So..

18mpgx17.2 gallon tank= 309.6 Miles Per Tank

[2.5T_/<ouki]

Originally Posted by Sileighty_85

I never really empty the tank I always refill at like 1/2 a tank, but I calculate my Tip OD with how much gas I put in the car So..

18mpgx17.2 gallon tank= 309.6 Miles Per Tank

I have to know your secrete!
My wallet is becoming verrrrry thin this way!

306 sounds really nice compared to 160-200....