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Discussion Starter · #21 ·
What really catches my eye is that i only get 25miles per half a quart so in a day to and from school(50miles) it takes a whole quarter which idont think is right

Do you mean that it is using 1/8 to 1/4 of a tank of gas to go 50 miles?
Did you ever install and ACDelco or Denso O2 sensor or are you still sticking with the Bosch?
What are the fuel trim readings at idle--both STFT and LTFT?
Raise the RPM to 2500-3K for 30 seconds and read the fuel trims again.
What are they then?
Are there any problems with how the the car runs? (Rough idle, hesitation, lack of power, etc.)



Yeah thats what imeant sorry but yeah i have put a new Denso02 sensor and no no problems whats so ever so rough idle ir lack of power at all
 

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What are the fuel trim readings at idle--both STFT and LTFT?

Raise the RPM to 2500-3K for 30 seconds and then read the fuel trims again.
What are the 2 fuel trims at 30 seconds?

This can clue us in as to what the problem is, such as a vacuum leak or something else.

How many miles has it been since the new Denso sensor was installed?

It's also possible that other issues are affecting gas consumption.
Going only by the fuel gauge may be misleading you.
They're not stellar in their accuracy.

You really should record the mileage when you fill the tank, then record the mileage and the exact number of gallons it takes the next time you fill the tank.
That way you'll know exactly what gas mileage you're getting.
 

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Discussion Starter · #23 ·
What are the fuel trim readings at idle--both STFT and LTFT?

Raise the RPM to 2500-3K for 30 seconds and then read the fuel trims again.
What are the 2 fuel trims at 30 seconds?

This can clue us in as to what the problem is, such as a vacuum leak or something else.

How many miles has it been since the new Denso sensor was installed?

It's also possible that other issues are affecting gas consumption.
Going only by the fuel gauge may be misleading you.
They're not stellar in their accuracy.

You really should record the mileage when you fill the tank, then record the mileage and the exact number of gallons it takes the next time you fill the tank.
That way you'll know exactly what gas mileage you're getting.

Do you think the fuel level sensor might be at fault? Because everytime ifill up when the Empty light turns on ican only get 11-12 gallons in after that the tank is full and from my knowledge ihave a 17.5 gallon tank
 

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Your fuel level sensor is inaccurate, as you definitely do have a 17 gallon tank.
The gauges were never super accurate but yours is worse than average.

If you calculate the gas consumption as posted earlier, I think you'll find the mileage is much better than you realize.
 

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Discussion Starter · #25 ·
Your fuel level sensor is inaccurate, as you definitely do have a 17 gallon tank.
The gauges were never super accurate but yours is worse than average.

If you calculate the gas consumption as posted earlier, I think you'll find the mileage is much better than you realize.
Yeah im guessing its that as well because ihave no problems with the car whatsoever. And id go off my Miles gauge but it doesnt work the LED gauges dont work ikno the fix just havent gotten around to doing it but ijust went off of my total miles to my destination and how much id put in gas.
 

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Fuel mileage

OK So just for the record MAF readings in Grams per Second with car warmed up, sitting in park should idle about 3.8 to 4.0 Gs-ish, too much more more and computer will think its getting more air than it actually need and will conversely add fuel much as you are seeing. So lets explain GM tune strategies. (basically computer is reading O2 in through MAF and left over O2 after combustion)(its a constant dance)

OBD1 GM used basically a large block scale if drawn on graph paper 256 across, 256 down. The set numbers were 128 on Block Learn and 128 on Fuel Integrator. Now in each square had separations of 10 inside. if the o2 sensor saw lean condition it upped pulse width, rich it drops down. If it maxes out the block, then it switches to next highest to richen, or lowest to lean out the fuel trims. The integrator is long term fuel use learned.

OBD2 they compacted this to long term/short term trims. In a a stock mode long term and short term should NOT add up to more than 10+/-.
So internally the computer reads B1S1/B2S1 and requests more or less fuel. Each percent on scan info more or less has 10 points inside but you never see this is its just for calculations. If the short term maxes out at 1 it goes to 2 then 4 then so on and so forth.
Now after set calculation time/run time/number of revolutions the long term REMEMBERS and maintains this number so its not relearning.

So basically if we saw this as digital, car running you would see
Short Term 1.0% -9.9% Long Term stays at 0%
It goes to the next level of ST10% LT goes to 1% ST resets to 0%
So ST goes 0% LT 1%
So every time ST goes over 10% the LT jumps.
IF your running right and the actual program is in control ST in 0%-5% is great.
So in general if your ST was 3%, LT was 10% you have an issue.
ST3% LT3% 3+3=6 your good.
Long term evaluation should always be after at least 20 minutes of driving , preferably high way.

NOW lets talk about WHAT controls these ST/LT percentages.
O2 sensors are the heart and soul of fuel control.
After your primary O2s are active you should see mV below .200mV and over .800 mV .
I prefer AC Delco, NTK or Denso O2 sensors. Bosch are the Autolite of the O2 world except for specific factory used applications.

you want O2s going low and high. low is lean, high is rich on most O2s.
Most secondary O2s are simply for converter condition/operation. SOME newer cars have tried using after cat but it just isnt required in actuality.

If your ST+LT = closer to 10% in performance applications your either air leaking into after maf, or exhaust leak OR misfires.

Checking O2s should range freely and use below .200 and above .800mV.
Now some cars use O2 crosscounts but generally those are just condition indicators not critical to diagnostics.

And this all should be with NO BOOST AT IDLE.
The rule of 1 gS per liter of engine still holds.
By the way I am a 30yr tech, diagnostic tech, performance builder/tuner for many of those years.


QUOTE:
okay so at idle STFT its Either at 0.0 to 1.6 bouncing back and forth and my LTFT is at a constant 8.6
So now at 2000rpm
STFT iseen 0.8 , -0.8 and 2.6
LTFT 7.0
And my O2 sensor ready at idle is bouncing around in the .100s so itd bounce any where from 0.100-0.760


ok SO HERE WE GO that high on the O2 of .760 means you seem to have a lean bias O2 and this will lead computer to adding fuel hence your higher than needed LT readings. O2 should read 0.100-0.860(or higher) and I bet LT will drop down.

Basic strategy is O2 drives the ST, ST drives the LT
and all of that drives the injector on time which uses those number plus vacuum/boost, air flow, coolant temp, air inlet temp, throttle opening to calculate the amount of fuel required.



See the engine is an air pump, the computer starts reading exhaust oxygen content(running parameters hard coded into computer program/design) and tries to balance remaining air in exhaust gases to air going into engine. Any screw up and you get a rich or lean condition.
Easy things to remember
1 gram per second per Liter hot/idle/park/no boost
Primary O2 below 0.200 and above 0.800 and active
ST/LT needs to be as close to 0 to 3 when added together to see proper tune.
Remember when ST hits 10% the LT jumps another 1% so if your LT is 8.6% your ST has reset 8 times and is working on another jump, if you add them its over 10% total and your running rich, which if your O2 readings are accurate, your O2 has a lean bias and computer thinks its running lean.
 

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My 3.8 iui did that and changed out a lot of usual things and ended up being the cam sensor. Changed it out in about 10 minutes and changed everything for the better. Mileage increased a lot, about 35mpg plus highway.
 
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