[ctrlz]

Originally Posted by Ailurus2SS

Under calm normal driving Im hitting between 9-10 mpg. If I drove it hard like before I'm pretty sure it would go lower

This is preposterously low. Is this the "instantaneous" fuel economy? And what does it show on a highway? You should be getting up into the 30's at highway cruise.

Once the car is warmed up and you are cruising, the car is running in closed loop. That means the air/fuel mixture is completely dictated by feedback from the oxygen sensor. There is no learning time for this.

The MPG reported by the trip computer is entirely based on injector timing data. It looks at how far you have driven and how long the injectors were open over that time. Assuming constant fuel rail pressure, it knows how much fuel you consumed over a given distance.

If you are getting 10 mpg at highway cruise, I would probably start by looking at fuel trims. If a scanner confirms it is running everything rich, I would think about a faulty oxygen sensor.

Well, at least the battery is holding charge!

[Ailurus2SS]

Originally Posted by ember1205

Is it possible that the ECU is still 'learning' and you're simply running a bit rich? Depending on how long the battery was disconnected, all of the trim adjustments may have been lost and will take some driving to get them re-learned correctly.

It sucks when issues that can't be reliably reproduced get addressed... All you can do it wait to see if it recurs, but you don't have a method to try and cause the problem. So, there's never any "proof" that it got fixed.

the car has been dead with them for about 4 weeks but idk exactly how the ECU is when it comes to relearning things. The reading are from the trip mileage and from the fuel economy page under 25 and 50 miles range

[Ailurus2SS]

Originally Posted by craigss50

I don't think mine could use that much fuel no matter how hard I drove it. Something doesn't sound right. Is your car modified?

Only thing modified is a Rotofab CAI and the cats both primary and secondary, were cut off of the stock headers. Since you get a CEL without cats I had the car tuned to remove the CEL for them but I don't think the fuel map in the tune was touched.

Weirdly enough i had to put my tune back on the car when i received it because I was getting both CELs again for the right and left O2s but they instantly went away with the tune reapplied.

[Ailurus2SS]

Originally Posted by ctrlz

This is preposterously low. Is this the "instantaneous" fuel economy? And what does it show on a highway? You should be getting up into the 30's at highway cruise.

Once the car is warmed up and you are cruising, the car is running in closed loop. That means the air/fuel mixture is completely dictated by feedback from the oxygen sensor. There is no learning time for this.

The MPG reported by the trip computer is entirely based on injector timing data. It looks at how far you have driven and how long the injectors were open over that time. Assuming constant fuel rail pressure, it knows how much fuel you consumed over a given distance.

If you are getting 10 mpg at highway cruise, I would probably start by looking at fuel trims. If a scanner confirms it is running everything rich, I would think about a faulty oxygen sensor.

Well, at least the battery is holding charge!

The reading were both coming from the trip page and the fuel economy page on the 25 miles setting and the 50 miles setting. Its only been about a 50-75 ish miles since I got the car back. Mostly city like driving because when I went on the highway I hit some traffic. Havent had a chance to cruise with it yet but normally cruising on the highway I average about 25 mpg

[MackSteelPrivateEye]

Well maybe the ECU is still learning and at least its holding a charge. The Lord works in mysterious ways.
Good night.

[ember1205]

The fact that you had to re-apply the tune almost certainly tells you that the ECU lost all previous settings. That means it reverted back to complete stock settings for everything including all little tweaks for trim levels and such for fuel/air. I would continue to drive and see what happens, but I honestly wouldn't get wrapped up in the in-car computer for mileage info - ever. Track it using a calculator between fill-up's otherwise the numbers are genuinely meaningless.

[Nitefall17]

Do you have any after market LED or tail lights ?????

[Ailurus2SS]

Originally Posted by Nitefall17

Do you have any after market LED or tail lights ?????

I had oracle headlights and underflows but those were all disconnected once the issues started to issolate the problem and the issue happened for a couple months after them being disconnected so it's definitely not them.

[Ailurus2SS]

So I have a SCT BDX and I've been using the gauge on it to monitor the fuel pressure and at idle and low acceleration (under 2k rpm) the pressure has been around 46 psi ±2. The mpg has still been around 9 mpg according to the 25 miles economy range.

If I paddle shift the car and let rev out higher I can get the pressure to low 60s and have had the mpg shoot up to around 11 but I need to test this further. Idk how that would make sense.

[JSH]

I avg. approx. 11 mpg and I take it redline in 3rd, 4th and 5th at least once a day

[ember1205]

Originally Posted by Ailurus2SS

So I have a SCT BDX and I've been using the gauge on it to monitor the fuel pressure and at idle and low acceleration (under 2k rpm) the pressure has been around 46 psi ±2. The mpg has still been around 9 mpg according to the 25 miles economy range.

If I paddle shift the car and let rev out higher I can get the pressure to low 60s and have had the mpg shoot up to around 11 but I need to test this further. Idk how that would make sense.

Ignore the in-car computer. Hand-calc between tank fills - it's the only way to get reliable numbers.

[Ailurus2SS]

Originally Posted by JSH

I avg. approx. 11 mpg and I take it redline in 3rd, 4th and 5th at least once a day

Yea I would get 12 doing about the same but I was trying to drive normal when I noticed I was getting 8

[ember1205]

Originally Posted by Ailurus2SS

Yea I would get 12 doing about the same but I was trying to drive normal when I noticed I was getting 8

You're going off of what the car is telling you, though. And that calculator is never correct. The question is: Is that calculation much further off than normal, or is the MPG significantly down? The ONLY way to know what you're actually getting is hand calc.

[Ailurus2SS]

Originally Posted by ember1205

You're going off of what the car is telling you, though. And that calculator is never correct. The question is: Is that calculation much further off than normal, or is the MPG significantly down? The ONLY way to know what you're actually getting is hand calc.

Just waiting for my tank to fully be empty to start fresh for hand calculations. Will update when I do.