Fuel Calculations way off after SC install

Hey all,

TUNERS HELP!!!

I installed a Roush R2300 supercharger kit on my 05 Mustang GT in early August.

After the install I took it to my local Mustang specialty shop to have it dyno-tuned.

The tune went well, and the car drives fine. WOW!

However.... ever since having it tuned the car's speedometer went off by about 5MPH at 60MPH.
This was easy to compensate for by changing the revs per mile.
But I have never had to do this before.

What is worse is that the computer thinks it is getting far better gas mileage than it really is, and it thinks its using far less gas than it really is.

Example: Car displays 22.2MPG.... actual MPG is 12.6.
Example: Car displays 8.5 gallons used... actual was 12.4 gallons from fill up to fill up.
Fuel gauge showed slightly above 1/4 tank needed 12.4 gallons to fill.

So the fuel gauge level seems to be off. Showing slightly more fuel in the tank than there really is.

The tune shop double checked that the fuel injector size and the axle ratio were correct in the tune file.

I should mention that the tuner had to add a Kenne Bell Boost a Pump since my pump could not keep up at WOT. I spoke with the folks at Kenne Bell.... they tell me this is likely a tune issue.
The live-link showed me that the fuel pump voltage never went over 10VDC, so the boost a pump doesnt even seem to be kicking in.

I spoke with the folks at Roush... they tell me this is likely a tune issue.

I have reloaded the tune, reset the KAM, and reset the entire ECU many times.
And I have driven well over 2000 miles. No change.

Anyone want to make a guess on what could be wrong?

Thanks.

was the pump assembly in the tank removed and reinstalled at all?

stkjock said:

was the pump assembly in the tank removed and reinstalled at all?

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I was told no. The actual fuel pump assembly was not touched.

That's all pretty normal stuff for our cars that have an SC. Not everyone who tunes our cars have the skills Lito has. Mine does everything you're does, always has.

I remember the fuel economy thing being spoken of in another thread years ago. I believe Lito knew how to correct it but I'm not sure.

You could send him a PM and see what he says.

I know there are certain tables in our cars that are "fixed" based on factory input. I'm sure they can be changed but some of them require guess work and only deliver an approximation or close enough output data.
Like for instance I can set up a Horsepower indicator in the scanner portion of my HP Tuners suite using "delivered torque" as the torque input in the horsepower formula RPM*torque/5252, which in a chevy is with in 10 HP of the Dyno. Same tool being used on my 08 Mustang indicates my N/A 3v make 462 HP because Ford uses a fixed preprogrammed table for "delivered torque" based off of a stock engine. So in that instance, no matter how I manipulate the inputs the formula uses when it comes to data logging a Ford I know that calculator is trash.

I remember Bruce talking about this. Something about pulses per mile. He was able to adjust his to get it dead on.

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01yellerCobra said:

I remember Bruce talking about this. Something about pulses per mile. He was able to adjust his to get it dead on.

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That adjustment is easy to make, you can also change the "revolutions per mile" as far as tire O.D. goes. I think the MPG computing is done with more than just the speedo's good info.

RocketcarX said:

That adjustment is easy to make, you can also change the "revolutions per mile" as far as tire O.D. goes. I think the MPG computing is done with more than just the speedo's good info.

Click to expand...

From what I have been told the cars computer looks at things like the fuel pump duty cycle, the fixed injector size, the mass air flow rate, engine load and perhaps even the throttle body position to calculate an estimated gallons used and miles per gallon.

So basically a lot information goes into it.

Since the speedo is now reading correctly, the axle ratio is correct, the fuel injector size is correct.... something else is way off.

maurice05 said:

From what I have been told the cars computer looks at things like the fuel pump duty cycle, the fixed injector size, the mass air flow rate, engine load and perhaps even the throttle body position to calculate an estimated gallons used and miles per gallon.

So basically a lot information goes into it.

Since the speedo is now reading correctly, the axle ratio is correct, the fuel injector size is correct.... something else is way off.

Click to expand...

That was my point

Speedo is an important variable here, if the tune is not hacked it goes by fuel weight used and normally no adjustments are needed.

lito said:

Speedo is an important variable here, if the tune is not hacked it goes by fuel weight used and normally no adjustments are needed.

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By "hacked" I assume you mean screwed up.

Considering the speedometer had never been off before the tune, and now it and pretty much everything else associated with the ECU's understanding of fuel consumption is off.... Its the tune?
Can you be more specific on which part(s) of the tune?

maurice05 said:

By "hacked" I assume you mean screwed up.

Considering the speedometer had never been off before the tune, and now it and pretty much everything else associated with the ECU's understanding of fuel consumption is off.... Its the tune?
Can you be more specific on which part(s) of the tune?

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ANYONE?????

My mileage is wayyyyyyyyyyyyyyyyy down after installing an aftermarket pump and blower!

eighty6gt said:

My mileage is wayyyyyyyyyyyyyyyyy down after installing an aftermarket pump and blower!

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Ha ha.... yes.
But does your cars computer still give you accurate MPG and gallons used info????

Nah. I think Lito purposefully messed with it so I always get 11 mpg! Goes to 11!

01yellerCobra said:

I remember Bruce talking about this. Something about pulses per mile. He was able to adjust his to get it dead on.

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Pulses per gallon. This is accessible in SCT's Pro Racer software so a tuner should be able to access this area of the tune.

46addict said:

Pulses per gallon. This is accessible in SCT's Pro Racer software so a tuner should be able to access this area of the tune.

Click to expand...

Thanks... I'll check into this.

Lito got it all taken care of.... tune issue.

At least from the initial 40 mile run using his tune.

Lito!!

I had the same issue with my JDM tune on my Saleen SC when I got it in 2009. JDM swore it wasnt the tune. I talked to them a few times with no luck. Got someone else to fix it.

Makes you really wonder how well these tuners really know what the hell they are really doing.