Can Piggybacks alter the MPG calculations?

getInline · 07-15-2008, 04:47 PM

Just curious? Since some piggybacks can (or soon will) intercept fuel pressure and duty cycle signals, can the ECU be tricked into thinking you are getting better mileage than your are or does it use some other flow meter for this calculation.

Now before anyone derails this thread into an A versus B:
- This isn't a big deal to me, I just have a technical curiosity.
- I'm not pitting one system against another, it's just curiosity (did I say that already?)

Clarification: I'm not talking about the 'actual' fuel economy of the car, but rather the calculated mileage that is displayed by the ECU. In other words can the calculated fuel economy numbers be wrong if fuel pressure and duty cycle signals are being intercepted?

darkphantom · 07-15-2008, 04:50 PM

well some owners of the sstt have said that it gives them +3 MPG - I have yet to see that, will let you know after a week of use.

getInline · 07-15-2008, 04:52 PM

Quote:

Originally Posted by darkphantom

well some owners of the sstt have said that it gives them +3 MPG - I have yet to see that, will let you know after a week of use.

Yes but are they really getting +3 MPG or is it just the computer that is reporting better fuel economy because the signals it uses to calculate mileage are being altered (offset). That is my basic question.

continentalg5 · 07-15-2008, 05:01 PM

I believe that with the new JB3 that is coming out, you can switch to a map that makes it like a 328, which would in turn provide better fuel economy.

getInline · 07-15-2008, 05:23 PM

Quote:

Originally Posted by continentalg5

I believe that with the new JB3 that is coming out, you can switch to a map that makes it like a 328, which would in turn provide better fuel economy.

Yes I know but you're missing a critical subtlety....I'm not talking about the real fuel economy, I'm talking about the value that gets displayed in the dash. That value may or may not reflect reality. In other words is the mileage value displayed by the computer CORRECT or is it INCORRECT if a piggyback is being used.

Choolgooz · 07-15-2008, 05:34 PM

i know what ur trying to say but i dont have an answer, best way is to calculate is the old fashion way after you fill up. I just got my SSTT installed like 20 min ago, i am gonna give it a week before i take any measurements. I dont think there will be a big difference w/ the TT, since it dont mess with the fuel calculations all that much.. or maybe i am wrong.

rideelement247 · 07-15-2008, 06:45 PM

With v2 I read 16.8 MPG...I figure I am getting less than that as I am always effin filling up

. I want to say I am getting closer to 14 MPG but I haven't done any research to prove this.

e90AW335i · 07-15-2008, 06:47 PM

I have recalculated mine over and over again and it is always very close.

Mr. 5 · 07-15-2008, 06:52 PM

Quote:

Originally Posted by e90AW335i

I have recalculated mine over and over again and it is always very close.

Me too.
I get absolutely great MPG on the freeway (29) and horrible on the city streets (16).

Malek@MRF · 07-15-2008, 07:01 PM

my gauge reads 20.9 with my BlackBox. It hasn't been reset for the last 3 fillups and majority of my driving is in the city. Doesn't see the freeway much. On average I get around 319 miles per fill-up.

The SSTT does not yeild a 3 MPG improvement over stock.

jadeddjay · 07-15-2008, 07:11 PM

i have v2 and its pretty accurate. i reset the odo every time i refuel.

my rule of thumb is that if i can squeeze out about 100 miles per 1/4 tank, thats about 22-23mpg i think.

rideelement247 · 07-15-2008, 07:14 PM

I get about 320 miles on a full tank

. Ticker shoots to 360 but then goes to 310 - 320 after adapting to the shitting driving conditions here in South Florida

.

itsbrokeagain · 07-15-2008, 07:16 PM

Quote:

Originally Posted by Mr. 5

Me too.
I get absolutely great MPG on the freeway (29) and horrible on the city streets (16).

Stock I get 30-32 (29 with the A/C on) and horrible as well around town...16 at the very best..usually 12.

I get around 340 on a tank to and from work.

My best ever was 514 and 502 miles on one tank of gas. And that was sucking it dry with 5 miles left to go on the tank.

getInline · 07-15-2008, 08:27 PM

Quote:

Originally Posted by e90AW335i

I have recalculated mine over and over again and it is always very close.

Interesting, if the ECU calculated mileage is close to reality then the ECU must be calculating the mileage based on fuel flow rates from a fuel flow sensor rather than calculating them based on duty cycle and fuel pressure. A seperate flow sensor would be the right way to do it since it would be more accurate.

RRGOO7 · 07-15-2008, 08:30 PM

How the hell are you getting 300+ out of a tank! My average is stating 17mpg...i usually get about 240-260 miles out of one tank....mostly city driving.

jcarlucci1 · 07-15-2008, 08:50 PM

Am I the only one who gets 12-13 mpg..stock?

e90AW335i · 07-15-2008, 08:52 PM

Quote:

Originally Posted by jcarlucci1

Am I the only one who gets 12-13 mpg..stock?

Yes. I am pushing ~370rwhp and I get 20-22mpg with mixed driving....

hotrod182 · 07-15-2008, 11:30 PM

Quote:

Originally Posted by jcarlucci1

Am I the only one who gets 12-13 mpg..stock?

I'm at 13.6 right now.
Piggybacks that alter fuel pressure will most likely throw off the accuracy of the MPG reading in the car. It will read higher than your are actually getting.

scalbert · 07-16-2008, 09:48 AM

Quote:

Originally Posted by getInline

Just curious? Since some piggybacks can (or soon will) intercept fuel pressure and duty cycle signals, can the ECU be tricked into thinking you are getting better mileage than your are or does it use some other flow meter for this calculation.

Now before anyone derails this thread into an A versus B:
- This isn't a big deal to me, I just have a technical curiosity.
- I'm not pitting one system against another, it's just curiosity (did I say that already?)

Clarification: I'm not talking about the 'actual' fuel economy of the car, but rather the calculated mileage that is displayed by the ECU. In other words can the calculated fuel economy numbers be wrong if fuel pressure and duty cycle signals are being intercepted?

Yes and no. With O2 sensor attentuation the DME is still controlling pulse width so MPG calculations would be accurate. The caveat now is with fuel pressure signal alterations. If you trick the DME into thinking the pressure is lower than it really is, the MPG calculations are off; MPG calculations would be higher than they really are.

That said, this only occurs under heavy load and has a minimal impact. An off the hip guess would equate to less than 0.5 MPG if even that high; it may be as little as a tenth.

getInline · 07-16-2008, 11:25 AM

Quote:

Originally Posted by scalbert

Yes and no. With O2 sensor attentuation the DME is still controlling pulse width so MPG calculations would be accurate. The caveat now is with fuel pressure signal alterations. If you trick the DME into thinking the pressure is lower than it really is, the MPG calculations are off; MPG calculations would be higher than they really are.

That said, this only occurs under heavy load and has a minimal impact. An off the hip guess would equate to less than 0.5 MPG if even that high; it may be as little as a tenth.

Thank You Scalbert! That's exactly what I was wondering. I understand that it's only something you would see under load so it's probably only something you would notice on a track day. Curiosity satisfied!

getInline · 07-16-2008, 11:40 AM

Quote:

Originally Posted by hotrod182

I'm at 13.6 right now.
Piggybacks that alter fuel pressure will most likely throw off the accuracy of the MPG reading in the car. It will read higher than your are actually getting.

Quote:

Originally Posted by jcarlucci1

Am I the only one who gets 12-13 mpg..stock?

Wow, you two either win the leadfoot award or the congested city traffic award.

For my city commute I get 19 if the traffic is good and I really baby it or 14-15 if traffic is bad or I'm on it. Downtown I'd probably drop into the 12-13 range. It really all depends on how much stop and go traffic you have.

Thanks for the fuel pressure info HotRod, that's what I was wondering.

jcarlucci1 · 07-16-2008, 03:15 PM

Quote:

Originally Posted by getInline

Wow, you two either win the leadfoot award or the congested city traffic award.

For my city commute I get 19 if the traffic is good and I really baby it or 14-15 if traffic is bad or I'm on it. Downtown I'd probably drop into the 12-13 range. It really all depends on how much stop and go traffic you have.

Thanks for the fuel pressure info HotRod, that's what I was wondering.

At 13-14mpg I am taking it really easy..just constant stop and go I guess

07-15-2008, 04:47 PM	#1
getInline Lieutenant 13 Rep 412 Posts Drives: 2008 335 Coupe, c32 AMG Join Date: Nov 2007 Location: Parts Unknown iTrader: (1)	Can Piggybacks alter the MPG calculations? Just curious? Since some piggybacks can (or soon will) intercept fuel pressure and duty cycle signals, can the ECU be tricked into thinking you are getting better mileage than your are or does it use some other flow meter for this calculation. Now before anyone derails this thread into an A versus B: - This isn't a big deal to me, I just have a technical curiosity. - I'm not pitting one system against another, it's just curiosity (did I say that already?) Clarification: I'm not talking about the 'actual' fuel economy of the car, but rather the calculated mileage that is displayed by the ECU. In other words can the calculated fuel economy numbers be wrong if fuel pressure and duty cycle signals are being intercepted? Last edited by getInline; 07-15-2008 at 05:00 PM.. Reason: Clarification
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07-15-2008, 04:50 PM	#2
darkphantom Banned 631 Rep 5,945 Posts Drives: E93 335i Join Date: Aug 2007 Location: The place for Bimmers iTrader: (4)	well some owners of the sstt have said that it gives them +3 MPG - I have yet to see that, will let you know after a week of use.
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07-15-2008, 05:01 PM	#4
continentalg5 Major 17 Rep 1,074 Posts Drives: BMW Join Date: Dec 2005 Location: Earth iTrader: (0)	I believe that with the new JB3 that is coming out, you can switch to a map that makes it like a 328, which would in turn provide better fuel economy.
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07-15-2008, 05:34 PM	#6
Choolgooz Lieutenant 8 Rep 450 Posts Drives: 08 335i coupe Join Date: Dec 2007 Location: Bay Area iTrader: (3)	i know what ur trying to say but i dont have an answer, best way is to calculate is the old fashion way after you fill up. I just got my SSTT installed like 20 min ago, i am gonna give it a week before i take any measurements. I dont think there will be a big difference w/ the TT, since it dont mess with the fuel calculations all that much.. or maybe i am wrong. __________________
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07-15-2008, 06:45 PM	#7
rideelement247 Lieutenant Colonel 61 Rep 1,677 Posts Drives: 08 335i, 67 Camaro SS Join Date: May 2007 Location: South Florida iTrader: (2)	With v2 I read 16.8 MPG...I figure I am getting less than that as I am always effin filling up . I want to say I am getting closer to 14 MPG but I haven't done any research to prove this. __________________ Legal Disclaimer: Anything I or anyone else says about my vehicle on this website(e90post.com or any affiliated or nonaffiliated sites), pertaining to modifications, is only to gain acceptance from my/our peers, and does not actually represent anything actually existing on my car, and thus, cannot be held against me in any issues, i.e. warranty claims, that may arise.
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07-15-2008, 06:47 PM	#8
e90AW335i Major General 144 Rep 6,608 Posts Drives: e90 335i Join Date: Sep 2007 Location: ...... iTrader: (4)	I have recalculated mine over and over again and it is always very close. __________________ I install all tunes, intakes, o2 simms, and most cosmetic mods. PM me for a quote.
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07-15-2008, 07:01 PM	#10
Malek@MRF Brigadier General 740 Rep 3,732 Posts Drives: E92 M3, E46 M3, G82 M4 Join Date: Jan 2008 Location: Irvine, California iTrader: (5)	my gauge reads 20.9 with my BlackBox. It hasn't been reset for the last 3 fillups and majority of my driving is in the city. Doesn't see the freeway much. On average I get around 319 miles per fill-up. The SSTT does not yeild a 3 MPG improvement over stock. __________________ BMW PERFORMANCE SPECIALISTS. Race Engines. Suspension. F/I. Brakes. Race Preparation. Factory Service. Alignments. OFFICIAL PARTNERS: KW. MOTON. Brembo. AP Racing. BBS Motorsport. iND. HRE. Turner Motorsport. VAC. BMW Motorsport. Facebook \| Instagram \| Yelp! \| Flikr Phone: 949-233-0448 \| E-Mail: info@mrfengineering.com
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07-15-2008, 07:11 PM	#11
jadeddjay Major 118 Rep 1,441 Posts Drives: e92 335i, f10 m5 comp Join Date: Oct 2005 Location: jackson, ms iTrader: (4) Garage List 2007 e92 335i [0.00]	i have v2 and its pretty accurate. i reset the odo every time i refuel. my rule of thumb is that if i can squeeze out about 100 miles per 1/4 tank, thats about 22-23mpg i think.
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07-15-2008, 07:14 PM	#12
rideelement247 Lieutenant Colonel 61 Rep 1,677 Posts Drives: 08 335i, 67 Camaro SS Join Date: May 2007 Location: South Florida iTrader: (2)	I get about 320 miles on a full tank . Ticker shoots to 360 but then goes to 310 - 320 after adapting to the shitting driving conditions here in South Florida . __________________ Legal Disclaimer: Anything I or anyone else says about my vehicle on this website(e90post.com or any affiliated or nonaffiliated sites), pertaining to modifications, is only to gain acceptance from my/our peers, and does not actually represent anything actually existing on my car, and thus, cannot be held against me in any issues, i.e. warranty claims, that may arise.
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07-15-2008, 08:30 PM	#15
RRGOO7 Colonel 377 Rep 2,451 Posts Drives: GTR Join Date: Dec 2006 Location: Miami FL iTrader: (13)	How the hell are you getting 300+ out of a tank! My average is stating 17mpg...i usually get about 240-260 miles out of one tank....mostly city driving.
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07-15-2008, 08:50 PM	#16
jcarlucci1 Lieutenant Colonel 70 Rep 1,642 Posts Drives: Jet Black 335i Join Date: Mar 2007 Location: Tampa iTrader: (10)	Am I the only one who gets 12-13 mpg..stock?
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