message center mpg
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Elder User
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From: Lunenburg, MA
message center mpg
what actually controls that? is it the pcm? before the supercharger install, it was pretty accurate...averaging around 15.5-16 on the highway....with my own calculations confirming that. after the install, it reads anywhere from 18-24 mpg on the highway, but when i do the math, it comes out to between 12.5-14.5 mpg. how would the s/c have affected it to be off that much?
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Joined: Jan 2001
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From: Central NYS
Navie Newbie here 
This is strictly a guess, but I thought the PCM kept track of the pulse width it supplied to the injectors and from that calculated the fuel used. And by keeping track of the VSS the PCM knew the distance traveled. Doing the math, the PCM then could display the MPG.
If you have raised the fuel pressure to compensate for the boost, or installed bigger injectors, the PCM wouldn't convert the injector pulse width to the correct amount of fuel used. (In other words, a given injector pulse width would squirt in more fuel than the PCM was using for its calculation.
I had a similar question about the message center: How do it know how much fuel you have added to the tank when it displays 'Miles to Empty'? Does it deduce the information from the voltage supplied by the fuel level indicator??
Hopefully, some one in the know will jump in here and shed some light on these mysteries.......
This is strictly a guess, but I thought the PCM kept track of the pulse width it supplied to the injectors and from that calculated the fuel used. And by keeping track of the VSS the PCM knew the distance traveled. Doing the math, the PCM then could display the MPG.
If you have raised the fuel pressure to compensate for the boost, or installed bigger injectors, the PCM wouldn't convert the injector pulse width to the correct amount of fuel used. (In other words, a given injector pulse width would squirt in more fuel than the PCM was using for its calculation.
I had a similar question about the message center: How do it know how much fuel you have added to the tank when it displays 'Miles to Empty'? Does it deduce the information from the voltage supplied by the fuel level indicator??
Hopefully, some one in the know will jump in here and shed some light on these mysteries.......
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Elder User
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From: Lunenburg, MA
there are bigger injectors obviously. i have an xcall II as well, and the truck was dyno-tuned. here is a copy of my dynochart....looks like it may be running rich up until 3k rpms?? maybe someone can confirm/deny that, and if so, lmk if it can be readjusted no to be that rich down low.
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Joined: Oct 2006
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From: SE Texas
You're actually lean up until 3000rpms-a street SC'd engine should be no more than 12:1 A/F at WOT. The message center gets it's data from the PCM and it uses load, airflow and displacement, along with the injector size to calculate the mpg. The problem is...alot of tuners ratio things in the tune to get load right and to get make the tune safe. That'll throw off the message center every time.
JL
JL
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From: Lunenburg, MA
Originally Posted by Johnny Langton
You're actually lean up until 3000rpms-a street SC'd engine should be no more than 12:1 A/F at WOT. The message center gets it's data from the PCM and it uses load, airflow and displacement, along with the injector size to calculate the mpg. The problem is...alot of tuners ratio things in the tune to get load right and to get make the tune safe. That'll throw off the message center every time.
JL
JL
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From: SE Texas
Originally Posted by 04markIII
so the a/f seems dead on then? guess the message center won't be right anymore....not that i don't like seeing 22-24 mpg....but it would be better if it was true!!
JL
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Your Dyo Chart shows your A/F ratio at WOT... or in Power Enrichment mode. This does not give any inication of what your part throttle operations A/F is... which should hol close to 14.7:1.
Your tune has an injector constant that was changed to compensate the computer calculations for the injector size.
Its probably the other tweaks the tuner had to make that is tossing off your message center.
BTW, that Torque curve looks awesome. I hope you are towing something because that kind of torque curve would be a dream to have... Especially if it stays that flat at 1/2 throttle.
Your tune has an injector constant that was changed to compensate the computer calculations for the injector size.
Its probably the other tweaks the tuner had to make that is tossing off your message center.
BTW, that Torque curve looks awesome. I hope you are towing something because that kind of torque curve would be a dream to have... Especially if it stays that flat at 1/2 throttle.
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From: Lunenburg, MA
Originally Posted by Kyle f
BTW, that Torque curve looks awesome. I hope you are towing something because that kind of torque curve would be a dream to have... Especially if it stays that flat at 1/2 throttle.
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