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Old 01-15-2016, 11:05 AM   #17 (permalink)
t vago
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Join Date: Oct 2010
Location: Cedar Rapids, IA
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The Karen-Mobile - '05 Dodge Magnum SXT
Team Dodge
90 day: 26.72 mpg (US)

Fiat Dakota - '00 Dodge Dakota SLT RWD Quad Cab
90 day: 16.67 mpg (US)

The Red Sled - '01 Dodge Durango SLT 4WD
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Well, made a few discoveries since last posting -

I had flashed the Magnum with a DiabloSport canned performance 93 octane tune a few years ago, and left it in there for up until a few days ago. I found out that this canned tune had caused my cold idle speed to be about 3000 (three thousand) RPM, and warm idle to consume about .55 gallons per hour.

I reverted the Magnum's tune back to stock, then played around with the stock tune with the limited tweaking capability built into the Predator. Basically, I advanced ignition timing by 8 degrees from 0-4000 RPM, and experimented with lowering the idle engine speeds (idle in P/N w/ no AC, idle in R/D/3/L w/ no AC, idle in P/N w/ AC on, idle in R/D/3/L w/ AC on).

Turns out that advancing stock ignition timing does wonders with fuel economy, above and beyond with what the performance 93 canned tune did. I got 28 MPG on a mostly-highway 29 mile drive last night, then got 25 MPG on a 6.5 mile city drive about an hour later.

Also learned that messing with the stock idle speeds is counterproductive, even with lowering the speeds by 50 RPM. When warm, the Magnum would attempt to idle at the lowered idle speed, then somehow the engine computer would experience some sort of underflow condition and cause idle speed to jump up to about 2000 RPM. I returned the idle speeds back to stock settings, and that solved the idle speed problem. I am also consuming about 0.35 gallons per hour in idle, now.

Also, the performance 93 tune messed with DFCO. The Magnum is now more willing to enter DFCO when I let off the gas.
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