How does the computer figure miles per gallon?
Melting Slicks
Joined: Mar 2005
Posts: 2,252
Likes: 181
From: NE OH
Originally Posted by white90conv
I believe it uses actual miles travelled and the injector pulse width.
There's a table in the PCM for injector flow rate (grams/second) versus manifold vacuum. Using the flow rate and the injector pulse width (in msec's) the PCM knows exactly (as long as the flow rate table is correct) how many grams of fuel is being squirted into each cylinder, per second.
Your MPG readings can become flaky if a tuner gets lazy and doesn't set the IFR table properly. When an AFR is off by say 10%, it's quicker to add/subtract that 10% from the fuel table, rather than adjust both the fuel and the air tables.
Melting Slicks
Joined: Mar 2005
Posts: 2,252
Likes: 181
From: NE OH
Originally Posted by Mike04
That all makes sense.
Is it also adjusted for differing fuel pressures? A 42 lbs injector would flow more fuel at 62lbs than 55lbs if the pulse width remained constent.
Is it also adjusted for differing fuel pressures? A 42 lbs injector would flow more fuel at 62lbs than 55lbs if the pulse width remained constent.
The comment about increased pressure=increase flow is dead on.
Drifting
Joined: Dec 2005
Posts: 1,720
Likes: 3
From: East Hampton CT
Originally Posted by muncie21
The C5 PCM doesn't have a table to compensate for fuel pressure as our fuel pressure is supposed to be a constant 58PSI.
The comment about increased pressure=increase flow is dead on.
The comment about increased pressure=increase flow is dead on.
SCALER FOR FUEL ECONOMY OUTPUT. Sure looks like there is a provision to "align" your DIC with the actual economy.
