new hemi mpg in an Abody?
In CMR on the Hemi PCM's I've seen it won't let you adjust the closed loop target AFR. If you closed loop it's going to give you 14.7 unless the fuel trims are soo far off it can't. Might be able to make something to fool the linear o2 sensors into thinking it's sub stoic so it will make it lean though. You'd probably want to hook it up to a vacuume switch so you don't get high 15 afr's at near WOT but still closed loop situations.
I didnt get into this thinking that most HEMI conversions have a programmable computer which generally allows you to adjust fuel/spark tables to whatever at will... BUT assuming that you cannot do it the nice way, here is what i do on my Breeze and the wife's Town & Country...
Wide band o2 sensors use a completely different technology and output V range. Because of this they "simulate" a narrow-band sensor via electronic controller...which is programmable, has several outputs (run gauge etc),
will data log! via serial port, and will actually work at very rich and very lean conditions. So the point is to shift the entire AFR readings and tell the computer that you are running richer than you actually are. i.e. a sensor detected 16.7:1 AFR will output to your PCM 14.7. 15=14 etc...
WOT is open loop, and your narrow band O2 dont work for crap at full rich power AFRs anyways. So max WOT HP is not affected.
Downsides?
slightly less HP at part throttle? if you go to far some drivablity issues. On my 2.0 anything past 16.8 runs like crap and will barely idle in hot weather. Anything <16:1 on both the breeze and caravan and you really cant tell the difference except at the gas pump.
If your down stream (after CAT ) O2 sensor doesn't throw a code when cruising your still burning gas in your CAT and not in the engine where it belongs. You;ll get a code because the computer doesn't detect an AFR difference before and after the CAT e.g. it thinks the CAT is not working.
So 60K+ miles latter, no problems, and verified 3-6 MPG improvement on my 2.0 4speed automatic. I went from 32-33MPG to 36-39MPG and a few better than 40. YMMV! going from 33-36MPG is a lot less gas saved than going from 17 to 19MPG.
I use innovate motorsport's LC1.
BTW you'llneed two for your Hemi ;-)
-Troj
