Dodge RAM 4.7L fuel cut-off

[ECONORAM]

Thanks MechEngVT, as I discovered the exact same thing this weekend. My wife and I just drove out from SLC Utah to OKC Oklahoma over the weekend, towing her car. I had the truck loaded to 6500 pounds, just a little under max. I happened to see my truck activate a decel fuel cut-off when we were going downhill several times. I ran the SC 91 tune, had the tranny in tow/haul mode, typically with cruise on (but not always), and was going around 65 mph. I noticed the truck would downshift, fuel flow would drop to 1.15 to 1.35 gal/hr, and then if the hill or decel condition continued for a few more seconds, fuel flow would drop to 0.0. However, as the hill leveled off the cruise would pull the throttle cable and fuel flow immediately resumed...or if cruise was off, I'd press the gas and the truck responded in the same manner. This happened far more frequently in the Utah/Wyoming mountains than after we got into Colorado and Kansas...although I did get it to engage while coasting to a Tollroad booth yesterday in southern KS.
I agree, the DCFO does seem to drag its feet while engaging. I think it should be more agressive. This weekend's drive is the only time I have seen it engage routinely. I watched my MPGuino to see when it kicked in. I agree, the wire I cut did nothing. If I knew which sensor to trip to make it kick in sooner, that'd be great.
For whatever reason, my overhead console does not show inst mpg, only the tank average. Is there a way to change that?
I am actually trying to avoid an engine kill switch, as I'd still like to watch rpms (and I don't want to kill my auto trans). I figured if I killed the power to just the injectors, everything else would keep spinning... I have asked Superchips to look into and see if maybe they can work something into their tunes.

[ECONORAM]

Update: I did contact Superchips, but they told me retuning the DFCO would basically required an OS rewrite...so no dice.
I also did some experimenting last weekend. I set the cruise control speed artificially low (around 45 or 50 mph) and was normally driving 70 on the tollway. When I hit a fairly steep hill or had to slow down for the tollbooths, I let off the throttle and sometimes even when on a level street the DCFO would kick in. It did on almost every downhill...but this required me driving like I did 20 years ago when I didn't have cruise.

[ECONORAM]

I know it's been a WHILE, but I finally got around to working on this some more. I chased ground wires in the harness a while, but after disconnecting two and still seeing a good connection to ground, I elected to cut all the injector ground wires and run a common wire from them to the cockpit, through a switch, and back. This works. The truck starts with the switch in "on" and won't with it off. Haven't road tested yet, but should be nice going down long grades or coasting up to toll booths...assuming the PCM doesn't complain about injector flow.

[t vago]

Boy, that's a weird critter.

My 4.7L has a common injector power wire fed from the ASD relay, and separate ground wires that are switched by the PCM. I might come up with something along these lines, because my truck will randomly go into DFCO You know, like it'll actually go into DFCO at a certain spot and a certain speed at a certain time of day, and on the next day it'll just laugh at me and continue to run at about 13.1 AFR at that same spot and that same speed at that same time of day.

[ECONORAM]

t vago, I have noticed my truck doesn't seem to be consistent with DFCO either. After I reset the PCM, I sometimes see it coasting up to the first toll booth on I-44. But after that, no dice unless I artificially force it with the cruise control procedure I detailed above. I am curious about my AFR since you mention it. Nuts, another gauge to buy.

[ECONORAM]

Originally Posted by ECONORAM

I know it's been a WHILE, but I finally got around to working on this some more. I chased ground wires in the harness a while, but after disconnecting two and still seeing a good connection to ground, I elected to cut all the injector ground wires and run a common wire from them to the cockpit, through a switch, and back. This works. The truck starts with the switch in "on" and won't with it off. Haven't road tested yet, but should be nice going down long grades or coasting up to toll booths...assuming the PCM doesn't complain about injector flow.

Well, it did cut off fuel flow, and the truck would coast along just fine...with the engine rolling at about 500 rpms. But the engine ran rough with the switch "on"; it seems the wire length was causing issues. I might try wiring in 8 relays to a common on/off switch. But I have better fuel saving ideas to work on first...

[t vago]

Do you have a CEL? Do you have codes? I suspect that you have "injector open" or "multiple misfire" codes.

[t vago]

Another wacky idea I had last night (for Dodge and Chrysler engines, anyway) to accomplish DFCO at the flip of a switch was to have a double pole relay in series with the signal output of the camshaft and crankshaft position sensors. It would be such that if the relay would be energized, the contacts would break, the engine computer would no longer see the outputs of these sensors, and as a result would stop firing the injectors and ignition.

[ECONORAM]

Oh yeah, I had all kinds of codes! But, I removed the whole harness I soldered in (what a drag that was) and reset the PCM, and all is well. My next thought was to put a relay at each injector where I'd soldered the harness in, as I mentioned above. But that will take a little more free time than I have right now...

[baldlobo]

from what i've looked at 2006 is the change over for the immobilizer function to be completely ecm based in chrysler vehicles; before that it was more looked at as an option, specifically before 2000 model year. my 99 tj(wrangler) has a fuse i can tap to turn off the ignition and fuel injectors it's part of the immobilizer function. 2001 to 2005 has a relay that can be by-passed if clever.