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Old 07-01-2010, 01:15 AM   #1 (permalink)
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Dodge RAM 4.7L fuel cut-off

Okay, I have been going through the wiring diagrams for my 4.7L, and it seems the injectors and ignition coils all ground through the same wires. My question is, if I insert a solenoid to interupt the electricity flow for all of them, will this be a bad recipe?
Here is a link to the wiring diagrams: http://www.dodge.com/bodybuilder/200...tionsystem.pdf
see pages 3, 5-6. Per page 3 (triangle A to S112), if I can find the wire, I can use one wire to stop them all...
I do not plan to do any EOC, as my auto trans is not up to that. I am basically looking to emulate DFCU with a push of a button. Any thoughts or tips on what to use?
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Old 07-02-2010, 09:48 AM   #2 (permalink)
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whats DFCU?

Is that the variable displacement thing the Hemi engine does where it shuts off half of the 8 cylinders when cruising? In that case it doesnt just shut off fuel, it also closes the valves to those cylinders so they stop pumping. That part is harder than shutting off fuel. Also im not sure how the ecu would work with the scheme.

edit: I think you mean insert a relay to interrupt the electricity not a solenoid.
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Old 07-02-2010, 12:33 PM   #3 (permalink)
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It should be written as DFCO, or Deceleration Fuel Cut Off.
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Old 07-05-2010, 05:24 PM   #4 (permalink)
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Nuts. Thanks Comptiger. Guess I hit the wrong key...
Mike, yes, either a relay or a simple switch for me to hit to break the electrical circuit. My truck does not have the MDS (multi-displacement system-HEMIs only). This is my attempt to create a decel fuel cutoff like my 91 VW Jetta, 1990 Audi 100, and my wife's 08 Dodge Avenger have.
Well, my first attempt had limited success. I dug through the wiring diagrams and isolated the ground wire coming from all the injectors and spark plugs, going into a large connector (C130) near my truck's PCM. So I cut wire #4 and ran a pair of wires into the cab so I could flip a switch and open the circuit. Well, it seems to only work if I am coasting down a hill with the throttle closed. If I try it with the truck idling in the drive, it keeps idling; or coasting toward a stoplight on close to level ground, it keeps idling. I have only seen the fuel flow on the MPGuino go to 0.0 when coasting down the steeper hill (@45 mph, in 5th gear). Reasearch continues....
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Old 07-05-2010, 07:19 PM   #5 (permalink)
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Dang I hate the wiring on newer Dodges. I would first recommend determining if this is worth wile. With some cars it is, with some it isn't. If you have a scangauge type tool you can see how long it takes to go into DFCO, and when and the such, and see how much more you could realistically run on manual DFCO. With my car it's not worth wile, but with with the Ram it might be.
Then you have to think about all the sensors that will through signals to the computer that will confuse it, primary to O2's, and i think you have at lest 4. You can rig up a fake signal that switches on when you switch on the manual DFCO on.
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Old 07-09-2010, 01:22 AM   #6 (permalink)
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Thanks Doc. Yes, Dodge is notorious in the wiring dept, I have discovered. I figure with my truck's ability to guzzle fuel, it will be worth it. I ended up pursuing this because I have been working on the aerodynamics enough that my truck is coasting pretty good, and letting off the throttle isn't really enough to slow things down quickly. Guess that's not all bad.
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Old 07-09-2010, 02:50 AM   #7 (permalink)
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My ex has a Dakota, and that beast coasts in D better than my little car does in N. Despite the ridiculous wiring i doubt that it's all that good a DFCO. Maybe instead of hooking up a way to keep the CEL off you also hook up a bat. kill switch so that you can clear codes with ease. (that would suck for your clock, and radio pre-sets)
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Old 07-09-2010, 06:16 AM   #8 (permalink)
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Whats the difference betweeen EOC and DFCO, the transmission being in drive instead of neutral? When is DFCO usefull? On a really long downgrades where you have to brake to keep under the speed limit or when your going from highways speeds to a stop? Is it usefull any other time?
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Old 07-09-2010, 10:16 AM   #9 (permalink)
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When my Jeep isn't in DFCO, it actually coasts better in D than N, (mostly from about 20 - 35 mph). It will sustain 15mph in 2nd, or 20 in 3rd (engine idling) indefinitely on flat ground, as the huge engine can push it enough at idle to keep it going.

DFCO is best used to keep from gaining too much speed on long downhills, and to drop speed coming off highways, as you expected.

DFCO is when the engine is still spinning (tranny in gear), but not supplying fuel. EOC is when you put it in Neutral and turn the engine off (most Auto trannies can be damaged by this, recommended for manual only).
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Old 07-10-2010, 10:56 AM   #10 (permalink)
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Quote:
Originally Posted by ECONORAM View Post
I have only seen the fuel flow on the MPGuino go to 0.0 when coasting down the steeper hill (@45 mph, in 5th gear). Reasearch continues....
Your switch hasn't done anything for you. The 4.7L does have DFCO, as I have verified in my own truck driving with a hand-held code scanner installed. If you have the overhead console with the MPG meter when you see it hit 99mpg instant chances are you're in DFCO. It's just that the DFCO programming is as non-agressive as it can be. Mine takes nearly 2 seconds of 2000+ RPM with no throttle sustained before it cuts injectors. It's more of an engine-braking situation, which is easily attainable with my manual trans but might be a problem for an auto truck. I find it more efficient to coast in neutral or EOC unless the hill is steep enough to require engine braking to prevent acceleration or unless you have enough momentum going into the downhill that you need to scrub speed due to traffic, signals, etc.

What you propose wiring is nothing different than an engine kill switch, which should be more easily accomplished by intercepting the cam signal sensor wire and installing a NC momentary switch directly to break signal when the button is pressed. I've contemplated doing the same in my truck as I do EOC, but I'm not sure how well of an imitation at DFCO this will do without actually shutting down your engine. You might need to keep the cam sensor active so you can monitor engine RPM while cutting fuel in your case as your auto will not bump start your engine for you.

If you weren't interested in OD you could install one of the VERY early 3-speed Torqueflite that has dual fluid pumps, one on input and one on output shaft, for the purpose of bump starting.

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