3 cylinder operation would be 240* of crank rotation or 120* cam. My chevy sprint was a 3 cylinder 1L, ran like a top. Just how much will the other 3 cylinders ,non firing, hurt? Interested in how this will turn out.
I'm talking about the location of the cylinders relative to the crank not the number of strokes involved for firing. I'm guessing that the valves being closed may in some way aid in reducing the vibration. When a cylinder fails to fire the engine vibrates worst at low rpm but smoothes out at higher rpm. I guess three cylinders in pairs serves as some knd of neutral point that is undetectable from a balance point, the only difference between the 3.9 running on three cylinders and the other engines running on three is that the valves are not opening and closing. I can't readily think of any adverse effect since fuel would be off, and I've seen many a car driven with at least one non firing cylinder annoyingly going on like nothing is amiss. I'm interested in how the balance will be. I'm not sure but perhaps the valves are shut down to remove the load from the valve train since they aren't doing any beneficial work on cylinders that arent' firing.
I recall the injector fuses being 5 amps, I'm not sure, but I don't see them in my fuse box and the labels are worn off.
Looks like it might not be as easy as I thought, I'm only showing one fuse for all 6 inj in the book, the twin 5 amp fuse feed was in a 4cyl car I converted to 6 cyl.
[This message has been edited by Joseph Upson (edited 05-29-2007).]
Okay, someone installed 20 amp fuses where the 5 amps were supposed to go. I tried it and it vibrates but not to bad, although I let it idle I didn't drive it. I can see how it might smooth out with increased rpm to where you might not notice it but a vibration is a vibration and I'm very curious to know if the actual engine designed to do this runs without a vibration and if it kicks down a gear to keep rpm up. There has to be a reason they are only using this feature on one or two cars instead of the entire specified fleet for the engine.
[This message has been edited by Joseph Upson (edited 05-29-2007).]
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09:38 PM
May 31st, 2007
Faster7 Junior Member
Posts: 8 From: Springfield, MO Registered: Oct 2006
I hate to get away from the original thread subject, but seems that the interest is here so I'll let it fly!
My mother has the AFM "Active fuel management" equipped Impala and I can tell you that it is SEAMLESS. If the display in the dash didn't show 6cyl or 3cyl operation (and the increased fuel economy in 3cyl mode) then you couldn't tell the difference. It's addictive to roll along at 40mph and turn on the cruise control (the only way it'll switch to 3cyl operation at low speeds) and cruise along as it shows 60-70+mpg.
The largest benefit of shutting down the valvetrain for the cylinders not in use is to reduce pumping losses, the trapped air in the cylinder acts like a spring. Pumping losses from trying to fill a cylinder with air with the throttle barely cracked open are what really kill fuel economy with gasoline engines, one of the major reasons diesels can be much more fuel efficient.
My understanding is that cadillac took an entirely different approach to accomplish this in the 8/4/6 series and that there is little to no comparison between the dyanmics between the two engines given that disabling one bank on a V8 will have an entirely different effect than disabling one bank on a naturally balanced V6.
I intend to pull the fuse for one bank of injectors while on the interstate to see what the effect is with 3 cylinders firing at an evenly spaced 120 degrees apart. Of course it will not be quite the same since the valves will still open on time but it's a start for an idea. Heck if the engine runs smooth enough I might see if I actually save gas. I recall a long time ago having one bank of injectors go out due to the fuse and the engine continued to run. I was astonished upon finding the blown fuse that it ran on three cylinders. I wasn't driving it to note the effect at the time.
My point was that the V8/6/4 system did not have an electronic throttle, so when the engine decided to drop a couple of cylinders, the driver had to push the gas further to maintain speed. This is not an acceptable level of intrusion in a modern car.
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11:28 PM
ryan.hess Member
Posts: 20784 From: Orlando, FL Registered: Dec 2002
Originally posted by Joseph Upson: I intend to pull the fuse for one bank of injectors while on the interstate to see what the effect is with 3 cylinders firing at an evenly spaced 120 degrees apart. Of course it will not be quite the same since the valves will still open on time but it's a start for an idea. Heck if the engine runs smooth enough I might see if I actually save gas.
You won't. The pumping losses outweigh the higher efficiency. There were some tests done on TGO and they all lost fuel efficiency. That's the reason DoD shuts off the valves.
You won't. The pumping losses outweigh the higher efficiency. There were some tests done on TGO and they all lost fuel efficiency. That's the reason DoD shuts off the valves.
My primary purpose for the experiment was to get a feel for the vibration level, I mentioned in another post shutting off the valves affects the efficiency, I'm not interested in converting an older engine to that function just trying to decide on which version of the 3.9 engine I'm going to purchase for my swop in place of the 3.5L. There is also an alternator modification that is activated at the same time the cylinders are deactivated on the 3.9L to correct the belt slack that occurs. The standard engine should produce good mileage numbers but it wouldn't hurt to have the fuel saver model to have the option to try and take advantage of it. Once I get a look at the wiring scheme I'll have an idea, if the cylinders are deactivated sequentially I may not bother given what I already have going to restore function to the VVT.
Keeping the thread alive, while ordering parts, I should have the new 3900 to replace the current 3500 next week. Working with time constraints so the install has to be complete for tuning by the weekend after next.
I'm very interested in this swap, in fact, deciding this one over the 3800 swap! I'll will probably do the 3500 over the 3900 until the VVT and AFM (DoD) issues are fully resolved.
As I understand so far, it is the same work as the 3800 wiring wise. Correct? Could you provide more information on the TB change to manual vs ETC and on mating to the 5 speed as well as the 6 speed?
I'm very interested in this swap, in fact, deciding this one over the 3800 swap! I'll will probably do the 3500 over the 3900 until the VVT and AFM (DoD) issues are fully resolved.
As I understand so far, it is the same work as the 3800 wiring wise. Correct? Could you provide more information on the TB change to manual vs ETC and on mating to the 5 speed as well as the 6 speed?
You should follow the 3900 thread which this engine was sidelined for where you will also see that the VVT can be blocked into straight up cam position. The 60 Degree V6 forum has the necessary items to help negotiate the 3500 at a very, very reasonable price. https://www.fiero.nl/forum/Forum2/HTML/084972.html
