Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

Get 8 cylinder to run as 4 cylinder

Is it possible to unplug 4 of the cylinders on my 2000 Dodge Ram pickup and only run on 4 cylinders?


Not easily, cheaply, or quickly. If you simply unplug the coils, the fuel injectors will keep spitting fuel. If you unplug the injectors next, then the ECM will freak out, set the CEL with a laundry list of codes, and maybe put you in ‘limp home’, which will burn more fuel than all 8 running.

Of course, Chrysler added Multi-displacement in truck engines in 2006, which cuts 4 cylinders when the conditions are right. The system boasts a 10%-20% improvement in fuel mileage. Maybe you can trade yours in for a used on made after 2006?

Or better yet, trade it in for something that only has four cylinders to begin with, unless you really need a big truck as opposed to simply wanting one.

Or renting one for those three days a year that it is needed.

Yes, with enough money you can do almost anything. That does not mean it is a good idea. It will cost you far more than you could save.

If you were to unplug both the spark plug wires and the injector connectors to the proper plugs such that the firing sequence was balanced it would probably run…but not well. Once you disconnect the high pressure injector spray at the injection ports, then the fluid dynamics of the manifold will be different when the intake valve opens and the piston continues down on its intake stroke. That powerful pull may just change the absolute pressure of the manifold in the paths where they’re feeding the still operating cylinders. It would probably also change the signals from the MAP sensor and the oxygen sensor to where the ECU would go nutty. Its program is designed to control the injectors and spark based on the signals it receives with all eight cylinders operating. I have no idea what this would do to operation. Cars that are designed to shut four cylinders down under low load disable the valves and are programmed for the 4-cylinder-operating ECU inputs.

I can guarantee that you’d have to put a piece of electrical tape over the CEL light. When it discovers that 4 cylinders aren’t firing it’ll light up with unusual enthusiasm. You’ll have more codes than a NYC intensive care ward.

Bad idea. You’ll ruin the catalytic converter in short order. It will be difficult if not impossible to drive. The engine ECU will have a conniption fit.

You would waste a lot more fuel doing this because your pumping losses would be astronomical. With the multi displacement engines that shut down 4 cylinders during light cruise, the valves are held slightly open in the “off” cylinders to reduce pumping losses to a much lower level.

Oh yeah, all the other things already mentioned too.

If you could, it would get incredibly bad mileage and have utterly lousy acceleration and driveablity. The newer Hemi motors do this neat trick by controlling the operation of the valves with oil pressure as well as having the computer programmed for this, so fuel injection and probably spark are shut off. Plus they likely have a cam profile that makes operation on 4 cyls. smoother when the other 4 are deactivated. There’s very little you can do to make this truck get better mileage. I had a 98’ and it got about 11 MPG in mixed driving. A shame, because otherwise it was a nice truck to drive most of the time. Times are a’ changin’ and it’s sad.

As an interesting note, there are portable air compressors that do this. One side of the V8 is the engine and the head on the other side is modified to be a compressor.

I’ve read about farmers converting old V-8 engines for use as compressors in basically this manner. I seem to recall there being a kit to do this, which I’m guessing includes different manifolds.

I remember seeing a compressor back in the mid-1960’s made, I think, by the Jaeger company. It had an inline Chrysler 6 cylinder engine. The front three cylinders provided the power and the remaining cylinders compressed the air. The engine had special heads and had an updraft carburetor on a special intake manifold. This compressor was powering jack hammers outside my building and it sounded as though it was missing when it idled. Curiosity got the best of me, so I had to go investigate. I haven’t seen one of these compressors since that time.

GM is doing this. It’s a revamped version of the 8-6-4 system Cadillac had back in the 80’s that failed miserably. Their newer system is suppose to work. Cruising on the highway it will shut off 4 cylinders and just run on 4.

It’s NOT something you can just unplug and expect it to work.

I’d be inclined to avoid it. GM’s history with “different” types of engine systems has been plaugued with pain. The Vega engines, the old GM V8 diesels, the Saturn engines, the 8-6-4 you mentioned… They seem to use the public to test new designs.

They seem to use the public to test new designs.

Most GOOD companies test new designs BEFORE they introduce them to the public. I was giving GM the benefit of the doubt…thinking that they might have learned their lesson and actually TESTED this new engine out before they started selling it.

Back in the early '80s, I worked part-time as a Limo driver. Since I was the new guy, I was given the V-8-6-4, since the other drivers HATED it.

I soon found out that it required a warm-up time of at least 20 minutes, even in the summer. Its “acceleration” was a dangerous joke, since you never really knew how many cylinders you would actually have at your disposal when you floored it. Most of the time, it was certainly NOT 8 cylinders, and that heavy limo took an incredible amount of time to gain speed.

After driving it a few times, I knew why the other drivers called it the Cadillac V-8-6-4-2-0. It truly was a ZERO in terms of engineering, but I believe that GM’s new design should be a credible effort on their part.

There was a simple fix for that car (besides driving it off a cliff). It could be set to run on all 8 cylinders all the time. This made the car at least drivable. I think Caddy only had this feature 2-3 years.

I believe the newer GM engines with cylinder deactivation use the same method as Chrysler pioneered with the new Hemis–they use oil pressure to control valve operation.

Oil seems to be becoming the new hydraulic fluid. I believe Honda and BMW both use oil pressure to control their valve timing.