Cylinder Deactivation

[OilBurner]

Hello! this is my first post here. I own both an 86 Mercury Grand Marq and an 88 Town car (among other things). I am Planning to drive the Mercury cross country from PA to CA and then back...and have been thinking about ways to effectively improve fuel mileage. Somebody on another forum had said they had seen a 33% increase in gas mileage experimenting with this, with a v8, but not on other v6 & I4 engines...

My idea would be to interrupt each injector with a relay and a set of switches, on the fly while driving...as to let the car run on 4 cylinders at cruising speed on flat highway, or possibly idling on only 2 while in a drive thru or even sleeping in the car with the A/C on... the easiest way to do it would only involve 4 relays and 1 switch to select either 4 or 8 cylinders, or i could have all 8 cylinders tied to 4 switches in pairs so i can select any set of 2 or 4...this would all be relatively easy to do i think, but im curious if i would need to also modify the O2 sensor circuitry to not compensate for the "off" cylinders/more oxygen state by running the "on" cylinders very rich... I figured this early Ford EFI was "dumb" and would be easy to work with...but don't know much about it on a specific technical level or know where to look to figure out how it actually works & behaves...

So what other considerations would i have with this? Any other thoughts/input welcome.

[johnunit]

First off, welcome. You've come to the right place.


I think you'd almost definitely have the mixture doing weird things to compensate for dead cylinders.


I'd also not operate a jerry-rigged (with no disrespect to your skills) cylinder shutoff for any length of time. An engine is very carefully tuned to have the cylinder firings balance each other out. Having half the cylinders not firing would probably put a LOT of stress on the crankshaft, bearings, etc.

These cars are ripe for ecomodding in general, but cutting out cylinders with a relay wouldn't be where I go unless I've picked off a ton of low-hanging fruit like an airdam or undertray, fender skirting, low rolling resistance tires, free-er flowing exhaust, warm air intake, optimized timing, tall gear ratios, etc.

[OilBurner]

I think it would be fine as far as balancing so long as the correct cylinders are being turned off...eg every-other one in the firing order...so on 4 cylinders it would just be skipping every other firing and getting a power pulse on every half-turn of the crankshaft instead of every quarter turn of it on 8 cylinders...and theoretically it would still be balanced on 2 cylinders again assuming the correct ones are chosen. But it would be off balance and likely jerky if it were running on 6, or the wrong 4 or 3 or several other combinations.

more specifically, how would the ECU possibly compensate for dead cylinders? If all its using is the O2 sensor to make its mixture decisions, then that would be pretty easy to send a false "perfect" signal to the ECU...but if it has a knock sensor or uses the speed/tach signal to influence the mixture also then im not sure how to deal with that...does anybody know what all the ECU actually uses to determine the mix? if its just the O2 or are there other inputs..

[sly]

The ECM would definitely think it was running lean as extra oxygen would be detected from the unused cylinders and it would pig rich the running cylinders to try to compensate and would probably start throwing misfire and lean codes all over the place.

[Mainemantom]

There are reasons that the GM 4-6-8 in the 80's never worked right. It is not worth messing up your good car. If it is tuned up it will give great gas mileage.

[gadget73]

There are no knock sensors, and the PIP input for engine speed probably doesn't have the resolution required for the ECM to know that a cylinder isn't firing. It does not have misfire codes for specific cylinders at any rate. Unless you fake out the oxy sensors, it will fatten the mixture heavily since the "dead" cylinders will just push a bunch of air into the exhaust. The trick with the oxygen sensors is that the ECM constantly tweaks the mixture from rich to lean to watch for sensor switching. If you fed it a fixed voltage that represents a stoich mixture, it may code out for no oxygen sensor switching detected and the ECM will probably begin to ignore them. At that point I don't really know what it would do. I'd also expect the engine to run rough since you'd be compressing several cylinders without a power stroke to go with it. The GM design from the 80s held the valves open so that the cylinders weren't creating extra load. They didn't have individual injectors, so messing with the valve action was the only way to make it work. More modern ones shut the injectors off but they change around which cylinders are shut down to keep them from building up oil and unevenly loading the cooling system.

[87stars_stripes]

Here's an interesting one for you. My next door neighbor who is an acclaimed engineer focused on solar power and green energy, was explaining to me how he modified his fuel injectors in his 4 Cyl Toyota Pickup to achieve 47 mpg. He basically turns the injector squirt into a fine mist reducing the total LPH but retaining the same volume of fuel burn and increasing efficiency at the same power level. Long story short. Look into modifying your injectors.

[OilBurner]

I definitely believe that... reminds me of the vapor carb. same principal. I would think that would involve turning the pressure up on the fuel pump, and doing something with the injector nozzles...so what pressure does our EFI system normally run at and how would one go about modifying the injectors..can they be disassembled at all and have stiffer springs installed in them? or what...

My long term plan for this car is actually to get rid of the 5.0 V8 all together eventually and build my own diesel/electric hybrid power plant with another VW Rabbit engine and an electric forklift motor...motor+engine move the car on acceleration, engine spins motor as generator & maintains speed once car is up to cruising speed...and then the other big idea is to put the 6.9 Diesel which is currently in my truck into the Lincoln once i replace it with the 7.3 IDI diesel that id rather have in the truck.. none of this is going to happen until i move and get my own large garage and sufficient funds to use for tinkering... thus why im looking into quick & basic/cheap things to do to improve efficiency now...dual exhaust might be the most im willing to throw at it right now but thats still a couple hundred $ probably even if i do most of the work myself (i do weld, but cant bend pipe etc).

[87stars_stripes]

Yes. He tells me that he modified fuel pressure and that he uses an air filter with holes drilled into it because the precise amount of airflow is very crucial. That's all I can tell you about that though...

[L1011tristar17]

OilBurner, you would definitely appreciate reading this:

http://www.thetruthaboutcars.com/201...oost%E2%80%9D/

Someone put a Ford Turbo 4cyl in a 1959 Edsel. It basically puts out the same power as the original engine and uses only half as much fuel. It looks really nicely done too.

[L1011tristar17]

And this is his thread on Ecomodder

http://ecomodder.com/forum/showthrea...ion-14594.html

[sxcpotatoes]

*sigh*, My first car, an '88 LTD eked out 28.5 mpg average with a 1000w amp and 4 12" subwoofers in the trunk (420 on the trip odometer). Easy. Keep the speed to 55, slap on a hi-flowing dual exhaust, and you'll get phenominal gas mileage, even out of a FULL SIZE CAR.

[gadget73]

much as I detest them, the 4.6 is actually decent on fuel. CFI cars are too, but they are fairly gutless.

[OilBurner]

I was actually fairly pleased with the 18mpg that i get currently with single exhaust. figured that was pretty good for what it is.

[pantera77]

You can easily get high 20's on the highway out of these cars, even in stock form.