Running the 2UZ-FE on only FOUR cylinders (1 Viewer)

[loganbrew]

Having been one of millions of folks to experience the blackout in Texas this week, I got a little experimental with my extra LC100. Basically, I used my 2003 for shuttling family (also without power) to my home and buying essentials, and the other as an electrical generator. I had a 1000W power inverter (12VDC to 120VAC) laying around that I fitted to my 2000LC's battery, which was sufficient to power the fan/fuel valve on my home's gas furnace, power my gas fired tankless water heater, and leave power to spare for a few lights and phone/laptop charging stations... and the very critical Swiss coffee machine. Made things fairly comfortable for the 20 or so hours until power returned.

To minimize fuel burn and reduce trips to the gas station (very difficult!!) was pull four of the fuel injector connectors - from cylinders 8, 3, 5, and 2. My thinking was that this would create the most balanced firing of cylinders (every other firing, see image below) and also lessen (halve?) fuel burn from the constant idle. My question is, would this actually halve fuel consumption?

Initially, the idle dropped 100-200 rpm, but after a bit the ECU figured things out and got the idle up to just under normal. I wonder if the ECU just doubled the fuel delivered to each of the four cylinders running, so to not burn any less than the normal 8 cylinders? It not being practical to compare running 4 cylinders with all 8 over the same time period, I really can't know, but I am curious if I can extend runtime this way, as I'm almost certain I'll do this again some day.

Note that I didn't run the full 20 hours. I don't know how long in total. I shut it off at night and other times when power wasn't absolutely necessary. Only burned 1/4-1/3 tank in total.

 

[thebeedeegee]

Wow man.

I would guess it would be obvious if it was dumping the same fuel into the running cylinder because it wouldn't run right, or it would smell extremely rich. I'm surprised the alternator could handle that load, or were you running either the furnace or the water heater never at the same time?

Hope you guys are doing alright down there.

 

[onpoint01]

Having been one of millions of folks to experience the blackout in Texas this week, I got a little experimental with my extra LC100. Basically, I used my 2003 for shuttling family (also without power) to my home and buying essentials, and the other as an electrical generator. I had a 1000W power inverter (12VDC to 120VAC) laying around that I fitted to my 2000LC's battery, which was sufficient to power the fan/fuel valve on my home's gas furnace, power my gas fired tankless water heater, and leave power to spare for a few lights and phone/laptop charging stations... and the very critical Swiss coffee machine. Made things fairly comfortable for the 20 or so hours until power returned.

To minimize fuel burn and reduce trips to the gas station (very difficult!!) was pull four of the fuel injector connectors - from cylinders 8, 3, 5, and 2. My thinking was that this would create the most balanced firing of cylinders (every other firing, see image below) and also lessen (halve?) fuel burn from the constant idle. My question is, would this actually halve fuel consumption?

Initially, the idle dropped 100-200 rpm, but after a bit the ECU figured things out and got the idle up to just under normal. I wonder if the ECU just doubled the fuel delivered to each of the four cylinders running, so to not burn any less than the normal 8 cylinders? It not being practical to compare running 4 cylinders with all 8 over the same time period, I really can't know, but I am curious if I can extend runtime this way, as I'm almost certain I'll do this again some day.

Note that I didn't run the full 20 hours. I don't know how long in total. I shut it off at night and other times when power wasn't absolutely necessary. Only burned 1/4-1/3 tank in total.

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Brilliant !! I must say I’m amazed the engine would run without stumbling. With regards to fuel saving at idle, I would say yes for sure. Your computer doesn’t know to add more fuel to your 4 connected injectors as the throttle body is only set at idle.

Hope things are improving out your way this morning. I may need to use this trick in the future as well so thanks for sharing.

 

[loganbrew]

Your computer doesn’t know to add more fuel to your 4 connected injectors as the throttle body is only set at idle.

Ah... this implies the ECU can control air-fuel ratio at idle from the throttle body, rather than increase the open time of the injector. I was thinking the TB was purely mechanical, being a 2000 with cable actuated TB (vs electronic TB of 2003+). But looking closer under the hood, the TB has an eletro-mechanical actuator on the right side. I'll bet that's what's adjusting AFR to get idle closer to normal. So yeah, it probably is consuming only half the fuel with half the cylinders!!

It definately ran low idle for a few minutes until the ECU made adjustments, but ran pretty smooth just sitting there and with the inveter loaded to drive the house applicances. It definately stumbled when I had to manuever the truck around in the driveway, but it never died. I was really ginger with the accelerator to avoid an engine stall.


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[loganbrew]

Image intended for last post didn't take. Trying again...

 

[loganbrew]

I'm surprised the alternator could handle that load, or were you running either the furnace or the water heater never at the same time?

Think of the 1000W inverter as a modern-day 1000W stereo amplifier (D-class, switching amp) or 1990's old-school 500W stereo amplifier (class A-B). The alternator has no issues with that load, but you have to keep the car running or the battery will drain pretty quick. Since the furnace and tankless water heater are gas-fired they don't draw much current. They only draw enough power for the control electronics (below one ampere each, 200-300W) and the furnace fan, which might have been 3 amps (~400W).

 

[hondarepairman]

Unfortunately I don’t think it’s really this simple. Just because you shut down half of the injectors doesn’t mean you halved the the air volume at a specific rpm. I would assume that the excess oxygen would be picked up by the fuel feedback system and result in an increased duty cycle to all injectors. Interesting to see what the fuel trim values would be while running. I do think that the fuel consumption would be less...just not half.

 

[loganbrew]

Unfortunately I don’t think it’s really this simple.

Agreed, fuel control is never that simple, and I'm drawing from having implemented fuel control on GE LM6000, Rolls-Royce Avon's, and other gas turbines. I guess I could put my Tech Stream on it and try to deduce fuel rate at conditions of 4 and 8 cylinders, but I doubt it would be so convenient as to show FI pulse duration. Maybe others can suggest how TS reports fuel rates?

 

[Eicca]

I imagine it would report positive fuel trims via the upstream O2 sensors since it's taking in the normal amount of air but only half of it is being burned in combustion. Which makes me wonder if it would try to make up for that non-combusted air by increasing fuel to the cylinders that ARE still running until the mixture is balanced at the sensors.

Or if that's even how it works...

 

[jLB]

Interesting improvised solution, although I do think I prefer my natural gas standby generator solution to the problem.

(Also in Texas, and also spent the past week dealing with cold/power/water issues)

 

[loganbrew]

...natural gas standby generator solution...

I hear you brother... Spec'd out a Generac 24kW (21kW max on nat gas) unit last night... I'm sure the lead time on those is going way up now, but as long as it's in ahead of the 2021 hurricane/flood season I'm cool with that.

 

[badlander]

Since the 4 cylinders that aren't firing are still compressing air (for nothing) it seems like it would be more of a loss than a gain. Maybe if you removed those 4 non-firing spark plugs it would help reduce the compression load but then you'd be sucking in dirt.

 

[smartparts]

Its a cool idea, but yeah I'm not exactly sure how much fuel you really saved. You would have been better off running the inverter, turning the heat up in the house, having the fam take showers and then just charge the battery rather than running the truck for 20 hours

 

[e9999]

yes, I was going to ask about the spark plugs. Without removing them, you spend a bunch of energy on compressing air for nothing. So that's a big loss. Think about coasting down a hill, it's that compression that keeps the speed in check (although at higher rpm of course).
Even if you do remove the plugs, you still have the friction on the 4 open cylinders, also a loss.
Now OTOH, if you have more cylinders running than is needed to deliver the power for the electric load, the excess energy -even at idle- would be lost as heat. More loss.

So, as to the question whether you have saved half the fuel, I would guess no, but there is not enough info to tell for sure how much. You may well save some by removing fuel and plugs from the other 4 cyls. But I think that also would depend a lot on whether the amount of energy given out by the 4 cylinders at idle is enough to power the load. If not, then you may be better off having more cylinders going.

Wrt to the big picture, you likely would be much better off running a small generator. An engine is optimized fuelwise to run at a certain operating point. And it isn't idle. So with the LC, even on 4 cyls, you are running a very big generator at a point very far away from optimum. My little generator (1600W) uses about a gal over 8 hrs or so at light load. If that were the case with the LC, it would idle for 8 days. I doubt that would happen.

But aside from any such consideration, in a pinch, it's a great way to go and you were creative at it too. And I have always been curious to know what would happen if 4 cyls were deactivated. But never tried. Congrats!

 

[loganbrew]

compressing air (for nothing) it seems like it would be more of a loss than a gain

Good point... added load with no productive work

...rather than running the truck for 20 hours

Didn't run continuously, but didn't know how long we'd be in the dark either.

Just bear with me and consider a more likely case (for any of us)... where there's cause for truly extended survivor mode under different circumstances. For example, one of us is stuck/demobilized, in the subfreezing cold, in a remote location, and you need to extend run time for just the truck's heater - until help arrives. I still don't know if pulling the FI connectors will extend that runtime, but based on badlander's keen observation, I'm sure as @#$% going to add the proper sparkplug socket to my travel tool kit now...

 

[nissanh]

No, if you run an 8 cylinder in 4 cylinders, the engine is strained as 4 cylinders are getting compressed without firing and needs more power from firing pistons at an akward crank angle, so more energy will be used.

I tried to run the furnance fan and fuel valve with my 400W invertor in the back of my 21 Tacoma and it failed. The fan uses about 12.8 amps which comes to about 1400 W.

How bad is the fuel shortage there?

 

[flintknapper]

Interesting improvised solution, although I do think I prefer my natural gas standby generator solution to the problem.

(Also in Texas, and also spent the past week dealing with cold/power/water issues)

Yep, no water or power for the last 5 days here.

But making it.

Have plenty of firewood, a fireplace, filled the tub ahead of the ice storm I knew we'd get...so we can flush toilets and do dishes.

Have a 10KW and 2800 watt gen-sets....so I can pretty much run anything in the house (just not all at one time).

Four cylinders (total) also.

 

[tincan45]

If you ran for 20 hours and only used 1/3 of a tank I would say you "might" have saved some fuel, but not a lot. You would really need to know exactly how long you ran it to make a good determination. OBDII estimates they burn about .5 gallons an hour at idle. I use .6 gallons an hour when off-roading (slow crawling trails) in my 200 and it's usually pretty close (MPG only makes sense on pavement).

20 hours @ .5gal an hour would have been about 10 gallons. So if you used a 1/3 and only ran for 10 hours, I don't see a huge difference.

Interesting experiment. Keep in mind, alternators don't run at efficient outputs until you get into higher RPMS (2200-2500). I would not try not to pull more than 30-35 amps from an alternator at idle. You risk burning it up prematurely otherwise. The cold temps work in your favor in this case.