Running 8 On 4
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Joined: Dec 2008
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Running 8 On 4
Has anybody tried to cut the fuel to four of the eight cylinders on a Ford diesel to save fuel? At highway speeds with no load it seems like a 7.3 cut in half would do the job just fine. It seems like this could be done by attaching some type of electric valve to four of the supply lines before the injectors which would divert fuel to the return on demand. I have a 1990 350 van that gets around 18 mpg, which isn't bad, but 30 would be better
Cargo Master
Joined: Feb 2008
Posts: 3,409
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From: back in SE Iowa
without fuel going there or oil i think your motor wouldnt last long.but i maybe wrong.but diesel fuel is also a lubricator.someone else will chime in with nore knowledge than i have.personally i wouldnt do it.
Cargo Master
Joined: Feb 2008
Posts: 3,409
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From: back in SE Iowa
you could try to find out how the newer v8 gassers do it.but my old boss had one and he didnt like it.it didnt make the difference it advertised.and was only about 3-4 mpg better but it doesnt justify the possible repair costs if anything went wacky
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Dean88 Hi! This firing order info comes from a post by PLC7.3
"The engine rotates in a clockwise direction as seen from the front of the truck, and for every 1/4 turn of the engine(crank) each next piston will arrive at TDC. So, When the line on the vibration damper is at the 2 oclock position, cylinders 2 and 5 will be at TDC. When the mark is at the 5 oclock position, cylinders 7 and 6 will be at TDC, 8 oclock has cylinders 3 and 8 at TDC, and back to 11oclock, 1 and 4 will be at TDC. Cylinder numbers are assigned 1,3,5,7 on the left(passenger) bank from front of truck to back, and 2,4,6,8 on the driver's side, front to back. Firing order is 1,2,7,3,4,5,6,8."
If the firing order is as I understand it, 1,2,7,8 would be balanced or 3,4,5,6 would be balanced without the other. So the outside four cylinders or the inside four could run pushing the other four cylinders balanced. Maybe thats way off, but it seems like it would work in theory.
"The engine rotates in a clockwise direction as seen from the front of the truck, and for every 1/4 turn of the engine(crank) each next piston will arrive at TDC. So, When the line on the vibration damper is at the 2 oclock position, cylinders 2 and 5 will be at TDC. When the mark is at the 5 oclock position, cylinders 7 and 6 will be at TDC, 8 oclock has cylinders 3 and 8 at TDC, and back to 11oclock, 1 and 4 will be at TDC. Cylinder numbers are assigned 1,3,5,7 on the left(passenger) bank from front of truck to back, and 2,4,6,8 on the driver's side, front to back. Firing order is 1,2,7,3,4,5,6,8."
If the firing order is as I understand it, 1,2,7,8 would be balanced or 3,4,5,6 would be balanced without the other. So the outside four cylinders or the inside four could run pushing the other four cylinders balanced. Maybe thats way off, but it seems like it would work in theory.
Postmaster
Joined: Mar 2008
Posts: 3,255
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From: Sweet Home, OR
I've wondered if you could cut half the fuel injectors off in my '91 Cherokee.
I just don't have the guts to try it.
I just don't have the guts to try it.
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Mountain Pass
Joined: Oct 2004
Posts: 243
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From: Kremlin, Ok
just a thought, i, unfortunately, had to drive a new tahoe awhile back that had the MDS crap on it. The only time it ever went into V4 mode, was when you are off the gas completely. I couldn't ever get it to go into v4 mode even if i was barely pushing on the gas. So I'm starting to think that was just a bunch of BS. it only got 16 mpg at 68 mph on the highway.
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Post Fiend
Joined: Nov 2003
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From: Nutter Fort, WV
The variable cylinder engines do more than just cut the fuel.
If you are still compressing air in the cylinders, parasitic loss would be to high to save anything.
The diesel fuel lubricates and cools the injectors, that would be an issue if no fuel were passing through the injectors in a very short amount of time.
Next issue to consider is your frontal area.
This chart shows the amount of HP required for a given frontal area at a speed of 55 MPH.
Area in Sq. Ft. - HP required
50 -------------- 56
60 - -------------66
70 - -------------78
80 - -------------89
90 - -------------99
Cutting 185 HP down to 92, then figuring the drive train power losses at say 30% so now you are down to 60 HP max at the wheels.
Add in the power lost compressing air not used, you may have 35 HP left to move you.
If you are still compressing air in the cylinders, parasitic loss would be to high to save anything.
The diesel fuel lubricates and cools the injectors, that would be an issue if no fuel were passing through the injectors in a very short amount of time.
Next issue to consider is your frontal area.
This chart shows the amount of HP required for a given frontal area at a speed of 55 MPH.
Area in Sq. Ft. - HP required
50 -------------- 56
60 - -------------66
70 - -------------78
80 - -------------89
90 - -------------99
Cutting 185 HP down to 92, then figuring the drive train power losses at say 30% so now you are down to 60 HP max at the wheels.
Add in the power lost compressing air not used, you may have 35 HP left to move you.
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