Disabled 4 cylinders on a TBI motor :) MPG Gain???

[HotRodPC]

I couldn't wait for a whole tank so I fueled up at 163.5 miles and got 16.8mpg. It's not that great but is in an improvement over the 13-14 I usually get. There has only been one driveability issue that I've had a couple of times. When idling with the a/c on and max blower in gear the idle has dropped so low that it died. I can deal with that. The funny thing is that I had an '87 burb years ago with the same engine/trans/gearing and it would regularly hit 17 on all 8.

You can rectify that AC idle issue with a High Idle solenoid that is set to get power when the AC compressor kicks on then it raises the idle about 200 rpm. Do you think it would have done better without the AC running? I'd imagine that AC compressor would bog it down pretty good.

 

[jpoole]

Do you think it would have done better without the AC running? I'd imagine that AC compressor would bog it down pretty good.

Definitely better with no a/c! I have to give it a good bit more throttle to maintain the same speed.

 

[jpoole]

You can rectify that AC idle issue with a High Idle solenoid that is set to get power when the AC compressor kicks on then it raises the idle about 200 rpm.

I've never seen one of those on a tbi. I figured the IAC would catch it but it doesn't.

 

[HotRodPC]

I've never seen one of those on a tbi. I figured the IAC would catch it but it doesn't.

Yeah, you'd have to add it yourself I'd imagine. Rig up a bracket and have it activate off the AC compressor power wire.

 

[Jims86]

Yeah, you'd have to add it yourself I'd imagine. Rig up a bracket and have it activate off the AC compressor power wire.

A/c signal is programmed to add via IAC. 16 mpg really isnt that great...last trip, I got 17.5 on all 8.
The key here, is to hook up an aldl cable to see whats going on.
I have a sneaking suspicion that the fact that the O2 is now only getting puffs from 2 holes, is richening everything up to 8 cyl spec

 

[towjoe]

2 things I see wrong with this whole idea

#1 without a pushrod in the lifter the cam will be short lived on a regular hydronic cam engine. Had dozens of them with dead cylinder and ended up with cam ate out from where someone had tried to hide it by pulling pushrods.

#2 in moderation horse power will improve mileage since engine dont have to labor to produce power. My dad built a 800hp big block for his pulling truck and went from 12 mpg to almost 19mpg. Same with his small block daily driver built it to around 350 hp and gets 16-17 in a 4:10 geared 3/4 ton 84 c20 with a turbo 400. The more effecent the better mileage one will get

 

[bluex]

A/c signal is programmed to add via IAC. 16 mpg really isnt that great...last trip, I got 17.5 on all 8.
The key here, is to hook up an aldl cable to see whats going on.
I have a sneaking suspicion that the fact that the O2 is now only getting puffs from 2 holes, is richening everything up to 8 cyl spec

Me thinks this feller is on to something here....

 

[GreaseDog]

2 things I see wrong with this whole idea

#1 without a pushrod in the lifter the cam will be short lived on a regular hydronic cam engine. Had dozens of them with dead cylinder and ended up with cam ate out from where someone had tried to hide it by pulling pushrods.

#2 in moderation horse power will improve mileage since engine dont have to labor to produce power. My dad built a 800hp big block for his pulling truck and went from 12 mpg to almost 19mpg. Same with his small block daily driver built it to around 350 hp and gets 16-17 in a 4:10 geared 3/4 ton 84 c20 with a turbo 400. The more effecent the better mileage one will get

Horsepower will not increase economy. Torque in the operating range will. Horsepower is just an imaginary number based on torque and rpm.

 

[HotRodPC]

Horsepower will not increase economy. Torque in the operating range will. Horsepower is just an imaginary number based on torque and rpm.

I agree with this statement, although I wouldn't necessarily call hp an imaginary #. It's a real #, but its a calculated # based off of torque and rpm.

As Carroll Shelby quotes, Horsepower sells cars, Torque wins races.

And who says Mr. E Ferrari said this too? I hate seeing quotes on the internet that are wrong.

 

[jpoole]

A/c signal is programmed to add via IAC. 16 mpg really isnt that great...last trip, I got 17.5 on all 8.

13.5 mpg up to 16.8 mpg is a significant increase for me

The key here, is to hook up an aldl cable to see whats going on.
I have a sneaking suspicion that the fact that the O2 is now only getting puffs from 2 holes, is richening everything up to 8 cyl spec

O2 sensor doesn't look at volume and since there is no extra air being put in...

 

[jpoole]

2 things I see wrong with this whole idea

#1 without a pushrod in the lifter the cam will be short lived on a regular hydronic cam engine. Had dozens of them with dead cylinder and ended up with cam ate out from where someone had tried to hide it by pulling pushrods.

Are you talking about the lobes for the disabled cylinders being "ate out" or the journals?

 

[jpoole]

The key here, is to hook up an aldl cable to see whats going on.

You are very wise, Jim
That's exactly what I need to do

 

[Jims86]

13.5 mpg up to 16.8 mpg is a significant increase for me


O2 sensor doesn't look at volume and since there is no extra air being put in...

o2 values are still way off reading from 2 cylinders vs. 4. now, if you were running a calibration for your 4 cylinder setup, it may change things.
But for right now, you are running 2.8L on a 5.7L calibration. ECM will do what it can to meet the calibration tables.
As far as mpg, and I am talking hwy, you should be Getting 15 or better. 13 sounds about right for combo or around town. Is your truck pretty much stock?

 

[jpoole]

o2 values are still way off reading from 2 cylinders vs. 4. now, if you were running a calibration for you 4 cylinder setup, it may change things.
But for right now, you are running 2.8L on a 5.7L calibration. ECM will do what it can to meet the calibration tables.

I would only need that if I were running both injectors
Yes, it's stock.

 

[Jims86]

The ecm has no Idea that you cut half the engine off. it still thinks its running a full 350. The only way for an ecm to tell what the volume of air is to run MAF. Map sensor just measures vacuum, and the ECM Makes demand adjustments based on that signal. The ONLY way for you to enjoy the full benifitsbfrom this experiment, which I think is really cool, is to have a PROM custom tuned for the 4 cyl incarnation of this engine. With tuning, you could see better MPG, and even more power. Same with the full 350. Optimization.