Jeep 4.0 Volumetric Efficiency

[BBeach]

So far, best mpg is somewhere between 60-65, at 25-26 mpg. It's been awful windy around here, so I've been getting headwinds and tailwinds depending which way I go. rpm is right at 1900 at 60 mph, so maybe that's the "sweet spot."
I'm a little surprised; I thought best mileage would be at lowest rpm in highest gear, which is 45-50 mph and around 1600 rpm, when overdrive kicks in. There's a shorter flat stretch of 2-3 miles that I tried at 45, but the SG2 reported 22-23 mpg. Maybe the ECU is programmed a little rich for power right after a gear change.

Any progress on your mileage model? The prime air/fuel ratio may get muscled out by wind resistance.

An old engineering saw is that several small, independent, random, variables will tend to average themselves out.

ScottB

Have you compared the scanner's mpg with what you actually get by the whole fillup and odometer checks? I usually travel at 2500rpm which is ~77.5 on my speedo but actually ~80.5mph. I get maybe 18mpg or so, never really checked with one of those computers. You know where you can get one of those for cheap, any site with them or something like it on clearance?

 

[BBeach]

And does it have an output and/or software to put it on a laptop?
It says it has
»Fuel Economy »Fuel Rate »Battery Voltage »Coolant Temperature »Intake Air Temperature »Engine Speed (RPM) »Vehicle speed (MPH) »Manifold Pressure
(not available on some vehicles)»Engine Load »Throttle Position »Ignition Timing »Open/Closed Loop What have you typically been seeing for these? And when at WOT does it update quickly? Theres a good chance ill look for one if you can put it on a computer and compare graphs of ignition timing, engine load and fuel efficieny. Nice find btw.

 

[MaXJohnson]

Peak Torque = peak VE = optimum fuel mileage.

What do you think would happen if you consider friction?

Real data vs anecdotal assumptions;
I'd believe the ScanGauge over your butt dyno any day. It's less likely to be compromised by gas leaks :moon:

 

[5-90]

What do you think would happen if you consider friction?

Real data vs anecdotal assumptions;
I'd believe the ScanGauge over your butt dyno any day. It's less likely to be compromised by gas leaks :moon:

Do some research - it's not a BD reading. Besides, Butt Dyno doesn't have anything to do with fuel mileage...

 

[BBeach]

What do you think would happen if you consider friction?

Real data vs anecdotal assumptions;
I'd believe the ScanGauge over your butt dyno any day. It's less likely to be compromised by gas leaks :moon:

Well one of the things that I just thought of is, sure its make some sense with a 4.0, but what about something like a civic where the peak torque is pretty high in the reve range (say 5000rpm for example), I cant picture the best mpg for a civic in top gear doing 5000rpm or so being the best mpg. Best mpg is the point in which the least fuel per mile is used. You hit an equilibrium somewhere in the rev range, but Im trying to find out where. And its going to be different with different mods as well. Ive got an intake, catback, and a few other things and from when I dynoed it it showed my peak torque to be at an rpm around 3500rpm, which is 113mph in 4th gear locked, but I doubt I could keep the engine in 4th gear without it downshifting to 3rd nevermind the fact that the drag forces at that very high speed would overwhelm the AFR to make it run pretty lean to keep it moving...not to mention that its 50mph over the speed limit....

 

[BBeach]

I see this and I wonder if its the same wiring standards as a regular ethernet cable and could be plugged into a laptop with the right software??

 

[BBeach]

Perhaps even plug it into a cheap hub and send one to the laptop and one to the "reader" itself...if only it was a few dollars less.

EDIT: And now that I think about it, perhaps I could just buy a backup cable for $20 or whatever and then find software or something for it. I read on another forum when I searched for it and they said the maker is looking into a USB connection for it.

 

[MaXJohnson]

Do some research - it's not a BD reading. Besides, Butt Dyno doesn't have anything to do with fuel mileage...

Since many of your "facts" are not based on factual data, but rather hearsay and loosely supported supposition, I think the butt dyno reference is valid.

 

[MaXJohnson]

Well one of the things that I just thought of is, sure its make some sense with a 4.0, but what about something like a civic where the peak torque is pretty high in the reve range (say 5000rpm for example), I cant picture the best mpg for a civic in top gear doing 5000rpm or so being the best mpg. Best mpg is the point in which the least fuel per mile is used. You hit an equilibrium somewhere in the rev range, but Im trying to find out where. And its going to be different with different mods as well. Ive got an intake, catback, and a few other things and from when I dynoed it it showed my peak torque to be at an rpm around 3500rpm, which is 113mph in 4th gear locked, but I doubt I could keep the engine in 4th gear without it downshifting to 3rd nevermind the fact that the drag forces at that very high speed would overwhelm the AFR to make it run pretty lean to keep it moving...not to mention that its 50mph over the speed limit....

Your Honda example clearly shows the fallacy of this "peak torque = best gas mileage" BS. It doesn't hold true with the 4.0 either, but to a lesser extent. Put a 4.0 on an engine dyno and measure gal/hr at 500 RPM increments and you'll find the most fuel efficient RPM to be below 2500. This is the closest practical test environment you'll get to the friction free world that 5-90 lives in.

 

[MaXJohnson]

I see this and I wonder if its the same wiring standards as a regular ethernet cable and could be plugged into a laptop with the right software??

Physically, that plug is the same as the RJ-45 used for Ethernet, but the pin-outs, signalling and speed and not the same.

 

[BBeach]

Your Honda example clearly shows the fallacy of this "peak torque = best gas mileage" BS. It doesn't hold true with the 4.0 either, but to a lesser extent. Put a 4.0 on an engine dyno and measure gal/hr at 500 RPM increments and you'll find the most fuel efficient RPM to be below 2500. This is the closest practical test environment you'll get to the friction free world that 5-90 lives in.

No need to be too harsh, but in any case one of these things could be a decent investment, I sent the guy an email seeing if he could just sell the software and cable to me for a cheaper price because I already have a laptop. We'll see what he says, cause Id love to find out where I can get better gas mileage as well as things like MAP and fuel rates to figure out more calculations for when I get bored. :read:

 

[MaXJohnson]

No need to be too harsh, but in any case one of these things could be a decent investment, I sent the guy an email seeing if he could just sell the software and cable to me for a cheaper price because I already have a laptop. We'll see what he says, cause Id love to find out where I can get better gas mileage as well as things like MAP and fuel rates to figure out more calculations for when I get bored. :read:

more than a decent investment, the Scangauge might be the best money you can spend to increase fuel mileage. It's like bio-feedback for your vehicle. I run one in my Focus and attribute an easy 10% limprovement in fuel mileage directly to driving habits I've learned by watching the Scangauge.

Software is built into the flash memory of the Scangauge, not on a disc and therefore cannot be obtained separately, and the cable would be useless without a protocol/signal converter.

 

[MudDawg]

Age and experience butts heads with theory and engineering...I love it...and the peak torque for a Civic is more like around 4,300 rpm.

But it's not apples to apples comparing a multi-valve pent roof way undersquare engine to an engine designed in the 70's to be cheap to produce, with little thought to thermal, frictional, or pumping efficiency. The ol' 4.0 is not a ricer motor.

Perhaps a valid arguement to the peak torque/best VE issue would be to design an engine package that attains peak torque at the TARGET cruise RPM as opposed to working with a less than ideal powertrain package to begin with.

As far as using empirical data goes...Google "Smokey Yunick" Virtually all of the development he did was based on empirical data.

 

[BBeach]

Age and experience butts heads with theory and engineering...I love it...and the peak torque for a Civic is more like around 4,300 rpm.

But it's not apples to apples comparing a multi-valve pent roof way undersquare engine to an engine designed in the 70's to be cheap to produce, with little thought to thermal, frictional, or pumping efficiency. The ol' 4.0 is not a ricer motor.

Perhaps a valid arguement to the peak torque/best VE issue would be to design an engine package that attains peak torque at the TARGET cruise RPM as opposed to working with a less than ideal powertrain package to begin with.

As far as using empirical data goes...Google "Smokey Yunick" Virtually all of the development he did was based on empirical data.

I was being sarcastic and exagerating when I said the 6000rpm (I even put it in paranthesis). In any case, 4300rpm for whichever motor you chose..I dont think that a civic on the highway spinning at ~50% redline at (this is a ballpark guess) at maybe 90mph (not sure of gearing but I know most cars are usually 2000rpm at 60mph but my friends accord is 3000rpm at 70mph so im giving you some slack.
And as far as the 4.0 not being a good example due to being a poor engine design (ive heard from some though it is old school thought was obviously put into it and it was one of the best designs around).
How about the S54 engine from an E46 BMW M3.....this ones pretty high tech. Peak torque is at 4900rpm. Im not positive on the gearing but I know from videos that an rpm like that in top gear is asking for well over 140mph...so what you're saying is thats where hes getting best mpg? Id say he's goign to have to keep it almost floored to keep equilibirum therefore making the AFR run rich and therefore getting less mpg than if he was travelling at a speed half of that. In top gears the revs/mile ratio is constant and the only variable you'd be looking at is AFR. The speed at which that vehicle in question hits hits the peak where the the ratio of fuel used per mile goes down, then so doesn the mpg. :dunno:

 

[MudDawg]

The intent in a production vehicle is not to get max fuel efficiency...it is a compromise....the engine does not run at peak torque rpm at normal cruise speeds...the customer demands sparkling performance and decent fuel economy.

I'm no engineer and am certainly no expert on modern control systems, but with modern engines having variable cam timing, port volume, etc, etc. the "max efficiency" number can also be variable...something a 4.0 lacks.

 

[czb83]

It plugs into the OBD2 port and reports what the ECU is seeing.
Real time readouts (~2 sec update):
speed, rpm, mpg, water temp, intake air temp, fuel consumption rate, closed/open loop, fuel pressure, ignition timing, engine load, manifold pressure, throttle position, voltage.
Haven't used them all, yet, but some stuff isn't reported by my ECU, like fuel pressure, so no data.
Also has a trip mode that reports:
max speed, max water temp, max rpm, average speed, average mpg, miles, time, fuel used
Has some setups that can show for current tankful:
fuel used, fuel remaining, distance, distance remaining, time, time remaining
Also acts as a scan/reset tool. Already used it to diagnose a bad o2 sensor. Check out the website, a pdf manual there, too:
http://www.scangauge.com/
Amazon has some resellers for a few bucks less. Worth it to me.

ScottB

Hey, I'm working on a standalone ECU, and have been messing around with ignition timing table. It had no reference point, so its been a pain. Do you think you could capture several data points for me. Like, what rpm do you get max advance, what is max advance, idle advance. Basically, it would be cool if you have several points of (map value, rpm, timing advance) that I could use to adjust my table. I don't have obd-II, so i couldn't get that info anyway. Thought I would ask, since this info would be very helpful to me. Thanks.

 

[BBeach]

On the topic of timing advance, do our Jeeps automatically retard timing if they sense knock? I heard something about that the older Renix will do this but im not so sure about the OBDII 4.0's. In the case that the timing is automatically adjusted, say if i was to put in 93, would it adjust it for the max potential advance, say a couple more HP?

 

[czb83]

On the topic of timing advance, do our Jeeps automatically retard timing if they sense knock? I heard something about that the older Renix will do this but im not so sure about the OBDII 4.0's. In the case that the timing is automatically adjusted, say if i was to put in 93, would it adjust it for the max potential advance, say a couple more HP?

Only renix XJ's had knock sensors. Putting in 93 octane fuel would do nothing for timing.

 

[BBeach]

Is there any way for us to set it forward manually?

 

[5-90]

The intent in a production vehicle is not to get max fuel efficiency...it is a compromise....the engine does not run at peak torque rpm at normal cruise speeds...the customer demands sparkling performance and decent fuel economy.

I'm no engineer and am certainly no expert on modern control systems, but with modern engines having variable cam timing, port volume, etc, etc. the "max efficiency" number can also be variable...something a 4.0 lacks.

Quite true - especially the angle on VVT. However, the 4.0 does have a broad, flat torque curve - which partially makes up for the lack of VVT (and does so without additional moving parts.)

Part of the reason cruise RPM tends to be so low, tho, is because that's what people have just come to believe. I don't recall all the theory behind it (although I have verified this "fact" experimentally - on the road, with friction and air resistance, parasitic drag, and even in various parts of the country with different fuel formulations!) but I think the "best cruise at best torque" works because the engine has the ability to produce more torque - so a lower percentage of that output is used, and the engine doesn't have to work as hard to maintain forward speed.

The fact of the matter (for the fourth/fifth gear comparison) is established experimentally - try it. This was in a 1988XJ - both with stock (237/75-15?) and oversize (30"-9.5-15) tyres. The gain was ~3mpg. Considering I was working with getting 15-16mpg before and 18-19mpg after, and I took notes (which I cannot now find...) for a month under each condition, I'd consider that "experimental verification."

I look forward to seeing what I can get when I finish renewing my engine management sensors - since they've got 280K on the clock, they're getting a little worn and slow...