Poor Fuel Economy?

MooseMeat · **Posted:** Sun Feb 10, 2008 11:31 pm

Mileage on my 2006 CRD sucks also, occasionally will hit 28mpg on a long trip but average long trips is 25mpg, I have gotten 30.7mpg once and 31.6 once (both times a steady rain the whole trip) in the last 45000 miles. I commute 20 miles one way at 60mph or take the interstate at 70mpg and get the same mpg either way. Average summer mileage is 22mpg no matter what I have done or tried.

This winter its been 18 - 19mpg, But its been snow lots of 4 wheel drive and colder then a witches hoohaw here. -6 degF here as I type this.

Far less than impressed with the mileage. My 2004 3/4 ton Dodge 4x4 got 20mpg to 24mpg averaged 22.5 all the time winter or summer.

chadhargis · **Posted:** Mon Feb 11, 2008 12:26 pm

The mileage you got out of your pickup was NOT normal. I had a Ford Explorer that got 14 city and 20 highway. I had a PT Cruiser that got 19 city and 26 highway.

My CRD gets about 20 city and 28 highway not towing. If I am towing my trailer, I get 25mpg on the highway. That's darn impressive! I've seen mileage as high as 30mpg on a long interstate trip at 70mph.

Last time I pulled my trailer I did it with my wife's Honda minivan. I got 17mpg on the highway. Yep! 17mpg!!! I towed the same route pulling the same weight with the CRD and got 24mpg. A buddy in his Explorer on the same trip turn 11mpg.

If you're unhappy with the MPG on the CRD, I don't know what to tell you. For my needs, there is nothing else out there.

retmil46 · **Posted:** Mon Feb 11, 2008 1:54 pm

Cold fuel will drop MPG like a rock. Remember that fuel temp sensor on the fuel filter?

Trip back from TX, temps in the teens, I initially was lucky to see 22 MPG. Next morning, blocked off the fuel cooler and all but 2 of the front grille openings. Once the fuel tank got somewhat warm, mileage shot back up to around 30 MPG.

That was almost a 50% change in fuel economy.

Ranger1 saw similar results. He said that from monitoring with his scantool, 60 F seemed to be the breakpoint - once the ECM sees incoming fuel temp below 60 F, it adjusts the tuning on this engine such that fuel economy drops like a stone. Just putting a piece of cardboard in front of his fuel cooler behind the grille gave him back several MPG's.

dgeist · **Posted:** Mon Feb 11, 2008 2:01 pm

Something to consider is that all the math is right. For example, I just learned recently that with the stock tires, my odometer is 6% off. It's easy to fix if you use a spreadsheet or similar (multiply your mileage field by 1.06).

Also, my experience is that the only way to have a consistent checkpoint for fuel calculations is when it's full (and that's typically when a auto-shutoff kicks in at retail pumps (or it's at least consistent if you always use the same pump at the same place).

Mine is a running average that only gets calculated when the tank is full and I do it like this:

for each addition of fuel
if ( tank is not full )
total fuel = (amount I just added) + (previous total)
else (if tank IS full)
total fuel = (amount I just added) + (previous total)
miles traveled = (current odo ) - (previous full odo)
MPG = (miles traveled * 1.06) / total fuel
total fuel set to zero
current odo saved as last full odo reading
done

I wrote it to disaplay on a web page:
http://www.polter.net/~dan/automotive/

and anyone is welcome to the code if desired.

chrispitude · **Posted:** Mon Feb 11, 2008 2:08 pm

retmil46 wrote:

Cold fuel will drop MPG like a rock. Remember that fuel temp sensor on the fuel filter?

Trip back from TX, temps in the teens, I initially was lucky to see 22 MPG. Next morning, blocked off the fuel cooler and all but 2 of the front grille openings. Once the fuel tank got somewhat warm, mileage shot back up to around 30 MPG.

That was almost a 50% change in fuel economy.

Ranger1 saw similar results. He said that from monitoring with his scantool, 60 F seemed to be the breakpoint - once the ECM sees incoming fuel temp below 60 F, it adjusts the tuning on this engine such that fuel economy drops like a stone. Just putting a piece of cardboard in front of his fuel cooler behind the grille gave him back several MPG's.

Another data point - we installed a FIA winter front and keep it closed pretty much all the time. My wife now sees about 23mpg during from her 50 mile one-way commute, up from 22mpg.

- Chris

midwest · **Joined:** Tue Apr 25, 2006 12:03 am **Posts:** 173

Just checked my mileage here in the bitter cold midwest. I tried to take it easy for the week. 340 miles/15.01 gallons= 22.65 mpg. When I start it after work I let it run for about 15 seconds then go. This is a combination of highway/city driving in all stock crd except ORM. The liberty is pushing 39k miles.

crd liberty · **Posted:** Mon Feb 11, 2008 3:25 pm

midwest.
That was about the best I had been able to get as well.
Have raised that to 24.4 last fill-up by 38 PSI in
the tyres, and running 6oz super tech and 4 oz
2 stroke oil to each fill.
Steve

nursecosmo · **Posted:** Mon Feb 11, 2008 4:13 pm

retmil46 wrote:

Cold fuel will drop MPG like a rock. Remember that fuel temp sensor on the fuel filter?

Trip back from TX, temps in the teens, I initially was lucky to see 22 MPG. Next morning, blocked off the fuel cooler and all but 2 of the front grille openings. Once the fuel tank got somewhat warm, mileage shot back up to around 30 MPG.

That was almost a 50% change in fuel economy.

Ranger1 saw similar results. He said that from monitoring with his scantool, 60 F seemed to be the breakpoint - once the ECM sees incoming fuel temp below 60 F, it adjusts the tuning on this engine such that fuel economy drops like a stone. Just putting a piece of cardboard in front of his fuel cooler behind the grille gave him back several MPG's.

Retmil try unplugging the Viscous heater and watch what the mileage does. When temps are in the teens it will cycle and make the economy drop. By covering the grill more heat is kept inside the engine compartment thus preventing heater cycling. Although the ECU is not "supposed" to change fueling for low fuel temps doesn't mean that it isn't doing just that. But if it is happening, why not try just unplugging the sensor on the filter head so that it defaults to normal range. Anyway if the fuel heater is plugged in it should be bringing the fuel up to 60+. I have noticed that my Heater will come on at about 30 outside temperature and as soon as the engine warms up it stays off but if the temps are 20 or lower it will cycle on frequently even if the ECT is in the normal range. I left it unplugged for a few days but my wife complained about the jeep still blowing cold air by the time she arrived at work. Cold wife in the morning commute = cold husband in the bed at night so I plugged it back in. Our day time temps here are usually over 30 anyway so I'm just loosing mileage in the mornings. I have had my Fia grill covers sitting on my desk for 2 weeks and am dieing to have time to put them on the jeep and especially on my Dodge (Brrrr).

dirtmover · **Posted:** Mon Feb 11, 2008 8:06 pm

And don't forget that the torque converter won't lock up until the fluid has warmed up. On a cold day, for me, it can take a good 10 minutes driving at 100km/h to reach this temperature.

KeighJeigh · **Posted:** Mon Feb 11, 2008 9:54 pm

As of today, I can attest to the importance of cleaning the MAP. I can also assure it only takes 10 minutes total - 1 screw holds it in and it is just a matter of spraying it off with some carb cleaner, wiping it down and putting it back in.
I have been putting this off as one of those "no big deal" tasks I would eventually get to. However, it IS a big deal - at least it was for my CRD.
I (carefully) measured a 3.5 MPG improvement after cleaning this and noticeable performance improvement! I'm beginning to think folks in this forum actually know what they are talking about....

Uffe · **Posted:** Tue Feb 12, 2008 3:21 am

KeighJeigh wrote:

As of today, I can attest to the importance of cleaning the MAP. I can also assure it only takes 10 minutes total - 1 screw holds it in and it is just a matter of spraying it off with some carb cleaner, wiping it down and putting it back in.
I have been putting this off as one of those "no big deal" tasks I would eventually get to. However, it IS a big deal - at least it was for my CRD.
I (carefully) measured a 3.5 MPG improvement after cleaning this and noticeable performance improvement!

Sounds excellent! I think I'll find a store to get some cleaner from and clean my MAP too!

KeighJeigh wrote:

I'm beginning to think folks in this forum actually know what they are talking about....

Heavens no! Well, I don't anyway :lol:

retmil46 · **Posted:** Tue Feb 12, 2008 2:58 pm

nursecosmo wrote:

Retmil try unplugging the Viscous heater and watch what the mileage does. When temps are in the teens it will cycle and make the economy drop. By covering the grill more heat is kept inside the engine compartment thus preventing heater cycling. Although the ECU is not "supposed" to change fueling for low fuel temps doesn't mean that it isn't doing just that. But if it is happening, why not try just unplugging the sensor on the filter head so that it defaults to normal range. Anyway if the fuel heater is plugged in it should be bringing the fuel up to 60+. I have noticed that my Heater will come on at about 30 outside temperature and as soon as the engine warms up it stays off but if the temps are 20 or lower it will cycle on frequently even if the ECT is in the normal range. I left it unplugged for a few days but my wife complained about the jeep still blowing cold air by the time she arrived at work. Cold wife in the morning commute = cold husband in the bed at night so I plugged it back in. Our day time temps here are usually over 30 anyway so I'm just loosing mileage in the mornings. I have had my Fia grill covers sitting on my desk for 2 weeks and am dieing to have time to put them on the jeep and especially on my Dodge (Brrrr).

In my case, I already had the grille blockers installed like Darby has rigged up, and the fuel heater on the Stanadyne filter was working it's rear off.

Problem was, I forgot about that fuel cooler I'd installed to keep the fuel from getting too hot in the summer. That small 6" by 3" cooler was removing far more heat from the fuel than the engine and fuel heater were putting in. That night, when I pulled over to get a room, I popped the hood before shutting it down and felt the fuel filters - stone cold.

Next morning, after covering that cooler over with cardboard, problem went away. MPG jumped back up, and when I pulled in for fuel about 200 miles down the road, the fuel filters were at least lukewarm if not warm to the touch - my guess is somewhere around 100 F.

That corresponded with the fuel pressure gauge. When the fuel was cold and I was getting poor MPG, I was seeing less than 3 psi downstream of the filters. With the cooler covered over and the fuel warmed up, it jumped back up to a full 4 psi.

Lessons learned - keep the fuel cooler covered during the winter, and when the fuel pressure gauge is reading 3 psi or less with good filters the fuel needs to be warmed up some before I can expect to get decent fuel mileage out of the beast.

Bottom line - if the fuel is too cold and you're making short trips such that you never really get it warmed up to a decent temperature, fuel mileage is going to suffer.

kccrd · **Joined:** Thu Mar 08, 2007 10:35 pm **Posts:** 267

Where is the plug for the viscous heater

Threeweight · **Joined:** Mon May 14, 2007 5:57 pm **Posts:** 679

You can buy a can of automotive electronics cleaner that will cut through the crud on the MAP sensor pretty well. I was a little nervous about using carb cleaner on the sensor, as I've seen carb cleaner screw up rubber/plastic in the past.

nursecosmo · **Posted:** Tue Feb 12, 2008 4:26 pm

kccrd wrote:

Where is the plug for the viscous heater

The heater is on the top right front of the engine. It has two heater hoses comming out of the top of it and looke a lot like a vaccum pump. The harness plug is on the top right hand side of the heater next to the airbox and reguires a small screwdriver to stick under the lock tab of the plug.

Poor Fuel Economy?

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