MPG dropping

rs4mtnitro · **Posted:** Fri Jul 20, 2007 2:24 pm

My fuel mileage is going to hell. With normal around town driving I use to see 21 mpg. The tank before last was 18mpg this last tank was down to 17.25 mpg. I pulled out my map sensor and it was dirty but not as bad as when it was replaced a couple of months ago. I just changed my fuel filter before the last tank which seemed to not make a difference. Any ideas on what is going wrong. I have tried the ORM in the past and it didn't seem to make a difference in MPG or power.

Thanks,
Mike

Cowcatcher · **Posted:** Fri Jul 20, 2007 3:04 pm

When you figure it out let me know since I am having similar issues. I know that part of my issues are the following:

A) Real Tires
B) Roof Basket
C) Air Conditioner

What I don't understand is that last summer I don't think I experienced much change in the mileage with the air conditioner.

What effect would a dirty intercooler and hoses have on mileage? I am waiting for my CEL to turn off and then taking the Liberty in for the blower recall. I am going to make them change the intercooler hoses at the same time and also try to get them to either clean or change the intercooler. When I get it back I am applying EHM.

RTStabler51 · **Posted:** Fri Jul 20, 2007 3:27 pm

Mine has fluctuated too.
Originally I thought it was the EGR and then the F37.
Then I did the ORM and it brought me back to the 20.X/21.x (in town)
Now I'm back to 19.X
:shrug:
Maybe its the ULSD I'm running since I haven't ran my normal B20?

dgeist · **Posted:** Fri Jul 20, 2007 4:28 pm

rs4mtnitro wrote:

My fuel mileage is going to hell. With normal around town driving I use to see 21 mpg. The tank before last was 18mpg this last tank was down to 17.25 mpg. I pulled out my map sensor and it was dirty but not as bad as when it was replaced a couple of months ago. I just changed my fuel filter before the last tank which seemed to not make a difference. Any ideas on what is going wrong. I have tried the ORM in the past and it didn't seem to make a difference in MPG or power.

Mike, are you running any mods for the CCV problem? (i.e. provent or EHM) Also, what's the mileage on your CRD. If there was significant oil residue inside your intercooler, that could be affecting the efficiency of the turbo and consequently dropping your MPGs. I'd pop off the intercooler hoses and take a look inside with a flashlight and see how heavy the sludge is. Could also be oil in the turbo itself... Basically: "oil in intake bad"

Dan

DarbyWalters · **Posted:** Fri Jul 20, 2007 5:42 pm

To really get a good idea of your true mileage you need to keep track for a month or so. I use https://www.fueleconomy.gov/mpg/MPG.do?action=garage to make it easy. You just have to adjust you MPG by the ~4% the odometer is off.

NOTE: Not saying anyone is not getting good results...but...too many times (myself included) I have hit a high number on one tank and then expected the same down the road. :wink:

naturist · **Posted:** Fri Jul 20, 2007 5:54 pm

Have you checked your tire pressures lately?

One tire of the original set on my '05 CRD has had a slow leak from day one, and my mileage goes down when I forget to keep it pumped up. The darn thing LOOKS just like its mates even when it has only 22 lbs of air in it, but boy can I see that on the mileage.

It'll soon be time to replace all those OEM tires, which should take care of THAT particular problem.

Cowcatcher · **Posted:** Fri Jul 20, 2007 5:54 pm

Yup, I understand that but hot weather, air conditioner, load rated tires and roof basket all came at the same time. :lol:

My mileage has dropped about 3-4 MPG as a result so it makes it a little more difficult figuring if it is something wrong or just my little rebuilds and the weather. :shock:

rs4mtnitro · **Posted:** Fri Jul 20, 2007 6:37 pm

I don't have a provent or EHM. I do have some residue in the charge air system. I have 28,000 miles on the clock. I just have a hard time believeing the tires would drop MPG by 4.

GilaMonster · **Posted:** Fri Jul 20, 2007 7:18 pm

I remember posts of people with failed EGRs (stuck open) that were getting bad gas milage. The bad milage was an indicator of the EGR failure.

Cowcatcher · **Posted:** Fri Jul 20, 2007 7:23 pm

GilaMonster wrote:

I remember posts of people with failed EGRs (stuck open) that were getting bad gas milage. The bad milage was an indicator of the EGR failure.

Shouldn't be my problem as I have been ORM'd until today.

nescosmo · **Joined:** Sat Jul 14, 2007 11:17 pm **Posts:** 202

My was that bad and one day I drove it like a rented mule, blow it nose 3 time the same day and ever since the milege went up to 22 city and 28 hwy. You guys can not drive the CRD like a lady. Remember you have a tank, drive it as such.

RedStapler · **Joined:** Fri May 11, 2007 10:04 am **Posts:** 77

I'd go with roof rack, new tires and more A/C use in declining order as your culprits.

Putting anything on the roof of your vehicle increases it frontal profile and can be a real killer at freeway speeds. More so on a car than our relatively aerodynamic "dirty" KJs but it still makes a difference.

New tires increase rolling resistance relative to a set that is 3/4 worn. If you went to a larger size and/or more aggressive tread pattern it gets worse.

A/C can vary with the vehicle. I've only noticed a 1-2mpg hit with heavy A/C use keeping all else about the same on my CRD. Now on the 90 Subaru Legacy using the A/C just killed the MPG, dropping from 27-29 Hwy to 21-22.

MOSFET · **Joined:** Sat Feb 25, 2006 11:40 pm **Posts:** 295

Could a degrading torque converter cause the mpg to go down?

I remember my mileage was at it's lowest levels ever, then I had the TC replaced and the mpg jumped back to normal levels.

retmil46 · **Posted:** Sat Jul 21, 2007 10:51 am

Hot weather itself may be one of the factors causing mileage to go down. Checking the VW TDI forums, they have a similar fuel temp sensor on thier vehicles. They've noted that when the fuel temp gets above a certain point, it causes the ECM to adjust the timing and fueling, pulling power and causing fuel mileage to go down. From reading thru the FSM, and some experiments conducted by another member, it looks as though ours does the same.

Perhaps that's why many VW TDI and GM Duramax vehicles have OEM fuel coolers installed from the factory.

rs4mtnitro · **Posted:** Sat Jul 21, 2007 6:10 pm

MOSFET wrote:

Could a degrading torque converter cause the mpg to go down?

I remember my mileage was at it's lowest levels ever, then I had the TC replaced and the mpg jumped back to normal levels.

I have a new trans with a suncoast converter. I wonder if it is possible that the higher pump pressure from the shift kit could be affecting it.

canlib · **Posted:** Sat Jul 21, 2007 7:38 pm

I think GilaMonster could be right. You say you tried the ORM in the past...is your ERG connected now? My mileage tanked when the EGR went bad and is better than ever with a new EGR.

rs4mtnitro · **Posted:** Mon Jul 23, 2007 7:58 am

canlib wrote:

I think GilaMonster could be right. You say you tried the ORM in the past...is your ERG connected now? My mileage tanked when the EGR went bad and is better than ever with a new EGR.

It is connected now. I never saw a difference in mpg or power with the orm so I plugged the maf back in.

MPG dropping

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