Poor Fuel Mileage

airmon · **Joined:** Mon May 23, 2011 2:25 pm **Posts:** 19

Hi all,
I've got a 2006 CRD that's completely stock ( except for pulling the viscous heater relay) and I'm getting what I think is poor mileage. Over the last couple of tanks we've gotten about 19 MPG. We haven't had our CRD long, so we don't have much history to go on.

I live in the Florida Keys, so I'm not experiencing a long warm-up times ( temps in the 80's or 90's ), but I am running the A/C constantly. We mostly commute to work ( 40 miles R/T ) on US1, which is very flat, all at sea level and a mix of 45 mph (30%) and 60 (70%) mph driving. It's steady speeds and only a couple of stoplights. It's not uncommon to not touch the brakes for most of the trip. Neither my wife nor I have a particularly heavy foot, though perhaps 20 miles on each tank included towing our boat ( 23' Carolina Skiff ) under the same road conditions.

The 4wd lever is in 2wd, and I'm pretty sure it's all disengaged, since I don't feel any binding in tight U turns on pavement. My brakes don't appear to be binding ( cool rims after a 20 mile drive @ 60 MPH ) and my tires are properly inflated. My air filter is new.

My temp gauge shows a half tic from straight up, though when I plug in my OBD tool it says coolant temp is 165.

I've cleaned the MAP sensor ( sooty but dry ) and once got a CEL ( turbo underboost ) light a couple weeks ago, but it stayed off after I cleared it.

I thought it was shifting late ( top gear @ 62 mph ) but after some searches here that appears normal, at least for F-37 ( how do I check if I have that?).

Does anyone have any suggestions?

Thanks!

papaindigo · **Posted:** Mon Jun 20, 2011 7:32 am

Prior to getting the GDE EcoTune I averaged about 18-19mpg for a 10 mile one-way commute on pretty much flat roads top speed 45-50 with a few more lights but only intermittant AC. In your situation I wouldn't expect a lot better. Are you basing your mpg on the EVIC, which is not very accurate, or a hand calculation? If the latter have you checked the odometer for accuracy with a GPS or equivalent and are you filling up at the same location and to the same level in the tank (when I've tested for mpg I've filled the tank to where I can see fuel in the filler pipe to ensure consistent fuel amounts) as either can throw hand calculation off. FYI after getting the GDE EcoTune in the same situation I'm getting more like 22-23mpg or a bit better with the viscous heater unplugged.

Your temp gauge position sounds about right.

Since you did get the low boost CEL I'd recommend you pull the turbo>intercooler and intercooler>engine hoses and carefully inspect them for damage (leaks) especially on the bottom side and while you are at it make sure the air box to turbo hose has not torn at the bottom end, just up from the clamp.

Top gear shift at 62mph equals F-37 has been done. Without F-37 that shift would be at 58mph.

If you have not already done so read the NOOB guide. Welcome to the forum.

airmon · **Joined:** Mon May 23, 2011 2:25 pm **Posts:** 19

Thanks for the reply.

I was under the ( possibly mistaken ) impression that when one of the CAC hoses fails it's fairly obvious - with hissing ( 20 psi, right ?), and a major loss of power. I will take your suggestion and remove the hoses for inspection.

I've been measuring by doing the calculations after each fill up, I don't have an EVIC. I'm not filling to where I see fuel, but filling to where the pump clicks off automatically. I hadn't thought of filling it visually, I guess because I'm in the habit of not topping off because of the gas cars I've always owned. There wouldn't be any evaporative canister on this, huh?
Still, if I'm not filling equally each time, wouldn't I get greatly varying mileage when I calculate? like 28 one time and 19 the next?

I have not checked the odometer for accuracy, though I know my speedometer is a few percent high ( 60 indicated is about 58 on my GPS ), which makes me think that if the odometer is off by a similar amount, I'm actually getting less mileage than I think...
I'll do a GPS test on the odometer.

The noob guide was very helpful, as was all the searches and archived threads I've read through.

I was considering the EcoTune, saving up the $$$.

papaindigo · **Posted:** Mon Jun 20, 2011 9:26 am

A small hole, as is sometimes reported, may not be all that obvious in terms of noise or power but since you did get the low boost code it's worth checking and if you have the factory hoses it's worth checking anyway. If you are filling up at the same place and stopping as soon as the pump clicks off that's probably close enough, it's what I do most of the time, and no there is no evaporation canister that I know of. I should have mentioned it in my first comment but I wouldn't fill to a visual level unless I was immediately driving enough to lower the fuel level enough to accomidate any heat expansion (translation - I've only done this on one long distance trip to get as accurate an mpg calculation as possible). Odometer and speedometer accuracy doesn't seem to interrelate. My speedometer is dead on but my odometer reads low (i.e. displays fewer miles than I've actually traveled) but stoutdog's are both off by different amounts than mine and some folks report errors of up to 5 percent or so.

jeepdan · **Posted:** Tue Jun 21, 2011 8:11 am

Also, check to make sure that you do not have any of the brakes dragging. I recently discovered that both of my rear wheels were hanging up. My park brake was froze up from rust at the rear wheels and not releasing.

airmon · **Joined:** Mon May 23, 2011 2:25 pm **Posts:** 19

jeepdan wrote:

Also, check to make sure that you do not have any of the brakes dragging.

Thanks for the suggestion. I've checked that the wheels & hubs are relatively cool to the touch after a 20 mile long highway speed drive. After I'm done checking the CAC hose I'll jack up the car and check the brakes for dragging.

Joe Romas · **Posted:** Tue Jun 21, 2011 9:54 am

Your mileage is about normal for a stock CRD with your driving. But as mentioned you can't really judge by a few tanks, you need a longer term average.

But since your driving at 60 MPH you either need to accelerate to 64 to get into 5th gear then slow down to 60 or get a TCM tune that will shift earlier. There are two and the easiest to get/find is the GDE tune for non trailer towing, it should tow your boat fine too since you have no mountains in Florida. I have a pre F37 transmission controler that shifts at 59 :BANANA:

and a GDE full torque Eco tune and my summer mileage that is mostly short trip intown is between 22 and 24 mpg. We also have spring, fall and winter in Ohio and my since new average is 20 but the tunes were added later at diffeent times.
My Tom-Tom indicates when my speedometer reads 69 I'm actually traveling at 65 so going up to 64 then backh down to 60 should not get you into any trouble. Since the Speedometer and Odometer are electronically controled they can and are totally different in their readings unlike mechanical units of old :juggle:

Our CRD odometers mostly report lower and Speedometers report highter then actual.
The best part is when towing our 3000-3200# camping trailer we average 19-20 mpg (uncorrected) :JEEPIN:

A better torque converter then stock is needed for the full torque tune.
The standard GDE Eco ECM tune and their TCM tune would work fine with your stock TC pulling your boat in Florida and you would see a big increase in mileage. And a much better running CRD :BINGO:

Tires and inflation pressure can help a lot too.

airmon · **Joined:** Mon May 23, 2011 2:25 pm **Posts:** 19

Joe Romas wrote:

you either need to accelerate to 64 to get into 5th gear then slow down to 60 or get a TCM tune that will shift earlier.

Thanks. I'll keep that in mind. My wife will love hearing that "she has to speed for good fuel mileage ". We can do the same thing for lower speeds, since it seems like the 3-4 shift happens about 53 or so, which will work for the 45 mph speed limit areas.

papaindigo · **Posted:** Tue Jun 21, 2011 12:10 pm

With a stock TCM and the F-37 pattern the answer is yes you have to exceed 60mph to get to that final shift point but then you can drop back to 60mph or a bit below to hold that gearing which will slightly improve highway mpg. The GDE TCM tune is totally different from the pre-F-37 pattern but does provide for lower shift points including the last one. See http://www.greendieselengineering.com/f ... st/89.page for an explanation of what their TCM tune does.

airmon · **Joined:** Mon May 23, 2011 2:25 pm **Posts:** 19

Quote:

There are two and the easiest to get/find is the GDE tune for non trailer towing, it should tow your boat fine too since you have no mountains in Florida.

I got the GDE Eco Tune. It was a snap to upload with the flash tool, though I'm a techie, so that helps.

The first thing I noticed was that idle at start changed a bit. It revs just a little bit, to perhaps 1200 RPM, then drops right down to 750 or so. "Throttle" response is better and it sure feels to me like it's got more power.

Most important to this thread, after two fill ups we're averaging 25 MPG or so. We're very pleased, because it just in time for a road trip to WI, including a couple hundred miles towing a small camper.

I'm very happy with the GDE ECO tune, and if I ever replace the TC, I'll be going back for a hotter one.

Roostre · **Joined:** Sun Oct 24, 2010 3:57 pm **Posts:** 195

Its hard to do, but keeping your acceleration revs below 2000 rpm at all times makes a huge difference in MPG for me.

Like papa said 18-19 is pretty normal before the GDE tunes. Especially with the A/C on. I still lose 3mpg or so when its hot and the A/C is mandatory.

airmon · **Joined:** Mon May 23, 2011 2:25 pm **Posts:** 19

It's been about 3 months since we installed the GDE eco-tune and in that time ( in addition to a 40 mile RT daily commute ) we took a three week driving vacation. We went round trip Florida Keys to Northern Wisconsin and towed a 4000lb-ish camping trailer for perhaps 300 miles in Door County, WI ( that finger of WI that sticks out into lake Michigan). Essentially, we feel we've driven it enough to get a pretty good sense of the difference the GDE tune made.

Conclusion: Definitely better mileage. Before the ECO-tune, we were lucky to get 20 MPG ( A/C on ) on our daily drive. After the tune, 25 MPG. Once the weather cooled off and we could start driving without the A/C, mileage has climbed another 10% or so. The last tank was 28 MPG and we saw as good as 30 MPG on the highway on our trip, with the car packed VERY full of camping gear and ticking along the freeway at 80 MPH.

We're still enjoying the better performance and the EGR code on the CEL went out and stayed out after installing the tune.

The engine seems a little noisier at idle ( particularly when cold ) but it's hard to say for sure how much louder without a side-by-side comparison with the previous setup and I'm not willing to mess with the ECU that much. I don't consider it intrusive, certainly not like my brother-in-law's F-350 Super Duty, where you have to speak up over the engine, just a little different.

All in all, we're still very pleased with the GDE ECO-tune.

Poor Fuel Mileage

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