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Bad fuel economy

4K views 48 replies 19 participants last post by  gasjr4wd 
#1 ·
Hi guys, hoping for some possible suggestions or ideas on why my fuel economy has been steadily dropping.

I am currently getting 430 kilometers to a 115 L tank of fuel. This is a significant drop to when I took the truck on a 8 hour trip and got 900 K to a tank a few months ago. I do not tow, or let the truck idle long, just a daily driver. Nothing has been changed since the time I got 900k, and always keep up with maintenance and filters.


Truck is a 2003. starts and runs good, no smoke, no haze at idle

Appreciate the responses.
 
#2 ·
Possibly winter fuel or a dead cylinder. Check oil level to make sure it's not making oil. Change your fuel filter. I would run a quart of cheap atf just to make sure injectors are clean. With that big of drop I would be looking for a leak in the fuel system.
 
#3 ·
I really cant see winter fuel making that much of a difference. I would expect a 50-80k difference, but not that much.

I check oil weekly, oil stays the same. Zero blow by as well. Changed fuel filter as well.
 
#6 ·
If you havent made any changes lately I would....

check the oil first
check the coolant... are they normal?

then change all the filters
air
fuel
oil filter (and oil)

check the turbo to make sure it spins freely.
do you have a boost gauge?
 
#7 ·
Just changed air filter last week. I am seeing boost between 30-35 psi. turbo spun freely, no shaft play

Truck does not blow any black smoke, very clean in fact.

All filters have been serviced recently. oil is changed every 5000k, does not eat up any oil.

Dont know if it helps, but I am hearing "injector rattle" much more often, when the motor is either hot or cold.

Truck is not visibly leaking fuel from what I can see.
 
#14 ·
Fuel economy with lift kits....... Two things that are like oil and water; they don't mix. Fuel milage concern with a lift almost gives me a nose bleed thinking about it..
 
#19 ·
You forgot to reset the trip odometer.

Nothing else would have enough effect to cut your mileage in half.

And any single tank of fuel is no gauge of mileage...what I mean is even if your claim of 1 gazillion kilometers per 1/2 liter of fuel is legit, it doesn't matter until you repeat it several times.

I once got 22.9mpg but you don't see me complaining on here 'for some reason I can only get 17mpg when this one time I got almost 23'....


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#20 ·
trip odometer was reset right after fill up.

And no, this has been happening for the past few months. This is not just a one time fill up decrease in MPGs...

I am not complaining that I "once got 900k per tank". I was getting approximately that before the decrease in economy. Again, I would not be "complaining" if this only happened once....
 
#21 ·
could be injectors. does it idle rough? when you rev it up does it act weird coming back down? possible your injectors are hanging? just something nobody has mentioned yet
 
#27 ·
Do you have any kind of guages for monitoring. I feel like this thread is on page 3 now and still has no direction
 
#29 ·
timing rattle.... will cause low fuel economy.... i still recommend starting with the atf...
 
#31 ·
...:coffee:...
mine isn't what it should be too...
 
#32 ·
Since I started working out of my own shop my daily one way commute has lowered from 25mi to about 8mi. The drive is still all hwy, however my mileage has dropped from upper 17s to low 16s when I only drive to work and home.

I believe the reason is simply because engines are not at full efficiency until they reach full temp. So on my previous commute the truck spent much more of the operating time at full temp, now I don't even get up to temp.

It's not a change in the truck as I just did a 400mi round trip for T-day and hand calculated 19.6mpg on winter fuel ( this may be the second time I posed this idk)

Point being, unless the OP is spending a lot of time at full operating temp then it'll be tough to get the high mpg that gets talked about.

To the OP: did you ever calculate your mileage?.. distance per tank is to subjective and could be as simple as a fubared sending unit.

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#48 ·
To take this farther: Coolant warm up is rapid. Engine oil isn't. And oils in transmission and drive axle even slower. I've not operated a light duty truck like these, or in a Class 8, where all the above temps come up to op temp before 45-miles steady state highway at 60-mph. Tires take over 75-miles. And this is in summer.

Grille block when solo from 70F down to 40F and then fully enclosed winter front.

Use of coolant heater at every start. Add oil pan heater. Park so as to block or minimize wind. No idling.

Short trips are tough. Cold weather short trips are murder.

It's not until AFTER that 45-miles in summer that condensation and acids start to burn off.

I haven't tried them (yet) but turbo and manifold blankets are another good idea.

FWIW, when I come in off the road after three weeks or three months I make sure to run a leisurely 100-mile trip out west a ways. Tire life also matters.

It's a short 34 to 50 hours off before going out again, but the truck means a lot to me.

As to fuel mileage, it's the average over several thousand miles. Be consistent. Don't drive like a damned Honda owner. Ease her along. Keep records.

MPG, like brake and tire life, separates men from boys. New consistent good habits takes erratic driving out of contention. And makes diagnosis far easier. A 10% mpg change SHOULD be obvious.
 
#34 ·
Subd.
Have same truck, but I am very consistent with 13.5 to 14MPG (6 KPL) with the TST Powermax.
If you get back up to where you used to be make sure to tell me how haha!
 
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#35 ·
I have the same issue, terrible fuel economy. I have replaced everything in the fuel system except the CP3 or injector feed tubes. CP3 is next in my case because it seems I have hardly any rail pressure as soon as I hit 2k RPM. In your case, do you have good rail pressure throughout all RPM? If so, I'd check the injector feed tubes next. Any little indentation on the tip will let fuel leak by and give you bad fuel mileage.
 
#36 ·
What?...really?

Where did you get this theory? Please share more.


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#37 ·
relax Nemachinist,

he's just another befuddled Dodge Cummins owner that thinks that overhead display won't LIE to him.
The more the connector tubes and the injector return valves leak the more LIES the overhead tells.

Let him suffer in silence

Plus that overhead LIAR gauge and the dash gauges make shops lots of money.
Unable to Duplicate Owner Complaint. No Problem Found
 
#38 ·
Yes Sir. I'm no mechanic, but I've seen this sort of thing happen before. The fuel lines that run from the fuel rail into the side of the cylinder head are connected to what are called "injector feed tubes". These tubes are connected to the side of the injector and feed it fuel. There are no gaskets or o-rings of any sort between the contact of the injector feed tube tip and the injector. Therefore, if there is any scarring or indents on the tip of the injector feed tube, fuel and fuel pressure is let by and as a result, bad fuel milage. It seems quite insignificant, but absolutely ANY scar or small dent will affect the whole process.

steelhead1, I don't go by the overhead. I know it's far from accurate. Just putting in my 2 cents worth.
 
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