Hi everyone!
It's been a while since Ive posted here.
Kinda a long post, forgive me...

I used to(when I first got the truck) get about 15-17 in city and 17-23 highway depending on speed, weight, and wind.

In the last year or two I have not been getting the best fuel milage. Ive chocked most of it up to being caused by a lot of in city driving and quick trips. In the last 6 months I have moved out of the city a ways and have to do abt 15-20 miles of highway driving each day and maybe 2-3 in city miles. My mileage has not gotten any better. I was getting between 12-14mpg.

Changed air filter back to the larger BHAF from NAPA and changed the fuel filter. I run pump diesel with 2-cycle oil@ 1oz per gallon plus whatever injector cleaner I happen to have(Amsoil, PS, ect...)

The last 5 tanks of fuel Ive averaged about 14.5mpgs...highest being 14.8.

So....it got a little better.

Whats the deal? I don't haul butt at every stoplight take-off. I drive relatively slow. I keep it 55-65 on the highway most of the time. Only push it to 70-75 when Im late or just trying to keep up with traffic but I usually just cruise.

I have made ZERO performance mods in the last 3-4 years, last of which was bump the timing 1/8. All I do is routine maintenance.

Is my lift pump fixing to go out? Injector pump? Trash in my fuel lines?

I was talking about this with a coworker and he proposed that maybe my injectors are just showing their age and need to be reworked or replaced. Interesting thought, but since Ive read about many other 12vs with way more miles than mine still running good on stock injectors....i dunno.

Any input would be great. I appreciate it.

Thank you

 

if it just happens in winter one possibly needs to accept it. i get 18 summer and 16 winter. owned one of them since 97 and does it every winter. gave up trying to figure it out.

 

You put on bigger tires or lift it?

 

If you are running winterized fuel it could be your problem because winterized fuel doesn't give off as much energy as normal diesel. I just get the normal stuff and put additives in it. It helps boost cetane levels and helps with cold starts too.

 

It's not your truck it's the fuel that we have now it's Garbage add some 2 stroke oil to the tank full and remember we are now into winter fuel .

 

Could be fuel. I get a 2mpg drop every winter.
When was the last time you changed your undercarriage fluids?
Any added drive train resistance will drop your mileage.
I don't have synthetic in my rear axle and now that it is COLD, it's like driving with the parking brake on for a while.

 

Tow something with some weight.
make than cummins work. reseat the rings
Using these motors as daily city commuter drivers is not what they were made for.

 

You could also have a suction side air leak. They don't leak fuel many times and can be hard to find. Try pressurizing the fuel tank with compressed air for a few minutes and see if anything leaks. This is how I found mine...Mark

 

I agree! Makes a world of difference to run them hard for a bit.

 

Fan clutch starting to lock up more than normal.

 

It's the fuel. I lost about 4 mpg's with the switch to the ultra low sulfer fuel.

 

I completely forgot about the winter fuel formula. That being said, I wonder if thats done for ALL diesel fuel sold in the US? I think, where I'm currently at and everything south of me, shouldn't need winterized fuel. Oh well, I guess those decisions are left up to smarter and better paid minds than me.

New tires, yes. Bigger no. running 305-75-15

I usually always add some kind of oil or additive. Either 2 stroke or WMO plus some amsoil/power service centane boost/injector cleaner. The first 5 minutes of every fill-up is measuring out a cocktail for the 12v

I know. It pains me that I dont tow a lot since I moved from home. Last thing I pulled was my 31' airstream but it was a slow cautious drive of maybe 15 miles. Slow because I was having trouble getting the trailer lights to work and was just cruising with the flashers on. But ill be pulling it across the state soon enough.

I though this as well. But I assumed air in the lines would cause the engine to struggle to start on its own, usually have to give it some throttle to go. Thats the prolonging issue a farmer friend has with his 2nd gen 12v.


I appreciate y'alls replies.

 

Mine started and ran beautifully with the only symptom being lower mpgs. I was really surprised as to how big the leak was. I was also having an intermittent no start problem, which I am sure that the leak contributed to, but fixing the leak did not solve that problem...Mark

 

For one thing if the injectors are the original ones it is inevitable (specially with our fuel) the mpg will decrease with mileage, and as You said You put WMO in it and that right there is NO good for Your injection pump and injectors at all unless You filter it with a centrifuge and still I wouldn't put any of that stuff on My rebuilt fuel system. Mine has been yielding less mpg lately as well and I took the heavy trailer approach for now.