What happened to my mileage?

[ragedracer]

****UPDATE PG 5***


86 M1009, ~66k miles.

When I picked this up last year, I was getting approximately 17 mpg on average. I lifted it 4" and put 33" tires on it about 6 months ago. At that point, I was getting ~18mpg, I guess due to lower RPM's required with the bigger tires.

Over the past 2-3 months, its been steadily dropping. My driving habits haven't changed. I primarily drive it only on weekends, about 80 miles, 60 of which are freeway. During the week I sometimes pick up the kids from school, etc. Over the past 3 tanks, I calculated MPG at 15, 11, and now 10. It's steadily plummeting.

What the heck is going on? It doesn't smoke excessively. I just took an emissions test, which I passed. This tests exhaust opacity - I was 16.8% opaque, compared to last year when I first got it, it was 7.7% opaque. Doubled! The limit is 20%.


Any ideas?

 

[SPECIALTYLC]

To get your milage back. Return to stock. Lift and tires will kill the milage everytime. Especially with the tall gears that the blazer comes with. The motor is working much harder now. And those 6.2 dont have that much to begin with.

 

[ragedracer]

To get your milage back. Return to stock. Lift and tires will kill the milage everytime. Especially with the tall gears that the blazer comes with. The motor is working much harder now. And those 6.2 dont have that much to begin with.

I'm not sure you understand. My mileage initially INCREASED when I put the lift on. It stayed that way for several months.

Now, my emissions have doubled, and my mileage has nearly halved. Something is amiss, and the lift has nothing to do with it.

 

[SPECIALTYLC]

I disagree. Lift and bigger tires NEVER gives better fuel milage. Motor may be getting tired.

 

[ragedracer]

I disagree. Lift and bigger tires NEVER gives better fuel milage.

Since you have nothing constructive to add, and choose to ignore the facts of my situation, find another thread to boost your post count.

 

[FMJ]

Filters?, fuel, air, CDR valve?

 

[ragedracer]

Filters?, fuel, air, CDR valve?

Air and fuel filter replaced recently. actually 1 tank ago. Mileage decreased even further when I did that. CDR valve was replaced approx 5000 miles ago.

 

[dskchevy]

I know this may sound goofy but winter blended fuel lowers mpg.
I just don't know if you get it in AZ...............

 

[ragedracer]

I thought of that too, I'm not sure if we get a winter diesel. Would that cause a ~30% drop in mileage though? That's pretty huge.

 

[FMJ]

How is performance?, could be an injection pump going south. . .

 

[ragedracer]

Seems to be running fine. 1/4 pedal or so to maintain 60-65mph on the freeway. Acceleration seems as strong as its always been.

My biggest concern is the doubling of crap coming out of the tailpipes. I haven't changed anything on the motor, and it's not burning excessive oil. Last oil change I lost ~1/2qt, and that doesn't count the oil filter. So less than that.

I think the exhaust stuff and the lowered mileage go together somehow. This is my first diesel, so I don't really understand how everything works.

 

[dskchevy]

How about the return line, I have to clean the fitting at the pump (with glass ball) every few weeks...

 

[73m819]

what kind of exhaust color, could be injectors

 

[KI4GSN]

Sounds like injectors to me too.

 

[ragedracer]

To be honest, there really isn't much of a color to the exhaust that I can see. If I really get on it, I get a grayish/black smoke, but very little. In fact, you almost have to a car behind you before you can really make it out.

Another thing I've noticed is spotting on the back of the truck. I've attributed this to my trans case leak (that's a whole other subject - it seems to be leaking from the driveshaft itself, not the seal), but it seems to go away. I don't know if ATF evaporates. Could it be raw fuel? And if so, what would cause that?

 

[Blood_of_Tyrants]

The spotting on the tailgate is probably unburnt fuel. Sounds like your injectors are wearing out and instead of a nice atomizing spray, they are squirting a stream of diesel into the chamber.

 

[Screamin' Metal]

I know this may sound goofy but winter blended fuel lowers mpg.
I just don't know if you get it in AZ...............

Yes...it could be the IP wearing out....but is most likely fuel quality. Blending of diesel fuels is probably the culprit. When they mix ethanol to fuels....sometimes it makes it way into diesel also....it doesn't burn good with high compression engines.

Just as a experiment......grab a couple of quarts of motoroil that you don't know the weight of.....put 3 or 4 quarts in your tank. You should immediately see a difference!

I've talked recently to reps for Kenworth and for Cummins both, and with the new diesel fuels that suppossed to be cleaner burning....they're 'dryer' than the old fuel.

Cummins has a system that takes a small amount of crankcase oil and adds it to the mix going to the engine to raise MPG's and to add some lubricity to the fuel.......

Uncle Sam has been doing WMO in Diesels for quite a while......since fuel quality is going down....it helps to use WMO in these trucks.....

Diesels were originally designed to run off canola and peanut oil at the processing plants....(free fuel).....it wasn't until the oil companys got a wiff that these folks were running their engines off waste oils and fluids that the oil co's can out with bonafid 'Diesel fuel'.....

In the engine manuals....your allowed to run about a 5 to 10% wmo on many engines.....These trucks we drive like the stuff.....

 

[Screamin' Metal]

IF you don't see a difference....
1. Engine load is going up.....(ie, brakes getting tighter, wheel bearing or pinion bearing going out, carrying more weight, trans troubles, etc...)
2. Engine wearing out or fuel system getting clogged.....possibly water in the diesel (extremely bad for the IP)
3. Air cleaner is stopped up or have a fuel system sucking air.....valves sticking, clogged injectors, etc.....

 

[ragedracer]

The spotting on the tailgate is probably unburnt fuel. Sounds like your injectors are wearing out and instead of a nice atomizing spray, they are squirting a stream of diesel into the chamber.

Is there anyway to test for this before I drop $500 on new injectors?

 

[Screamin' Metal]

Is there anyway to test for this before I drop $500 on new injectors?

Yes....theres some additive you can add to your fuel that'll help....it'll probably take a couple of tanks to clean them sufficiently....its as close as your favorite automotive parts store......