From 16mpg to 10.5mpg

RustyRecycledT

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Just like the title says, my mileage has taken a HUGE dump! Before my trip to Ft Worth,TX in August to pick up the M-B I bought my IP busted. It was still pumping fuel and running the truck, it was just pumping alot of it out the hole in the side of the IP.
So I installed a new IP. The shaft on that one broke on the way home from getting the timing set by the diesel shop I had time it. Seems they left some bolts loose. It busted the shaft after 53 miles.:mad:
So I again installed a new IP & had it timed before I hit the road for my trip. It ran great for the 70 miles from my house to their shop, EGTs stayed below 1000* even pulling the long grades heavy on the throttle.

So The morning after I picked the truck back up, I loaded my aux tank in the bed and hit the road. I had loaded enough "fuel" to carry me round trip non stop with enough extra to allow for a 2-3mpg difference due to towing an '85 M-B 300D on the return trip based on my average of 16mpg prior to the IP problem.
Found out roughly 185 miles later that I was not in fact getting 16mpg any longer but was getting close to 10mpg.:confused: Doesn't take a rocket scientist to figure out I'm gonna be out of "fuel" long before I make it back home.(not a good time to find out that just because Tx has oil, does not mean they have cheaper diesel. IIRC I got it at the bargain price of $4.87 at the time)

So here's my question, is it possible that my IP did not infact get timed correctly, thus causing my dramatic decrease in mileage? One of the smaller voices in my head keeps telling me that the IP is outta time. I've even gone so far as turning the IP down to the point that maintaining steady speed on an average grade around here means putting the pedal to the floor.By doing so I have not gained enough increase to even bother mentioning.:rolleyes: I want at least part of my mileage back, and ALL of my power back. As it is right now, the Bus gets better mileage than the truck does. If I can't change that, I'll be using the bus to pull my trailer,fetch lumber,etc.:rotflmao

To avoid confusion, all this applies to Smaug in my sig.

Sure hope someones got some ideas...I've run out of them.
 

typ4

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I would say turn the fuel back up and have the timing set or at least adjust it by ear to see what you like, if there isnt enough heat in the exhaust to keep the turbo happy you will be driving farther in to the throttle to maintain a given speed..
Also make sure you dont have dragging brakes, been there twice already.
 

RKOCH

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Here is the problem a wore out pump will be on the retarded side witch will give you great high cruisng power and wonderful fuel milage. This is because of the wear in the cam ring, as it wears the slope changes retarding it and the height of the ring wears down not pushing as much fuel though the plunger IE the plunger does not move as far. Just like when your engine camshaft wears out. So your marks don't physically move on the pump but internally as it wears it retards the timing. Now you go put a nice new pump on there line up the marks and time it correctly and you will hear a total change in the engine, you have increased the timing a great deal where it really should beplus the plungers are now giving you a full stroke of fuel and when you advance pump timing you will see a increase in low end power but a loss of fuel milage. I have never owned a stock IDI that ever got over 12 mpg when timed correctly but they ran great.
 
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Andylad13

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also some more usefull information is...

"While wearing of the injectors advances the timing, the wearing of the IP retards it. Usually to a greater extent than what injector wear can do to advance it. That's why I usually advocated swapping the pump and injectors together. That way they wear together and you will have less drift of your timing than if you were to replace just one or the other. "
- Mel
 

Freight_Train

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ummm,How did they time the pump?By ear,By lining up timing marks,Just pull it in,look at it,then drive it out saying they did it right,used an actual timing meter hook to the #1 cylinder though the GP hole or Injector line and the crank pully for the actual location of the crank?Only way to correctly time it is last way.You cannot line up timing marks....or do it by ear.The timing mark it only for the factory original pump and was marked after it was timed by a meter at the IHC factory.
 

mankypro

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Well I get 16-20mpg depending on my foot empty. 10-11mpg when towing a 5x8 trailer well laden. Have you towed before with this truck?

I think 10-12 for towing is pretty normal.
 

RKOCH

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All of mine have been C-6 4.10 4x4's also so the milage will not be as good as a 2wd with 3.55 or od tranny.
 

Diesel JD

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12mpg is very good for an IDI with 4.10s and a C6 especially if it sees any real work or any highway driving at all.
 

RustyRecycledT

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The whole thing about the worn IP retarding timing makes sense.

As for the question of whether I have ever towed with it before......yes, quite often.(hauling in another truck tomorrow)

I would say that the combination of the new IP and my driving habits are probably the culprits here. My crappy mileage to and from TX was running with the cruise set at 65mph. 4.10s,C6,OEM size tires,turbo,and 65mph probably not a recipe for outstanding mileage. Hell, even when I pull the trailer I'm running 60-65.

I'm not exactly sure how they timed it to be honest. I was still really POd about the previous pump dying at under 60 miles, sitting in the hot sun for 3 hours waiting on a wrecker, and a $165 tow bill. At that time, I had no time to shop around for someone else to time it. I had obligations in TX to take care of in short order.
 

RKOCH

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From what you just said you hit the nail on the head. @ 65 with 4.10 gears a C-6 tranny and OEM tires you should be at or just over 3000 rpm, excactly the same way mine are set up and your driving habits sound a lot like mine. 10 to 12 Mph is right in the ball park.
 
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