I've read a bunch of mileage posts, trying to determine whats causing poor mileage, and i feel like i've adressed just about everything but can't figure this out. Here's what i've got: 2500 w/ 3:54 rear 4x4. Everything else is in sig. I bought thetruck w/ 135k on it and was getting 18/19 mpg mixed and 19/20 highway w/ 265s. Went to 33s and dropped about a mile per gallon. Now, up until last summer, that stayed pretty steady even w/ the 35s. when my cam gear broke, and we did most of what is in my sig (cam, head, exhaust, intake, 3gsk, timing) I expected an INCREASE in mileage, but it went down to about 16/17. Didn't check the mpg for awhile, but late this fall I thought it was getting less than it should so I've been checking the last few tanks, and it's been getting 13.5-14 mpg!!! Can't understand it!
Now, the lift pump and rubber lines were new about a year and a half ago, and the fuel heater came out at the same time. I JUST replaced the overflow valve about a week ago w/ one from TST. Can't see any leaks anywhere. Here are my questions:
- I have the original tranny/converter in. New from Goerend are on the way now. Could slippage inthe tranny possibly cause a 4-5 mpg drop?
- Can a cam design DECREASE the mileage? It was supposed to help mpg. or could my porting the head hurt? It seems like increasing airflow should make it more efficient.
- Is there anything I'm missing in the fuel system that should be checked? Any common places for leaks? If it leaks on the return side I should see it and if it leaks on the suction side it should start and run poorly,right?
- Could my stock injectors w/ 266k mi be worn out and running that inefficiently?
The only other clue I have is that I feel like the truck should be running hotter (EGTs) and have more smoke than what it does for running an 8 plate and a stock turbo. I NEVER have hit 1000* and can't make it. I only get a puff of smoke when I first take off if I hit it a little hard or when driving if i give it a quick tap on the throttle, then it cleans right up. Makes me think something is wrong in the fuel delivery, but don't know what else to check.
Any suggestion?
thanks. -Josh
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