cluckmaster

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

alexschultz1

just a guess but is the engine heating up to the right temp? my thermastat got stuck open and wouldnt let the block heat up to optimal temp so i wasnt burning as much fuel as i could with a hot block.

also did the mpg drop after you put the lift pump in

TxDiesel007

HOw is the fuel pressure?

the new OFV might not always do the trick, secondly did you unplug the filter in the tank? thirdly what about the pre filter on the fuel heater assembly?

Just some other ideas to look at..

Rick

cluckmaster

I put a new thermostat in her this past summer when we had it apart. When I removed the fuel heater permanently i cleaned the pre heater screen filter. Don't have a fuel pressure gauge yet- on the list. The mileage didn't really go down until this summer and fall. I changed the lift pump and lines about a year and a half ago.

The filter in the tank- by unplug, do you mean clean it, or is it electric and literally have a plug connection? stupid question i know....I thought that the filter was a sock type- never cleaned it before. If it's plugged, would that cause a drop in mileage? Thanks. -Josh

9512vCTD

welcome to my world, thats avg. milage on my 95

cluckmaster

This is also posted on TDR and a couple of people have suggested slipped timing...going to check as soon as I get a chance.

Anyone know about the in-tank filter? Is it a sock type? Can it get clogged and cause decrease in fuel mileage/power? Thanks!

frostytj

[hijack] Why did you ask about the lift pump? I just swapped mine out 2 weeks or so ago due to it ticking. My first trip after the swap saw my worst towing mileage ever. I havent been through another full tank of fuel since then so I am waiting to see what I get for normal daily driving mileage. But I think its down from what I normally see. If you want to PM me instead of taking over cluckmaster's thread that is fine. [/hijack]

waldersha

The filter in the tank is a screen type on the bottom of the sump. I had mine off and looked at it, but it was pretty clean. Seems to me that the screen would come off, but there wasn't an easy way to clean it. I just pulled it and did the best I could.