Engine/Transmission (1994 - 1998) Fuel mileage woes....

[JGheen]

I have been trying to figure out this lower fuel mileage I have been getting recently and have looked into just about everything.



I have checked my entire truck and fuel lines for leakage and nothing found, but if air is getting in the lines or somewhere else, wouldn't the engine stumble some when pinning the throttle if there was a leak? I have noticed a bit of oily looking substance on the top side fuel tank under the truck but it is not wet enough to make me think that it is the source of a leak that would send my mileage way south.



I asked my local fuel station about a winter blend, they said it could be possible but didn't know for sure and that could be the culprit as some of you guys suggested before, but how bad can the blend send mileage south?



I have been running my #10 plate full forward for sometime now and as long as I keep my foot out of it, it seems to get the desired mileage, but how many of you get bad mileage with you #10 full forward?



Although my mileage is bad, it seems to get the norm when on the freeway for long periods, but around town, it's like I can almost watch the gauge go down a notch at a time cruising to work, on the lunch hour and going home. When comparing it to the odometer, it looks really bad cuz in the past it used to be very consistent with the odometer. Keep in mind my truck is lifted and the odometer has not been calibrated with my 37" tires, but even though it is not calibrated, it used to put out very consistent numbers when I checked it after filling up and now it seems to get lower and lower.

Part of me makes me think it is just my fuel gauge reading wrong, but it has been reading pretty consistent when it gets low and the light comes on everytime I fill up and compare the amount filled to the odometer and fuel gauge.

Anyway, sorry if I am rambling, but I just want to find the source of this possible bad mileage I seem to be getting. Please offer me any advice you guys can on this from your experiences as I am getting frustrated with what is causing this.



Thanks in advance, guys, I really appreciate it!



Joe

 

[NHouse]

Hey Joe, I have seen as much as a 5-10% decrease in mileage on winter fuel, but now I run about 9 months a year with the fan off which seems to balance that out some. As far as tires and odometer readings, I know mine is off by about 8 or 9% with 285's. I imagine yours could be off by 20% or more, but you probably know that. You didn't mention what your in-town mileage is but just for comparison the worst I've ever seen with mine empty is 16. This was last winter we had snow all week and I was in 4 wheel drive most of the time. Usually empty in town is about 19 if I keep my foot out of it. Like you I haven't noticed a mileage difference with the #10 in any position if I'm easy on it.

 

[Forrest]

Is your afc spring set for smoke or conservative. It'll make a difference.



I'm on winter fuel & ok on mileage, basically the same plate setting low to mid range & mileage is ok. I've been driving easier too ... more like 65 instead of 70 & easier on acceleration in town. The Valet switch has been on more too.

 

[ndurbin]

I see about 15 or so on a good day on a tank with mostly intown driving. But I have a pretty heavy right foot. And thats with my plate about halfway forward from the stock position.



I've been watching a post on another forum about getting out and running your truck pretty hard acouple times a week. Some of them claim it helps their mileage afterwards. I dunno how much truth there is to it. But they claim it removes carbon (or something) build-up from the injectors when you get the engine heat up on a wide open run or on long trips.



My fuel gauge reads kinda funky too. It's pretty close on the 1st 1/4 tank, but between the 3/4 tank mark and the 1/4 tank mark it reads low. The last 1/4 tank until empty it reads fairly accurate sometimes (sometimes the empty light comes on at 5 gal. or at 10 gal. left). I watch the trip odm. more now than the fuel gauge.



Nathan

 

[Vaughn MacKenzie]

JGheen, I came up with a pretty good way to figure out if the fuel system is sucking air.



Get a long 1/4" ID hose and connect one end to the fuel drain fitting on your filter. Run the other end into a large, clear plastic container such as a 2-liter soda bottle.



Start the engine and lift up on the drain to allow it to open partially. After you flow about a quart into the container to clear air out of your drain line, let the flow stop to clear those bubbles. Then open the drain again, making sure the hose end is submerged in the fuel you just drained. Watch carefully for tiny air bubbles. If you're drawing any air, you should be able to see some tiny bubbles continuously streaming out the end of the hose.



Vaughn

 

[JGheen]

Nhouse - My in town mileage right now I would take a guess at maybe 10-14 depending on driving conditions. On the freeway it is normal, 17 to sometimes 20, yes even with the big tires and lift. I actually run my truck with the fan off and almost never use the air conditioning in the summer. I can understand your mileage loss with the driving constantly in 4x4, I had that when I lived in Colorado. But all this mileage loss is sudden, and since you mentioned the winter blend again, I am more and more leaning towards that, but as I remember it for the longest time, I used to get close to my worst highway mileage for in town mileage and now it has gone down to the above listed.



Forrest - I have not touched my injecion pump settings for over 4 months and this has happend in the last two. Could something have moved? I have only adjusted my AFC 3/4 way to all the way backed off and it has been that way for a while.



Ndurbin - I have noticed that when the engine runs for longer periods or I hammer on it for a while it seems to run better and the mileage as well seems norm.

Recently it has been in the 40s every night and a high of 50 throughout the day, I run my block heater every night for easier start ups and the trip to work is very short, like 6 miles and 10 minutes. So the truck has been go for short trips lately.

I am taking a 4 hour trip north soon which will be the ultimate test of how it is doing, but that is in a couple weeks still, so I will keep looking.

Keep the opinions and thoughts coming as I can use any advice, thanks!



Joe